BYPASSING A GAIN STAGE - QUERY

[NGW]

Hi Kevin & fellow Tone Chasers,

It has been a while since I finished this amp repair and modification and I thought I would share the details of what happened.
It was a lot of work, but it turned out very well.
That said, I don't recommend that anyone else do this type of mod to a Blues Deluxe; I won't again.
Quicker to build a complete new eyelet board and fit an Fx Loop and a digital Reverb.

Attached is the Modified Preamp Schematic and some gut shots of the end result.

What I did:
Replaced every electro cap in the amp.
Stiffened the PS with 220uF & 47uF filter caps.
Screwed R85 & R86 to the chassis using 15W aluminium body resistors, to avoid the usual PCB burning from the original setup.
Added three auxiliary boards for: an adjustable Bias, the added Gain Stage using V2B, and the extra decoupling caps & resistors.
Made separate B+ nodes for each preamp stage.
Changed the Volume and Drive Controls from rheostat to potentiometer operation.
Reconfigured the wiring of the Relays to effectively select Clean or Drive and mute the Drive stage in Clean mode, to avoid any bleed-through.
Altered the circuit as per the schematic to achieve a much better Drive sound, while maintaining the desirable Clean sound.
Replaced the Ribbon Cables with individual wires.
Removed C50 and changed C18 to 470pF.
Changed R50, R51 & R52 to 10k, 91k & 110k.
Changed R57 & R58 to 1k.
It is fitted with JJ valves; V1 & V2 - ECC83S, V3 - ECC81, V4 & V5 - 6L6GC.

It has been working well again, for a while now and has been received well by all who have heard it.

It doesn't hum or hiss, has a very good Blues/Rock Distortion sound and the very nice Blues Deluxe Clean sound.

Thanks to Kevin for his valuable advice.

Cheers, Noel

   
   
   
   
[attachment=57]