Help Needed!! Tubescreamer build; Pot noise problems

[eviljoe]

Dear all,

Just getting together a Tubescreamer from the tonepad pcb. We can't easily get the exact parts here in the UK, so a few substitutions;

one of the 510k 's is a 470k
0.027uf is a o.022
0.22uf's are normal, not tant
51pf is a 47pf
1uf np s are both standard (enormous!) orange jobs
tone pot is 22k not 20k

The problem- low effect output, and when I try to turn up any of the pots, I get a screaching sound- not the 'screaming' I was hoping for!

Voltage readings;

9v = 9.33

ic1 =

1 = 4.65
2= 4.8
3 = 4.56
4= 0
5=4.66
6=4.66
7=4.65
8=9.33 which sounds ok?

q1=

c= 9.33
b=2.95
e=2.61

q2=

c=9.33
b=2.95
e=2.61

From using a probe Ican detect that the screaching is coming from the pots, esp the level one, and also the second 1uf capacitor

Please does anyone have any ideas?

Are my substituted componants causing problems? If you hadn't guessed, I'm a bit new to this game, and it's all a bit trial and error- any thoughts much appreciated!!

Cheers

Joe

[SY]

Can you post or link to a schematic?

[eviljoe]

sure;
tubescreamer

any thoughts greatly appreciated !

[Brion55]

It sounds like the circuit is oscillating. The original TS had a 100mf from the +supply to ground to keep this from happening. I would try adding one.

[eviljoe]

seems better now- some earthing problems!

cheers guys

[Nigel Goodwin]

Originally posted by Brion55
It sounds like the circuit is oscillating. The original TS had a 100mf from the +supply to ground to keep this from happening. I would try adding one.

I would say that's an essential component, it's asking for trouble atempting to leave it out.