Fisher 500C Static on Right Channel

I have been getting intermittant static and very slight popping noise on the right channel(not loud or affecting signal) but annoying. Would this possibly be one of the 7591 drive tubes or perhaps one of the 12Ax7's or possible a dirty tube socket or loose connection someplace. Also, my signal strength bulb went out a couple of weeks ago and was going on and off before it went dead. Otherwise the unit sounds great. Any help appreciated.

Since yesterday, I pulled all tubes out nd cleaned the tube sockets. Also twisted dead signal strength bulb and it came back on. The static/popping noise has now been reduced by 80 percent or more and the only time I can hear it is if I put my ear right to the speaker. So, for now I am satisfied. I did however put my ear to the left speaker and it is dead quiet as it has been. Perhaps I have a tube that is slowly dying. At least, for now, the unit sounds great again from my listening position.

Try switching the phase inverter tubes (the ones right in front of the output transformers) and see if the noise moves. Repeat with the left and right pairs of output 7591 tubes. For those tubes, make sure you've turned the unit off.

You can also swap those 12AX7s in the amp around.

Next, pull the V102 mpx tube from the screwed in multiplexer module with the unit on. If that takes out the noise, it is a power supply problem.

Good to rule out what it is NOT first and you've done a good job of starting that already.

You mentioned pulling and cleaning tube sockets, but you didn't mention whether or not you cleaned all the switches and controls. That's always the first step.

Annoying poppimg noise gone-Speaker Terminal Question

Thanks to all for advice. However the unit seems to work just fine and so far the right channel is just about as quiet as the left with no input signal. I do have another question regarding the speaker binding posts on the unit.I am using adaptors(screw in spade to banana to use heavier gauge speaker wire sold at PE and eBay) but this is not easy to work with as the screws on back of the Fisher easiliy loosen up after hard tightening. I happen to have one of those Adcom speaker swithching boxes that has heavy duty binding posts and I want to know how long a wire I can run from the Fisher(thin wire obviously to fit the Fisher terminal screws) to the Adcom box without signal loss as I would like to try some very thick MIT Speaker Cable to tame the highs just a bit on my Proac Studio 1's which otherwise are a great match for the unit.

If it's in the same room you'll be absolutely fine.

Just wanted to say "thanks" for this post and information, as it helped me solve an annoying problem with noise in one of my Fisher 500c channels. I tried swapping the phase inverter tubes, then the output tubes, then the phono preamp tubes, all without any change. Then I swapped the low and high filter amps, and causes the noise to move to the other channel. In the end, I swapped the 12AX7 from the high filter amp with the 38KC sync OSC 12AX7, and the noise is gone!

audiodon said:

Try switching the phase inverter tubes (the ones right in front of the output transformers) and see if the noise moves. Repeat with the left and right pairs of output 7591 tubes. For those tubes, make sure you've turned the unit off.

You can also swap those 12AX7s in the amp around.

Next, pull the V102 mpx tube from the screwed in multiplexer module with the unit on. If that takes out the noise, it is a power supply problem.

Good to rule out what it is NOT first and you've done a good job of starting that already.

Click to expand...

Fisherdude said:

You mentioned pulling and cleaning tube sockets, but you didn't mention whether or not you cleaned all the switches and controls. That's always the first step.

Click to expand...

Don't forget to clean the phase inverter adjustment pots too. I had this same issue with my 500C and that was it -- a little deoxit and exercising them banished the static completely. Just be especially careful you mark the exact position they were in when you found them!

FK