JTM 45 fixed!

[martin manning]

OK, that all looks good... do you have 1R resistors from cathodes to ground, or some other way to measure current draw? If so next I'd put the power tubes in and see if you can get more or less equal current.

[Reeltarded]

Yeah 1R. I am scared to check it.

I haven't made any mistakes with the output sockets, yet something has to be wrong there, correct?

Oh, another thing is I don't like this bias trimmer AT ALL. Not even smooth like every other one I ever lived with.

[martin manning]

Crank the bias max negative to start... If you want power up and check the voltages on all the power tube socket lugs before you put the tubes in to make sure everything looks good.

[Firestorm]

Leave the output tubes out and make sure you have signal through the pi. Then do what Martin said; max negative bias. Then dial down.

[martin manning]

Firestorm, no signal needed yet (no preamp tubes or PI tube installed)- just trying to see if we can set a DC operating point on the power tubes

[Firestorm]

K. That should be pretty straightforward, yes?

[Reeltarded]

Ok. I played without a bottom plate with the amp upside down and rolled back bias until it sounded good. Turned it off and turned around then it fell off the 1x12 cab it was on takiing out all the tubes except for the rec.

(Dave, these 6ca7s don't work in my amp.. rofl)

Only one valuable tube died in the crash, and 4 brand new JJs.

You may recall that a friend dropped my last amp from atop a full stack.

I am worried about using the el34s I have. I have a bunch of 6550 pulls. I wonder if this PT can take the current draw... or at least pretend to..

[Firestorm]

I don't know what to say. Now you're doing physical damage. Maybe take a breath and settle down.

[Reeltarded]

It works though. It reads low bias on one tube but they seem to be acting the same. I can't account for that. When my order comes in for other components I am going to rebuild everything on the output sockets and try again.

The wooden floor in my house has just enough bounce to flip an upsidedown amp. heh

As much trouble as it's been, it deserved it.

[Firestorm]

As much trouble as it's been, it deserved it.

I have room where I lock up all the amps that refuse to be fixed. Serves'em right.

[martin manning]

Ouch! That's unfortunate. Look for and repair any damage to the sockets caused by the impact. When you get going again we'll track down the reason for the low bias on one side.

[Reeltarded]

I retubed it last night after a once over and went right back at it. I locked it in a closet, alone. The fall didn't fix that side though. Firestorm is right.

Most annoying to work at electronics when it's not an obvious problem. "No light! Oh, plug it in...".

[martin manning]

Man are you a glutton for punishment!

OK, so with no PI tube in, what current (in mV at the cathodes) do you see the power tubes drawing? They probably won't balance exactly, so switch them and measure again. Measure bias voltage at the pin 5's too.

This DC-only test should tell you if it's just a miss-match in the tubes or if there is some party going on in the circuit that nobody told you about.

With no signal from the PI, an ultrasonic oscillation can only occur downstream of there. If the unbalance doesn't follow the tubes, then there is likely some lead dress issue.

[Reeltarded]

I need to rebuild everything on that socket first, Martin. I left the original heater wiring and never once turned a screw. I believe the whole thing is based on a registering but poor ground on the #5 socket.

I do so appreciate the help. I can't wait to make this thing sing like a bird.. a tremendous carnivore of a thing flapping wildly about with..

Oh, sorry.. lost in gothic/goric prose for a moment...

[martin manning]

Ah, your subtlety was just a bit too slick for me. Oh well, the above is the next step, whenever you get going again.