Everything is great until I pull out my guitar cable

[pbob42]

I got this amp from a guy I know -has a 12ax7 in it as some sort of preamp but there is no power at all. Sounds great if you supply a preamped signal. Has 2 el34s to drive it. Problem is when you pull out your signal cable it just starts humming like crazy. I am a newbe here, but I figure there is some pretty easy fix to solve this.

[defaced]

Sounds like the input jack might not be a shorting jack - usually they are, or its dirty. Basically when the plug is removed from the jack, the connectors on the jack short the input to ground which keeps noise from being amplified from the amp. If the contacts are dirty, the dirt can keep the switch from making a good connection. This can be remedied by unplugging the amp from the wall, opening the amp, making sure the filter caps are drained an no lethal voltages are present in the amp. Once you've done that, the amp is safe to work in. First check to see if the input jack is indeed a shorting jack (if it's not, you'll have to swap it out with one that is). If it is a shorting jack, then see if the contacts are clean and making a connection between the tip and ground when a plug is not in the jack. If they are making good connection, something fishy is going on and you'll need to post some details for us to help you. If they are not making good connection, find out why and see if you can fix it.

[olddawg]

Are you sure that this isn't just a stand alone power amp and the 12ax7 isn't just the PI tube? If that's the case it is working exactly the way it was designed to. You usually don't unplug the input to a power amp while it is operating. No reason for shorting jacks.

[pbob42]

That could be it. I put a 6 pin hammond connector on it figuring I would keep those leads "covered" and put it in a leslie speaker. It is hooked up to an A100 Hammond with an internal speaker. When I switch to the hammond's internal speaker I get the buzz again. The switch cuts off the positive signal lead to my amp.

I am figuring there is a ciruit I can throw in there to fix this, some caps or something. Hoping someone here has an answer.

Thing sounds pretty nice. It pairs up nicely with the amp in the hammond.

[Chuck H]

Problem is when you pull out your signal cable it just starts humming like crazy.

So don't use the amp with the signal cable pulled out (sorry...Had to)

[pbob42]

Really Chuck. 3,771 posts and you hit a newbe with that. I think there is massive negaive amp karma headed your way.

But really - there has got to be a simple (hoping) fix for this. Couple of caps to ground. Resister here or there. Put in a preamp circuit. Something.

[olddawg]

Try soldering a 1meg resistor across the amp's input jack. Or...if you have made the switch you mentioned, from the floating connection to ground if that is easier. You could also use a dpdt switch an wire it to ground the amp input when not used.

[pbob42]

Positive amp karma on the way