GE H87 console radio questions

[RetroHacker]

I've been working on this GE console radio that I accquired a couple weeks ago.

The radio was silent as found, with slight static from the controls - but no audio. According to the seller, it "worked until last month". It had clearly been worked on sometime in the recent past, the grille cloth had been replaced with burlap, the speaker was replaced with a Realistic bookshelf speaker, and the wiring to the speaker and antenna was modern plastic coated wire.

Under the chassis, a couple of caps had been crudely replaced with orange drops, although most were still old paper capacitors.

I replaced the remainder of the paper caps, and the radio was still silent. I eventually found the problem - the pushbutton switch assembly. This radio has a row of pushbuttons on the front, for presets and to turn the set on and off. They're all in series, the first one being the setting to enable the tuning cap. It was so dirty, that no signal was getting through, so no sound.

After removing the assembly, thoroughly cleaning it and putting it back, the radio came to life and played very well. I touched up the alignment a bit "by ear" using a weak station, and soon had it clear and loud. There are a couple of nagging problems though:

There is a slight crackle in the audio, on all stations. It sounds a lot like record static, but it happens on talk radio too.

There is a high pitched whine in the background. Seems most noticeable when tuned to a station, but could be all the time.

The AVC doesn't automatically control volume. After getting a good clear signal on a weak station, I dialed over to a strong local station, and it was incredibly loud!

All the tubes test good (or at least good enough) on my simple emissions tester. All the paper caps except for two have been replaced (one's 1000v, and the other is 1600v, and I don't have those yet). These two seem to be only in the audio output stage. One's between the audio output transformer and the chassis. The filters are original, since I don't have any more high voltage electrolytics.

This is a power transformer type set, with two 5Y3 rectifiers, and push pull 6Y6 audio.

Any suggestions?

-Ian

[ekimetsok]

Ian: A couple of easy things to try. First, turn your computer off. Any flouresent light bulbs or fixtures? Turn those off too. Wall warts? Unplug 'em. Light dimmers? Turn 'em off. No gaurantees, but these can individually or collectively be causing the high pitched whine.

[RetroHacker]

I thought about interference, and tried turning off the workbench computer, and the fluorescent lights, no change. Just tonight I decided to clean the bench, so I put the chassis back into it's cabinet temporarily, and connected it up to the original Super Beam-O-Scope antenna. The radio is now located away from other running electronics, and it still has this whine. Seems to only happen on strong signals. I'm thinking there's something wrong with the AVC circuit here, since the AVC also doesn't work very well.

There is also a pretty constant background crackle. It's affeted by the volume control and is always present. This set is too early to have "silver mica disease", correct? All octal tubes, early 40's I think. It uses the large style IF cans with the brass adjustment screws.

-Ian

[Dave A]

Are you missing any tube shields?

Dave A

[Celt]

Just wanted to add something about EMI/RFI. Many modern TV sets and nearly all laptops use switching power supplies which are incredibly noisy. While my lappie doesn't seem to be too bad in this regard, I have to unplug one of my TV's to listen to AM or SW anywhere in the house.

[Old1625]

Ditto on the switching power supplies and computer equipment. That stuff generates all kinds of buzzing and hash.

As for the AVC issue try to find one of the IF secondary return leads and measure the voltage there while tuned to stations of varying signal strength, and compare. It's possible that a bypass capacitor was missed, and could be leaky enough to kill the AVC voltage. Also might be a good idea to check the pentodes in the RF/IF stages to see if perhaps some wise guy subbed in a different # that might have a different cutoff characteristic. Subbing in a sharp cutoff pentode where a remote cutoff type should be can upset the whole apple cart.