[Guest]

I'm in the process of restoring this great console. It's working but, after its on for 5 minutes or longer the sound becomes a bit distorted and the phono part loses most of its rich volume. I have the schmatic but do not have a tube tester. The only tube that is not orignial is the rectifier (5Y3GT). I was thinking it could be the DET-AVC 1st Audio (7C6) breaking down. Any suggestions?

[Ron Ramirez]

This sounds like a classic symptom of bad paper capacitors.

Have you replaced any of the paper and/or electrolytic capacitors?

That is my suggested starting point.

[Guest]

No I have not replaced any capacitors. I was in the process of cleaning it up and replaced the line cord because it was dry rotted. I figure it has not been used in 35 years.

[Ron Ramirez]

Then please, if you value your radio, replace all paper and electrolytic capacitors before attempting to operate it again. Also check all resistors and replace any found to be more than 20% off rated values.

The distortion you heard was the paper capacitors breaking down, not the 7C6 tube.

I've heard the same thing, back in my younger and more foolish years, when I would attempt to operate an old radio with original capacitors. Slowly, the sound would get lower and more distorted. Replacement of all paper and electrolytic capacitors solved the problem entirely.

Too many people are under the mistaken impression that they need to automatically change all of the tubes in an old radio when they acquire one; that the new tubes are a cure-all.

They aren't.

If you do this, you are unnecessarily depleting the finite stock of tubes for no good reason. Most of the time, the tubes in an old radio are still good. Not always, of course, but mostly.

Please understand that I am not fussing at you. I do hope you understand that I am merely trying to help you to see how important this is if you value your radio.

Here's what can happen if you continue to operate your radio in its present condition:

At best, the sound will get worse...and worse...

At worst, one or more of the electrolytic capacitors could short out, which will cause your power transformer to fail. This is an expensive part to replace.

Keep this in mind, and I wish you good luck as you restore your set. Please feel free to ask lots of questions here; that's what we are here for.

[Guest]

Thanks Ron for that valuable advice. I will start with the capacitors and go from there. If I hit a stumbling block I will call again, and thanks for your patience.