Peavey Classic 50/50 No output - tubes are not lit

[innerservice]

I have resolved this issue - MB

[Prairie Dawg]

I have resolved this issue - MB

How?

[innerservice]

Resolution

Hi, the resolution was something I have never run into before - it was actually
a bad fuse on the heater circuit - the strange thing was the fuse actually tested ok with an ohm meter but it was not working in the amplifier - I have never seen this before but when I put the fuse back into the holder and tested the the two point with a voltmeter set - it showed 6 volts - so I then did a bypass on the fuse the the tubes lit up. So ... I ventured out and bought a new ceramic 10A fuse and replaced the faulty unit.

Never seen a fuse show continuity but fail operations - but It is now working fine so I am happy and may have problems trusting a continuity fuse test again.

Thanks

MB

[innerservice]

One thing - I found some of the existing threads on Peavey Classic encounters a great help - one actually was in the same fault isolation and the procedure actually led me through the voltage points (yellow to transformer) test points and this led me to the fuse susupect - thanks for the great site - excellent references for amp enthusiasts.

And on a closing note - while cleaning tubes and sockets I managed to get zapped off the main circuit board - ouch... seriously lit me up. Don't experiment with this - not worth the lesson. Unit was unplugged and I suppose it may be a worth while lesson to discharge the caps somehow before probing about.

Good thing I don't have a heart pacemaker.

Thanks all and Happy New Year... I lived again!

MB

[Jazz P Bass]

Ouch

One of my first amp repairs had a faulty on/off switch.
ZAP!!
Since then I have a clip on 1K 2 watt resistor that is the first thing that I touch the amp with after hooking a meter to the B+.
Safe the amp.

[Prairie Dawg]

One thing - I found some of the existing threads on Peavey Classic encounters a great help - one actually was in the same fault isolation and the procedure actually led me through the voltage points (yellow to transformer) test points and this led me to the fuse susupect - thanks for the great site - excellent references for amp enthusiasts.

And on a closing note - while cleaning tubes and sockets I managed to get zapped off the main circuit board - ouch... seriously lit me up. Don't experiment with this - not worth the lesson. Unit was unplugged and I suppose it may be a worth while lesson to discharge the caps somehow before probing about.

Good thing I don't have a heart pacemaker.

Thanks all and Happy New Year... I lived again!

MB

We've all had that experience. My brown Concert did it to me and that may ultimately be why I sold it. I was biasing it, and I had it face down on the floor with the chassis opened up and resting on the cleats. Reached over for something-it was the summer and I was in a short sleeve shirt and a little sweaty-and kaBAM! It felt like when you see those polar bear dudes breaking the ice to go swimming-just incredibly strong and physical. I was a little shaky for the rest of the day.

[R.G.]

it was actually a bad fuse on the heater circuit - the strange thing was the fuse actually tested ok with an ohm meter but it was not working in the amplifier - I have never seen this before but when I put the fuse back into the holder and tested the the two point with a voltmeter set - it showed 6 volts - so I then did a bypass on the fuse the the tubes lit up. So ... I ventured out and bought a new ceramic 10A fuse and replaced the faulty unit.

Never seen a fuse show continuity but fail operations - but It is now working fine so I am happy and may have problems trusting a continuity fuse test again.

It was probably not the fuse - it was the oxidation on the fuse and the fuse holder. In a high current, low voltage situation like this, the fuse gets hot, a bit hotter than the already hot inside of the cabinet. That grows metal oxides on the fuse and the fuse holder. This both softens the fuse clip metal and grows more crud. An amp-tech friend of mine told me about this, starting with "I don't like heater fuses. They can go open or just not let enough current through because of the clips."

I used a soldered-in pigtail style fuse in the Workhorse amps for just this reason.

So maybe the thing to do is to trust a fuse continuity test, but trust it from pin to pin on the soldered ends of the fuse clip, not just the fuse itself.

[Jazz P Bass]

Oxidized fuse

As a matter of practice, I wipe a little silicone grease on all fuse ends & header pins.
Especially Peavey amps.

[Enzo]

If you test the fuse while still in its clip, you are also measuring the very low resistance of the tube heaters and power transformer in parallel with it. That can look like a good fuse, when the fuse it self is actually open. ALWAYS pull the fuse from its clips to test.

Jazz, that silicone grease is meant to improve thermal conductivity, not electrical. You'd be better off wiping Deoxit on there.