Drake SPR-4 Shortwave Receiver  - Page 1
Forum section: electronics / rf-microwave

author: xrunner
author_rank: Super Contributor
timestamp: May 24, 2019, 12:18:53 am
content: I never could afford this one as a kid but I ran across one on Ebay, so I went for it. It uses crystals for each 500 kHz range, but is still a highly regarded receiver. This one has the original crystals for the major shortwave broadcasting bands, as well as additional ones that cover the ham bands.You can see the actual unit in the pic, complete with icky blueish LEDs. I'll be restoring the original lighting look as best I can, as well as taking a lot of pictures. Surprisingly, except for the outside and typical shots of the top and bottom chassis, there aren't a lot of detailed pictures available for different parts of the circuits.I'll also do a complete alignment and detailed cleanup. Should be here by next Wed., so consider this a placeholder for the time being.

author: xrunner
author_rank: Super Contributor
timestamp: May 26, 2019, 02:41:58 pm
content: After Googling I think I found the retrofit lights that are in the SPR-4 (but won't know for sure till mid-week when I get it). They might be these designs -http://www.radiolabworks.com/products/4linelamps/4linelamp.htmlHowever, after looking at a whole lot of pics of this radio and others that have the original blue, they sure don't look like the right color to me.In any case - more to come ...

author: Stray Electron
author_rank: Super Contributor
timestamp: May 26, 2019, 11:17:30 pm
content: FWIW I found shorted caps in the Drake receiver that I inherited.

author: xrunner
author_rank: Super Contributor
timestamp: May 27, 2019, 12:40:05 am
content: Quote from: Stray Electron on May 26, 2019, 11:17:30 pmWhat model Drake was it?This one is working fine (well it was before it shipped) so hopefully it will survive the trip. I do plan on replacing electrolytics though.

author: Stray Electron
author_rank: Super Contributor
timestamp: May 27, 2019, 04:55:57 am
content: An R-8 if I recall correctly. It's packed up and I haven't touched it in years. I replaced it with a Racal RA-6790 and now it's developed problems too

author: xrunner
author_rank: Super Contributor
timestamp: May 28, 2019, 02:02:54 am
content: Quote from: Stray Electron on May 27, 2019, 04:55:57 amOh OK, yea that was one of their more modern receivers. You should unpack it and see if it still works.Still waiting on the SPR-4. I did some research on the serial number from this database -http://www.wb4hfn.com/DRAKE/DrakeSNDatabase-P2.htmSPR-4 Receiver 0134 May 25, 1970SPR-4 Receiver 1652 Feb 07, 1972SPR-4 Receiver 2193 Sep 02, 1972SPR-4 Receiver 4331 Feb 20, 1975SPR-4 Receiver 5973 Nov 10, 1976SPR-4 Receiver 6289 Apr 26, 1977SPR-4 Receiver 6318 May 18, 1977The unit I'm getting (see pic) SN 3881, appears to have been made between 1972 and 1975, just about the time I was wanting one as a kid. Pretty cool.

author: Specmaster
author_rank: Super Contributor
timestamp: May 28, 2019, 10:27:47 am
content: Quote from: xrunner on May 26, 2019, 02:41:58 pmPersonally I think that the before modification photo is much more readable then the after photo, I thought I'd throw my in views on it just in case.

author: bd139
author_rank: Super Contributor
timestamp: May 28, 2019, 10:46:40 am
content: Agree.I'd go as far to say that blue LEDs are a visual cancer on this planet IMHO. I rather like an incandescent lamp.

author: xrunner
author_rank: Super Contributor
timestamp: May 28, 2019, 11:51:48 am
content: Thank you for your comments.Quote from: Specmaster on May 28, 2019, 10:27:47 amI agree 100% Specmaster. There's a slight chance its a "camera thing" and the blue LEDs don't really look that bad. But I doubt it.Quote from: bd139 on May 28, 2019, 10:46:40 amThere will be NO blue LEDs in it after I'm done bd139 - rest assured.We'll just have to see how it goes as far as other options. Even using original lamps isn't out of the question. From the schematic they are type 47 bulbs rated @ 6.3 VAC 150 mA. I'll order some type 47 bulbs just to see what we have as far as the original look.From what I understand, they are trying to compensate for the original plastic tint piece losing it's color over the years. The root problem is really the plastic tinting parts, not the lamps (unless you want to get rid of the heat they produce). The best option would be to replicate the blue plastic parts. I'd rather call the color turquoise, after looking at a t lot of pictures of the Drake line from back then. They used the same color in their other units such as the ham radio line receivers and transmitters. There might even be a part for my 3D printer to play in this, as I've seen turquoiuse filament for sale ... wouldn't that be interesting.Original Color Examples:

author: xrunner
author_rank: Super Contributor
timestamp: May 30, 2019, 12:48:45 am
content: I got the Drake SPR-4 today and it's in very good shape. I really receives great but the blue LEDs look pretty bad. I will be posting the inside pics soon, and looking to see what we've got going on inside. Then I'll do a complete alignment and get that backlighting looking the way it was meant to be.

author: Kosmic
author_rank: Super Contributor
timestamp: May 30, 2019, 02:31:32 am
content: I agree with everybody, the blue LEDs are weird and make the scales harder to see. I really like the original light though.

author: bd139
author_rank: Super Contributor
timestamp: May 30, 2019, 07:30:18 am
content: Looks like it’s in pretty good condition

author: Specmaster
author_rank: Super Contributor
timestamp: May 30, 2019, 07:44:46 am
content: Quote from: Kosmic on May 30, 2019, 02:31:32 amCould be worse though, they could be purple

author: xrunner
author_rank: Super Contributor
timestamp: May 30, 2019, 06:09:39 pm
content: Here's the first set of pics for reference. Mostly looks good. I did find a resistor soldered only at one end, and a capacitor in the same condition. Will investigate these. Also a narly electrolytic. Those all will be replaced, as well as tantalums.

author: Specmaster
author_rank: Super Contributor
timestamp: May 30, 2019, 06:41:13 pm
content: It looks as if someone has been in there before, some very dodgy looking joints there. The 4th and 5th crystals don't look to be fully seated in their sockets either. Apart from that I like the way that each section has its own pcb, makes it easier to a full recap etc board by board.

author: PA0PBZ
author_rank: Super Contributor
timestamp: May 30, 2019, 07:20:15 pm
content: Interesting noise blanker you got there

author: bd139
author_rank: Super Contributor
timestamp: May 30, 2019, 07:23:37 pm
content: Looks pretty good inside. The thing will be easy to debug at least as each bit of the signal chain is separate.

author: xrunner
author_rank: Super Contributor
timestamp: May 31, 2019, 12:18:28 am
content: Quote from: Specmaster on May 30, 2019, 06:41:13 pmI found out what the capacitor and resistor with loose ends were for. The capacitor is OK to be there, it is connected across the loop antenna jack (I do not have the loop antenna). I do not know why it was disconnected, it may have popped off. I re-soldered it.The resistor too is OK to be there, it is an optional mod the user can install at those terminals to control the AVC time constant. The SPR-4 comes with no resistor or wire connected across those terminals. The user was experimenting with a 3.2 Megohm value which is a valid value in the range indicated in the manual. They obviously didn't keep it connected. I will remove it for now and experiment with that later.For today I replaced three electrolytics and one tantalum on the audio board. All went well. The wires you see next to the old caps were what the assemblers used as tie wraps, back in the day. I will replace some of them to keep it vintage.Next board - please step up to the soldering station.Quote from: PA0PBZ on May 30, 2019, 07:20:15 pmYea, that board is rare and I do not have it.Quote from: bd139 on May 30, 2019, 07:23:37 pmYes it's old school and pretty open to troubleshoot.

author: xrunner
author_rank: Super Contributor
timestamp: June 01, 2019, 12:00:56 pm
content: Removed all knobs and removed the front panel. Cleaned all lexan dials. All the original felt panel "spacers" simply turned to dust when touched. Removed with alcohol and replaced with new felt dots.The filter cap for the power supply has a couple of electrolytics in a can - 500 uF & 1000 uF. Found a small company that custom makes them. I ordered the replacement can cap, may take 5 - 10 days.

author: bd139
author_rank: Super Contributor
timestamp: June 01, 2019, 01:11:48 pm
content: Looking goodI have “drake” added to my eBay search list now

author: Specmaster
author_rank: Super Contributor
timestamp: June 01, 2019, 08:57:53 pm
content: The lighting colour is so much better now and wonderfully clear to read to.

author: xrunner
author_rank: Super Contributor
timestamp: June 02, 2019, 01:44:18 pm
content: Thanks for the comments!SPR-4 calibration oscillator and S-MeterJumped over to the 100 kHz calibration oscillator and replaced the 10 uF tant cap on it. I had to replace the speaker cable too. I didn't want to lose the original plug but I had little choice - the internal connections of the sealed plug were just too far gone and causing intermittent audio. I dug through my audio cable box and found a gray color that matched pretty well and replaced it with that.I removed the S-Meter for cleaning. You can see that they achieved the tinting by wrapping a piece of blue film around the side next to the lamp. It's held on by some sort of paper tape around the rest of the housing, which had yellowed. I took it all off and re-worked it, using white electricians tape to hold it. You can also see the grease on display on the shaft below the S-Meter.I think I'll take a quick look at the S-Meter calibration because all the readings seem too high when I've scanned the bands, be they actual signals or just the noise level.

author: bd139
author_rank: Super Contributor
timestamp: June 02, 2019, 02:50:17 pm
content: Awesome workThere’s something sexy about those big 100Khz calibrator crystals. I keep bidding on them here but they go for silly money

author: Specmaster
author_rank: Super Contributor
timestamp: June 02, 2019, 04:00:31 pm
content: @Xrunner, very good indeed so far, looking forward to seeing the completed item and seeing how it performs. The 10uF tant, replaced because its a "bastard tant" or because it is duff?

author: xrunner
author_rank: Super Contributor
timestamp: June 03, 2019, 12:47:58 am
content: Quote from: Specmaster on June 02, 2019, 04:00:31 pmJust replacing them for peace of mind you know - S.O.P. here.I ran into an interesting issue trying to cal the S-Meter per their procedure. I will have more on that when I figure out a better way perhaps tomorrow.This thread is for future reference for hopefully many people outside the EEVBlog who are searching for SPR-4 information. I found some out there, but some of what I'm experiencing and will experience hasn't been written about on the internet as far as I've seen. So I hope it will help a few people with these radios. I'm sure all the alignment procedures have much more to keep me on my toes besides the run-in today with the S-Meter procedure.

author: xrunner
author_rank: Super Contributor
timestamp: June 03, 2019, 12:05:03 pm
content: Thought I'd do a quick check of the S-Meter accuracy, and did the little calibration procedure from the alignment procedure shown in the attachment. I used the Agilent 8648A to inject the 10,000 uV signal at the antenna terminals. I suppose they liked to use that type of nomenclature back then but in effect it is close to -27 dBm at the ant. terminal (~50 ohm). Then you're supposed to adjust for 4.5 volts on a terminal ...But, after doing the adjustments the way they say, the metering accuracy sucks, even knowing that many S-Meters aren't that great anyway. Everything seemed to be biased way too high. I know this because I compared it to the standard S-Meter set points in the attached document "Signal Level Strength Meter Calibration and IARU" and my Icom IC-7300, switching the same antenna back and forth.So I said to myself "Why don't we just calibrate the actual S-Meter directly, using known set points to it's scale? That's what the scale on it is for." A crazy idea but it just might work.So what I did was tuned in WWV @ 10 MHz on the 7300 and noted the average S-Meter reading, and then tuned off a bit and read the noise level. I then calibrated the SPR-4 to those settings using the two pots in the instructions while it was tuned to WWV. Well, that resulted in pretty good S-Meter readings.I then compared the S-Meter response to the set points in the document using the Agilent as the antenna input and it really compared quite well. S9, which is supposed to be -73 dBm, resulted in the meter reading just a tad above S9, and the readings below S9 tracked within reason. Readings above S9 were off a little but fell within the expectations of this type of simple circuit.So, I don't know who wrote or transcribed that S-Meter cal procedure but it doesn't work very well as far as I'm concerned. I suspect I'll be running into more as I go on that will require a certain amount of common sense to be substituted for what is written.

author: bd139
author_rank: Super Contributor
timestamp: June 03, 2019, 02:27:18 pm
content: Think that's standard operating procedure for radios. Had the same experience with a Howes kit I bought ages ago and the K2.

author: xrunner
author_rank: Super Contributor
timestamp: June 04, 2019, 11:38:34 pm
content: I hadn't seen any measurements of the accuracy of the crystals in the SPR-4, so I did some quick checks just for fun.Due to the mixing scheme employed, the crystals are 11.09 MHz greater than the resultant MHz band. So for the 1 MHz band crystal you have 1.0 + 11.09 = 12.09 MHz, etc. Anyway, the results of some of the crystals are shown in the screen shot of the spreadsheet.I hope to proceed with the alignments very soon.

author: xrunner
author_rank: Super Contributor
timestamp: June 06, 2019, 01:23:03 pm
content: Drake SPR-4 50 kHz IF AlignmentI'm consulting some notes gathered from this link -http://www.zerobeat.net/drakelist/drakemod/drmod101.htmlThese are my notes on the procedure shown in the attachment from the SPR-4 manual - 50 kHz IF, BFO, and LC Filter Alignment. I took a pic of the bottom of the radio before I started. It shows the original setting of many things. If you need to you can refer back to it. Most adjustment screws and coils are not very far from the original position. You radio may be different - take a picture before you start, you won't be sorry!Refer to annotated schematic for helpful circuit points highlighted for youYou need some tuning sticks, especially one with an open slotted end for the L11 - L14 transformers. If you don't have them stop now and go to Ebay ... they look like the tools in the attached pic.Do not connect a "VTVM", a.k.a. modern DMM to the AVC line due to it's high impedance, I tried it and it completely changed it's response. Look at the S-Meter instead. You can also look at the signal at the output of T-16 with a scope.Use headphones to listen for a zero beatT15 and T16 are very broad tuning. In fact I hardly noticed any change as I went through the entire range of each one, so I just went back to the original settingOtherwise the procedure is straightforward

author: bd139
author_rank: Super Contributor
timestamp: June 06, 2019, 01:36:37 pm
content: niceInteresting schematic. Dead simple filter. Watch those early dual gate MOSFETs though. They have no protection diodes. Look at them wrong and they're gone!

author: xrunner
author_rank: Super Contributor
timestamp: June 07, 2019, 11:58:51 am
content: Quote from: bd139 on June 06, 2019, 01:36:37 pmOh yea I'm being extremely careful.Yet another part of the project involves the dial decals. Back in the day when you bought a new crystal for a 500 kHz band segment it came with a new decal for the selector knob display. I have three new crystals coming from Ebay sellers, which do not have decals - 8.0, 8.5, and 25 MHz. The 8 - 9 MHz band has some utility signals like WEFAX that I want to send to my PC later for decoding. As you can see from the pics, the additional decals that were added a long time ago do not look very good now either. However the original printing does look very good.I initially thought to add them with clear labels from my TZ tape label maker, but even the smallest font size is too large. The next thing to try is clear sticky label sheets for the ink jet. I found a pack on Ebay A4 size, which I ordered.Will get back to this mini-project a little later ...

author: xrunner
author_rank: Super Contributor
timestamp: June 08, 2019, 02:40:54 pm
content: Drake SPR-4 5.645 MHz IF AlignmentThe procedure is straight forward. T8 & T9 are critical and need to be carefully adjusted. Again use the S-Meter not the AVC voltage.I did run into a problem however. There are two crystals - 5.595 & 5.695 MHz that are to be adjusted with trimmers C115 (LSB) & C113 (USB). You are told to adjust for "zero beat'. Two problems arose. One is that is was very difficult to hear the exact zero beat. The other was that when I though it was near zero beat both trimmers were at maximum clockwise rotation (maximum capacitance). There should have been a range through which the trimmers would go and not max out at a maximum physical rotation.I decided rather to examine the frequency generation using a more exact means. I just used a small pickup coil placed near the board and fed it into my spectrum analyzer. when I did that I found that the LSB could be adjusted very accurately and I was able to get it from 56 Hz off to nearly zero Hz off (which indeed was almost maxed out).The USB adjustment was truly maxed out. It could not be adjusted any closer than 56 Hz (max clockwise rotation). Since this was also max capacitance it indicated to me that adding a few more pF in parallel it should allow it to be adjusted better. I picked a 10 pF cap and temporarily tacked it in place across C113. This proved to be a good value. I was then able to back it out and then adjust it through the zero position.Like I said before, this procedure was written 45 years ago and things were done a little differently then. Also this procedure was included in the owner's manual and written so that many people without more advanced test equipment could do some of the procedures. If you have a nice set of test equipment, you can do a little better.

author: Specmaster
author_rank: Super Contributor
timestamp: June 08, 2019, 03:11:35 pm
content: Good fix, all working nicely now?

author: bd139
author_rank: Super Contributor
timestamp: June 08, 2019, 03:18:10 pm
content: Nice jobAlso nice QSL card collection hiding there. Still waiting for my first batch. Takes bloody forever via RSGB and I’m not doing eQSL or LOTW. I’ve got one damn QSL card so far sent direct.

author: xrunner
author_rank: Super Contributor
timestamp: June 08, 2019, 11:10:02 pm
content: Quote from: Specmaster on June 08, 2019, 03:11:35 pmApparently it's working OK Specmaster, I lashed up a Signalink to it and the computer. It's receiving a weather fax from NOAA station NMG out of New Orleans on 8.504 MHz pic attached.Quote from: bd139 on June 08, 2019, 03:18:10 pmYea direct QSL cards take a long time and can cost money too. I've also lost quite a few in the mail system of several countries such as the likes of Venezuala and several African countries (you know who you are).But it's still cool to get a "real" QSL from another country. Hope to work you some day so I can send you one!Here's another pic of more on the wall. Also a letter from your neck of the woods with a QSL card in it from some DXpedition I worked. I guess I should open it this evening LOL.

author: Specmaster
author_rank: Super Contributor
timestamp: June 08, 2019, 11:58:38 pm
content: Cool, I see that you have some RGB LED strip running along beneath your shelf, I got some to under mine but before I got them installed I also got a Dlink 4 drive NAS which just happens to be same height so I cant now use the LEDs in that location

author: bd139
author_rank: Super Contributor
timestamp: June 09, 2019, 08:44:25 am
content: Quote from: xrunner on June 08, 2019, 11:10:02 pmNice shack. Drake fits in there rather nicely. Excellent work. Nice to see a good old rig doing something useful as wellThat’s a cool collection. I’ve heard things about bad postal systems. One of my South African friends was telling me a story about the ZA post office and they said they deliver 99% of all packages. This turns out statistically speaking they can lose about 5 million a year then. I wonder if they get opened as the old “send a dollar” thing is still well known. Fingers crossed we’ll catch a QSO. Probably not until I get a new house and a beam

author: xrunner
author_rank: Super Contributor
timestamp: June 10, 2019, 01:16:10 am
content: Quote from: bd139 on June 09, 2019, 08:44:25 amThe way I send for a card is to write their address on the envelope with NO ham callsign - and some of the addresses are, shall we say, extremely odd (to me at least). I enclose my SASE with the green stamps (dollar bills) and my QSL card. I then put in a piece of black craft paper the same size as the inside of the envelope, so it's near impossible to shine a light through it. In the US we put a Global Forever stamp on the international letter. That is the best you can do. If it gets stolen you know you've done your best. Wait 5 or 6 months and see what happens.As far as the SPR-4, the to-do list is -Install new phono jacks for the antenna and speaker - both are well worn out. Parts should arrive in the next few days.Make new stick-on labels for the crystal dial selector. I have been working on a word processing file that will duplicate the font and spacing very closely. All I have to do is print it on the clear label sheet and test fit it. I will make the file available of courseInstall a new can capacitor (1000 uF / 500 uF) which should also arrive soon.I hope this thread will be referenced in the coming years, and I can be of help to anyone restoring one of these. I know from past threads I've done on Tektronix plug-ins and other repair projects, going back and looking at the # of views of the pictures after a year or so, that people do come here and look at your work. They don't post anything, but I think they do help people searching for information.

author: Specmaster
author_rank: Super Contributor
timestamp: June 10, 2019, 01:36:21 am
content: So its almost completed, well done so far. It looks to be almost new now and fits right in with your bench

author: xrunner
author_rank: Super Contributor
timestamp: June 10, 2019, 10:26:30 pm
content: Quote from: Specmaster on June 10, 2019, 01:36:21 amYep getting close to done. Today I got the replacement phono jacks. They look almost identical and are Switchcraft 3501FP RCA Chassis Panel Jack obtained from an Ebay seller. The only difference was the new ones went to a metric sized nut, but I chose to go with the original nuts for consistency with the other original jacks. Pretty easy job replacing them. Now I got a nice tight fit for the antenna and speaker.

author: xrunner
author_rank: Super Contributor
timestamp: June 12, 2019, 03:31:47 am
content: The can cap just shipped today. Also I obtained a new set of dial inlays, hey they were only $8

author: xrunner
author_rank: Super Contributor
timestamp: June 13, 2019, 10:02:25 pm
content: I received the custom made can cap for the SPR-4 from Hayseed Hamfest LLC. Well I have to say, it's really a work of art. I don't think I've ever taken this many pics of a capacitor before LOL. But here it is!

author: bd139
author_rank: Super Contributor
timestamp: June 13, 2019, 10:23:31 pm
content: That's a pretty nice bit of work that is actually. I've seen them before on YT videos usually but not up close like that.I'm pretty lazy and cheap with those things though. If they haven't leaked I usually snip the terminals off the bottom and chuck new radial ones under the chassis

author: xrunner
author_rank: Super Contributor
timestamp: June 13, 2019, 10:32:07 pm
content: Quote from: bd139 on June 13, 2019, 10:23:31 pmYea that would work just as well of course, but this is special.Shoot, I almost don't even want to install it, it looks so freakin' nice. But, it'll go in tomorrow morning. That way I can admire it all evening.

author: xrunner
author_rank: Super Contributor
timestamp: June 15, 2019, 11:50:33 am
content: Few more items:Found a cracked tantalum - replaced.Installed new knob inlays. Very clean look and no scratches.New can capacitor installed.I received the A4 size sheets of clear label material for ink jet printers. I will be working on the new stickers for the crystal selector control to replace some of the faded ones and also to add for several new crystals.I also added a new SWL antenna outside. I had a long wire in the attic which was almost useless. Now I can have a dedicated antenna for any stand-alone receivers.

author: xrunner
author_rank: Super Contributor
timestamp: June 16, 2019, 10:54:43 pm
content: We're pretty much down to the cosmetics now. I pulled all the original stickers off the dial (the basic frequencies it came with from the factory are permanently marked). They were stuck on very well but I managed to get them off and cleaned the residue with alcohol.I pulled out some of the crystals that needed to be re-ordered from low to high and put them back in the radio way I wanted them to appear on the dial.I then tried a printout of the new labels using the clear label paper and they appear to be good looking.I also made a template from some plastic that I will use to draw around the labels and cut them out.To be continued ...

author: KK6IL
author_rank: Regular Contributor
timestamp: June 17, 2019, 08:22:03 am
content: I had an early SPR-4, S/N 304 as I recall. after a few months, dial lights kept burning out. Found out the zener diode in the voltage regulator was open circuit and the regulator was putting about 18 volts on the 12 V line. Analyzed the circuit and found there was more than 1 watt power dissipated in the zener, which looked like a 400 mW size. Changed the 47 ohm resistor supplying the zener with a higher value and never had any more trouble.Made a mod to the mode switch so that the BFO was off and AM detector output selected with an added front panel toggle switch when in USB/LSB, so that AM stations could be listened to with the narrower SSB bandwidth.Have an MSR-2 now.http://www.jlkolb.cts.com/John

author: xrunner
author_rank: Super Contributor
timestamp: June 18, 2019, 12:01:39 pm
content: Quote from: KK6IL on June 17, 2019, 08:22:03 amThat's strange in that the lamps (in this unit) are powered directly from the transformer (AC) and do not depend on the DC voltage. I don't know why that would have caused them to burn out, unless the early units were different. I only have the one schematic.I made a little light table from a LED panel so I could trace out the little template from the back of the printout. I then used a razor blade and steel ruler to cut out the labels for the crystal selector. I applied the labels to the empty dial slots. As you look at the dial, the original printing is to the right of the center, and the new labels are the center and to the left. I think they look pretty good.I did notice that after I changed out the main power supply capacitor, the S-Meter seemed to be uncalibrated from my previous tweaking. After wondering what I did wrong , I realized that the DC voltage wasn'texactlythe same as it was, which wasn't a big deal except for the S-Meter circuit, which is very sensitive to the supply voltage. So all I did was do a quick recalibration using the Agilent and all is well again.

author: Specmaster
author_rank: Super Contributor
timestamp: June 18, 2019, 12:32:58 pm
content: I think they look perfect

author: bd139
author_rank: Super Contributor
timestamp: June 18, 2019, 12:39:18 pm
content: Indeed. They look excellent

author: xrunner
author_rank: Super Contributor
timestamp: June 20, 2019, 01:28:42 pm
content: So here she is - the fully restored Drake SPR-4 in it's rightful place on my radio desk.Now, back to Ebay!

author: Kosmic
author_rank: Super Contributor
timestamp: June 21, 2019, 12:57:23 am
content: Quote from: xrunner on June 20, 2019, 01:28:42 pmGood job, look really good

author: bd139
author_rank: Super Contributor
timestamp: June 21, 2019, 08:03:37 am
content: Indeed. Excellent work

author: Specmaster
author_rank: Super Contributor
timestamp: June 21, 2019, 08:44:52 am
content: Looks really good there, what's next?Sent from my POT-LX1 using Tapatalk

author: xrunner
author_rank: Super Contributor
timestamp: June 21, 2019, 01:26:00 pm
content: Thanks a lot guys.I found an MFE3007 dual-gate MOSFET the SPR-4 uses for the rf amplifier transistor on Ebay (NOS) for cheap, so I got it in reserve in case needed someday.What's next? As far as a project not sure. However, 6 meters is really alive in the day now so I might just use what I have for a while LOL. Just this week I worked three new DX entities on 6m - Belize, Costa Rica, and St. Martin using the homebrew beam. We had a high windstorm last week and it looked like one element of the beam was bent by the wind but it was only torqued at the screw joint. I got up there and was able to tap it back with a garden tool. After the season I'll take it down for the winter and look at making some of my own mechanical improvements. It needs to hold the elements a bit better. I see the 3D printer involved in some way. Some of the fittings are already made by a 3D printer my friend's friend made for this project. He made them out of PETG which is tougher than PLA.I designed my own style of antenna end-insulator right after I got the 3D printer. I don't like most of the types you can buy. I want my antenna wire to pull straight out of the insulator and not wrap around and/or tie in knots. I installed them this spring on two different fan dipoles. Two are printed in gray and two in white. The material is PLA. I want to see how they hold up after the blazing heat of the summer. Some say they will get soft and stretch. That is what I will find out. So far, they look just fine. If anyone wants the CAD for the insulator to use or mod let me know. Hmmm ... might ask DAVE if he can add .stl as a file attachment type (or could be zipped I guess).

author: xrunner
author_rank: Super Contributor
timestamp: September 21, 2023, 11:11:04 am
content: I received a PM regarding the file I used to print the dial numbers. I will attach the Open Office file here for anyone who might need it. The font and spacing should be OK. Edit the file with your specific band details. But you must use clear adhesive "paper" to print it.

author: carlos2007
author_rank: Newbie
timestamp: July 25, 2024, 01:36:08 pm
content: Hello,Interesting post, I am going to align my SPR4 but I see that the OP only made the 50 Khz and 5645 khz if alignment. What about the preselector and injection alignment (mixers circuits) , local oscillator.....?I would be very pleased if somebody could explain the rest of steps since is not very clear.I have came across with a website that explain the rf amplifier and mixers more in detail:http://www.dashdist.com/1u2u/SPR-4/improve/improve.phpI attach an old invoice that came with the SPR-4 I have purchased

author: Smoky
author_rank: Frequent Contributor
timestamp: July 25, 2024, 03:04:02 pm
content: That's a cool looking radio. Great job Xrunner

author: xrunner
author_rank: Super Contributor
timestamp: July 25, 2024, 04:12:03 pm
content: Quote from: Smoky on July 25, 2024, 03:04:02 pmThanks.Quote from: carlos2007 on July 25, 2024, 01:36:08 pmWhat about the preselector and injection alighment do you want to know? It's been 5 years but I only made posts about the steps I thought needed explaining if I did it differently from the service manual, or that I thought needed more explanation. Just because I didn't post about every step doesn't mean I didn't do them.The only problem I ran into was that I didn't have several of the accessory xtals, probably because they weren't available.

author: carlos2007
author_rank: Newbie
timestamp: July 25, 2024, 07:34:51 pm
content: Thanks for the prompt answer. Is the rest of the alignment difficult? Did you find any remarkable problem in the rest of alignment?By the way I am a bit confused about the 50 khz LF filter alignment there are four transformers, T11 to T14, are adjustable but they have a small spring and I am not familiar with this type of adjustment.How is the method for aligning this type of slug, do I have to pull out the spring or just turn it? Spring or white and red discs need to be hold? Photo is attached.Regards.

author: xrunner
author_rank: Super Contributor
timestamp: July 25, 2024, 09:25:37 pm
content: Quote from: carlos2007 on July 25, 2024, 07:34:51 pmNot that I can remember, but it was 5 years ago.QuoteWell you caught me off-guard with that question. I couldn't remember pulling any springs so I took mine apart. OK, what these are is a coil of very hard wire that can beturnednot pulled. Sort of a miniature version of the coil that goes into your sewer when they snake it. On the end the coil is flattened so that you can use a tuning wand with a slot on one end. You have to adjust these with the caseONfrom the back of the receiver and without using metal tools. You might have to buy a set of plastic tuning wands if you don't have any ... but ...It looks to me from your pic that a gorilla has got hold of yours and mucked around with the end of that coil, perhaps twisting it or trying to turn it with a pair of pliers or something. I think they ruined the flattened part so a tuning tool might not work now. I'd have to think about what to do if the end is ruined, maybe some readers here will have an idea.

author: carlos2007
author_rank: Newbie
timestamp: July 26, 2024, 02:09:36 pm
content: I know now because it lacks a a bit of sensitivity, maybe last owner tryed to calibrate it without propers tools. I have two SPR'4s and the other has a very good sensitivity in all bands but needs an alignment too,This one that has the springs broken is almost new in minty condition, however the other looks like older and well used but works quite nice.Just an idea, could work if a small solder tin drop cover the spring? Or could enworsen the spring?

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: July 26, 2024, 03:35:19 pm
content: These cans with the "spring" adjust are found in many older HAM radios/ The "spring" is connected to a tuning slug which tunes a coil. They are usually held in place by wax or glue at the top. I do not know if this Drake used anything to hold the adjustment. Collins and Yaesu seemed to be fond of these things also. In a lot of tuners they are "ganged" together.The "spring" is essentially a screw adjustment attached to a ferrite "slug". It does not matter it the end is flattened or not. Sometimes the thing is so sensitive that touching the spring can change the alignment. Mostly you can attach a hemostat to the spring and it does not affect anything until you turn it to tune the radio..

author: carlos2007
author_rank: Newbie
timestamp: July 26, 2024, 06:51:16 pm
content: Yes. I will touch them very carefully maybe a slight turn will be enough. The preselector has 5 similar transformers but the movement is up and down.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: July 26, 2024, 08:39:24 pm
content: The tuning coils in the picture are the same thing but they are ganged together and adjusted with the tuning dial. To align these coils the red stuff on the top needs to be removed and then the coils can be fine tuned by turning the coil. After everything is aligned, you are supposed to glue this back to secure it.

author: carlos2007
author_rank: Newbie
timestamp: May 19, 2025, 05:13:44 pm
content: Well, after a year I have decided to align a couple of SPR-4 that I have. I have already made the first step 50 khz if BFO and adjusted T17 for zero beat. Problem start here: I have been trying adjusting T15 and T16 but no deflection in the S-meter, in both receivers, I have no scope but I have an analog voltmeter that can help instead of the S-meter. Where hould be placed the voltmeter? I am not able to find the right spot that the manual says.Maybe am I doing something wrong with the TinySA Ultra signal generator?