Pro Junior tonestack lift

[rogbHW80]

Hello to all here!  I built an eyelet board Pro Junior from the info here using Hammond iron. It works well! I have a switched V1 cathode cap and NFB lift as mods, also a simple Master pot replacing the 1M resistor pre phase inverter.
I'm not that familiar with this type of tonestack, in the past I've lifted the Mid pot ground for a bypass.
Any suggestions how I could bypass the Pro Junior tone pot? Thanks Rog!

[sluckey]

I'd do it like this...

[rogbHW80]

I'd do it like this...

Thanks Steve, that's very helpful, I'll give it a go and report back.
Regards Rog

[sluckey]

If you followed Hoffman's layout, this will be quick and easy.

[HotBluePlates]

... I'm not that familiar with this type of tonestack, in the past I've lifted the Mid pot ground for a bypass. ...

This type of Tone circuit doesn't have a big mid-scoop that is removed by disconnecting from ground.  Therefore you should not expect a big signal-boost.

[rogbHW80]

... I'm not that familiar with this type of tonestack, in the past I've lifted the Mid pot ground for a bypass. ...

This type of Tone circuit doesn't have a big mid-scoop that is removed by disconnecting from ground.  Therefore you should not expect a big signal-boost.

Interesting you should say that,  it sounds and feels like the volume drops when the tone circuit is bypassed.
Noise floor decreases too.
This effect could be useful but not as a mild boost as I hoped.

[rogbHW80]

If you followed Hoffman's layout, this will be quick and easy.

It's definitely working - not hard to implement thanks to your layout, but as I posted seems to cut volume and noise, much in the way of increased NFB, but this is not unpleasant, just not the PAB I hoped for.

[stratomaster]

If you want a big boost put R6 on Sluckey's schematic on a switch that lifts it.

[passaloutre]

If you want a big boost put R6 on Sluckey's schematic on a switch that lifts it.

Or a switch that shorts R5, or both.

[Jennings]

You could also try putting a cathode bypass cap for V1b on a switch, which means you'd get to keep the tone in circuit instead.

[rogbHW80]

Thanks a lot for the suggestions. I've disconnected the tone lift as it didn't boost as I'd hoped. I have the unused switch in place so I'll try the R6 lift and maybe the V1b cathode  bypass too.
Regards Rog

[rogbHW80]

The project is finished finally.
I ended up with switched cathode bypass caps on V1a and b and switched NFB lift.
NFB is very subtle in this circuit.
It sounds good with a pair of NOS Russian  6P14P-EV into 12" Celestion Neo Creamback.
Following the Hoffman schematic, I'm not getting much breakup even after halfway on the volume, just gets louder but way more organic and warmer than my Class D power amps!

More gain (and noise) with the caps in circuit.
It will be mostly a pedal platform so probably just as well it's  loud and relatively clean.

My wall voltage here is 242 vAC in the UK, so corresponding voltages are some 8-10% higher than Hoffman states. I think the Hammond BJ PT also is generous with its output.

All told, it's a good sounding circuit in a 21lb combo (built from 9mm ply, originally as a lightweight speaker cab). The amp in its chassis weighs around 6lb!
Thanks for advice again, all help has been much appreciated.

[rogbHW80]

If you want a big boost put R6 on Sluckey's schematic on a switch that lifts it.

The NFB lift has very little effect so I thought about replacing that redundant switch with a 100k pot to replace R6 56k and get some gain control. What do you think?

[stratomaster]

If you want a big boost put R6 on Sluckey's schematic on a switch that lifts it.

The NFB lift has very little effect so I thought about replacing that redundant switch with a 100k pot to replace R6 56k and get some gain control. What do you think?

100k probably won't be much higher gain than stock.  Plus a pot there would just be in parallel with the volume pot, making it redundant.  Just lift it.

[rogbHW80]

If you want a big boost put R6 on Sluckey's schematic on a switch that lifts it.

The NFB lift has very little effect so I thought about replacing that redundant switch with a 100k pot to replace R6 56k and get some gain control. What do you think?

100k probably won't be much higher gain than stock.  Plus a pot there would just be in parallel with the volume pot, making it redundant.  Just lift it.

OK thanks I'll give it a go. 
It's just advice for the original Fender PJ I read was reduce to 22k for more headroom and 80k for more gain, so I figured I could have best of both worlds.

[rogbHW80]

Well I finally got to play the PJ out, with my Strat and a small board with a dual drive and reverb. A couple of other guys played through it too.
It sounded absolutely fantastic!  Loud, warm and full of character. More than enough gain options too. I'm really pleased with it.

Today though I replaced the 1M MV with a 30% taper pot I had as it was hard to dial in a good level.
I also replaced the 56k R6 with 100k pot,  after ditching the NFB lift, so I could rein in the gain a little with pedals.
This amp is really going to get some use,  as I  can carry it, small board and guitar on the bus🤣
I can recommend the Hoffman interpretation of the Pro Junior to anyone wanting a good small powerful tube amp, especially with some good iron like the Hammond PT OT.