Help, Voltage problem in Power Section

[dab]

I am testing my new Ceriatone Liverpool build and I am having a problem I haven't seen before.

My voltages all look fine until I put the Power Tubes in. With the tubes in ALL my voltages drop by about half. Something is sucking a lot of current.

I have rebuilt the power board, replaced all of the power tube sockets and rewired them, still have the same problem. I disconnected the OT primaries and it still didn't change anything. I replaced the power tubes with known good ones from another amp to no avail.

Seems like its got to be something in my wiring in the tube socket area but I have spent 20 hours trying to find it and can't seem to locate the problem.

Have any of you experienced this and if so what was the culprit?

By the way the amp plays like it is just not as good as it should.

FYI...my camera is on the fritz so I cannot provide pictures.

Thanks...Dave

[tele_player]

Are the cathode resistor and bypass cap correct? Connected correctly? What's the DC voltage across the cathode resistor?

[Bob-I]

My voltages all look fine until I put the Power Tubes in. With the tubes in ALL my voltages drop by about half. Something is sucking a lot of current.

I disconnected the OT primaries and it still didn't change anything.

Wow, this is a puzzler. No OT to supply voltage to the power tubes, and yet they're dragging the voltage down. Are you testing with JUST the power tubes or are the preamp tubes in also?

[thinking out loud]It seems that the only thing connected at this point is the screens. It doesn't make since that screens draw that kind of power, but where else could the draw be? What happens if the screens are disconnected? [/thinking out loud off]

Good luck, I wish I had a silver bullet for you.

[dab]

Cathode cap is 220uF which is what is shown in the layout

Cathode resistor is a 50 ohm 10 watt which is what Nik sent with the kit. The layout however shows a 62 ohm 10 watt. Shoud be okay I think.

Looks to wbe ired correctly. I triple-checked.

Thanks for your feedback.

Dave

[tele_player]

What is the voltage across the cathode resistor, with the tubes installed?

[Bob-I]

Hmm... try removing the bypass cap. If it's shorted you might be drawing current through the cap

[dab]

What is the voltage across the cathode resistor, with the tubes installed?

4.2 volts

[Bob-I]

What is the voltage across the cathode resistor, with the tubes installed?

4.2 volts

That's only 21ma per tube. You're problem is not in the tube or tube wiring.

[dab]

Hmm... try removing the bypass cap. If it's shorted you might be drawing current through the cap

Remove the cap but leave the resistor or remove both?

Thanks...

[mlp-mx6]

You MUST have the resistor. The amp will not function properly (will EAT the tubes, and maybe the transformer) without that cathode resistor.

You need to understand what you are doing better.

[Bob-I]

Hmm... try removing the bypass cap. If it's shorted you might be drawing current through the cap

Remove the cap but leave the resistor or remove both?

Thanks...

With the voltage measurement you posted I doubt if that will make a difference, but always leave the resistor. This resistor bias' the tube so that it doesn't run away with high current burning out the tubes or the xformer.

[dab]

That's what I thought but I confess I am a rookie on the learn as you go plan. This is my 5th build but I do lack electronics credentials. I working on picking up the technical stuff as I can.

Dave

[dab]

Hmm... try removing the bypass cap. If it's shorted you might be drawing current through the cap

Removed it. No change.

[Bob-I]

Hmm... try removing the bypass cap. If it's shorted you might be drawing current through the cap

Removed it. No change.

As expected.

Are you sure it's just the power tubes that drag the voltage down? It doesn't make since with your voltage measurement across the cathode resistor.

[dab]

Hmm... try removing the bypass cap. If it's shorted you might be drawing current through the cap

Removed it. No change.

As expected.

Are you sure it's just the power tubes that drag the voltage down? It doesn't make since with your voltage measurement across the cathode resistor.

With all tubes out I get 350VDC everywhere. Light bulb limiter shows no current draw (filament not glowing)

With preamp tubes in but no power tubes I get 350vdc to the Grids on the Power tubes, I get 350vdc on the OT Secondaries (Pin 7). light bulb limiter shows no current draw.

With all tubes in I get 180ish vdc where I got 350vdc before. Light bulb limiter glows (although not at full brightness.

Dave