Repairing an old Grundig tube radio

The intermittent right channel will likely be something very simple, such as a bad joint or dirty tube base, but the low level left channel is likely to be something more challenging, and if you don't have any experience working on this sort of kit, is probably best left to someone who does. Just one quick thought though. Some of these old radios had a ' GRAM ' input on the back for a record deck, and a selector switch, sometimes part of the wavechange switch. If this were the case on yours, could be bad switch contacts, particularly if you don't change band very often. Could even still be this if it doesn't have a gram input. You might try giving the bandchange switch a vigorous scrub back and forth if its a rotary type, or a good " working " if it's the old Grundig piano keys.

As far as going inside yourself, the high voltages involved can be dangerous, and I would hate for you to get a serious electric shock. If you have any old mom and pop TV shops in your area, there's bound to be someone there who is still tube-savvy, and could sort these problems for you. Failing this, bit more of a long shot, but there are still lots of tube amps in use by musicians. If you have a local musical instrument store that takes in repairs, they will likely know someone experienced in tube equipment repairs, that may be able to help.

Arfa

Try to shake the tubes when the problem is on. It this helps the tube sockets/pins need cleaning. Removing tubes half an inch and placing again back should help for a while. Do this few times to clean the pins and sockets.

I use pencileraser to clean tube pins. Do _not_ use files or any kind of hard cleaning method like sanding.

You can drop a small amount of LPS-1 spray to each pin and rinse the extra fluid off and then assemble the tube by moving them up and down some times to clean the socket.

Matti, Why do you oppose cleaning the tube pins with sandpaper / emory cloth ? Just curious as I've done that before as well as using a very small round file to clean the pins of the tube socket.

Start by swapping Speakers R/L - L/R ! even if it means you must unsolder to swap speaker leads.

Yukio YANO

Because these tools are scratching surfaces. Especially if you have silver plated pins or socket these are gone if you use file or sanding for removing oxidation. All the tiny scratches can oxidate and the cleaning is harder and harder in the future.

The pencileraser (if you are able to find one) is very good when cleaning all kind of connectors. There is one exception. If the equipment has sensitive electronics this pen can produce some high voltage which can destroy something. Never happened to me.

Other nice tool cor cleaning connectors is glass fiber pen. Its is very sensitive method but you must be aware of tiny glass fiber "threads" which easily cut off. They can penetrate your skin.

If you want use emery paper please use 1200 which is very very fine. Or you can use "used" 600 paper. Cleaning the sockets is harder. I use alcohol and tiny carved woodstick.

I do remember the old static problem, supposedly caused by rubbing edge connectors with the eraser. Never did see any damage (no recalls). I pulled a few fiberglass pen fibers out my finger too and gave up on using them. I've worked in the A/V and Instrument repair business for over 30 years, sounds like we have similar experience. Take Care, Kevin