Help with Liverpool -no sound

[Littlewyan]

Try swapping the OT Leads like the others said, see if that calms down the howling a bit, if it does then we're making progress. Next step is to start pulling pre amp valves to see where the squeal is coming from. Could be a bad pre amp valve.

[WinstonN]

Martin, Richie, Littlewyan - swapped the OT primaries. That did it. Apparently, the guide I had either had it reversed, or the transformer was wired that way. In any case, it is up and running.

Now I need to run down a pretty loud "hum/buzz" issue. Gets bad as the amp is turned up with guitar full volume, and touching guitar strings gives a little pop. Switching amp bright switch to brightest makes the amp squeal.

Any thoughts on how to chase this down?

I really appreciate all of this help. I didn't expect to be learning so much.

[WinstonN]

V1 12AX7 is very noisy - it rattles like crazy when touched. Swapped it - still rattles, so not the tube.

The voltages on all 12ax7s are still a little high:
174 on V1, Pin1 (spec 160)
1.7 V1 Pin3 (spec 1.4)
157 V1 Pin 6 (spec 143)
1.2 V1, Pin 8 (spec 1.0)

When I contact multimeter with pin 1 on all 12ax7s there is a pop and static.

[kwijabo]

glad you got the first two issues resolved. with regards to probing the pin 1's....i'm not suprised at what you're describing. pin 1 is where the signal comes off of that stage, so by probing that point you're creating a slight, momentary change to the signal. so a pop is not unexpected. not sure about the static, though.

regarding the hum...the two issues i've had with hum were caused by:
1. no bottom plate on the chassis. turned out the room i build amps in has quite a bit of 60Hz noise. as soon as i closed the chassis with a bottom plate the hum went away
2. a bad ground connection. i tightened the ground connections. if that connection from the power tubes was bad, i would check all ground connections.

[martin manning]

The oscillation with the bright switch is most likely a lead dress issue. Try chop-sticking around the control and grid wires.

[Littlewyan]

Once you've got it quiet as possible by adjusting your lead dress and checking your grounds keep on trying different valves. Out of 4 valves I got the other day only 1 was quiet in V1, so don't be surprised if you keep finding microphonic valves in that position, its very sensitive.

[WinstonN]

I'm adjusting lead dress with minimal success, but I'll keep trying. I will try different tubes in V1, as well.

I found the the wire connecting the middle lug of the bright switch to the middle lug of the volume pot is by *far* the most sensitive in the amp. The slightest touch with the wooden stick is extremely loud, and touching the connection to the bright switch middle lug, or running the stick along the length of the wire causes lots of static. Mean anything?

Also, when I touch a string after not touching one for a few moments, there is a pop. Am I wrong in thinking that indicates a ground issue?

On a positive note, horrible buzzing aside, the amp sounds GLORIOUS. Wow. I can't believe I waited so long to give this design a try.

Looking for more 12ax7s now...
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[Littlewyan]

Can you try another guitar? As it could be a grounding issue on that guitar. Also try a different room. In my room if I have my wireless printer on my guitar will pick it up, unless I touch the strings.............explain that one!

Also I can't see the lead dress very well in the photos but it looks like you have a few leads on the pots that can be shortened. The bright switch wiring is very sensitive, I found on my amp that if I go near it with pliers the amp screams!

[martin manning]

You can also try a small grid stopper resistor (~1k) soldered at pin 2 of V1, on the end of the wire from the volume pot. That will suppress oscillation and help reduce the hiss. There may be one there already, but it's hard to tell from your pic.

[WinstonN]

There is no grid stopper resistor (~1k) soldered at pin 2 of V1. I've swapped many tubes. Tried several guitars.

When the guitar is NOT plugged in, the buzz comes from the wire between the bright switch and the volume pot - even getting my hand close makes it get loud.

With the guitar plugged in the problem is diminished slightly with hand on strings, or I touch the chassis anywhere. Still loud, though.

It almost seems like there is too much gain early on. When I have the amp on 30%, I can't turn up the guitars all the way - just start feeding back. Sounds pretty cool before it gets there, though! Just touching the V1 tube is very loud.

I might be running low on "help credits". I sure do appreciate all the help and suggestions you guys have been willing to throw my way.

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[Bob S]

The ground bus is soldered to the back of the pots otherwise I'd recommend turning the Vol/Gain pot 90 degrees so that the lugs are very close to the bright switch.
Anyway I'd glue the bright cap to the side of the mini toggle & make the wiring to the pot as short as possible.
Also look at the TMB wiring in the Files Section - get yours as close as possible to that, then chopstick to find the best position for them.
You'll like the beast once you get a it stable. 10% back from the edge of stability & let rip.
Good Luck.

[WinstonN]

Will do Bob. Shortening the bright switch --> Vol pot wires makes sense. I don't understand what you mean by gluing the bright caps to the bright switch - shortening them?

I'll spend time looking at TMB wiring, too.

I really want to get this playable. I've never played anything like this. Such beautiful cleans, OD is just visceral, dynamics off the scale...ride on the edge of linearity.

[Bob S]

I don't have access to the info on my regular pc right now so I cant send a pic.
I use 2 different values of bright cap on a 2 pole 3 position center off mini toggle - values based on personal taste. Looking at the back of your switch I connect 1 cap to the top 2 lugs, the other to the bottom 2, then wire the center lugs to the vol pot. I glue the caps to the top & bottom of the switch keeping the leads as short as possible. Helps with vibration.
For a 2 position switch just leave leave out 1 cap.
Liverpool cleans are great but the mean is something else...
Hope this helps.
Bob

[Littlewyan]

If you look at the layout file we have here you'll see that the bass and middle wirings coming from the turret board are pushed back against the edge of the chassis. Also all wires between pots are kept as short as possible.

[hans-jörg]

Hi,
here are also some very good samples shown how to wire a bright switch. Try search function.
But to find out if the amp is running stable, disconnect the switch wire going to left and middle lug of volume pot. If than the amp runs stable you can try to find a way to wire the switch proper to it, without oscillating.

I had a similar problem and fixed it by shortest wire between switch and pot.

Hans-Jörg