Fisher 400 woes!

dualhead

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Hey gang, I have my beloved Fisher acting funny on me. The left channel is weak with all sources and the right channel seems overly strong. When the balance is turned to about 9 o'clock the right channel is still really blaring. When the balnce is turned further from 9 to 7 the sound cuts out. Is this output tube issues? I had Terry DeWick refurb this some months ago, so it should be mechanically decent. Thanks in advance.
 
There is no way to diagnose your problem with the information you have provided. Did you swap inputs to verify it's the amplifier? Did you clean the pots and switches? Have you tried swapping the tubes between channels? Can you get full output on the weak channel? In what stage do you lose gain? Is there distortion? Does the situation change as the unit gets warm?
 
There is no way to diagnose your problem with the information you have provided. Did you swap inputs to verify it's the amplifier? Did you clean the pots and switches? Have you tried swapping the tubes between channels? Can you get full output on the weak channel? In what stage do you lose gain? Is there distortion? Does the situation change as the unit gets warm?

It is definitely the amp. I'll swap tubes tonight, and I'll check what happens (If anything) when the unit gets warm. No distortion. And the headphone jack works fine.
 
You mean the headphone jack does not experience the unbalance? If that's the case, check the speaker wiring and the speakers themselves. Most headphone jacks are at the amplifier output so that would rule out the amplifier.
 
You mean the headphone jack does not experience the unbalance? If that's the case, check the speaker wiring and the speakers themselves. Most headphone jacks are at the amplifier output so that would rule out the amplifier.

That's great news. Hope it is something that easy. I'll check first thing tomorrow and let ya know. Thanks for the replies, Nat.
 
Check impedance selector wire, make sure the terminal and wire have a secure connection. Also make sure the impedance terminals are clean and tight. I had some strange issues with my 400 and found it to be as simple as a corroded wire and terminal connection.
 
It is definitely the amp. I'll swap tubes tonight, and I'll check what happens (If anything) when the unit gets warm. No distortion. And the headphone jack works fine.

The others are right. The HP jack is practically the end of the line on these.

If it's not the speaker switch, I'd be looking at the speaker wiring and connections. I'd also peek at the circuit around the center channel jack, but I don't think that's your problem.
 
Actually the phone jack is connected via the impedance jumpers which pretty well indicates they are connected OK. This leaves the speaker switch as a likely suspect. Had the schematic handy as I have just put a new (pull) discriminator transformer in one, the old one had the slug frozen, impossible to do alignment.
 
I fiddled with the speaker wires, and switched the tape monitor, loudness contour, and speaker on/off switches rapidly a few times and it seems all is well again? Strange beasts these tube amps. Hope this does not prove to be a regular thing. Thanks for the replies.
 
I fiddled with the speaker wires, and switched the tape monitor, loudness contour, and speaker on/off switches rapidly a few times and it seems all is well again? Strange beasts these tube amps. Hope this does not prove to be a regular thing. Thanks for the replies.

As gugusse said, you should clean all the pots with DeOxit. Flush them good and work the pots many, many times fast with full sweeps. Make sure you unplug it first and allow it to dry very well (over night), before you power it back up. Sounds like that will get you going again.

Good luck,

Ron
 
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