1st mod = learning the hard way

[Smokebreak]

Go off board if you need to, no one's looking.
I don't understand why losing the NFB will accomplish anything with either amp, regardless of what you are trying to do with both of them incestually speaking.
You would need to completely redesign both amps if you took away their NFB. They need NFB. They are both beasts, as they are, with it. Take it away and everything goes to shit.

But yea look at the Rocket or a Vox schematic for how to lose NFB

[studiodunn]

Thanks Smoke.

I don't need to lose the NFB, I just need to get both circuits in the way they are.
It sounds like going to a single input, through a switch is what I need to look at. The whole ABY idea is were I got off track.

[studiodunn]

Sorry for all the dumb questions and not having this to present before asking.

Does this look OK?

[TUBEDUDE]

You might want to use the other side of the channel switch to ground the unused channels signal.

[Smokebreak]

I would do it like this. It's good you had a cap before the switch for each channel(ultimately if it's a relay you'll want to keep DC from the Xpress side odd of the relay), but switching at the grid of the PI may cause popping, perhaps even with pop resistors, which you can see I added in a few places (10M) to keep a constant reference to ground at all times. They shouldn't screw with the response too much.
But you can try with just the correct value caps before the switch, but add some pop resistors. Maybe it won't pop the grid.
I find that on those 36 amps, a nice 1n to ground somewhere early, either across the Rp or the gain control does a lot of good

[studiodunn]

Thank you guys.

And if I wanted to go the Foot switch route I assume $15 spent here would
take care of it - http://www.mojotone.com/amp-parts/Relay-Switching-Kits

[Smokebreak]

Yes but I think that's an unpopulated board. Granger sells good ones and even better, forum member Colossal sells finished boards and power supplies, and provides excellent customer service, and downright help on installs. He'll be along shortly I bet, but here's his stuff : http://www.colossalamps.com/boards.html
Do you know how you will power the relays? Some folks tap right off the heater 6.3v or unused 5V winding, but sometimes that doesn't work. You can get a small 6V xformer for like $10 if need be.

[studiodunn]

Yes but I think that's an unpopulated board. Granger sells good ones and even better, forum member Colossal sells finished boards and power supplies, and provides excellent customer service, and downright help on installs. He'll be along shortly I bet, but here's his stuff : http://www.colossalamps.com/boards.html
Do you know how you will power the relays? Some folks tap right off the heater 6.3v or unused 5V winding, but sometimes that doesn't work. You can get a small 6V xformer for like $10 if need be.

Great! Those boards look like a much better deal, and I would love to support members when I can.

I was planning on using the 6.3v heater tap. I am waiting on the new OT from Triode, but this is it - http://www.classictone.net/40-18004.pdf

It looks like I would have to have his power relay as well and feed it off the 6.5v tap.

[Smokebreak]

Yes one board has the actual relay switch, and associated components, and the other board rectifies the 6.3VAC to DC, and regulates it at 12V IIRC which is what actually triggers the switching in the relay. So you need both.

Is there something wrong with your current power transformer?

[studiodunn]

Yes one board has the actual relay switch, and associated components, and the other board rectifies the 6.3VAC to DC, and regulates it at 12V IIRC which is what actually triggers the switching in the relay. So you need both.

Is there something wrong with your current power transformer?

So the amp was in really bad shape when I got it. Even after just a cap job, the output was really low. The OT took a dump during some tweaking of the current circuits and took the PT with it. I'm not sure what happened, but after unhooking both and testing, they both are bad.

I hadn't replaced the screen resistors and one was way off of 470. I also hadn't replaced the rectifier diodes, so maybe a problem there.

I'm not totally unsure that my "finding a solution" for the 2 pre-amp situation with alligator clips didn't inadvertently aid to the PT's demise.

I understand my own carelessness probably led to it's death, so once I get the new Trannies in and everything wired up I am taking the amp to my tech for a once over and proper fire up.


live and learn

[jjman]

Using mixing resistors will weaken the voltage of each signal 50% from the voltage division. (This is less then a 50% reduction in "volume.") Injecting each preamp in to opposite sides of a LTPI preserves the full strengths. Look at an 18watt Marshall on how to do it.

If using pre PI MVs, it won't matter as much. With a Post PI MV, you want a strong potential signal to the PI.

Being able to run both channels from the same guitar is a nice option to have. Phase cancellation would be bogus so may as well wire to avoid it.

[studiodunn]

Using mixing resistors will weaken the voltage of each signal 50% from the voltage division. (This is less then a 50% reduction in "volume.") Injecting each preamp in to opposite sides of a LTPI preserves the full strengths. Look at an 18watt Marshall on how to do it.

If using pre PI MVs, it won't matter as much. With a Post PI MV, you want a strong potential signal to the PI.

Being able to run both channels from the same guitar is a nice option to have. Phase cancellation would be bogus so may as well wire to avoid it.

Thanks jjman.

I am about done with the rebuild and went the relay route, as to have things footswitchable.
I will post pics and a clip once things are finished.

[studiodunn]

Does this sound right for wiring a relay up?

Channel 1 into Pin 9
Channel 2 into Pin 11
Pin 13 into PI

Pin 9 to Pin 6
Pin 11 to Pin 8
and Pin 4 to ground