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Bassman 6G6-A Head

6/11/2003 12:49 AM
Bob M.
Bassman 6G6-A Head
I've got my friend's 6G6-A Bassman on my bench. He loves the normal channel but hates/doesn't use the Bass channel and I concur. It sounds bad, at least in comparison to the Normal channel.  
Now there were three different Bassman circuits in quick succession: 6G6, 6G6-A and 6G6-B. Although the production/ tube chart tag inside the amp says 6G6-A, this amp has the power transformer with the rectifier taps (125P5A, like in a 6G6) but they are snipped off near the bell and it has a ss rectifier installed and wired. It has the 4 ohm output tranny (125A13A) as a 6G6-A should. In fact, studying the changes (schematics) between the 6G6 and the 6G6-A, this amp has about half the parts for one model and about half the parts for the other. And it looks 99% original; a true transition model amp.  
The Bass channel is one of the reasons Fender kept changing the Bassman and each rev has a slightly different spin/ variation of this channel, with some parts changed or altered.  
Is there any consensus on which design is the best sounding Bass channel for guitar use? I'd even consider trying the AA864 (blackface) variation. I know this has been a 'much discussed' amp here and I'd rather not have to re-invent the wheel, if possible, but learn from the experience/expertise of others. Also, are there any accepted tweaks/value changes/ mods to make this bass channel more guitar friendly?  
Thanks in adv for your comments,  
Bob M.
6/11/2003 5:23 PM
Winnie Thomas

One of the blond amps uses this preamp on the bass channel:  
I like this one's sound. You'll notice that it uses both of the 12AX7's completely.  
If you want to make a change, wire the bass channel like a 5F6 (tweed) bassman. I wired the bass channel in my Blackface bassman that way. You'll have a wasted 1/2 a 12AX7 but the BF bassman had that anyway.  
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6/11/2003 5:38 PM

Did you wire it with the normal imputs or the bright?
6/11/2003 6:59 PM
Bob M.

Try it each way and see what you like.
6/11/2003 6:58 PM
Bob M.

Thanks for the reply.  
I've considerd the 5F6-A as a possibility but I'd thought I'd first explore how good the 6 -series preamps could sound with toneful little tweaks here and there.  
I've noticed that the 6G6 Bass channel has local feedback between the two stages of the 2nd 12AX7A (V2) whereas this idea is eliminated with the 6G6-A. The said amp on my bench, although an 'A', has this also. The way the Volume control ties into the tone stack for this channel is slightly different for all 6-series model Bassmans. I wonder which way will sound best. I might have to try all three. (It seems I can temporarily sub a pot into there.) In the 6G6-B, the treble control is moved up one stage but bypass caps are used across both plate and grid load resistors of this stage, something I'm normally not fond of employing in preamp designs. I guess that's a nod from Fender that this was supposed to be a bass amp. Also the 'B' changes the smallest tone stack cap value, which could work well for guitar. There's lots to explore here.  
I think I'll convert the bass channel to a stock 'A' preamp and work sideways from there.  
Bob M.
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