Mark Oppat's
Old Radio Parts
Your source for vintage and reproduction electronic items
 
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THE "BAD TRANSFORMER" INQUIRY...

Dear Friends... I often talk customers out of buying parts they don't need... here's a typical example (I get this one A LOT!):

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Hi Mark,

I have a Silvertone Model 4565 that I am 95% sure has a bad power transformer. It is chassis number 101.410, and in Riders Volume 10, p.8-35. Would you have one or the equal? If so, how much?

Thanks,
Charlie Livingston, Jr.

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Charlie,

First, how did you test your old tranny? The test is to pull out the rectifier tube and run the set. All the filaments and bulbs will light but no B+ (high voltage DC) will flow, of course. Let it run for 5-10 minutes and check that the transformer doesn't get warm or hot, or make any sizzling sounds.

Does it pass this test? If so, it's usually OK. Remember, nearly ALL xfmrs are driven to failure; they don't "just go bad" (except AK80 series ones!).

If I have one, it'll be in the $40 range for a good used one. I would need the dimensions of your old one. Is it horizontal or vertical mount? It takes a while to find them here... gotta sort through the stock.

Mark

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Hi Mark,

You were right, it wasn't the tranny. It was a wiring issue... humming right along now.

Thanks,
Charlie

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FURTHER NOTES:

Transformers can often have wax or a tar-like goo oozing out of them. This is not any indication of a bad transformer, as is often thought! - It's just years of slow melting. If enough of the varnish melts out, it can make the transformer buzz a bit, but otherwise the goo means nothing. However, if it smells really "burnt" around a transformer where the leads come out... THAT can be a bad omen.

Always run the xfrmr test described above on any radio that comes onto your workbench. I like to test the tubes while this test is taking place. It saves time since the tubes are pre-heating, and it keeps you near the set so you can check the transformer for noises or overheating.

- Mark

HOW TO LOOSEN A FROZEN CONTROL SHAFT

I've received email from folks wanting to buy replacement controls or bandswitches from me. Why? Because their existing one has a frozen shaft. Well, we can fix that!

The main thing is to get the shaft soaked at the bushing with WD-40 ®, Break-Free ®, or a similar solvent/lubricant.

Now, using a 30 watt or higher soldering pencil or gun, heat the bushing part of the control. This will expand the metal and draw in the lube, and also melt any old, dried grease. Hold it on opposing sides of the bushing for at least a couple of minutes, or even several minutes if necessary.

A control is usually left in the off position, but with a bandswitch, you better be sure you are turning it in a direction it is intended to go! Being stiff, one has the tendency to turn it too hard with pliers or something... then "snap" goes the phenolic parts.  You NEVER want to have to replace a bandswitch!!!   It's WAY too much work, and WAY too hard to match up the original part.

- Mark

...AND HERE IS A SPEAKER REPAIR TIP I RECEIVED:

Hi Mark,

I owe you some thanks. I sort of combined a bunch of the advice you gave me about speaker repair and came up with a method that fixed an old 8" PM speaker with a voice coil rub. I used nail polish remover to loosen up the felt dust cover. Then, I cut up strips of manila envelope to use as shims to get the coil aligned right (it was a matter of finding an envelope with the right thickness).

Once I had the shims in place, I soaked the adhesive around the voice coil on the front side with nail polish remover a few times until it softened up. Then I left it overnight so the adhesive could harden back up. I pulled out the shims, and it worked! No voice coil rub.

So, thanks for sharing the know-how. It worked great.

- Joel

   
     
   
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