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Well I've finally finished soldering everything together, and the tramp starts up! No strange sounds, pops, etc. It actually sounds really good with my strat plugged into it. The problem is that the Power Level knob (VRM) doesn't seem to be doing anything when turned except turn the amp on. All of the other controls seem to be functioning correctly. Here are some voltage readings that don't seem to be correct:

407 at the 50uF cap (target > 400), this does not change regardless of the power level setting.
Pin 1 of 12ax7 tube: 166 (target 203)
Pin 6 of 12ax7 tube: 164 (target 191)

Any ideas? I'm using the stock setup with a 6V6. I'll be going through all the connections again tomorrow.

Thanks!

Glad it's almost working and sounding good.

Yes, check all your connections. Especially the ones in the VRM area. Make sure lug 1 of the pot connects to the 220k resistor and the other end of the resistor connects to ground. There's also a chance your Mosfet is shorted source to drain.

Also check the connections to the 47k resistor that feeds power to the anodes of the 12AX7.

Well I checked everything out and as far as I can tell the connections are solid. I'm not sure how to check if the MOSFET has been grounded to drain (sorry, I'm very new to amp building)? I went ahead and attached the rest of the voltage readings and a few pictures of the amp. I can definitely get some closer images if necessary. Thanks again for the help.

B+ (goal 400+): 406 this does not change regardless of the power level setting.
B+3 (goal 340): 328
12AX7 pin 1 (goal 203): 165
12AX7 pin 6 (goal 191): 164
To 6V6 bias resistor (goal 29): 29
Volume pot to pin 8 12AX7 (goal 1.7): 1.70

Not really sure why the voltage is low at B+3, but that would account for it being low at pins 1 and 6 of the 12AX7.

Try tracing the B+ as it goes through the various feeds. Check it at the Mosfet and the first filter capacitor. You said this is 406 volts which is good.

Then see if you get the same reading where it joins the 1k resistor on the terminal strip.

Then check the other end of the resistor where it joins the 1k that feeds the 6V6. This is B+2. It should be a bit less than B+.

Then see if you get the same reading at the left end (when viewed from the front of the amp) of the 47k resistor that feeds the 12AX7. The right end of this resistor is B+3 which you said is low. It looks like you have a 47k resistor in this location, but it's worth checking it with an ohmmeter just to make sure. You should disconnect one end to get a true reading.

Also, make sure the jumper on the bottom of the board going from the 47k resistor to the two 220k resistors has solid connections and isn't shorted to anything.

As for the other problem, the Mosfet could be shorted drain to source. Here's a link to a YouTube video that shows a simple way to test Mosfets with just a DMM. You have to disconnect the Mosfet to test it.

https://youtu.be/RBJGOOTEwfU

I understand there was some cross wiring and it has been fiXed. Lucky to not blow the FET!

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Vacuum tube circuitry isn't an exact science. Not in guitar amps anyway. Your voltages are only about 15 to 20% off the expected values. That's lower than the usual 10% variance, but if everything checks out and the amp sounds good, then I wouldn't worry too much about the lower voltages. If you have another 12AX7 you could try it and see if the voltages are closer to the expected values.

I guess you had the switches set to the way it says in the manual when you measured the voltages.

Sounds like you got the VRM working, too.

Yeah, everything is working and sounds great! Just have to put together a cabinet now. I had a friend take a look at the layout and I found that I had a couple wires crossed on the power/level pot. I guess that just goes to show the value of having a fresh set of eyes look at something; I missed that even after double checking my connections! Lucky nothing blew up in my face.

Thanks again for everyone's help.

Glad you got it working and it's sounding great.

Yes, I see now in your picture you had the wires reversed on pins 2 and 3 on the Power Level pot. That wouldn't cause any harm because of the 220k resistor running from pin 1 on the pot to ground. But as you experienced, as far as the Mosfet was concerned it would be like the pot was up full all the time.

It's easy to miss things like that when checking the wiring, no matter how many times you do it. A second set of eyes is definitely helpful.

Hope you enjoy the Tramp and good luck with your cabinet!

Good stuff, congrats on build and getting your amp up and running! Good luck with your cab too.