Zenith MJ1035: low volume

[Jeffhs]

My 1965 Zenith MJ-1035-1 works, brings in lots of stations with just a length of wire on the FM antenna terminal (typical Zenith ), but the audio output is so weak I can barely hear it--I have to have my ear right up against the speaker to hear anything, even with the volume control at maximum. It has been suggested to me that the volume control may be open (I know for certain the left-channel volume control is shot, but I think the right-channel pot, the one that controls the volume of the speakers within the radio's cabinet, may still be good).

I would agree with the open-pot theory, except for one thing. If the volume pot is truly open, why am I getting any sound at all? An open pot would kill all audio output, would it not? I'm baffled.

Thanks in advance for any and all advice on this; I haven't done much with the radio for a while, but I think I'm ready to go at it again. If the volume pot is in fact open, where if anywhere could I find a replacement? AK member old1625 suggested looking for the old Clarostat controls, but the only radio/TV shop anywhere near me (five miles from me, in the next town) likely wouldn't know anything about them; I know this because I asked them a few years ago to look at my 1951 Zenith H511 and they refused, even though the shop has been in business since 1947. Is there a TV/radio repair shop anywhere in northeastern Ohio that still works on these old sets, or am I up the creek? Most of today's TV shops won't touch tube-powered anything, televisions and even radios (!), with a 10-foot pole; the shop I mentioned is only one of them.

If the 1-megohm volume pot my MJ1035 uses is in fact unobtainium (as I suspect it may well be after 44 years), would a random-value potentiometer work at all? I realize a different value will affect the audio output, but I'd like to get the radio working as soon as possible, and I have several small potentiometers in my junk box. How low (or high) in value can I go before I either lose all output or, Heaven forbid, damage the output transformer?

[mr_fixer]

Capacitance, much in the same way you can hold your finger near the grid circuit and induce hum into the audio. You can always test by substitution. Connect another vol pot with jumper leads and see if the audio works. Logan

[Jeffhs]

Originally Posted by mr_fixer

Capacitance, much in the same way you can hold your finger near the grid circuit and induce hum into the audio. You can always test by substitution. Connect another vol pot with jumper leads and see if the audio works. Logan

Thanks for the prompt reply, Logan. I'll try that tonight when I can pull the chassis.

However, I am still wondering why I am getting any sound at all if the right-channel volume control is open. As I said in my post, I thought if the control was open, it would kill every bit of audio output and I wouldn't hear a thing, as this would be an open circuit.

[Reece]

First, wiggle all the tubes while the radio's playing. Could have a bad contact that needs to be cleaned.

On the volume control are three terminals close together. The center one is the rotor. With the radio on, take a piece of insulated wire a few feet long and touch one end of it to the center terminal. You should get a loud hum which tells you the audio amplifier circuit is working. If no hum, there's trouble in the audio amp or output transformer.

If you got a loud hum, then looking at the control from the back, with the terminals facing upwards, the terminal to the right of the center one is the high side. Clip a test lead from the center to the high side and play the radio. If the amplifier was good, and the control was bad, the set should play with maximum blasting volume now (just for a few seconds before you turn it off!) If no change in volume, the trouble lies elsewhere, and we can go from there.

Reece