CRATE BV amp Ch1 prob- "Crunchy" Noises.

[Jazz P Bass]

The Jfet should be D, G, S, with the flat face towards you & the legs pointing down.
From Left to Right.
A Jfet is a 'normally closed' device.
It takes a current at the gate to pinch off the channel (ie: higher resistance between D & S))
The J176 is spec'd at 250 ohms from D to S, no gate signal applied.
This can be verified with an ohmeter.
If you measure the two outside legs & it comes in relatively close to 250 ohms, then you are good to go with that part.
In this type of circuit the drain & the source can be interchanged, so there is no need to worry there.
As long as the gate pin is the middle leg, it will work fine.

[Sea Chief]

Drain, Gate, Source. Got that. Im sure it will measure ~250ohms: I guess ebay seller would know to check this and not sell a 'flat' one as it were.. I hope morelike.. but I'll defo measure from D to S. Good to know what these do now too- another thing then Ive learnt here. terrific JazzP. My fingers crossed and all else too.

Hope to be in touch with good news tmrw/ thurs or so. Excite!

[Jazz P Bass]

Just to add, my intension was not to check the device, it was to verify that the D & S leads are in the proper order (outside legs).

[Enzo]

You know, I can count on the legs of a 2N5088 always being the same or a 2SA1815. But I ALWAYS check the legs of ANY JFET before I install it, You may find all the J174s the same, but there are soo many types that are interchangeable, I always check.

Two legs will have a low resistance between them. The OTHER leg is the gate. All I have to do is identify the gate leg and get it in the correct hole, and I am OK. The source and drain can be either end, they are interchangeable here.

[g1]

Well, I hope you can understand I'm a little nervous about getting hopes up due to the shifting nature of this problem.
So I would suggest some more checks without Q4.
Reconnect C17 and verify that the problem is gone from both channels (with master up). If so, C17 can now stay connected.
Then, short across R30 and check there is no noise in Ch.2 (with master up).
If the noise is gone in all cases, I'll be satisfied a new Q4 should solve the problem.

[Sea Chief]

Reconnect C17 and verify that the problem is gone from both channels (with master up). If so, C17 can now stay connected.

Done: quiet/ noise gone (lovely quiet too).

Then, short across R30 and check there is no noise in Ch.2 (with master up).
If the noise is gone in all cases, I'll be satisfied a new Q14 should solve the problem.

Done: quiet/ noise gone (lovely quiet)!

Fab! Ive got good vibes about this now. Report back with Q4 in, any day. Huge thanks chaps.

[Sea Chief]

Just to add, my intension was not to check the device, it was to verify that the D & S leads are in the proper order (outside legs).

Understood JazzP. I must find the two that see ~250~ ohms acroos them, and single out the other as the Gate/ middle hole on board.

I must get this right 1st time, the tracks will not tolerate me taking it out again/ they will disintegrate.

[Sea Chief]

New Q4 gone in.. Gate identified, & its flat side as per the board diagram where it is..

no sound at all. No noise, nothing from spkr it seems (not even a v quiet normal hum) a very dead feeling amp. GTR plugged in, nothing. All leads/ everything double-checked/ no daftness. hmm.

[Sea Chief]

I just switched Q4 round.. nothing. a really dead-amp feeling. and a stomach-sinking feeling too. Nothing via GTR. Urgh.

I have a feeling the 'lovely quiet' noise was just too quite/ ie s'thing-not-right-quiet which started after removal of Q4 & this might have done some damage? blown OT? godamm sh*tsters. The tracks of Q4 are nr fried now too.

[52 Bill]

I just switched Q4 round.. nothing. a really dead-amp feeling. and a stomach-sinking feeling too. Nothing via GTR. Urgh.

I have a feeling the 'lovely quiet' noise was just too quite/ ie s'thing-not-right-quiet which started after removal of Q4 & this might have done some damage? blown OT? godamm sh*tsters. The tracks of Q4 are nr fried now too.

I assume that you have removed all of the earlier test jumpers, etc.

You could always remove the new FET and rejumper to test the amp signal path.

I really doubt that you have a bad OT. Recheck your work and make certain that you have replaced any wires that were pulled to do the soldering, etc.

[Sea Chief]

Yep- all checked, Ive had the board out & prepared for the Q4 I was waiting for. So last thing I did 3 days ago was put back C17 leg > tested with Q4 out again (vv Quiet).

My jumper wire is so obvious Id never have left it, or anyhing else daft in either, or s'thing not soldered etc.. nope, all t's crossed & i's dotted.. I make 3x certain b4 turning on each time.

I just put a new Q4 in, checked each leg for good continuity to its next point in circuit, checked neither outer leg had any continuity to middle leg. Then hooked all up all wiring as Ive done so manty times now. Check. Check again > Power on.

[Jazz P Bass]

Well then.
I would advise starting a new post.

[Sea Chief]

Well then.
I would advise starting a new post.

Ok thats an idea. I need a fresh start here. If not the OT then again its a q of locating the prob point.

[It'll be 'Dead Crate- need help!'.]

thanks anyway chaps, shame its not happened.. but I will persevere (the amp albeit w'noise was -the one- for me).

[Sea Chief]

END.

{New thread/ re-booted to
http://music-electronics-forum.com/t34398/#post319661 }

[Jazz P Bass]

Something happened after post 177-179.
Messing with C17 & grounding the V2 grids, you stated the noise ceased.
I am assuming that lifting the grounds would , at this point in time, make the amp noise.
It is not stated that this is true.
Post 179 you had a slight hum.
Since then you removed the Jfet (no noise) & reinstalled a new one.
And now?
Not even a hum?
I would check the wiring on the chassis & speaker.