Which filter layout to use for AB763?

[markmalin]

Hi All,


I'm building a one-off for myself to use, a single channel AB763 with reverb and no tremolo and a pair of 6L6 output tubes.  Regarding the filter board in the doghouse, I was reading on Rob's page about the 2 board configurations in the AB763 doghouse and I'm assuming most people are familiar so bear with me.  Both configurations use 5 filter caps, the Deluxe Reverb has the first 2 caps in parallel and uses 2 10K dropping resistors.  All other AB763's use the second configuration where the first 2 caps are larger value (80uf) in series (with 220k resistors in parallel with each cap), then use I think 1K and 4.7K dropping resistors. 


My questions:
- why did Fender use two different configurations?
- which would be recommended for my amp?  (AB763, one channel, 6L6's, non tremolo)


Humbly,
Mark

[sluckey]

- why did Fender use two different configurations?

Because they have a low power 6V6 version and several higher power 6L6 versions. The voltage requirements for each are different.

- which would be recommended for my amp?  (AB763, one channel, 6L6's, non tremolo)

Why would you even consider using the DR power supply in a 6L6 amp?

[markmalin]

Thanks, Slukey. 
What was confusing me was in the Hoffman AB763 1 Channel layout diagram it shows the caps laid out like the DR version, and in the BOM he has 5 22uf/500v caps.  I realize there are differences between the 6L6 and 6V6 AB763's parts list, and the notes speak to that, but I didn't find any discussion on the power supply section being different.  Maybe I missed something.  I had ordered off this BOM so I have the 5 22uf/500's on hand, so I'll go ahead and order two larger caps


https://el34world.com/Hoffman/files/Hoffman_AB763_1.pdf


Cheers,
Mark

- why did Fender use two different configurations?

Because they have a low power 6V6 version and several higher power 6L6 versions. The voltage requirements for each are different.

- which would be recommended for my amp?  (AB763, one channel, 6L6's, non tremolo)

Why would you even consider using the DR power supply in a 6L6 amp?

[sluckey]

If you look at the two channel docs you'll see the differences between versions annotated. Still no reason why. My guess is that the 6L6 versions require higher B+ for the small tubes in order to get a higher signal to drive the 6L6s to their screaming potential. 

You've probably seen this but look again, paying attention to the "parts in blue". You still need the BOM pdf to know what the actual values are...

     https://el34world.com/Hoffman/files/Hoffman_AB763_2.pdf

[markmalin]

Ahah!  Thanks - dang, I don't know how I missed that link.  That lays it all out.  I guess I was just looking in the 1 channel doc.

Mark

If you look at the two channel docs you'll see the differences between versions annotated. Still no reason why. My guess is that the 6L6 versions require higher B+ for the small tubes in order to get a higher signal to drive the 6L6s to their screaming potential. 

You've probably seen this but look again, paying attention to the "parts in blue". You still need the BOM pdf to know what the actual values are...

     https://el34world.com/Hoffman/files/Hoffman_AB763_2.pdf