1940 Buick -- Sonomatic Radio Restoration

[Weaver_Drafting]

So I'm a new comer to this site, so bear with me if this question has already been asked.   A family member has a 1940 Buick that he is trying to restore (very slowly with very limited funds).   He has asked me to look at his Sonomatic Radio to see if I could 'make her sing again'.   How complicated of an exercise is this going to be??   I've worked on other 'old vintage radios' before (Wood Cased and BakeliteTube Radios from the 1940-50s), but never had the occasion to open up an old car radio.   What are the 'land mines' that I need to look out for.   I haven't been able to physically get my hands on the radio yet - have to wait for Thanksgiving Dinner with the Family - then I'll be in town to examine and collect the radio.   Any advise or suggestions would be greatly appreciated.   Thanks!!

[Larry Schramm]

I have been told that most of the capacitors in old radios usually need to be replaced.  

 

Other than that, Delco made car and household radios in that era and I would expect them to be similar.

[Steve_bigD]

The most critical thing is to replace the electrolytic caps first, then all paper/wax caps.  Mica and ceramics usually will be OK.  The vibrator most likely will need replacing as well and there are modern solid state equivalents available.  Any rubber wires will be brittle and cracking and need to be replaced but cloth wires are usually OK.  After a good cleaning do a alignment with a signal generator for best reception.  Schematic and alignment info is available at among other places:

 

http://www.nostalgiaair.org/Resources/

 

Steve D 

[Buicknutty]

If you have experience with electrical and electronics, with advice and the schematic you should be able to repair it. Parts are out there, but depends what you will need. They are not that complicated, but of course they have vacuum tubes, and you need to be able to understand them, as well the basics as to how these things work. If already know this, forgive me, but vacuum tubes run at fairly high voltage, even though the input is only 6V, its' transformed to much higher voltage and you can get a nasty shock from the capacitors, even with the power off.

In addition to the vibrator what has already been mentioned, there is a rectifier tube which often fails. That and the previously mentioned vibrator are typically the things that caused them to fail when in regular service. Though at this point, as mentioned the old style capacitors are almost certainly bad too.

 Though before you do any other repairs, make sure that the transformer is still good, otherwise, you're wasting time and effort.

 One thing to consider is a solid state conversion. This replaces all the old tubes, etc., with new stuff, gives you FM radio, and usually an MP3 input using the original case and speaker. Depends on how bad the original is when you get into it, as this might not be much different in price compared with rebuilding the original.

 Just some options to consider.

 Keith

[Joseph P. Indusi]

As stated above the electrolytic filter capacitors are the first thing to replace, then the paper and wax capacitors, especially coupling capacitors that go from the plate of one tube to the grid of the next.

Tubes and vibrator need to be checked and replaces as needed.

Finally there is one capacitor that will be near the vibrator and rectifier tube and this is the buffer capacitor(s).   These are usually rated 1200 to 1600 volts and are supposed to quench the voltage spikes in the power supply as the vibrator operates.  If shorted or open they will kill a new vibrator in short order.

Schematics are often for sale on eBay or other sources.

Good luck.

Joe, BCA 33493

[37_Roadmaster_C]

2 hours ago, Joseph P. Indusi said:

As stated above the electrolytic filter capacitors are the first thing to replace, then the paper and wax capacitors, especially coupling capacitors that go from the plate of one tube to the grid of the next.

Tubes and vibrator need to be checked and replaces as needed.

Finally there is one capacitor that will be near the vibrator and rectifier tube and this is the buffer capacitor(s).   These are usually rated 1200 to 1600 volts and are supposed to quench the voltage spikes in the power supply as the vibrator operates.  If shorted or open they will kill a new vibrator in short order.

Schematics are often for sale on eBay or other sources.

Good luck.

Joe, BCA 33493

 

This is a MUST DO!!!  The buffer cap should be replaced each time the vibrator is replaced.  It is not really possible to test it reliably, so just replace it.  If bad or failing, your new vibrator wont last long enough to enjoy one cruse night.

 

Robin

[Kenneth Carr]

The 1940 Sonomatic Radio (980620) is built the same as the 1941 model 980650. They both use a synchronous vibrator, model no. 8630. The synchronous vibrator has two sets of contacts instead of one. One set creates the interrupted 6-volt DC which when fed to a step-up transformer provides a sort of ‘simulated’ AC at higher voltages. This AC is then rectified by the rectifier portion of the vibrator to make DC to create tube plate supplies (B+).

These vibrators require a very high working voltage capacitor called a buffer capacitor. In your radio it is a dual (2-part) capacitor (p/n 7236075) made up of two 0.015 capacitors (not electrolytic!) that are rated at 1,500 working volts each. The buffer capacitor is located under a sort of triangular shield that you will see upon opening the metal case. You need to replace those capacitors and the electrolytic filter capacitors at the minimum to get a working and reliable radio. You will also need a good circuit diagram.

 

There are various ways to restore a non-working vibrator. One involves sending it a high voltage surge. Another involves opening the shell and filing the contacts. These methods are both covered in various videos on YouTube. I will leave you a couple relevant links below. I have not tried either of these since the only Sonomatic I worked on (for my 1941) had a good vibrator.

 

Reference Book: Servicing the Modern Car Radio, by A. L. Hurlbut, 1946 and 1948

 

Vibrator Repair, 6-volt, Pontiac (applies to all)

 

AACA Buick Pre-war forum, discussion on repairing Sonomatic.

 

Fix That Vibrator, discussion on AntiqueRadios.com about ways to fix a vibrator

 

To properly repair this radio you really need to replace all the capacitors as mentioned above. This came to about 16 pieces in all when I did mine. I can recommend justradios.com as a good source of capacitors and resistors.

 

Photos: First one shows two electrolytic caps inserted into evacuated top mounted filter cap ... ready to solder into circuit.

              Second photo shows radio with most caps replaced. Note coffin-shaped structure on left. Underneath that is found the 2-part buffer capacitor that has been replaced by two new high voltage poly capacitors.

             Third photo is of a repair kit offered at one point on ebay. It included the two caps to replace the buffers (brown drops at top) and some electrolytics. I lost that bid! Good thing my vibrator was OK.

 

Edited February 7, 2022 by Roadmaster71
Correction to text (see edit history)

[Jolly_John]

At last....Roadmaster71, thank you for the clear explanation of the synchronous vibrator ALSO acting as the current rectifier. The use of a synchronous vibrator on BUICK DELCO radios began prior to W.W. ll and continued well after the war.

 

This means there is NO NEED for a rectifier tube in these car radios. That's also the reason there is no solid state plug-in vibrator replacement for these particular radios (or at least there wasn't several years ago). In order to use one of the solid state plug-in replacement units in these radios you have to also add a solid state rectifier circuit to the radio. Thanks also for all of the other very helpful info. John

Edited February 7, 2022 by Jolly_John (see edit history)

[Kenneth Carr]

You are welcome, John. The funny thing is that I was trying to post this as a response to a more recent inquiry and I ended up posting it here by mistake. So, I just copied it all to the other area too, I think!

[Daves1940Buick56S]

Nice post John!

 

Yes the synchronous vibrator saved them 1 full wave rectifier tube.

 

I would also suggest checking the values of the resistors as you go. Since you have to unsolder the caps anyway it's not a lot more work to lift one end of a resistor to check them. You will likely find at least a few off tolerance. Look at the schematic to confirm values, placement, power dissipation and tolerances. After many years of use in a hot environment you can't really depend on the resistor color stripes any more.

 

Cheers Dave

 

[Jack Worstell]

We re-did the radios in our 1937 Cadillac 60  and in our 1937 Buick Special

 

As suggested above....we replaced all capacitors .   Even the ceramics and the micas...maybe a 

bit of overkill

 

Where resistors were easy to  get to and we had replacements on hand...we replaced

some of these too

 

Definitely get a solid state vibrator.  We found ours thru  PEKO in Florida.   The latest version

of their SS vibrators include diodes...makes the job a little easier

 

Jack Worstell              jlwmaster2@aol.com

[Bloo]

For a radio of this period, I would NOT recommend replacing ceramics and micas (capacitors), especially not micas, in most cases. This isn't written in stone. Of course there can be exceptions.

 

There are a few types of early ceramics that had a high failure rate, but that is a special case and ceramics were not in common use in 1940 if they even existed. Micas were once considered failure-proof, except for some very specific brands and types. Some micas are failing today.

 

There are 2 issues. Micas and ceramics tend to have small values of capacitance and were generally used in tuned circuits. If you replace capacitors in tuned circuits, the whole radio needs to be put on the bench and aligned from scratch. This is done with a signal generator and a VTVM, or a signal generator and an oscilloscope. Otherwise, performance will suffer. There is about a 99.5% chance that this would be unnecessary if the old micas (or ceramics) were left undisturbed. The other issue is temperature compensation. Mica caps in the 40s-50s, and ceramic caps in the 50s were available in a wide range of temperature compensation (tempco) ratings. In the tuned circuits, components would have been chosen to cancel frequency drift as much as possible. If they picked a different tempco than what is available today, then the radio might drift off station worse as it warms, and might perform a little worse in general. Or maybe not, depending on which parts the engineers picked back in 1940.

 

In my opinion, in this radio, replace the paper and electrolytic caps and leave the micas (and ceramics) alone unless one is proven to be bad. Then replace that one.

 

One caveat for 1940: There were some paper capacitors made by a company called "Micamold" that look like mica caps. The company also made mica caps. A good rule of thumb is if the value is a smaller than 0.01uf (1000pf), it is probably really mica.

 

Another caveat: Do not twist micas on their leads to read them. It accelerates failure by unsealing the wires. If you need to know the ratings, get it from the service info.

 

This is general advice. Of course there will be some rare cases where everything should be replaced. Your mileage may vary.

 

 

Edited February 8, 2022 by Bloo (see edit history)

[Jolly_John]

Jack, it's good to learn that someone can supply a solid state vibrator for our BUICK radios that originally had a synchronous vibrator. Thanks for the info. I'm not familiar with the vendor "PEKO". Could you provide their contact info? Thank you. John

Edited February 8, 2022 by Jolly_John (see edit history)

[Jack Worstell]

Jolly-John

 

Here's a link to PEKO            PeKo Radio (pekorf.com)

PeKo Radio (pekorf.com)

Or you can GOOGLE this

 

I can't guarantee that they have a SS vibrator for your specific radio.....but

I would bet they do

I suggest you call them and discuss your application....they are very helpful.

 

Jack Worstell

 

PS   Bloo's advice on capacitors trumps my thoughts...he knows what he is doing

       ......and I did have the two radios "aligned" by a pro when I had

           finished my work

[37_Roadmaster_C]

@Jack Worstell, thanks for the information on Peko Radio. They have a GREAT offering.

 

[Jolly_John]

Yes, Jack, THANK YOU for the link to the PeKo people. John

[kgreen]

Great old topic, if I might hijack with a question or two.  Could I get an identification of the vibrator by location, photo or description?  I have two radios and have never put power to either one.  I was sending one off for a rebuild and debated sending the second one.  Problem is they are very heavy units so shipping cost will be rather high.  If the vibrator is such a hard to replace part, I could remove it from one radio and send it along as a possible spare, if I knew what I was looking at.  I have identified D&M radio restoration out of Greenville, SC to make the repairs.

[Bloo]

Usually a cylindrical thing a couple or three inches in diameter made of some soft dark gray metal that appears to be zinc or lead. They typically plug into a tube socket, and since this one is synchronous, I am guessing a 6 pin tube socket.