Adding a Variable Line Out jack

[greg]

I am building a 5E2 Princeton with 2 parallelled 6V6s and would like to be able to run it straight into a recording console (bypassing the internal speaker).

Ideally, the line out volume would be controlled by a pot.

Can anyone point me in the right direction (ideally, to a schematic)? I don't want to damage the amp!

Thanks
Greg

[Chuck H]

You will get very little overdrive from a single ended Princeton if you bypass the power amp. If your after that class A overdriven little amp sound then you need to push the whole package. You can try running some kind of speaker replacement (like a HotPlate or a big resistor) but that won't sound the same either. Still, that is probably your best bet.

If you place the line out behing the power tube you can then shut down the power tube by either grounding the grid or lifting the cathodes ground reference safely. Your line out would then be an Lpad placed at the end of the preamp. You would still need some EQ circuitry to keep it from being harsh and boomy. But even then it won't sound anything like the amp.

Those little amps are simple devices. You cant really eliminate anything. Theres not much there to start: preamp tube, output tube, output transformer and speaker. What you propose would eliminate 3/4ths of that amp and leave only the preamp tube.

Sorry but HTH

Chuck

[greg]

Actually, I'm not too concerned with getting a good sound of this jack - just something to keep me from having to buy a POD or deal with a straight direct sound. I just recalled that I borrowed a Bad Cat Mini a few years ago and it had a line out that worked fine for my purposes and allowed the speaker to be disconnected - and I just found the schematic at schematicheaven.com (attached).

I suppose the question now is how to make the output variable (safely).

Thanks,
Greg

[Chuck H]

I said: "You can try running some kind of speaker replacement (like a HotPlate or a big resistor) but that won't sound the same either. Still, that is probably your best bet."

This is what the Bad Cat is doing. That 10r 10w resistor is a sub for the speaker load. Your new build will have more power than the Bad Cat so you'll want to use a 15w resistor at close to whatever your speaker load is. Other than that you can wire the line out the same as the Bad Cat. Replace the
3.3kr in the schem with a 2.5k pot and solder the + terminal on the jack to the wiper. Then it will be variable. If you have somewhere to put a pot, you could do the same thing to the Bad Cat too.

Chuck

[greg]

Thanks for the info, Chuck - I'll give it a go.

Greg