Build complete - 6G6B Bassman Redux

[Structo]

SWEET!

I'd love to build an early Bassman someday.

[Firestorm]

That is seriously nice! Love the TungSols; I have those in my '54 Twin. Just kill, don't they?

[Firestorm]

V5 & V6: NOS Tung Sol Made in USA 5881/6LGWGB

435 VDC plate, 434 VDC screen, biased at 65%

Just noticed this part: 65% is pretty hot for a "traditional" Fender sound. Leo biased pretty cold. But if you like it...

[CHIP]

Beautiful build, TM.

[ToneMerc]

V5 & V6: NOS Tung Sol Made in USA 5881/6LGWGB

435 VDC plate, 434 VDC screen, biased at 65%

Just noticed this part: 65% is pretty hot for a "traditional" Fender sound. Leo biased pretty cold. But if you like it...

Yes, you are correct. I usually will burn them in hotter and then back it down, the one I sent out 3 weeks ago was biased at 54%.

TM

[Firestorm]

V5 & V6: NOS Tung Sol Made in USA 5881/6LGWGB

435 VDC plate, 434 VDC screen, biased at 65%

Just noticed this part: 65% is pretty hot for a "traditional" Fender sound. Leo biased pretty cold. But if you like it...

Yes, you are correct. I usually will burn them in hotter and then back it down, the one I sent out 3 weeks ago was biased at 54%.

TM

Pretty amazing how sensitive later Fenders are to bias. Client of mine had a'64 SR and we played with the bias just for jollies: 65%: he hated it; 60% he hated it; got down to that 50%-55% range and BINGO! A lot of really early Fenders are damn close to Class A, but 6s and 7s are SO AB1, it's impressive.

[ToneMerc]

Pretty amazing how sensitive later Fenders are to bias. Client of mine had a'64 SR and we played with the bias just for jollies: 65%: he hated it; 60% he hated it; got down to that 50%-55% range and BINGO! A lot of really early Fenders are damn close to Class A, but 6s and 7s are SO AB1, it's impressive.

True, funny you should say that. The first build, I left it right a 50% after break in, but the client thought 50% was kind of low.

TM

[Firestorm]

Well, it's always the client's ears that matter. But if you look at what Leo was trying to do it seems like he wanted the most watts for the least bucks. Bias at 70% and you've lost power; bias near 50% and you max it (for a typical 60s or 70s Fender circuit).

[LeftyStrat]

Don't mean to hijack this thread, but you guys observations for bias in Fender circuits are interesting.

What is your experience with Fender cathode biased circuits wrt bias point?

[renshen1957]

Finally got around to finishing my personall build. The Gomez chassis didn't fit the Marsh faceplates so I started over with fresh boards using Speer CF, Blue sozos Marsh chassis and cabinet which is Mojo built. In the meantime I had Heyboer wind me a modern higher line voltage blonde Bassman PT transformer.

I'll take a few more pics when the faceplate installed and it's in the cabinet.



Heyboer custom Bassman power
MM blonde Bassman OT
Sozo, Acro and ITW blue caps
Speer CF and Takman MF on cathodes
F&T and Vishay lytics

TM

Hi,

Looks great! How do you like the Blue Sozo?

Best Regards,

Steve

[ToneMerc]

Finally got around to finishing my personall build. The Gomez chassis didn't fit the Marsh faceplates so I started over with fresh boards using Speer CF, Blue sozos Marsh chassis and cabinet which is Mojo built. In the meantime I had Heyboer wind me a modern higher line voltage blonde Bassman PT transformer.

I'll take a few more pics when the faceplate installed and it's in the cabinet.



Heyboer custom Bassman power
MM blonde Bassman OT
Sozo, Acro and ITW blue caps
Speer CF and Takman MF on cathodes
F&T and Vishay lytics

TM

Hi,

Looks great! How do you like the Blue Sozo?

Best Regards,

Steve

Steve other than thinking they look nice, I don't have any comparative analysis of other caps in this exact amp. I did like the yellow as well in this circuit, as far as I know it could be the same cap internally.

I will say this, across the board I don't necessarily fall for or drink the Mercury Magnetics red Kool-Aid, but in this case the MM tone clone iron would be my first choice.

Mike

[Firestorm]

Don't mean to hijack this thread, but you guys observations for bias in Fender circuits are interesting.

What is your experience with Fender cathode biased circuits wrt bias point?

They seem to be awful close to Class A, but part of that could be the higher plate voltage as the wall voltage has crept up.

[JazzGuitarGimp]

Don't mean to hijack this thread, but you guys observations for bias in Fender circuits are interesting.

What is your experience with Fender cathode biased circuits wrt bias point?

They seem to be awful close to Class A, but part of that could be the higher plate voltage as the wall voltage has crept up.

They have to be biased hotter by design, to keep from sliding into class B, and producing crossover distortion. The harder you hit a self-biased tube with signal, the more current flows through the cathode, pushing the cathode voltage higher than at idle, which also pushes the bias further away from class A.