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April 15, 2024, 01:34:28 AM

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David eden WT300 mysterious transistor ...

Started by mccutter, January 13, 2024, 09:41:12 AM

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Hi there !
Who can tell me what transitor fits at the end of the yellow wire on the photo ?
(It's not on the design of the schematic circuit ...)
Thanks guys !

Jazz P Bass

Is there an issue with the amplifier?
The resistor in question may be a factory fact.
Please provide a schematic and a pic of the underside of the board.



Hello !
Thank you for your replies ... There was a transistort here, and no resistor ! It's a factory modification. As the transistor burns, I dont know the reference, either the purpose.
Here is the schematic I have. There is no match with this circuit !
My amp is a WT300, but the board is labelled WT400 !
Should I just put a resitor ?


Here are the pics of the bord and the faulty transistor. Looks like the others mps8599 or 8099 on the board.

Jazz P Bass

Holy Moly.
What a rat's nest.
All because they didn't use a double-sided board.
I cannot find Any component designators that match that schematic.


Looking at a WT300 PCB (R74, R75) it shows that location as a 22k and 47k resistor at the 12AX7, bottom left of the WT300 schematic.
Looking at the WT400 schematic it shows the same thing just different component numbers.(R81, R82)

I presume they used a WT400 Preamp PCB to build that WT300 amp.
There are no stupid questions.
There are only stupid mistakes.


Progressing : i put a BC557 at the mysterious transisor place. Nothing seems to fry !
Now, I try to check up signal path. I put à 220hz sine wave in the input jack. If U3, U4, U5 ad U6 are not on the board, the signal is ok at the fx send and at the phones jack.
So, there is a problem with the eq stage and / or the preamp op amp. voltage at all tl072 is correct.