Noisy Liverpool!

[Bickster]

I finally got around to building a wreck! It is basically the ceritone layout with two el84's. My biggest deviation was the inclusion of the tube sockets on the circuit board. I felt that I could have better socket layout with this approach. It makes it a bitch to troubleshoot I can tell you that! It sounds VERY good but when you stop playing it will rumble, tick, howl, motorboat, or any other amp sound that you can think of! It is rather random but is effected greatly by the tone controls. All 12ax7's are mullard and known good. Changed el84's as well with no change. Just changing the tone controls settings will set it off! I'm really regretting my layout choice. It seemed like a good idea! Thanks.

Bob

[Allynmey]

got a pic?

[Bickster]

I was afraid you would ask for that! I'll post a pic of handy work when i get home.

Bob

[Bickster]

Be kind! My builds are neat until I start to troubleshoot. I thought that putting the tubes on the board would shorten the wiring and save alot of hated metal working. It sucks to check for cold joints under the board. Originally I had a lot of hum. There is no CT for the heaters so I quick and dirty did the 100 ohm thing. I started with a Hoffman grounding scheme but re-worked it to the Ceritone layout. Both resulted in much reduced hum. It sounded good with my mim strat except for a little noise in the pots. I switched to my humbucker Charvel and the problems started. Many leads are way long because I wasn't sure what the best routing was going to be. I could turn the board 180 degrees to avoid routing over the tubes but the controls will be reversed. Thanks.

Bob

[Allynmey]

Interesting layout. Heat looks like your number 1 problem. That cap on top of the cathode resistor will fail quickly. The power section is too close to the pots. The leads, as you said, are too long. I'm not totally opposed to that board mounted preamp idea but, the power tubes need to be more remote. Looks like a lot of oscillation hunting in your future. Did you take any pics of the bottom of the board before you wired it in?

Allynmey

[Bickster]

What if I rotated the board 90 degrees. That would keep the pre section close (or closer!) to the pots and move the power section away. This would also put them closer to the OT. No underboard pics yet but I'm gonna pull it out so pics will follow. I did quadruple check it before installation because I knew that it would be difficult later. Layout wise the jumps from the tube socket to components are well spaced and don't cross. If you look at the power section you'll see I brought the grid leads through the board to prevent crossing them. The PI tube seems kinda sensitive. I calms down a little if you get your hand close to it. I put sheilds on all of the tubes but that didn't do a thing. Interesting layaout indeed! I wish I didn't have this overwhelming need to re-invent the wheel! Thanks for your input.

Bob

[lastwinj]

nice .022uf caps ya got in there.

mount the tubes at the back of the chassis. that will do wonders., but would have to redo the board.

leads on the tone stack are way too long. i would also space the tubes farther apart.

germ

[VacuumVoodoo]

Are the tube shields grounded?

[Bickster]

The carbon films should look familiar as well! I need more so look for a PM. I did ground the sheilds when they were installed. I'm not going to fool around with this one too long. I feel that I may have gone a little too far this time. I will rotate the board and re-route the leads but by the end of the weekend it is going to sink or swim. Lucky I bought a big sheet of G10! Would you change any of the PI values because of el84 x2? Many thanks!

Bob

[paulruby]

I agree with everything said so far... If it were me... I would gut it and take a saw to the board, cuting off the tube sockets, leaving the very nicely laid-out circuit area for re use (but definately separate the cathode resistor and bypass cap).

Mount the power tubes near the OT so the OT primary lead are nowhere near the circuit board or pots. And, I would keep the preamp tubes on the opposite side of the circuit board from the pots.

In short, I would convert to a traditional JTM45 style layout, because that's what I always use.

[Bickster]

Any advice on the PI values for using two el84's instead of four? I could use the 18 watt PI but that wouldn't make it a wreck would it?

[Bickster]

Underboard pics

[Bickster]

180'ed the board, relocated the cathode bypass cap, shortened up the leads, and put sheilds on V1&2. Mucho better but one problem remains. The GUITAR volume must be wide open or off. Any significant adjustment and all hell breaks loose. There is much scratch and then it starts to hooting. The amp volume control works fine as do all the controls. Just the guitar volume! Yes, I tried my other guitar.

Has anyone tried a 12ay7 in V1? It a great blues tone.

[Bickster]

Well there is 121V on at the end of the guitar cord. I will kill myself one of these days!

[paulruby]

The GUITAR volume must be wide open or off. Any significant adjustment and all hell breaks loose.

This is strong evidence that the wire from the volume pot wiper to the tube grid is picking up noise. It is low impedance when all the way down or all the way up, so doesn't pick up noise. All positions in-between are suseptible to noise pick up. Since the line is shielded, the noise is likely something very close to the pot or the next tube grid. (Like maybe the green line from the presence pot getting close to the pot wiper.)

- Paul