Help on Sonomatic radio

[Drakeule]

Can anybody shed some light on working on a 1940 (980620) Sonomatic? I get nothing from the vibrator when energized, and most things I've read say that if the thing isn't buzzing while in circuit, it's bad., If I look at the schematic, there is very little between the power source (battery) and that vibrator. Any input appreciated!

CD, Potomac, Md.

[jbbuick22]

It's not a good idea to put a new vib without replacing the filter capacitors first .

The orig are probably shorted due to age

 

John

22-6-55

[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.

[Drakeule]

All:

 

Big help. Makes me want to ask more questions:

 

Agreed, buffers and filter (10 mmf/20 mmf) caps should be replaced. Filters look like electrolytics and just insert where those honking cans are in my chassis (Roadmaster71; looks like your 1st photo shows just one cap. Correct?)

"Coffin" holds the poly "drop" non -electrolytics, correct? Schematic shows either end of secondary coil going to a reisistor, then to the buffer cap, and finally to ground. So, just make sure each poly connects to ground and solder the 2 other leads where the old ones were, correct?

 

I hope these questions aren't confusing things! I do appreciate the good feedback so far.

[Kenneth Carr]

Drakeule … I will have to check the circuit drawing and get back to you. I can confirm that the buffer caps are not electrolytics and they are in the coffin which originally contained one capacitor package that was actually two caps in the same wrapper. I put in those two brown poly drops to replace the buffers. I don’t recall how they were connected. I usually just put the new ones in the same way the old came out. I will check.

 

I believe there was only one can electrolytic and it contained two capacitors with a common ground ; thus, three leads coming out of the can. I will confirm this.

 

Do you need a schematic? My copies are not great but better than nothing.

[Drakeule]

Roadmaster71:

 

Thanks for the response. I have a copy of the factory installation and operating instructions from Buick which contains the schematic. You explanation of the cap hook up is pretty much as I thought. I am awaiting a NOS vibrator; I do think mine is beyond help. I hooked it up (very momentarily!) directly to the battery and got nothing. I am sure it should have at least buzzed.