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My Tramp has very little volume. Changing tubes had no effect.

Mains measures 121.2 V.

With VRM max'd, first 50 ,u cap measures 337 V, and 445 V at second.

All other voltages are low compared to those in layout.

With VRM turned right down, first cap measures 293 V, second cap still at 445V.

Is there a simple way to bypass the VRM?

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Second cap is actually the first in the power supply chain! A bit confusing.
If you look at the schematic, you can pull the end of the 100R 5W power resistor that goes to the VRM control, and jumper to the first cap. You might be able to jump directly, and short out the MOSFET, but I dont like doing that.
This willestablish if it isVRM related, ut it does soundlike it. At this point, I dont suspect the MOSFET, but a components or solder joint or even the control?

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

Before messing with the VRM I took some voltage measurements. All controls at max. Mains 121.2 VAC
(target voltages in brackets):
C12 (400): 37VDC
V2 pin 8 (29) : 1.15V
C6 (340) : 33V
V1 pin 7 (191) : 26V
V1 pin 1 (203) : 29V
V1 pin 3 (2.3) : 49mV
V1 pin 8 (1.7) : jumping around

Does this suggest anything?

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What's the HV AC voltage coming from the PT?

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Can you try another 12AX7?

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

I measure 322 VAC at D1 and D2.
Tried a couple of 12AX7 tubes with little difference.

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V1 is so strange, I suspect a solder joint, jumper issue /component feeding the plates or cathode ground. Got to be in that area.

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

Also I noticed the voltage at the cap at the end of the board by the MOSFET (C12?) rises to about 140 V on start-up, and then falls pretty quickly to 37 V and stays there.

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Tried chopsticking around. I couldn't get the readings at V1 to change.
All solder connections appear solid.
Suggestions?

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Did you try bypassing the power control yet? That would be my next step.

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

Bypassed the VRM.
Volume is up, although 'tude mode is much louder than tweed.
Here are my voltages now:
All controls at max. Mains 121.2 VAC
(target voltages in brackets):
C12 (400): 402VDC
V2 pin 8 (29) : 21V
C6 (340) : 330V
V1 pin 7 (191) : 175V
V1 pin 1 (203) : 186V
V1 pin 3 (2.3) : 1.7V
V1 pin 8 (1.7) : 1.56V stable

Can these be considered satisfactory?

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Yes. Although the B+ on the 6V6 plates is high, I wouldnt use an old NOS 6V6 in there, but for sure a 6L6!! Do a power calculation and see if you are happy with the 6V6 power dissipation. If you are going to leave the VRM bypassed, I would recommend a b+ Zener dumper,and a 3 way power switch where one positionis ON and another is STANDBY. We use a progressive switch on the TRIWATT but you can use other forms of switches for this use.

Or figure out which component is bad, and fix the VRM. Could be a solder joint esp on the MOSFET.

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

Starting to trouble shoot the VRM. Have continuity from each of the legs of the MOSFET to the other side of the solder connection on the board.

Unsoldered the three terminals of the control pot (left the switch part connected).

I get no resistance reading between the outer terminals, nor between the wiper terminal and either end terminal (control at max).

Is the control pooched?

Should I be able to find one of these at my local electronics shop?

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Sounds like the pot may be "open", this could definitely be your issue.

You might be able to find the pot at a local shop. The only thing tricky is that you need a 1M pot with the SPST switch built in.

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You may be able to get that pot at a decent shop. Same control as in the Champ. But we can send one as well. Shipping will cost 3X the cost of the pot!

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

Could you tell me how to figure out the correct position for the 6L6/6V6 switch?

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Measure the resistance across the 750 ohm 5W power resistor. In 6V6 it is 750 ohms, in 6L6 it is around 320 ohms.

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

Thanks Steven - I'm going to finally label that switch.

I have a VRM control on order. Should see it in a day or two.

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The pot came in and turns out to be 2.5 meg. Would this work OK?

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Can you put a 1 meg resistor across the two outside terminals? I think it will work but not sure how well the control will be.

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