Can someone please tell me what this is for

[pbman1953]

I noticed a jack next to the external speaker jack. It's not stock , reason being that it's not straight with the other jacks and it's not in the manual. It's grounded to the chassis and the positive line goes to the tube side after the .022 cap coming from the Output control. I suppose its a signal output to and input f another amp if desired.


In the picture , lower right, you'll see a light green wire coming from the Output to the .022 cap. The white /red wire is connected on the other side of the .022 cap. The white/red wire goes to the speaker jack on the back wall.

[mxrshiver]

looks like a very minimal pre phase inverter preamp out. based on the schematic, it appears as if that red/white wire connects directly to V4 pin 2, the phase inverter input grid. it doesn't load down the grid at all and doesn't use any extra components, which are the upsides... but bringing the grid out directly across the whole chassis like that may introduce some noise and/or oscillations. there's also no independent level control, the level is determined entirely by the Output control... i'm not really familiar with this amp overall, or the preceding distortion circuit, but i'd say it's likely the signal level could get very high at this jack. probably too high for most mixing boards or interfaces that expect line level. this seems like a jack for directly driving a different power amp, to me.

[pbman1953]

Thanks, I had a feeling.  I have no need to use a tandem amp. I'll probably remove it and cap the hole


Thanks!!

[SEL49]

lit appears as if that red/white wire connects directly to V4 pin 2, the phase inverter input grid. it doesn't load down the grid at all

Connecting anything (even your volt meter) directly to the grid of that LTP PI will load down the grid and upset the bias of that triode. That's a bad idea. Best to just disconnect that wire.

[pbman1953]

will do!
Thanks!