Test Equipment - Page 1
Forum section: electronics / beginners

author: mc1822
author_rank: Contributor
timestamp: March 04, 2023, 02:11:45 am
content: I would like to learn how to repair vintage tube radios including tube shortwave receivers. I already have some experience with electronics as I have built several stereo tube amps and I am proficient at soldering. I have several multimeters (both digital and analog) a variable isolated power supply, a temp controlled soldering station plus various hand tools. My question is: Which would be better as my next piece of equipment, an RF generator, audio generator or a function generator?

author: xrunner
author_rank: Super Contributor
timestamp: March 04, 2023, 02:18:39 am
content: Quote from: mc1822 on March 04, 2023, 02:11:45 amOf those three items, I'd pick an RF generator that can output a calibrated level of power (dBm). You need this to check the receiver. For example, S9 should be -73 dBm at the antenna input of a shortwave receiver. Then you can check the S meter and have confidence that the receiver and S meter is working properly. This RF generator won't be cheap but will be very useful.

author: coromonadalix
author_rank: Super Contributor
timestamp: March 04, 2023, 03:11:46 am
content: and you have to learn playing with high voltages in them

author: Technical Ted
author_rank: Contributor
timestamp: March 04, 2023, 12:11:54 pm
content: Of those three you listed, I too would suggest the RF signal generator. Since many refer to arbitrary function generators as "signal generators" here is what I own and the type of equipment I refer to when I say signal generator: Agilent 8648B Signal Generator. I had good luck buying this one from eBay for close to $700 and it is in excellent shape.I didn't see a few other pieces of gear mentioned in your post.... ie do you have a decent oscilloscope? Frequency counter? I personally would want an oscilloscope for sure.Ted

author: Zenith
author_rank: Frequent Contributor
timestamp: March 04, 2023, 01:02:02 pm
content: Definitely an RF signal generator with an attenuator which goes down to sub µV levels. You'll need that to align the tuning and the IF stage. They have a built in AF generator as a modulation source and often it has an output, if you need an AF signal source for some reason. I've never found AF signal generators that useful for working on radios.Note that RF signal generators are usually very well shielded against RF leakage. Function generators many not be so well shielded and don't produce the low signal levels which can be useful.If you are working on shortwave receivers of any sophistication, you will need to do swept alignment, and for that you will need a sweep oscillator and an oscilloscope, or a spectrum analyser.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: March 04, 2023, 11:23:07 pm
content: I repair both tube radios and transistor radios, Mostly HAM equipmentI would recommend that the OP look into a Service MonitorThere are plenty of models of various brands. I use an HP 8935 E 6380. Service monitors are mostly used equipment.You get a RF generator, Audio generator, Spectrum analyzer, power meter and more in one unit. You can use the audio generator to modulate the RF carrier for an AM signal. SSB receiver function can be evaluated using the AM signal also.Almost everything you would ever need. You can use the SA to observe the IF frequencies, just use an oscilloscope probe.Everything you need most of the time.Of his list, I would think a RF generator would be the most useful.Power Supplies for tube equipment are different in that they are high voltage. Probably not necessary unless you are designing equipment.The OP probably knows this.

author: Zenith
author_rank: Frequent Contributor
timestamp: March 05, 2023, 12:25:30 pm
content: The problem is he's starting on this path and an HP8935 is an expensive piece of kit.If he's got any sense he will work on domestic radios and simple SW receivers, (not needing swept alignment) first. These have the advantage of being fairly cheap and you don't feel too bad if you wreck one by making a mistake, or you find you've bought one with a burned out mains transformer etc.For an RF signal generator there are all sorts of options, depending on how much he wants to spend. A lot of folks who restore domestic radios manage very well with a fairly simple solid state or vintage vacuum tube RF signal generator, available for about $50 or less.

author: mc1822
author_rank: Contributor
timestamp: March 06, 2023, 11:16:59 pm
content: I plan on only working on tube radios from the 40's and 50's. As far as shortwave radios, I will be mostly looking at the same period. I would especially like to find some old Heathkits because the construction manuals are easy to come by.

author: themadhippy
author_rank: Super Contributor
timestamp: March 06, 2023, 11:34:59 pm
content: Quoteif you got the manuals why do you need the kit?

author: bdunham7
author_rank: Super Contributor
timestamp: March 06, 2023, 11:46:47 pm
content: Quote from: mc1822 on March 04, 2023, 02:11:45 amI have all three but I find that a decent AWG is actually sufficient for anything within it's frequency range. In my case that is 120MHz, so AM, shortwave and FM, but not things like marine VHF or some avionics. You do need attentuators to get low signal levels. In addition, the AWG will do audio and a lot of other handy things.

author: james_s
author_rank: Super Contributor
timestamp: March 07, 2023, 01:00:24 am
content: RF generator definitely, however if by "tube radios" you mean AM broadcast radios then most function generators will cover the frequencies you need. Almost all of these radios have an IF of 455 kHz and the top of the dial is under 2MHz.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: March 07, 2023, 12:18:02 pm
content: I did use old Eico an RCA RF signal generators. This is what the tecks at the time used for service.You can get these things very inexpensively.Some of them even have the IF frequency on a output.The downside is the lack of accuracy of the dial, which you can remedy with a freq counter.Also the output magnitude is a bit hard to control.But these things were used a lot for service and you may like keeping to the common technical limitations of the time period you are talking about.Definitely "Old School"

author: james_s
author_rank: Super Contributor
timestamp: March 07, 2023, 09:46:06 pm
content: A modern synthesized signal generator is far superior though. You can punch in the exact frequency and it will go right to that and won't drift. In many cases you can save multiple configurations and recall them on demand.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: March 07, 2023, 10:10:36 pm
content: This is largely a how beginner and what budget kind of question.There is no question that RF signal generation is his number one need for his stated purpose. And these can be very inexpensive. Any modulation needed can be cobbled together easily, or even generate by a personal computer.An arbitrary function generator can do most of the job better, with the two potential weaknesses being low level outputs and possibly inferior shielding. But the application doesn't require precision attenuation and it is easy to build a simple attenuator which provides a few key output levels. With a little thought and work there are even ways to get accurate low level outputs. Shielding is harder to improve but their are possibilities. Biggest downside is cost. But might be the right answer for someone either committed to the hobby long term or with good financial resources.I would skip the audio generator completely unless you get involved in high fidelity audio. There are many cheap and practical workarounds for the need for audio signals. But, for the under 2 or 3 Mhz signals required to work on these vintage radios there are relatively inexpensive audio sources that generate the required signals up to a few MHz.It might come down to what the best deals are on Ebay and at Ham swap meets during your shopping interval.

author: james_s
author_rank: Super Contributor
timestamp: March 07, 2023, 10:30:48 pm
content: A modern budget waveform generator is arguably both an RF signal generator and an audio signal generator. Not as good as dedicated instruments but plenty good enough for the purposes under discussion here. The FY6800 is inexpensive and works up to 60MHz, that's certainly RF. It can do various forms of modulation too.

author: SuzyC
author_rank: Frequent Contributor
timestamp: March 07, 2023, 10:49:56 pm
content: You don't need any high-cost test equipment at all. Your next piece of equip is none of the above. You could certainly benefit from an old 20-MHz analog oscilloscope to trace signals, see distortion, see power supply faults, etc. You can sometimes find these almost given away at HAM meets or even flea markets.Refurbishing older radios is primarily a process of replacing leaky coupling capacitors and electrolytics p/s caps that have lost their uF.You don't even need an oscilloscope, you can find bad filter capacitors by measuring ripple voltage on p/s capacitors with the AC volts function on a multimeter. You can always test a filter capacitor by bridging across them with a new electrolytic.Nearly All paper capacitors and almost all older mica capacitors will need to be replaced.Repair is also a process of repairing rotting paper that make tairs in speaker cones. You will face cleaning dusty tuning capacitors and replacing worn out or broken or slipping dial cords.You will find with an ohm meter there are always resistors that have drifted way out of value that need to be replaced. Old volume and tone controls need to be sprayed with a shot of WD40 to rid them of bad spots.In the case where one or more tubes that need to be replaced, and if you have enough old radios in stock, you can borrow a tube or two from one radio to test or fix another. Tubes can still be bought on ebay.It is easy enough to tune RF superhetrodyne circuits using known AM radio stations to make them match the mark on the dial of the receiver. 455KHz IF stages can be accurately tuned with a small tweak(a screwdriver or plastic hex adj. tool) to achieve the best amplification. A weak distant radio station is the ideal modulated signal for alignment of all RF and IF circuits.Finally, you may have to deal with the problem of broken knobs and rotting fabric that covers the speakers and damaged wooden and plastic radio cabinets need to be carefully cleaned or repaired with casting resin.BTW, there is one or more ~100 USD (This incl ship to the north pole, much less ship cost to USA) old school RF signal generators right now on Ebay.comThe most important thing to learn is how to keep one hand behind your back when troubleshooting HV power supplies!

author: Zenith
author_rank: Frequent Contributor
timestamp: March 07, 2023, 11:30:23 pm
content: Yes. Restoring vintage domestic radios involves a lot more than dealing with the electronics, such as cabinet and dial restoration and what lengths should be gone to to to preserve the original appearance.Back in the day, the repair shop probably wouldn't have much test equipment beyond a VOM. I doubt they would have touched the IF stage set up in the factory, but 70 years on it's a different story.I think the OP would be well served by a Heathkit/Eico/Advance/etc RF sig gen, which can be picked up cheaply at swapmeets or even ebay. There are also web forums dedicated to domestic radios and TVs, where he could pick up a lot, such as tips on how deal with obstinate IF transformer cores.

author: james_s
author_rank: Super Contributor
timestamp: March 08, 2023, 12:24:18 am
content: A lot of that vintage stuff has achieved collectible status now so it's not really much if any cheaper than modern Chinese gear. I repaired several radios last year and found more than one collector online that said they used to use one of those vintage RF generators and replaced it with a modern inexpensive signal generator, they claimed the modern gear works much better. I already had a AWG so I used what I had and it worked fine. I was able to align it significantly better than by using a radio station. If you have a source of 455kHz you can align the IF stage to the correct frequency easily.

author: SuzyC
author_rank: Frequent Contributor
timestamp: March 08, 2023, 04:16:04 am
content: What, in terms of actual radio performance, did you notice after achieving "significantly better alignment"? Could you make a comparison of alignment on the same radio to realize a noticeable significant difference in performance?455KHz is 455KHz and 1100KHz is 1100KHz, and these test signals are the same from a 400Hz modulated breadboarded 455KHz RF osc circuit or from an old Heathkit or using a weak AM radio station or else from a 6000 USD HP signal generator from the standpoint of aligning an old AM radio.I used what I had and it worked fine.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: March 08, 2023, 11:49:16 am
content: Around here the vintage stuff is still being almost given away. I pretty much gave mine away, cannot keep everything.But for the most part any RF generator will do, you do not even need an accurate signal level, or to be spot on in freq. You are tuning for MAX most of the time.As far as IF adjustment is concerned, Most of the time, adjustment of the IF stages is done to get the most signal. Usually the S meter of a radio or the audio output can be used, maybe with any old scope on it. Especially in old radios. For AM there is not much you need, usually all you need is to be close. for SSB you need the ability to change frequency of the injected signal accurately.It is nice however to be able to modulate the RF though, and to have AM and FM modulation.Since the OP built a tube stereo amp, he probably is interested somewhat in FM radios.By the way, I did build the bigger audio amp from the back of the RCA manual when I was a kid. The tubes were not cheapI used the metal box of my Gilbert Chemistry set for the chassis and old transformers from broken radios.Edit,If I remember correctlysome of the old RF generators had a built in AM modulator (which you could also use as an audio generator) , in addition to IF freq generator.I kinda liked the RCA "Senior"

author: james_s
author_rank: Super Contributor
timestamp: March 09, 2023, 06:39:06 pm
content: Quote from: SuzyC on March 08, 2023, 04:16:04 amI didn't try both methods and do a detailed comparison, but I did achieve vastly improved performance relative to when I received the radio with numerous stations coming in clearly that I previously was not receiving at all.Is there something that bothers you about perfectionism and wanting to align everything as close as possible to what the designer intended? I had the tools to do it right, so I did it right, and it worked out very well. If "close enough" satisfies you then do it your way, but I'm going to continue to squeeze every last drop of performance possible out of my old radios simply because I can, it's a hobby and I enjoy it. A signal generator is <$100 and makes the task much easier.

author: mojoe
author_rank: Frequent Contributor
timestamp: April 08, 2023, 12:57:02 am
content: Having repaired dozens of old tube radios, I agree with SuzyC. As a general rule, I would replace all paper caps, all epoxy-dipped caps and all electrolytics, without bothering to test. Test the other caps, and the resistors. Generally, the resistors would drift high in value. For caps that sit above the chassis, either pull the guts out and solder a new cap inside, or clip the leads beneath the chassis and solder a new cap underneath. It depends on how original you want things to look. Tubes are generally good.If you find a selenium rectifier, definitely replace it. They give off toxic gas when they fail. If you want to keep that original look, disconnect it and hide a modern diode underneath.High voltage caps are getting harder to find. There used to be a guy in Canada who specialized in selling high voltage caps. I don't know if he is still around. There also was a guy selling authentic vintage knobs. You can even buy modern cloth-covered wire, and new dial string.One piece of equipment that you definitely want is a "dim bulb tester". You can make one yourself, for very little money. I guess the trick is, finding an incandescent bulbNever power up old tube gear without limiting the AC voltage in some way. With bad filter caps, you may fry the rest of the circuit. If you want to be fancy, a variac and an isolation transformer are nice to have (the isolation transformer especially on the AA5 radios that don't have an AC transformer).Yes, an RF generator will let you do a better job of aligning the stages. Whether you buy a vintage RF gen, or a modern one, you don't need anything fancy or expensive. A modern synthesized RF gen is orders of magnitude more precise than what all the repair shops used.Some of the old RF gens had a crystal socket, or some built-in crystals for common IF frequencies. In the early days, there were several different IF frequencies in use. Later, everyone used 455 kHz for AM.For repairing speaker cones, some rubber cement, a piece of a coffee filter and a black magic marker does a good job.Some invaluable resources (I uploaded these a few years ago):https://archive.org/details/riders_202008/Index%2001-15/page/n9/mode/2uphttps://archive.org/details/philco-radio-1928-1937https://archive.org/details/aligning-philco-receivers-by-john-f-riderhttps://archive.org/details/zenith-vol-1/Zenith%20Vol%201/mode/2upAnd a good forum on this topic:https://www.antiqueradios.com/forums/index.phpQuote from: SuzyC on March 07, 2023, 10:49:56 pm

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: April 08, 2023, 11:23:07 am
content: The OP might wish to hang out at some Hamfests. Lots of old equipment cheap.If he was in my area I could easily set him up with lots of working old equip for a few hundred bucks, Even including tube testers.I still think that a good freq generator is important. For aligning short wave radios it is difficult to find an AM station to use as a tuning pointFor standard commercial AM bands a local station works fine, likewise an FM station can be used for aligning FM Broadcast radios.WWV is quite helpful also.He already has multimeters which are the most used pieces of equipmentTuning tools like plastic hex wrenches are necessary, All sorts of sizes and shapes are necessary. I never seem to have the "right one"Worn out tuning tools can break the slugs. Candle wax is really good for lubricating and sealing the slugs, use heat from soldering iron. The old slugs are frequently coated with beeswax.A signal generator of any kind that is halfway accurate is very nice to have. It does not need to be super accurate.One that goes to 30 MHz is advisable for short waveOne that goes over 100 MHz is used for FM Broadcast.moejoe is entirely correct, a modern signal generator is really much better than the old ones. Just make sure the freq range meets your needs.Modern generators are entirely acceptable in their accuracy for your needs.If the generator is entirely analog (old unit), a good, again not the best, freq counter is very helpful. Heathkit, for example, had a few very good ones.Moejoe also made a good point about xtal tester being part of old freq generators. When you need one later then get it (or if you find one cheap, say $10). I use a spectrum analyzer for xtal freq, but sometimes an xtal looks OK on SA but does not work in the oscillator while another xtal does work.I did suggest Hamfests as a source of equipment and parts.There are historical radio clubs that may be more helpful. Here in Indiana we have the Indiana Historical Radio Society.They are notoriously cheap and have all sorts of equipment from the era he is talking about. Both test equip and old restorable radios. Including parts especially tubes.Some of these people take pride in using only old test equipment for their work.Lots of them have duplicates of their test equipment (newer and ancient) and can be cajoled into selling for reasonable prices.Some of the results are "better than new" I even had a 1938 Hallicrafters SW radio that was totally restored by one of them including ALL new caps and resistors and new paint including new silkscreen lettering on the faceplate. Sold it to a Hallicrafters collector.Perhaps before you buy anything you could attend one of their flea markets and get face to face recommendations..Here is an example of an old radio "club", in NW US:http://nwvrs.org/For schematics and pictures here is a good source:https://radiomuseum.org/also really good tube data.Be careful about buying test equipment, you may end up having to join "Test Equipment Anonymous" TEA Thread.

author: n4u
author_rank: Contributor
timestamp: April 08, 2023, 01:26:02 pm
content: IMO u shoud start with spectrum analizer or VNA.Generator can be easily done with filter, amplifier, level control loop and adf43XX or similar. Sure - to measure receiver u will need some signal - but u may need only antenna or transmitter to get it - but without measuring result / parasitic frequencies etc generator cant help enought.

author: mojoe
author_rank: Frequent Contributor
timestamp: April 08, 2023, 05:40:43 pm
content: All of this fancy (expensive) equipment is gross overkill. For decades, radio shops used nothing more than an RF generator and an analog meter to repair and align tube radios. In fact, an analog meter is very useful if you need to peak an adjustment for max voltage.A tube tester is nice to have, but seldom needed. I had a Hickok tube tester, and of all the radios that I worked on, I found almost no bad tubes. The OP said he was interested in radios from the 40's and 50's, so buying a handful of commonly used tubes to swap would be much less expensive.Take a look at some of the alignment instructions in the service documents that I posted links to. This is not rocket science, and doesn't require a lab full of test equipment. You don't need high precision, either. The component tolerances on most parts was +/- 20%. A reasonably accurate signal source and a good ear is plenty good enough.

author: james_s
author_rank: Super Contributor
timestamp: April 08, 2023, 06:24:20 pm
content: Quote from: n4u on April 08, 2023, 01:26:02 pmI have a spectrum analyzer and I have never once used it while restoring an old radio or amplifier. What on earth would you even use one for in that context? I find it strange that you would suggest such an expensive and specialized piece of equipment for that task. Maybe if you were trying to align tranmitters?

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: April 08, 2023, 07:03:50 pm
content: I use a spectrum analyzer all the time in aligning amateur radiosMany radios have filters that remove spurs. Nice to see them go away with the adjustments.Not necessary for most Rx radios and a bit expensive, it is very helpful to get clean transmit and to see transmit sidebands.There are lots of cheap SAs around now but I have not even tried to use any of them and do not know how easy they are to use.They do look like fun though.Edit, SAs include a freq readout which is very helpful.

author: n4u
author_rank: Contributor
timestamp: April 09, 2023, 10:35:10 am
content: U dont have to buy sth pricey even rtlsdr is cheap - frequency characteristic is not linear but having a multimeter its all what you need for measurement / diagnostics of receiver in 500k-1.75GHz when u have some input for it. Fixing an FM radio u already have signal, already have some noise - u need just use it. For am u may make simple transmitter with sound card and oscilator. Generator is needed only when u havent any input for your device. But u may buy some dds and use it as noise source - but imo spectrum analizing is more important

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: April 09, 2023, 11:27:36 am
content: Another thought:Evaluating big old capacitors is problematic. Many of these old radios have caps rated in hundreds of volts.Most current cap testers do not provide the hundreds of volts necessary to test them. Tube radios commonly use hundreds of volts.Old cap testers like the Heathkit, Eico ones have high volt test capabilities.These testers had a "Magic Eye" tubeTheir accuracy is not important mostly but the ability to test for leaky big old caps is necessary, unless you just replace all the old caps which is not a bad idea.The accuracy of the caps is secondary consideration to their leakiness. Most of these old caps had quite a range of stated capacitance relative to their actual capacitanceAgain, old "magic eye" testers are really cheap.Testing these caps is more important now than when the radios were built since the caps deteriorate with age.