[ 'Dead CRATE BV- need help! ]

[Sea Chief]

The only thing that remains unclear re thie JFET, is whether my new one was bad -exactly- as the old Q4. Unlikely. And I tested as you suggested prior to putting in. But the fat 5w failure occured before replacing so masked innitial appraisal of my new Q4.. but once new fat 5w in (and new Q4 in) crunchy symptoms remain you see.

If Im not mistaken, this has ruled out Q4 has it not?

Or do you suggest I take out my new one too, for other testing reasons?

[Jazz P Bass]

O/k, then remove C16.

[Sea Chief]

O/k, then remove C16.

Done that JP: noise remains.

[Jazz P Bass]

Ground the top of R19.

[Sea Chief]

Ground the top of R19.

MEF awol for a while over here- delayed reply.

Did that: top [edit: as in C12 neg side?] of R19.. huge hum, but no discernable crunchy noise, I think- cant be sure as hum's so loud.

thx SC

[Jazz P Bass]

Seeing that grounding V2 A pin 2 left a slight noise I would supect that it is still threre after grounding R19 (under all of the hum).
To recap this issue.
Grounding C20 (R34 side) stops the noise.
Grounding V2 A pin 7 stops the noise.
Lifting out C16 (which also eliminates Q4) does not stop the noise.
Lifting C17 does what? If I recall it does not help.
So is the noise being generated in V2 A or B?
It may help if you disable V2A (remove the plate resistor R25).
Then run a jumper from C11 (R15 side) to C15 (R27 side).
If the noise is still there, then it is a V2B problem.
It may be that you will have to disable V2 A.

[Sea Chief]

Hi JP.

To recheck/ C17 leg out (& C16 is also out still): noise remains.

[Sea Chief]

.
It may help if you disable V2A (remove the plate resistor R25).
Then run a jumper from C11 (R15 side) to C15 (R27 side).
If the noise is still there, then it is a V2B problem.
It may be that you will have to disable V2 A.

Done: noise there, but 1/2 as loud as I usually hear. hmm.. what else can this amp produce to confuse me?!

[Jazz P Bass]

Then disable V2A, as stated above.

[Sea Chief]

Then disable V2A, as stated above.

Done (for #53) ie Ive removed R25 > added the C11 to C15 jumper: nosie remains.

(Ch 1 is in fact normally noisy/ just done test again, but oddly Ch2 noise is 1/2 as loud as mentioned in #53).

[Jazz P Bass]

Leave V2A disabled.
Remove R33 (V2B plate resistor) & run the jumper from C11 (R15 side) to C 20 (R34 side).

[Sea Chief]

Leave V2A disabled.
Remove R33 (V2B plate resistor) & run the jumper from C11 (R15 side) to C 20 (R34 side).

Done; noise ceases. (c16 still removed btw- just to note/ prob fine as is).

[Jazz P Bass]

I would imagine you know what is next.
Reconnect V2A.
Reconnect the plate resistor (R25).
For now, leave C16 out.
Leave the jumper on C20 (R34 side) & connect it to C15 (R27 side).

[Sea Chief]

I would imagine you know what is next.
Reconnect V2A.
Reconnect the plate resistor (R25).
For now, leave C16 out.
Leave the jumper on C20 (R34 side) & connect it to C15 (R27 side).

Roughly on board still JP!

Done: noise remains (about 1/2 loud ch1, 1/4 loud ch2. ?!)

[Jazz P Bass]

"Done: noise remains (about 1/2 loud ch1, 1/4 loud ch2. ?!) "
And that would be amplified by V2B.
Not too sure where to go next.
Both V2 A & B have noise problems.
Sleep on it.