DSL 401

[Valvehead]

Another jcm 2000 project ....

this one is a dsl 401

The clean channel works fine- sounds great , but switching to the OD ch. , i have almost no volume...if the gain and master are on 10 i can barely hear signal on OD2 mode...od 1 is silent.

i have a big voltage drop somewhere on the power rail to the pre tubes ...yet the clean channel acts normal

for example i have 0v at the junction of r77 and r81

all the resistors are good down the rail starting at R32 , but after each one the voltage is dropping very low

all the plate resistors test good , im somehow getting 90dvc at pin 1 - V1 , but no voltage at the plates at v2 / v3

i noticed r55 / r77 / r79 are getting very hot , but r81 is cool to the touch

i just cant find any bad resistors....could it be one of those transistors such as t9 / t12 etc, shorting to ground?

after V1 it says "ODMUTE" after pin 7, what is that?

[Jazz P Bass]

ODMUTE is on the channel switching circuit/ page 2.
The signal rides on it or not.

The Ch Sw uses jfets.
Think of them as a switch.
On/ Off.

DSL 401.zip

[Valvehead]

ok, so they wouldnt be part of the problem ?

[Valvehead]

if any of the filter caps on the rail were bad....i would hear hum and noise on the clean channel, yes?

[Valvehead]

If anyone was interested.......I found the problem.

One of the filter caps was shorting to ground....C59? i think.....it was a 10uf/450v.

amp works perfect now !!

[Jazz P Bass]

Well, the hint was R 71 getting hot & R81 not getting hot.

Glad that you figured it out.

[Valvehead]

thanks-- i started testing parts to ground and narrowed it down...what a relief to find it