New Liverpool build - humming tx, LOUD hum when off standby

[klauswilliams]

Hi all - first post here. First off, this forum and posters have been exceptionally helpful to my amateur amp building skills. I've made a handful, had problems with every one of them, and used forums just like this to get me through. Many thanks.

I have a new Liverpool build that I've run out of ideas on. It hums as soon as I power up (coming from tx), and then when taken off standby it quickly goes from hum to incredibly deafening hum in about 0.7 seconds, even with no guitar plugged in. I know it's something totally stupid that I've messed up, but I've checked and re-checked against the schematic and it looks ok to me. Obviously it ain't...

I took voltage readings and a few pics. For background, it's a Ceriatone kit with Heyboer tx's (5199 and 5200). I know, not for purists, but I'd never used a kit and thought it might be fun. I tried to follow the recommended wiring here. Anyway, here are the voltage readings with NO tubes installed, powered up.

V1/pins 1-9: 205, 0, 2, 3.5, 3.5, 182, 0, 1.32, 3.5
V2: 260, 0, 3, 3.5, 3.5, 0, 0, 0, 3.5
V3: 230, 8 (and slowly drops), 62, 3.5, 3.5, 235, 33, 68, 3.5
V4-V7/pins 1-8: 0, 0, 0, 3.5, 3.5, 0, 370, 0, 370 (all pt's read the same)

B+1 = 405
B+2 = 402
B+3 = 310
B+4 = 290
B+5 = 275

Obviously some of those are high without tubes. Any tips/comments/suggestions/anything would be greatly appreciated. I was so stoked to rock this thing out but I was quickly brought back to the reality of my limited skills when it didn't work.

[fishy]

If the amp runs away (oscillates) it might well be the OT primaries being the wrong way around. A common issue on startup.
Disconnect the feedback and see if it still does it. That is usually easier than swapping over the primaries.

Nice looking build

[jerrydyer]

2nd that. you can reverse the two wires coming off the plates of PI

[Structo]

Did you buy your boards and chassis from Ceriatone?

[klauswilliams]

That did the trick! Thanks a million Fishy, you are the man in my book. I never knew those needed to be hooked up in a specific order, but then again I am a newbie at all this. Good thing is I seemed to get everything else right, as it blasted me away as soon as I tried it again (in a good way this time).

WOW the volume gets on you quick!!! Almost frightened me.

Structo - I ordered the full kit minus tubes and transformers from Ceriatone (includes chassis). Chassis is great, real thick and sturdy as hell. While I'm not complaining about it at all, there were a few misaligned screw holes where the boards mounted that required re-drilling. And, 2 caps on the board were SO big and tall that they didn't fit in the chassis, so I swapped them out with Sozo's. Lastly, I can't figure out how the tube retainers mount, but I don't really care and will likely leave them off. Otherwise, seems to me like a fairly high quality product.

Thanks again guys

[Allynmey]

Get rid of that 50 Ohm power tube cathode resistor and replace it with a 60 Ohm. With those voltages, it will be biased too high.

[fishy]

Did you do a voltage chart with the tubes installed?

Allynmey makes a good point and you should at the very least verify the voltages are where they should be when the amp is up and running.
It will also prove invaluable if you ever have to poke around in there in the future.