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I'm a first time builder -I finished my Tramp kit today and after fixing a couple obvious mistakes that prevented it from making any sound at all was able to get it to work. However, right now it's REALLY quiet. I'm only really able to get anything I'd consider audible out of it when when the power level is max and the volumes are around 6 or 7. I know that the Tramp isn't supposed to open up until that point anyways but it gets to a level that could easily be spoken over.

Before powering it on I noticed that some of the voltages were low:

Rectifier pins : 657 V

50uf Caps:
Cap 1 VCM Idle : 4.84 VDC
Cap 1 VCM Max: 49.6 VDC
Cap 2 VCM Idle: 454.9 VDC
Cap 2 VCM Max: 450.0 VDC

Preamp Pin 1: 32.2 VDC
Preamp Pin 6: 35.0 VDC

Power Pin 3: 50.28 V
Power Tube Cathode: 2.9V

Heaters are: 6.95 VAC


Thanks

Hi, welcome to the forum.

Sounds like you have problems with the VRM.

50uf Caps:
Cap 2 VCM Idle: 454.9 VDC
Cap 2 VCM Max: 450.0 VDC

It's best to refer to the parts by their designations on the schematic so we all know which ones you mean, but I assume you mean C13 here. So then the power supply is working but the VRM isn't letting much voltage get to the rest of the amp.

Cap 1 VCM Idle : 4.84 VDC
Cap 1 VCM Max: 49.6 VDC

Assuming you mean C12, then you should have about 400 volts here with the Power Level control at maximum.

Check all your connections to Q1 and all its associated parts (R20, R21, R22, R23, VR1 and Z1). Make sure everything is wired properly and the solder joints are good.

There is a chance Q1 itself is bad, too. If all the connections are good and you still don't get full voltage, then you could try bypassing the VRM to test the amp. This can be done by removing Q1 and connecting a jumper between its D (drain) and S (source) connections on the board.

Checked the parts associated with the VRM and they seem good so I took all the leads off the board took to board out to look at the underside of the MOSFET. Turns out that the Drain pin had not been bent properly so the solder had not made a connection. Fixed that and reinstalled the board with all the leads.

However, once the board was installed again I went to turn the amp on and the LED was no longer turning on. Now nothing is getting any voltages except for the mains. Now I'm a little bit stumped as I didn't touch anything off board.

The LED is on the 6.3 volt heater supply, so if not even that is getting power it sounds like the power transformer isn't getting any voltage at its primary. You say AC mains is coming in OK but it's probably not making it to the transformer.

I assume the fuse is OK. Check your connections to the power switch and the transformer. Taking the board out and putting it back in might have stressed one of the AC wires.

Turns out the fuse was blown. Thought it was alright because I test the mains voltage at the switch in the minute before it blew. Going to take out the board and see if I can get it to turn on with out blowing another fuse. The only thing that changed between not blowing a fuse and blowing a fuse happened around the VRM so i think the problem might be around there.

Read through the forum looking for other people who have had fuses blow and someone suggested checking continuity to ground on each pin of the VRM. I'm getting continuity beeps on the source pin.

You are on the right track.

First see if the power supply still works with no load. I would leave the MOSFET out for now and the Power Level control completely disconnected. The fuse shouldn't blow and you should read about 450 volts on the positive terminal of C13 like you did before.

If the power supply is good, then connect a jumper between the drain and source terminals on the board and see if the amp works.

It's best to get an amp working properly before you do anything that messes with the B+ like installing a VRM.

If the amp works you can put the MOSFET and Power Level control back in. But first do a quick check on the MOSFET with your meter to see if it's blown or shorted. There is lots of information and videos on the Internet about testing MOSFETs. Here's a link to one video on YouTube.
https://www.youtube.com/watch?v=gloikp9t2dA

Took out the MOSFET and the Power Level control and got 450v on C13 again, no fuse blown. But when I installed the jumper between the drain and the source I blew a fuse again.

Nothing seems to be accidentally making contact with the chassis or other eyelets. However, when I do a conductivity test on the leads of C12 I'm getting conductivity beeps. Since the negative lead of C12 leads to ground could this be what is causing the fuse to blow? None of the other capacitors have this happen. I've tried doing some research but can't find anything definitive on whether this could indicate a broken capacitor.

C12 might be bad. Try removing it and testing with your ohm meter to see if it reads shorted or a low resistance. A good electrolytic capacitor should start with a very high resistance reading that slowly gets higher the longer you leave the probes connected.

Silly question, but C12, C6, C7 and C11 are all installed with their negative leads connected to ground, right?

Also check all your wiring very carefully. You say nothing is shorted, but make sure everything is connected where it's supposed to be.

Then see if the amp turns on without blowing the fuse with no tubes in place.

Then plug in V1 and see if the voltages there look reasonable. They might read high but the fuse shouldn't blow.
Finally plug in V2 and a speaker. All the voltages should be close to the expected readings now, the fuse should hold and the amp should work.

Then if your MOSFET is still good you can put it back in along with the Power Level control.

So I was able to get it turned on with the tubes installed without blowing a fuse. I had installed the two 220k resistors under the board and the one that bridged C12 had lined up perfectly with one of the transformer mounting screws. It looks like the screw rubbed off some of the insulation on the resistor and made a connection with the metal film causing the positive side of C12 to be connected to ground. After shimmying the resistor out of the way the amp turned on without blowing fuses.

I sheepishly checked some of the voltages last night once it was on but was too exhausted to write down what I was getting but the low voltages I was noticing before were around where they needed to be.

Good eye spotting the resistor that was contacting the mounting screw.

I'm not big on putting parts on the underside of boards for that very reason. A few jumpers or the fly-off leads are OK on the bottom, though. You could piggy-back those 220k resistors on top of C12 and C13.

The amp sort of worked originally because the bad connection you had to the MOSFET didn't let enough voltage through to cause problems. Also the short to the mounting screw could have been intermittent or it only happened when you put the board back in after removing it.

Hopefully the amp works now and is producing some nice Tramp tones!

Check the voltages again and note what they are. They should be close to the expected values. Then try putting the MOSFET and the Power Level control back in.

I've had the exact same issue, here's what the resistor looks like after coming in contact with the transformer mounting screw.

This creates a short from 400V to the chassis. These resistors have got to go somewhere else.

Regards,
Drew

Thanks for helping mitch.
We dont recommend putting resistors or parts underneath the board. There is space on the top side for these in the area around the capacitors.

_________________
Stephen
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