New Liverpool build, first fire-up

[plook]

I just completed the chassis for my first TW Liverpool style amp based on the Ceriatone layout and it does not sound right. With the volume on about 1 to 2 there is the most awful howling and screeching, feedback and the amp has so much treble and no bass it could take your head off.

I'll check everything later on, but i wonder if you might look at my voltages and tell me what might be wrong. I can say that there are two places in the amp where i did not have the correct value resistors and approximated. One is the 39k connecting to the Presence where i used 33k. The others are on the power supply board where in place of the 9k1 i used 10k Is this my problem.

Voltage chart attached.

Thanks

[Fischerman]

Those voltages don't seem out-of-line. A small % difference in voltage isn't going to make that much of a difference anyway. If it sounds that bad then there is probably a wiring problem. Take some good pics and post and somebody will likely spot it.

Also, those slight resistor changes won't make that much of a difference either. Those, and your voltages, are just fine-tuning.

[dcribbs1412]

With the volume on about 1 to 2 there is the most awful howling and screeching,

Not sure but maybe switch OT leads?

[selloutrr]

yes OT phase or a bad ground around the tone stack. possible a dislexic pot wiring?

[plook]

Thanks, i will have a good check over everything later on this evening and i will swap the OT wires around. I'll let you know. Appreciate the advice on the resistor values.

[Noval_novice]

Would definitely reverse the OT leads.

[plook]

Here's apicture.

if you see any mistakes please let me know. Try to overlook some of the cheesy caps and untidy layout.

Problems:

Too much treble, no bass, howling and screaming on low volume.
I'm heading to the shop now to work on it.

[Noval_novice]

Thanks for the pictures. Check the wiring of V1. It looks like your wires to pin 1 and pin 3 are switched.

[dartanion]

A couple of observations. One that was already mentioned is the OT plate leads are probably reversed, which causes positive feedback and massive squeal. This would happen at any volume. The other is the routing of your NFB wire. It snakes between the grid leads to the power tubes then over to the impedance switch. I would re-route that wire to come around the end of board, then straight down under the grounds and directly to the impedance switch. Having the NFB wire where it's at now is quite likely to cause problems with stability.

[plook]

I've had a chance to have a look around and i found a missing ground on the left leg of the Middle pot. I swapped the OT wires around and it fired it up and the amp sounds so much better. Just two problems to resolve:

1. Excessive hum, not reduced by moving any leads.
2. Still way, way too bright and not enough bass.

Just notciued the NFB recommendation. Will do that now.

[Noval_novice]

Ah, nevermind what I said. Damn cell phone display! Glad you've got it up and running at least!

[dartanion]

Check out the layout listed here:

https://tubeamparchive.com/download/file.php?id=10374

Your filament wiring around the power tubes could be part of the hum issue. As well, grossly unmatched power tubes can cause hum. Also be mindful of where signal wires cross the filament wires, make sure you separate them a bit and cross at 90 degree angles. There are also photos of real Liverpools in the files section, so those are always a reference. The Ceriatone layout works, but isn't very accurate to a real wreck.

[plook]

I started out with thart layout and wanted to follow it but didn't have many of the power board parts and ended up doing the Ceriatone.

Studying that layout i see the filament wires feeding the power tubes and then switching to black and grey wires and then when they cut over to V3 the black wire goes to pin 8. That is something i don't have on mine.

Brand new JJ tubes all round.

Hum reduces if i put my hand on the chassis. I will look into the filament wiring around the power tubes.

I have an Edcore OT with a 6.6 and 5.2 wireup which i have on a DPDT. There is no discernable difference to my ears.

[selloutrr]

make sure all the grounds are soldered

all bolts are tight

make voltage is not touching or running next to signal.

[dartanion]

Studying that layout i see the filament wires feeding the power tubes and then switching to black and grey wires and then when they cut over to V3 the black wire goes to pin 8.

Brand new JJ tubes all round.

Hum reduces if i put my hand on the chassis. I will look into the filament wiring around the power tubes.

Well, the pin 8 connection is wrong, it should be to pin 9.

New JJs doesn't ensure that they are well matched power tubes. I have gotten many bad JJs right out of the box.

If you are playing through the amp with the chassis open to the air, you can be picking up EMI from various sources, mainly fluorescent lights. If you have fluorescent lights, try turning them off to see if the hum reduces. You can also try the elevated filaments trick, which is to connect the filament CT to the tube side of the PA's cathode resistor.