6g7-A Blonde (Brownface) Bandmaster project

[StrummersOfThunder]

You might recall id been considering a 6g14 showman build. I've sensibly down graded to a two out put tube amp...6g7-a blond bandmaster
I have the chassis, blank face plates, OT (bassman 1760j) and some of the small parts for this build. BG is on the case for the head and matching 2x12.

Some questions for the amp gurus/amp literate/amp curious

1. Is it feasible to sacrifice one of each of the dual input jack sockets to add a mid pot to each channel? I know it would need a little butchery and jiggery to get things to line up. Less keen to run wires to the back of the chassis to utilise back plate but this might be the only good way.

2. Thoughts about making the normal channel blackface tone stack (kind of the opposite of what people do with their blackface builds/mods).

3. If you were approaching this build from scratch are there any 'must do' mods you'd recommend?

Aim is to have a blonde piggy back surf music stack that isnt vintage valuable like my 62 tremolux, that has a SS rectifier and beefy tight low end (thus the bassman OT) sparkly highs but with that brownface mid bump when i want it to sound a bit more 'setzer' but also the ability to get a good Dick dale scooped miserlou sound. The trem on this is a somewhat radical harmonic trem that sounds incredible on clips ive heard.

[jeremyb]

If you’re not using a fender harmonic tremolo you’re just playing with sparkling volume modulation.

Amp sounds awesome btw

[RectifiedAmps]

You might recall id been considering a 6g14 showman build. I've sensibly down graded to a two out put tube amp...6g7-a blond bandmaster
I have the chassis, blank face plates, OT (bassman 1760j) and some of the small parts for this build. BG is on the case for the head and matching 2x12.

Some questions for the amp gurus/amp literate/amp curious

1. Is it feasible to sacrifice one of each of the dual input jack sockets to add a mid pot to each channel? I know it would need a little butchery and jiggery to get things to line up. Less keen to run wires to the back of the chassis to utilise back plate but this might be the only good way.

2. Thoughts about making the normal channel blackface tone stack (kind of the opposite of what people do with their blackface builds/mods).

3. If you were approaching this build from scratch are there any 'must do' mods you'd recommend?

Aim is to have a blonde piggy back surf music stack that isnt vintage valuable like my 62 tremolux, that has a SS rectifier and beefy tight low end (thus the bassman OT) sparkly highs but with that brownface mid bump when i want it to sound a bit more 'setzer' but also the ability to get a good Dick dale scooped miserlou sound. The trem on this is a somewhat radical harmonic trem that sounds incredible on clips ive heard.

Nice! The few amps I've seen with harmonic trem have all sounded awesome. My take on your questions, FWIW:
1. Yes, the tone stack is physically close enough to the input jacks that it should be fine to repurpose one of the inputs. You'd just be replacing the fixed 10k resistor with a potentiometer, right?

2. It's just a matter of your preference really - no comment

3. For mods to the original schematic, there's heaps you could do to 'improve' things:
- separate the shared cathode RCs on the first 2 gain stages. It's just Leo being cheap again and you don't want interaction between channels. You'd need to use separate 1k5 cathode resistors and 10uf bypass caps to keep things strictly equivalent, but 22uf caps would be fine too.
- put the 0.1uF presence cap on 'top' of the 5k presence control, not underneath it - to reduce scratchiness
- add 1k5 grid stopper resistors to each 6L6GC, to prevent farting out (blocking distortion) when overdriving the output stage. If it still sounds bad, drop the two 220k bias feed resistors to 100k (or 150k). If it STILL blats, increase the grid stoppers to anything up to 5k6.
- add a B+/HT fuse for protection. You could put it on the centre-tap of the SS rectifier section, or perhaps immediately after the standby switch. Fusing the cathodes of the 6L6GCs is okay, but might not save you if the screen or anode shorts to the grid. Also note that for 240vac the mains fuse should be 1.5A - not the 3A in the american schematic.
- if you want more bottom end, you could up the 1nF coupling cap feeding the phase inverter to a 10nF but it might induce blocking distortion as well. A 4.7nF might be a good compromise.

Otherwise, it's probably best to just build it and see how it sounds, then set about tweaking things that bother you.

[StrummersOfThunder]

You might recall id been considering a 6g14 showman build. I've sensibly down graded to a two out put tube amp...6g7-a blond bandmaster
I have the chassis, blank face plates, OT (bassman 1760j) and some of the small parts for this build. BG is on the case for the head and matching 2x12.

Some questions for the amp gurus/amp literate/amp curious

1. Is it feasible to sacrifice one of each of the dual input jack sockets to add a mid pot to each channel? I know it would need a little butchery and jiggery to get things to line up. Less keen to run wires to the back of the chassis to utilise back plate but this might be the only good way.

2. Thoughts about making the normal channel blackface tone stack (kind of the opposite of what people do with their blackface builds/mods).

3. If you were approaching this build from scratch are there any 'must do' mods you'd recommend?

Aim is to have a blonde piggy back surf music stack that isnt vintage valuable like my 62 tremolux, that has a SS rectifier and beefy tight low end (thus the bassman OT) sparkly highs but with that brownface mid bump when i want it to sound a bit more 'setzer' but also the ability to get a good Dick dale scooped miserlou sound. The trem on this is a somewhat radical harmonic trem that sounds incredible on clips ive heard.

Nice! The few amps I've seen with harmonic trem have all sounded awesome. My take on your questions, FWIW:
1. Yes, the tone stack is physically close enough to the input jacks that it should be fine to repurpose one of the inputs. You'd just be replacing the fixed 10k resistor with a potentiometer, right?

2. It's just a matter of your preference really - no comment

3. For mods to the original schematic, there's heaps you could do to 'improve' things:
- separate the shared cathode RCs on the first 2 gain stages. It's just Leo being cheap again and you don't want interaction between channels. You'd need to use separate 1k5 cathode resistors and 10uf bypass caps to keep things strictly equivalent, but 22uf caps would be fine too.
- put the 0.1uF presence cap on 'top' of the 5k presence control, not underneath it - to reduce scratchiness
- add 1k5 grid stopper resistors to each 6L6GC, to prevent farting out (blocking distortion) when overdriving the output stage. If it still sounds bad, drop the two 220k bias feed resistors to 100k (or 150k). If it STILL blats, increase the grid stoppers to anything up to 5k6.
- add a B+/HT fuse for protection. You could put it on the centre-tap of the SS rectifier section, or perhaps immediately after the standby switch. Fusing the cathodes of the 6L6GCs is okay, but might not save you if the screen or anode shorts to the grid. Also note that for 240vac the mains fuse should be 1.5A - not the 3A in the american schematic.
- if you want more bottom end, you could up the 1nF coupling cap feeding the phase inverter to a 10nF but it might induce blocking distortion as well. A 4.7nF might be a good compromise.

Otherwise, it's probably best to just build it and see how it sounds, then set about tweaking things that bother you.

Epic reply

I think tis a fixed 6.8k in the 6g71 schamtic but yes thats the idea.
Good advice regarding fuses and those sound like smart easy mods tone stack wise.
In terms of prefernce, the vibrato channel will be voiced differntly due to the circuit so maybe the fact they will have mid pots will get close enough to black face on the normal channel without going to over board.