My First Tube Radio Restoration Log - Page 1
Forum section: electronics / projects

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 05, 2013, 02:53:02 am
content: Hello everyone!I was able to get my hands on an old tube radio today. It's not in the original casing, I assume the original radio cabinet broke and then all of the components were transfered into this decent looking homemade box.This is the log where I'll be showing all the steps of me restoring this radio, which is actually my first tube radio restoration project.The first thing I did was tear it apart and clean it up. Here are some pictures of the pieces.First, the tubes from inside the radio:Two 6D6 TubesAn 80 and 76 TubeA 6A7 and 42 TubeMaybe I'm wrong but it looks to me like all of these tubes are original!These are the metal covers that were over 4 of the 6 tubes.This is the homemade box for the radio.This is the electronics chassis with the front controls and display.A closeup on the display.Top down of the electronics chassis.Back view of the electronics chassis.The plate on the back of the electronics chassis.And finally a view of the inside of the electronics chassis.And on that plate we can see this was a Crosley Model 635 originally. Here is what it looked like originally (not my picture)

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 05, 2013, 03:37:11 am
content: Okay so my initial questions are:Why is there metal cases on some of the vacuum tubes and are they actually needed?I've heard this radio can do three ranges, police, shortwave, and "Broadcast". Does that mean AM?What are those large rectangular cans protruding upward from the chassis. One has a wire connecting to the top of a tube. Are these capacitors?Theres four wires going to a single speaker?Thanks for all of your help guys!

author: vk6zgo
author_rank: Super Contributor
timestamp: August 05, 2013, 05:57:36 am
content: Why is there metal cases on some of the vacuum tubes and are they actually needed?The metal cases are to provide RF shielding for the tubes--& yes,if they were fitted originally,they areneeded.I've heard this radio can do three ranges, police, shortwave, and "Broadcast". Does that mean AM?Back in the day,the Police operated on Shortwave (HF),so that is why it is marked on the dial."Shortwave" (HF) is nominally between around 3MHz or so to 30 MHz.You will probably find that this radio will tune up to maybe,12MHz.It is an AM radio,so it will receive AM stations on the Medium Wave Broadcast Band,& Short Wave AM broadcasts on the "Shortwave" bands.Hams,& other Communications users on HF,usually do not use Amplitude Modulation,although if you are very lucky,you might find some.What are those large rectangular cans protruding upward from the chassis. One has a wire connecting to the top of a tube. Are these capacitors?They are Intermediate Frequency (IF) transformers,which are tuned to the IF frequency,which is usually around 455kHz,although some old radios use 175KHz,or 221kHz.The wire to the top of a tube is probably so the secondary of the transformer can be connected to the Control grid of the tube it is connected to----some tubes,but not all,had this configuration.Theres four wires going to a single speaker?Back in the day,Electrodynamic Speakers were common,as Permanent Magnets were not developed to the level they were in later years.The HT line from the power supply was run through the magnet coil,doing two jobs--acting as a smoothing inductor for the power supply,& an electromagnet for the speaker.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 05, 2013, 06:13:34 am
content: Thanks for all the info.Do you mean the output from the transformer creates a stationary electromagnet in the speaker and that is in series with the rectifier tube?Maybe I'm mistaken but it looks like this entire radio runs off of the output of the transformer which I think is very low voltage because it looks like the little incandescent bulbs for the front display are going directly off of the output of the transformer.I think I might disconnect the transformer and measure it'd output right after I make sure it's good and solder on a new cord.Oh and about those metal covers, if I only want AM radio are they really nessary? Other radios don't have them and I'd prefer not too as we'll because these look very dingy and not cool like the tubes themselves. I guess if I need them then I'll use then though. Im pretty sure I remember where they all go.

author: G7PSK
author_rank: Super Contributor
timestamp: August 05, 2013, 08:13:40 am
content: The speakers in those days were often used as a choke for the HT. So beware of the voltage on one of those pairs feeding the speaker it will be in the order of 2 to 3 hundred volts, the wire leading out of the if transformer will also be HT coming from an anode cap on one of the valves. You will quite likely find the chassis is live as well. According to my valve data book the 6A6 uses anode voltage of 300 volts at a max of 70mA. Heater voltage of 6.3 volts it was quite common to run the filaments in series and use a small light bulb that illuminates the dial as a fuse so the heater voltage can also be quite high I have even seen the mains fed directly across a whole string of valves.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 05, 2013, 03:01:23 pm
content: Quote from: G7PSK on August 05, 2013, 08:13:40 amOh okay. I was removing the transformer and noticed that this whole time I failed to see four other wires going into the transformer and going straight to the rectifier tube. These must be the higher voltage wires.So is it safe to replace this stuff with some 300V wire that's like 18AWG?I'm assuming that wire would be fine because 300v sounds like enough to handle whatever is in this and this entire radio is rated to pull only 55watts so I can't imagine the HT would have a big enough amount of amperage to be a problem for 18awg.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 05, 2013, 04:39:05 pm
content: I got the transformer completely removed now and cleaned up.I still need to know if some 18AWG 300v wire is good enough for the HT output of the transformer.I'm asking because I have a lot of that wire in different colors from computer power supplies. I am also wondering if it's safe to assume the yellow wire is also rated for 300v because the red and black wires from the same psu's have it printed on them but the yellow wires have no printing at all but look the exact same.

author: c4757p
author_rank: Super Contributor
timestamp: August 05, 2013, 04:46:41 pm
content: Quote from: EpicIntelGamer on August 05, 2013, 03:01:23 pm1) You underestimate the insanely high voltages used in vacuum tube equipment. I have a vacuum tube function generator that can only put out up to 20V RMS and uses a 420V rail. Have you measured the voltage the transformer puts out? (Becarefuldoing this)2) Amperage has nothing to do with it.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 05, 2013, 05:19:14 pm
content: Quote from: c4757p on August 05, 2013, 04:46:41 pmI'm not trying to underestimate it but when all I see are mostly 200v rated caps, you have to assume it can't be too much or that those caps arent subjected to the highest voltages.I'll go measure this carefully.And the reason why I mentioned amperage is because I thought the heaters used a good amount of amps and I wanted to make sure people didn't think I was going to put flimsy wire on the heaters.

author: G7PSK
author_rank: Super Contributor
timestamp: August 05, 2013, 05:19:32 pm
content: I doubt that there is more than 200 mA from the transformers and the valves maximum operating voltage is 300 Volts so the most likely are run around 250 to 275 volts. As previously stated its not the amps that regulate the wire so much as the insulation ratings so as long as the wire is rated above the maximum voltage seen in the circuit you should be OK, and at the voltage involved with these valves I would choose a wire with insulation rated to at least 400 volts but no doubt some one will gainsay me on this.The valve heaters are only 6.3 volts and up 800 mA each.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 05, 2013, 05:21:19 pm
content: Quote from: G7PSK on August 05, 2013, 05:19:32 pmI'll go measure the transformer and then if it's pretty high then I'll hunt around on eBay for some cheap 400v wire.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 05, 2013, 05:44:30 pm
content: WOW that has some real HV!One winding gets all the way up to about 600VAC!Another seems to have about 5VAC.Then there is another winding which looks like it is supposed to have a center tap, however, there's a problem. This wire actually broke off VERY close to the transformer and the little bit that's left shows infinite resistance to all of the other wires coming from the transformer.The two sides of the winding that I think is supposed to have a center tap show about 7VAC and I think its for the heaters.I guess I'll post a picture of where that wire broke off of the transformer.

author: c4757p
author_rank: Super Contributor
timestamp: August 05, 2013, 05:50:47 pm
content: Quote from: EpicIntelGamer on August 05, 2013, 05:44:30 pmCould be a center-tapped 300V winding, maybe another wire broke off. They're often center-tapped so you can have a full-wave rectifier with only two diodes (a tube diode is a lot more expensive than a 1N4007...). That'll give you 424V peak, probably 350-ish after the hilariously inefficient vacuum tube rectifier. Also remember that they're usually meant for 110V input, mains here is 120V nominal now and can easily run high (I've seen 130), so you could be looking at 10-18% higher voltages.As for the broken windings - you're in for a real treat if you want to repair that transformer. Have fun!

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 05, 2013, 05:59:18 pm
content: Quote from: c4757p on August 05, 2013, 05:50:47 pmSee off of the one side of the transformer is 4 wires, 2 red and 2 yellow. One color makes 600V, the other color makes 5v or so.This wire that was broken off comes from the other side of the transformer, so I thought it would have to do only with the little winding on that side, not with those 2 sets of colored wires on that other side.I was wrong, your absolutely correct. That is the center tap for that 600v winding! And what do you know, now that I'm measuring the right wires, there is continuity and I measure from center tap to either side about 300VAC (according to my horrible DMM).Oh and by the way, the plate on this chassis says input 100-125 so I guess it has quite a bit of tolerance and I'm also running this on a ballasted variac so I can get whatever voltage I wantSo it looks like there is just barely enough exposed wire from that broken one for me to solder on a new one and then cover it in globs of liquid electrical tape? Unless someone else has any better ideas.It'll be tricky because there's only 1 or 2mm of wire left coming out of the transformer.

author: SeanB
author_rank: Super Contributor
timestamp: August 05, 2013, 06:52:40 pm
content: The winding with 5V centre tapped is for the rectifier valve only. the heater is connected to the cathode so as to reduce voltage stress on it, as otherwise the heater cathode insulation has to withstand 400V or so at red heat, which is very difficult to do reliably in a very small space while having good heat transfer to heat the cathode. The rectifier valve has 2 anodes, you probably can look through the glass to see the 2 separate large plates around the heater with a gap in the middle.This is to give a half bridge, while still making it easy to make a simple valve, a 4 diode full wave rectifier needs 3 separate heater supplies insulated to the peak of the AC output of the supply transformer and isolated from the AC input, output and each other by that amount.The rectifier will have the cathode connected to a large electrolytic ( large being relative here, it might be 8uF, 16uF or go up to 47uF at 450VDC) and then it goes to the speaker energising coil to be used both as a choke to reduce noise, in conjunction with another 8uF capacitor, often a dual or triple unit in a single can, and to actively reduce hum, as the residual ripple will still be on the speaker wiring from the amplifier as it normally has a very poor supply rejection ratio. Thus if you have hum on the speaker you turn the wires on the speaker transformer the other way round so as to reverse phase, one way will have less hum.The triple capacitors are typically 8uF, 8uF 450VDC and 50uF 20VDC in the same can, the 50uF unit being used as a cathode decoupling capacitor on the speaker amplifier. They do die after a few decades, and you probably need to replace them before turning it on as they will be dead. Use modern radial unit of 22uF 450VDC and 100uF 50VDC as replacements, just put them under the chassis and clip the leads from the original cap and leave it there. Sometimes people remove the insides of the old cap and place the 3 units inside the capacitor body and reseal it to look original.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 05, 2013, 07:25:10 pm
content: Quote from: SeanB on August 05, 2013, 06:52:40 pmThere is no 5v center tapped, only a 600v center tap.I can see two black objects on either side of the inside of the rectifier tube.I have only one large electrolytic can, and I'm not too sure about its specs. I can see on the side a few different voltages but I don't see any MFD values and I also don't want to remove it because there appears to be no way of knowing which wire goes to which of the three terminals.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 05, 2013, 08:05:49 pm
content: Hey guys I've got a question.Ovbiously I need to replace all of the paper caps in this radio.One for example, says, "CAP. .05-200V" which I guess means Capacity is .05uF and 200Volts. Most other caps have a small value as well.I'm wondering if I can use those 250V rectangular AC capacitors that you would find on the input of computer PSU's (given that they have a similar uF).I'm hoping that I can use those because I have pretty many and might not need to buy any caps then.

author: c4757p
author_rank: Super Contributor
timestamp: August 05, 2013, 08:08:34 pm
content: In most places, yes.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 05, 2013, 08:18:47 pm
content: Quote from: c4757p on August 05, 2013, 08:08:34 pmWhere can I not (besides the electrolytics)?Also, how close do these need to be rated (I'm talking uF, not voltage) to the original paper caps?I also need a bit of help with those rectangular caps. I see on there they will say something like: "0.33uF +-10% X2"Its that X2 that I'm wondering about. Its all the way on the right hand side but still on the same line as the other writing. These only have 2 legs so they must be a single capacitor but are they saying that that .33uF cap is actually .66uF?

author: SeanB
author_rank: Super Contributor
timestamp: August 05, 2013, 08:25:29 pm
content: X2 is the insulation class, these are designed for mains filtering, so they have to be classified that they will survive spikes. This just means that they self heal on overvoltage and eventually fail as open circuit, but can short as a failure mode. The ones marked Y or Y2 are designed to fail open only. You can use them on high voltage with no problems. Rating wise in most cases if they are slightly higher in value up to about twice the value there will be no problem. Only ones that are critical are those used in tone controls ( where you will find capacitors of around 1 to 100n) and in the tuning circuits, where the value is between 1 to 1000pF and they generally are a ceramic capacitor.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 05, 2013, 08:32:13 pm
content: Quote from: SeanB on August 05, 2013, 08:25:29 pmOkay then so I guess I can use these caps for most of them.What should I use for that .05uf paper cap for example. Oh and is that actually .05uf, is that what that means? I guess I couldn't use a .33uF cap for that could I?Would a .1uF cap work for that (I guess it should).

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 06, 2013, 12:08:48 am
content: Quote from: EpicIntelGamer on August 05, 2013, 08:32:13 pmWill that work?

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 06, 2013, 01:28:11 am
content: Will a .1uF capacitor be a good replacement for a .05uF paper capacitor?Will a .68 and .47 work to replace a 1uF paper capacitor?I need to know so I can get started on this!

author: c4757p
author_rank: Super Contributor
timestamp: August 06, 2013, 01:31:53 am
content: We'll have to install a service bell for you to ring...I'd use .047. If you don't have it, then two .1uF in series = .05uF. I don't know what this capacitor is doing so I don't know if it's OK to double it.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 06, 2013, 01:36:57 am
content: Quote from: c4757p on August 06, 2013, 01:31:53 amI don't mean to be rude but I like to get stuff done.I don't have a .047 but I do have two .1's!Now I'm not sure about wiring caps in series so I'll ask, if both are rated to 275V, are those wired in series okay to replace the 200v cap?

author: c4757p
author_rank: Super Contributor
timestamp: August 06, 2013, 01:39:46 am
content: Yep.Ideallyvoltage ratings would add, so two 275V = one 550V. In real life you really need to put high-value balancing resistors across them (1Meg or so), which could ruin the performance depending on what they're being used for. But you don'tlosevoltage rating.

author: c4757p
author_rank: Super Contributor
timestamp: August 06, 2013, 01:43:20 am
content: Oh, by the way, the decimal point was invented to make engineers miserable when it's hard to see. It's 47nF and 100nF.Damn font designers making it so small it's a single pixel at GUI sizes.... I can hardly make them out on my laptop display!

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 06, 2013, 01:52:13 am
content: Quote from: c4757p on August 06, 2013, 01:43:20 amAlrighty, I'll write it out next time (its the least I can do in exchange for all of this information).Now I know that there is voltages that are way over 200V in this chassis but if all of these caps are rated at 200V then wouldn't it be fine to use some 300V wire just for the wire connecting directly to the caps?

author: c4757p
author_rank: Super Contributor
timestamp: August 06, 2013, 02:08:53 am
content: I know I repeat this over and over here, but remember thatvoltage is differential. You don't have "200V", you have 200V betweentwo points. The capacitor's voltage rating is for the voltage between its pins. The wire's voltage rating is between the wire and anything it could ever possibly touch. That capacitor will be perfectly happy stuck between +400V and +200V but the wire will not.Now..... (*looks around cautiously*) now that nobody is listening.....in my experience decent quality 300V-rated wire can usually handle 400V in a pinch.But I didn't tell you that, you reckless jackass! Why would you think to do that? And certainly don't if it happens to say "Wun Hung Lo" on it. Or if it's entirely unlabeled.I really wish you'd track down some 600V wire, it's not hard to find.

author: xrunner
author_rank: Super Contributor
timestamp: August 06, 2013, 02:16:32 am
content: Quote from: c4757p on August 06, 2013, 02:08:53 amI saw what you did there.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 06, 2013, 02:24:08 am
content: Quote from: c4757p on August 06, 2013, 02:08:53 amLOLI already soldered in a capacitor with 300v wire, but I guess I'll have to dismantle it and put in some 600v wire. I did find some cheap and available in different colors on eBay:http://www.ebay.com/itm/10ft-18-AWG-Black-Appliance-Stranded-Wire-105C-600V-/111010425643?pt=LH_DefaultDomain_0&hash=item19d8bcab2bUnfortunately this wire I was using was probably not decent quality, and even if it was I'd like to keep everything safe if it only costs like $4 for enough 600v wire for the whole radio.So I guess I'll just fix whatever else I can while I wait for that 600v wire to come.Quote from: xrunner on August 06, 2013, 02:16:32 amSSSSHH! You'll attract attention from theSafety Police!!!

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 06, 2013, 08:08:29 pm
content: So ishttp://www.ebay.com/itm/10ft-18-AWG-Black-Appliance-Stranded-Wire-105C-600V-/111010425643?pt=LH_DefaultDomain_0&hash=item19d8bcab2bgood?

author: Chryseus
author_rank: Regular Contributor
timestamp: August 07, 2013, 01:09:59 am
content: I've never actually seen a wire rated for 200V fail even on several hundred volts, maybe if you're putting a lot of current through it but I'm still skeptical.Anyway I'll give you a few tips that might help.Pick the nearest value for capacitors particularly if they are in the RF stage, avoid using series or parallel combinations as that will just result in more mess and confusion if you should sell it later.Any capacitor directly across the mains should be replaced with a safety type, elsewhere it does not really matter, I suggest adding a fuse in any case at some point.Check that the tube filaments glow and there are no shorts, if any tube appears to be white rather than silver it's junk.Replace all the wax paper caps as these are most certainly bad, if you want to keep to the original look consider restuffing them, other caps such as mica are generally good so hold off replacing them.The case of the electrolytic cap is usually the negative side, this may not be true if there is an insulator between it and the chassis, the output may be marked on the can if not refer to to the schematic.Which brings me to getting the schematic, I've had a brief look around but cannot find a free source, so unless it's in the case you may have to buy it as distasteful as that is, don't forget to redistribute it afterwards, seriously selling schematics and service manuals makes my blood boil.Repairing tube equipment is a lot of effort but also very fun and educational, good luck!

author: c4757p
author_rank: Super Contributor
timestamp: August 07, 2013, 01:19:31 am
content: Quote from: EpicIntelGamer on August 06, 2013, 08:08:29 pmLooks OK to me.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 07, 2013, 01:29:51 am
content: Quote from: Chryseus on August 07, 2013, 01:09:59 amYeah I imagine it takes quite a bit to break down the average piece of insulation, but then again, 600v is quite a bit.I have no idea where the RF stage is (please don't hurt me, I'm not too good at electronics) I'm also not going to be selling this so I'm not going to worry too much about confusion, other than the confusion that I'm already experiencing lol.There is no caps across the mains. A fuse will be added as well.It's going to be at least a week before I get to turn this on for the first time and see if any filaments fire up. I can tell you that I think all of the tubes are original and that they all have that shiny spot intact (the one that is supposed to go away as it absorbs contaminants and gasses).I'm replacing all of the caps right off of the bat just to be safe.I'm not sure what's up with that large can cap. I also think its a shame you can't buy a new one of those, you have to just use normal modern electrolytics and then leave the can there "for show". I hate leaving stuff "for show" but not so much that I'd remove it. I just wish it could look good and work you know?I did manage to find a schematic for the radio on some other site for free.Yeah this is going to be quite an in depth thing to do.Thanks for all of your informationQuote from: c4757p on August 07, 2013, 01:19:31 amGood, I'll order some of that tomorrow then, along with some heat shrink, caps, and a fuse holder.

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: August 07, 2013, 08:55:39 am
content: I wouldn't bother with the cap across the mains, it won't do anything meaningful to an old tube radio, though the fuse would be a good idea.The reason why you cannot buy a replacement filter cap, is that back then each model from each brand frequently had its own, custom type. So you would need to fabricate a gazillion different type for a vanishingly small market, to be able to supply everyone. The usual way of getting around this, is to disconnect the original cap, leaving it in place, and discretely mount modern electrolytic caps below the chassis. I wouldn't even bother testing it, it doesn't work.Depending on how much time you wish to spend on this, then I may be able to provide a few tips and tricks. The usual way of restoring radios of this age, is to do so very, very slowly and methodically. You cannot rely on *anything* working, so frequently you'd proceed methodically in a set order. The intent of doing so is to reduce the chance of letting the blue smoke out of something, which you will need later.Any chance you could post or link the schematic, please?

author: Rascal
author_rank: Contributor
timestamp: August 07, 2013, 12:34:57 pm
content: Im always reluctant to replace original components in a restoration project - but you usually find some need replacingPaper caps should be replaced. Electrolytic caps I will try to reform (usually successfully). Mica caps should be okay.Resistors I leave alone if they are within 20% of value.Cloudy tubes are no good.Use a variac.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 07, 2013, 02:55:08 pm
content: Quote from: ElectroIrradiator on August 07, 2013, 08:55:39 amYeah I'm just going to replace the old huge cap but leave it there for looks.I agree, I don't want to take any chances and end up blowing up any tubes so I'm going to replace all of the caps and any wiring I feel is too degraded.The schematic was found onhttp://www.nostalgiaair.org/Resources/If you look for crosley and then for the model 635.Quote from: Rascal on August 07, 2013, 12:34:57 pmI'm just going to replace all of the caps just to be safe.No tubes are cloudy.I will use a variac, with a ballast.Thanks guys for the info!

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: August 07, 2013, 04:07:33 pm
content: Quote from: EpicIntelGamer on August 07, 2013, 02:55:08 pmGot the schematic.There are some additional, simple things you might consider doing, in addition to replacing the caps, to try and maximize your chance of success under full power.It is a bit hard to judge the condition of the radio from over here, but I don't mind writing up a few additional suggestions to check. They might come in handy later, if you think you might want to restore more radios in the future. All of them can be done without AC mains power, so you could do them while waiting for parts/wire.

author: Chryseus
author_rank: Regular Contributor
timestamp: August 07, 2013, 04:21:39 pm
content: If you want to you can remove the contents of the electrolytic can quite easily and put the new caps inside, just uncrimp the end or cut the can, apply some heat to melt the tar blob at the top of the can and the guts should slide right out.Referring to the schematic 16 is the safety cap that you can either leave out or replace, 10Z, 10Y and 10X are the electrolytics in the main can with the negative side going to the can.

author: fpliuzzi
author_rank: Regular Contributor
timestamp: August 07, 2013, 04:54:00 pm
content: The following ebook can be useful for an antique radio restoration project. Richard McWhorter wrote a 212 page book entitled "The Vacuum Tube Shortwave Radio (understanding and troubleshooting)" and has generously made this ebook available as a free pdf download...www.richardmcwhorter.com/vacuumtuberadio/The pdf does ask for a password when opened (password is allamericanfiveradio). The ebook is fully indexed so it's easy to jump right to the sections needed.The pdf's intro states that the RCA 8Q2 radio was chosen as the example radio for the book because all the vacuum tube circuits of the 8Q2 are representative of a very popular architectural design dating from the late 1930's through the early 1960's.Regards,Frank

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 09, 2013, 11:26:00 pm
content: Today I was cleaning up a bit and I guess one of the tubes got stuck under my chair and when I sat down, CRUNCH!!!Looks like I'm going to have to buy a "76" tube now. It also looks like since I broke this, this radio no longer has all original tubes.

author: c4757p
author_rank: Super Contributor
timestamp: August 09, 2013, 11:38:46 pm
content: They're not quite like transistors, are they?Damn things. I've broken a few too, and nice ones at that

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 10, 2013, 12:35:08 am
content: Quote from: c4757p on August 09, 2013, 11:38:46 pmUnfortunately not.This is the cheapest listing on eBay for 76 tubes. Which brand should I get (they have a drop down menu of different brands for the same price)?http://www.ebay.com/itm/231018533109?var=530178370454&ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649

author: c4757p
author_rank: Super Contributor
timestamp: August 10, 2013, 12:51:39 am
content: Damned if I know... Eeny-meeny-miney-moe?

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: August 10, 2013, 07:07:44 am
content: Quote from: EpicIntelGamer on August 10, 2013, 12:35:08 amDoesn't really matter from a technical point of view. They either work, or they don't. Back then it wasn't unusual for one manufacturer to sell 'raw' tubes in quantity to another brand, who would then sell the tubes with their own branding stamps printed on the glass. You may see minor, mechanical variations between tubes made in different factories, and the amount of the silvery gettering may also vary, that is about it.The tubes in the auction are all 'ST' shape, meaning coke bottle as seen in the photo. So if possible you may want to just match the brand to that of the other ones in your radio, perhaps?

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 11, 2013, 12:51:34 pm
content: Quote from: ElectroIrradiator on August 10, 2013, 07:07:44 amAll of the other tubes in the radio are the original Crosley branded tubes. I guess I'll just choose a brand at random.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 15, 2013, 05:02:45 am
content: I did not order a tube yet but I did receive my 10Ft of 600v 18awg wire. I notice it actually has two different layers of insulation and proudly states it is 600v on the wire so I feel pretty good about this purchase.The only thing I've done is to solder on a piece to the little stub of wire where the one broke off of the transformer (it's the center tap of the 600v winding) and covered it in heaps of liquid electrical tape that I let soak into the windings to make sure it doesn't have any possibility of arcing.I'm also going to put heat shrink over the joint and another layer of liquid electrical tape just to make sure everything is good and safe. I'll also heat shrink any rough looking parts of the existing transformer wires that I want to keep.I'm also using electrolysis to clean off those metal covers that cover up 4 of the 6 tubes, it's slow but its working quite nicely!

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: August 15, 2013, 07:21:33 am
content: There is no particular reason to insulate the center tap on the transformer. It is connected to ground, giving you two 300V phases for the rectifier. All you need is a good mechanical and electrical connection.If you get grief from the transformer, then it will probably be due to shorted internal windings, or internal arching due to broken down insulation. If moisture has been able to build up in the insulation, it may have swollen up and/or partially lost some of its insulating properties.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 16, 2013, 04:46:10 am
content: Quote from: ElectroIrradiator on August 15, 2013, 07:21:33 amI already tested the transformer with no load and it didn't pull any current from my 30watt ballast that I was using so I assume we're good.The only problem is that the wires coming from the transformer were crammed in really tightly to the actual frame that mounts to the electronics chassis and now if I move the wires they just break off so I guess I need to break them off and replace them.More work for me.....

author: G7PSK
author_rank: Super Contributor
timestamp: August 16, 2013, 07:53:07 am
content: You really need to megger the windings of the transformer. Old style varnish insulation absorbs moisture which will lead to breakdown of the windings, either put the transformer in a warm oven (not hot) to dry out or short out the secondaries and apply about six to twelve volts to the primary winding in order to warm the transformer safely, Keep the transformer just warm to the touch for eight to ten hours this will drive out the moisture.

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: August 16, 2013, 08:01:27 am
content: Apply the same treatment to the audio output transformer, now you are at it.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 18, 2013, 07:32:42 pm
content: Quote from: G7PSK on August 16, 2013, 07:53:07 amI appreciate the suggestion but unfortunately most of the outside of the transformer is covered in liquid electrical tape and is quite sealed up (due to the repairs of the wires I had to do). So I'm not going to be doing this to the transformer, I'll cut my losses and just continue onward.Quote from: ElectroIrradiator on August 16, 2013, 08:01:27 amI don't think there is an audio output transformer on this radio....Thanks anyway guys!And a bit of an update, I took apart one of the IF transformers because the wire that was going in the top was in need of replacement. A lot of the coating on the windings have broken off but I patched it up with liquid electrical tape and hopefully everything will be good to go.

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: August 18, 2013, 08:56:47 pm
content: Quote from: EpicIntelGamer on August 18, 2013, 07:32:42 pmThere has to be one. Philips didn't start to experiment with direct drive speakers in domestic tube radios until the late fifties.Schematic claims the output transformer is not on the main chassis, but may be attached directly to the speaker. Check whatever is connected between '50' (the speaker connector) and '46' (the actual speaker).

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 19, 2013, 12:53:48 am
content: Quote from: ElectroIrradiator on August 18, 2013, 08:56:47 pmWell now that you mention it, there is a transformer on the speaker itself.Like I said though I really cannot be bothered to do any of that elaborate stuff to these transformers.Thanks anyway.

author: Chryseus
author_rank: Regular Contributor
timestamp: August 20, 2013, 04:41:14 pm
content: You don't need to generally do anything with the transformers, I've never had a transformer that has a good resistance check fry itself.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 20, 2013, 06:43:41 pm
content: Quote from: Chryseus on August 20, 2013, 04:41:14 pmGood then!Also, more good news/updates. I figured out how to wire up and test the speaker!I applied 15VDC through a 330ohm resistor (just to make sure it doesn't pull too much current but really I found out its not needed) into the field windings and I managed to clip on some crocadile clips to the output of the audio transformer (directly to the voice coil) and I powered it using a very small few watt amplifier that I had and it seems to work just fine!I'm very happy to know that the speaker is working and doesn't sound too bad either!I also managed to re-install and completely connect the main transformer after replacing all but 2 wires coming off of the transformer and consulting with the schematic for about an hour.I'm also ordering all of the capacitors tonight so I'll post a list here shortly that I hope someone can look at and see whether or not the ones I've chosen for replacement will work.Thanks.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 20, 2013, 08:29:17 pm
content: So can I use these (in no particular order) to replace the caps in the picture below? (the top three in the picture are all in the big electrolytic can)Electrolytics to replace the big can (top three in the list in the picture)mylar and ceramic for the restWill this work? Also, what are those mmf caps? I didn't try to find replacements for those.

author: fpliuzzi
author_rank: Regular Contributor
timestamp: August 20, 2013, 09:18:41 pm
content: using the nomenclature shown in your example capacitor list Mmf means micromicrofarad, which is the same as picofarad.1 Mmf = 1pF1450 Mmf = 1450pF = 1.45nFand so on...FrankPS, On old schematics I've seen micromicrofarads written as mmfd, MMFD, MMF, Mmf, PF, pF (etc).

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 21, 2013, 01:08:48 am
content: Quote from: fpliuzzi on August 20, 2013, 09:18:41 pmThanks for the info! I do believe though that they actually are not normal capacitors, but rather variable caps and possibly part of the tuning thing so I guess I didn't need to know anyways, but its better to know it for later anyway!I just ordered all of the caps and the tube I broke and surprisingly it came out to be almost exactly $50 on ebay! That's on top of the $20 I've already spent on heatshrink and wires!This is getting quite expensive but hopefully this will be all I need to buy.Thanks.

author: fpliuzzi
author_rank: Regular Contributor
timestamp: August 21, 2013, 02:46:52 am
content: Quote from: EpicIntelGamer on August 21, 2013, 01:08:48 amIf I'm looking at the correct schematic, it looks like items 11, 12, and 23 (the 4.72nF, 1.45nF, and 1pF caps) are not depicted as variable capacitors. All three are shown on figure 3 (bottom view) of the pdf I downloaded as though they're fixed value capacitors.The 1pF cap (item 23), shown in figure 3 between the two wafers of the front panel center switch, may be a mica type capacitor. If it is you will not need to replace that one, unless it is cracked.Depending on the construction of items 11 and 12, these two capacitors may have to be replaced, along with the electrolytics and any paper type capacitors. From the bottom side photo that you supplied, the silver colored capacitors (items 11 and 12 with the dots painted on them) may be flat paper capacitors in plastic shells. If they are, they'll be very unreliable after all these years.Anyway, that's my take on those three particular capacitors using the info I have on hand. I now defer to the forum members who work on vacuum tube antique radios on a regular basis (possibly for decades).Regards,Frank

author: Chryseus
author_rank: Regular Contributor
timestamp: August 21, 2013, 08:59:59 pm
content: Any square shape mica caps are usually good, as for a 1pF capacitor you can just twist two insulated wires together and that will work fine.If you're unsure if 11 and 12 are mica (I can't tell either) just leave it in place, you'll notice poor performance on the medium and short wave bands if they're bad.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 23, 2013, 06:03:21 pm
content: Good news guys!I think I have all of the parts now so it should just be a few hours to solder in the rest of the parts and then I should be able to power this up for the first time later today!I'm really excited!

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 23, 2013, 06:55:12 pm
content: Well it looks like I actually don't have two of the caps, must still be in the mail.They are tiny value caps that are replacing some paper caps.I'm thinking I might just go ahead with the rest of the replacement and then just leave those originals intact. I'm going to run this on a tiny ballast, and with a variac so what's the worst that can happen?Let me know what you think everyone.

author: Chryseus
author_rank: Regular Contributor
timestamp: August 23, 2013, 08:09:21 pm
content: Give it a go, I usually give a radio a run after replacing the main electrolytic, assuming none of the paper caps are completely gone you should get something out of it.My method of repairing a radio is as follows:Replace main electrolytic can and any leaking or exploded capacitors.Using a variac and / or isolation transformer with a ballast (I.E 40W lightbulb):Disconnect the HT output so you only have the rectifier tube and main filter capacitor, check that the high voltage comes up to the correct range (usually will be high due to little load) maybe 260V depending on various factors, check the filaments all light up.Insert an ammeter in series or just monitor the HT voltage, connect the HT to the rest of the set and power it up, all being well the voltage and current draw should remain at a reasonable level and you should get sound out of the speaker if all is well.If the current draw is reasonable but the HT is low then you probably need a bigger ballast or you can go without it which I usually do at this point.If you get excessive current draw then you most likely have a bad capacitor or in some cases a shorted resistor (although I've never actually seen a shorted resistor).Once it's working leave it on for a couple of hours to make sure nothing fails, particularly if you've only replaced some components, after that you can tweak it and perform an alignment as needed.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 23, 2013, 08:22:47 pm
content: Quote from: Chryseus on August 23, 2013, 08:09:21 pmI did try it out, first slowly, only going to about 80V then shutting it off to check the caps and what not. I brought it up to about 115 a few times and I notice that when I turn it on it initially draws a bit of current, then draws less for about 4 seconds, then the current returns to its initial range. I'm guessing that initial current is the filaments warming, then it settles when they warm and then it raises when the tubes begin to function?Unfortunately all I get is a hum out of the speaker. The rectifier and output tubes get warm, but the other 4 tubes are not getting nearly as warm and are taking extremely long to warm up.I'm pretty sure the speaker is wired on correctly but I could be wrong.Help?

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 23, 2013, 08:32:15 pm
content: Oh and there was another knob on the front of this, but its contacts were horribly broken and I removed it.The only two connections to the knob were from the rectifier's one leg to the one side of a capacitor. I don't know what this knob did and if maybe that is whats stopping this from working.EDIT: after looking at the schematic, I found it is the tone control knob.It looks like it either connects the cap to the one pin on the output tube or the other pin. Or maybe just one. The schematic isnt too clear on switches.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 23, 2013, 11:52:59 pm
content: Any help? I don't know about tuning knobs, does anyone else?

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 24, 2013, 01:26:49 am
content: Actually I think that judging from the schematics as well as the hum that I don't have the main filter caps hooked up correctly.The schematic isn't very clear as to the polarity of the electrolytic filter caps 10x 10y and 10z, can anyone help.

author: G7PSK
author_rank: Super Contributor
timestamp: August 24, 2013, 09:43:42 am
content: My experience with those old radios is that they always hum without a signal, it sound like your output stage is working have yo tried turning the volume control the hum loudness should alter as you do, if it does you need to work backwards checking the if stages and ending at the input. This is where some form of signal injector comes in handy, there are plenty of designs around using just one transistor. It could well be that replacing the capacitors has altered the tuning of the if transformers so they will need adjusting but don't touch them yet.

author: Chryseus
author_rank: Regular Contributor
timestamp: August 24, 2013, 10:45:24 am
content: The tone control switch isn't critical and should not stop it working, if you want to replace it just get a single pole switch and connect it between capacitor 22Y and the screen grid of the 42 (output tube).Capacitors 10X and 10Y have their negative leads connected to the chassis, 10Z is connected between the positive side of 10Y with the negative side of 10Z going to the center tap of the transformer high voltage winding.

author: G7PSK
author_rank: Super Contributor
timestamp: August 24, 2013, 05:08:15 pm
content: One of the oldest ways to get rid of hum is to switch the low frequency transformer leads over.

author: Chryseus
author_rank: Regular Contributor
timestamp: August 24, 2013, 06:17:50 pm
content: Quote from: G7PSK on August 24, 2013, 05:08:15 pmI can't really see how that works..

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 24, 2013, 07:27:45 pm
content: There's something not working correctly in the radio part of this radio. Me and someone else online have been troubleshooting it and I have got audio out of it but only by connecting in my own audio.

author: mamalala
author_rank: Unknown
timestamp: August 24, 2013, 08:30:56 pm
content: Quote from: Chryseus on August 24, 2013, 06:17:50 pmOld tube radios (and also tube amplifiers) usually have AC heating for the tubes. Then, the rectification is usually not perfect. There is the "trick" to inject some AC (or "rectified" DC) at a 180° phase shift, which in turn will cancel out some of that. I have seen a lot of professional tube amps (for example the 30 watts amp in the Klein+Hummel OX studion monitors) that had a pot especially for that purpose: to adjust the amount of "directly injected hum" that cancels it out.Or simplified: -1 + +1 = 0....Greetings,Chris

author: Chryseus
author_rank: Regular Contributor
timestamp: August 25, 2013, 12:26:06 pm
content: Quote from: mamalala on August 24, 2013, 08:30:56 pmThat's a pretty neat idea, thanks!