Jca50 v3 plate voltage off

[Disabled_shredder]

So I have been toiling with a Jca 50 head and the v3 plate voltage is around 300 with no load and drops to 50v under load. I cannot figure out what is causing it to drop. The amp is distorting something bad and I cannot find the culperate. All parts are stock and no parts are bad. I think I might need to adjust the resistor to force the voltage up. Any oxy have any ideas.?

ThanksZ

[Stevem]

What is the cathode voltage at when the plate is pulled down to 50 volts, do you have a shorted cathode bypass cap?

[Disabled_shredder]

I will check when I get home from work tonight and post voltages.

[sluckey]

V3 has two plates. One is a cat biased gain stage and the other is a cat follower. So, which plate?

[Disabled_shredder]

Pin 6. it has a 220k resistor and the other plate on the tube does not have a resistor. I will have to look at the schematic when I get home to see exactly.

[JMFahey]

To begin from the beginning:
1) what do you call load?
2) how do you apply it? ... Where?

Any other diagnose/suggestion is moot if we don't know what we are talking about.

And talking about "V3" without a schematic doesn't really help, we aren't talking about, say, a Champ or a JTM45 or some other classic amp where everybody knows the schematic by heart, so please post it too.

[Disabled_shredder]

Absolutely right sorry for being vague. Under load means that the tubes are in and no load means no tubes in. The cathode follower is ran off the first triode and the plate voltage in question is the second triodes plate. The only schematic I hav is the drawing that I drew and verified through Michael soldano. I can take some photos of it and post it but not sure how the quality will be. I think there are schems out there but all of them have an inconsistency somewhere. I will post proper voltages and details this evening when I get home from my day job. I will look into posting a photo of the schem but I'm only working from a phone and not sure how viable it will be.

[Stevem]

I found a schematic on line after a bit.

[Disabled_shredder]

http://starin.info/Product%20Info/Jet%2 ... ematic.pdf that is a link to a schematic that on first look is right at last for the tube issue I am having

[Stevem]

If you feed the signal from the effects out Jack into any kind of other amp is that output still distorted?
Can you get your hands on a Oscilliscope for trouble shooting ?

[Disabled_shredder]

I will have to check that. I do have a scope but I still haven't fully grasped its full potential. Normally I just plug the scope to the output make sure it doesn't distort and call it good. Haven't gotten into to probing different sections.

[Stevem]

Scope use wise it's the same thing, you just need to set the scope for a lower voltage / smaller wave form reading and then for the safty of the scope hook up a lenght of wire with like a .022 uf 600 volt cap on the end to probe to use to probe the amp with, the cap will block any scope killing HV dc from getting in should you by mistake hit a B+ plate node.
I cut up a old voltmeter lead to do that so I have a regular probe end and if you care to you can buy new voltmeter leads that will let you screw a clip lead onto the end of it.
Signal wise driving any amps input with a .150 volt sign wave will be plenty to drive a amp to its max clipped output stage wattage if all the gain stages are even only working at 75% of what they should!