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PostPosted: Wed Apr 29, 2020 9:36 pm 
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Hello everyone!

Hope everybody is doing well and are staying safe with the current world situation.

Finally had some time to work on my Tramp kit I got ages ago. Now always being home with the family, and being a teacher for my kids. Finally managed to get my tramp up and running.

Followed the start up procedure. Wished I could find a replacement bulb for my homemade current limiter, every store I have called seem to only have LED bulbs. Anyone got a source? Regardless I took the chance and went at it and applied first power.

No smoke (thank goodness), went through my voltage checks, seems good. Tubes in, speaker connected and checked voltages again, great! Let's grab an axe and go.

However, the vrm circuit doesn't appear to be working correctly. Anything lower than 7 on the level and the amp slowly loses volume until it is silent, odd. Max level the amp is fine no hums or anything odd sounding but it is a lot lower in volume than I was expecting. I am used to playing a Princeton, but have played Champs or a vox ac4tv so I expect a bit more volume than I was getting. Voltages all appear to be on point. Had them written down for posting purposes, but my youngest son discovered the paper shredder today...bye-bye dad's notes.

Going to trouble shoot tomorrow or this coming weekend.
Mostly wanted to touch base with the community, and with a bit of luck hopefully another Tramp will be born. Going to order up a few tubes to play with as well.

Again to all, stay safe. For those of you who have suffered a loss during these times. My deepest condolences my heart goes out to you all. Do hope that everyone is getting the support needed, whether financially, emotionally, or otherwise.

Cheers,
Kim


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PostPosted: Thu Apr 30, 2020 10:11 pm 
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Pics?

Maybe someone will notice something wired wrong with the VRM.

Mine works fine. Love the amp. Running the "Big Can", KT88. You'll like a 6L6 I'm sure.

Scott


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PostPosted: Fri May 01, 2020 6:33 pm 
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Hello,

So here are some pictures of my build. Isn't the cleanest of some other I have seen. Mind you it's been a while since I've been behind the iron.

Going to get those voltages messured again soon. And will post those as well. Did read over another form post with vrm issues and re-read that in the trouble shooting section as well. One step at a time.

Cheers,
Kim


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PostPosted: Fri May 01, 2020 9:30 pm 
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Kim, a problem I had when I built a Tramp was the leads from the MOSFET to the board would come unsoldered when heated with the iron, you might loosen the board mounting screws and take the nut off the MOSFET and lift them up gently and slightly to see if this is the case. I wired the power switch wrong on another and the amp worked, but no effect on voltage. Your wiring is correct on Pwr switch, so I'm guessing a bad connection.

Also, looking at your pics some solder joints at eyelets are not filled and some are beaded up (should be smooth). Could be bad solder joints. I respectfully suggest that you read "Of Soldering and Solderability" on page three of Forum Resources page, since I don't know your skill level. JoeyVelour apparently used to or still does production electronics.

A working VRM really brings a change in the number of the tones you can get, so good luck and hope you can get her running at her full potential. :thumbsup:

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Last edited by Hankules on Mon May 04, 2020 2:09 pm, edited 1 time in total.

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PostPosted: Mon May 04, 2020 2:03 pm 
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Kim, any luck w/ the VRM problem? Hank S.

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PostPosted: Mon May 04, 2020 5:41 pm 
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Hello!

So I redid all my voltage messurments. Something appears to be odd with the preamp section.

V1
Pin 1 = 168.5 target = 203
Pin 3 = 1.89. target = 1.7
Pin 6 = 167.8 target = 191

V2
Pin 3 = 398 target = 398
Pin 4 = 386. target = 395

Vrm voltage at max is 402

Pretty sure my voltages in the preamp area are low. But again I am not a tube amp expert. Going to triple check everything and reflow my joints. The soldering article in the resource section was a great read, eye opener for sure. I have a bad habit of cleaning my tip after doing a soldering joint. Put a sticker on my soldering station that says "dirty in, clean out" to help me remember to stop doing that!

Edit : I am using a 16 ohm 12" speaker WGS G12C/S - 75 Watt. Next Gen guitars was having a clearance sale on their speakers so I got it cheap.

Edit : just found an error! I have the 750 and 560 5watt resistors mixed up. Fixed this error. Amp sounds better however the vrm still makes the amp fizz out anything lower than 7. It slowly just dies, and the volume just isn't there even at full bore. Going to try to keep plugging away with this as time permits. Might have to wait till the kids go to bed however.


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PostPosted: Mon May 04, 2020 9:14 pm 
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Make sure all your solder joints are good! Check the joints on the 47K resistor between the two filter capacitors. It supplies power to the preamp.

Also make sure everything is wired properly in the VRM area and there aren't any accidental shorts or anything like that. It looks OK, but sometimes it's hard to tell just looking at pictures. Also check to make sure the Zener diode is a 6.2 volt one. The numbers on the diode in your photo look like 47. Not sure if it should say 62, or maybe the 47 is just part of the part number. Maybe someone who built a Tramp from the kit can verify what it says on the Zener.


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PostPosted: Tue May 05, 2020 12:36 am 
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The VRM problem could be the MOSFET, too. What does the B+ measure when the amp fizzes out?


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PostPosted: Tue May 05, 2020 9:06 am 
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mitch m wrote:
The VRM problem could be the MOSFET, too. What does the B+ measure when the amp fizzes out?


Hi Mitch,

So I messured B+ when the amp fizzled out on the vrm. It sits at 250V. This is with the VRM set at around 7. When it's at full power the B+ is 400-402V.

Edit : Found a questionable joint at the Zener diode connecting to the Gate of the MOSFET. Had to move some wires around to see it. Reflowed everything so all the eyelets are properly filled and "jewel" like. The VRM appears to be working correctly now. Amp however still sounds anemic. Still getting low voltages in the preamp section. Going to messure everything again with and without tubes, and post the results here. Again thank you everyone for your help!


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PostPosted: Tue May 05, 2020 10:31 am 
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FYI The 6.2 zener diode looks to be correct compared to the ones on both Tramps I've built. I still think you need to consider reflowing the solder on your board eyelets to ensure you have good connections, especially at power section.
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PostPosted: Tue May 05, 2020 5:22 pm 
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So I have removed the board. Re-did every joint. Wired it back up and checked it over again. Here are all my messurments:

No tubes
Heaters = 7.1vAC
Power at c13 = 442v (vrm at max)
Power at c12 = 451v
Power from transformer = 660vAC

Tubes installed
Vrm @ idle = 6.6v
Vrm @ 6 = 15.06v
Vrm @ 8 = 81v
Vrm @ 9 = 253v
Vrm @ Max = 401-402v

Heaters = 6.7vAC
Bias voltage (6v6) = 22v target is 29v
B+3 = 322v target should be 340v
Vb1
Pin6 = 169v target 191v
Pin8 = 170v target 203v
Pin 3&8 = 1.87v target 1.7v

Maybe it's okay? I don't know. Might have to give my eyes a break. Been at this since sunrise today.


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PostPosted: Tue May 05, 2020 9:54 pm 
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The V1 voltages are within 11 to 16% of the expected values, so that's not too bad.

Looks like most of the action takes place between 7 and 10 on the VRM pot, though. 80 volts is pretty low so that's probably why the amp fizzes out below 7. I've never installed a VRM so I don't know what the normal range is from maximum to minimum, but I'd say yours is going too low. Check to make sure pin 1 of the VRM pot isn't accidentally shorted to ground. It should connect to ground through a 220K resistor.

Hank, maybe you can check your Tramps and see what the B+ measures with the VRM set at max and min.


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PostPosted: Wed May 06, 2020 7:41 pm 
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mitch m wrote:
The V1 voltages are within 11 to 16% of the expected values, so that's not too bad.

Looks like most of the action takes place between 7 and 10 on the VRM pot, though. 80 volts is pretty low so that's probably why the amp fizzes out below 7. I've never installed a VRM so I don't know what the normal range is from maximum to minimum, but I'd say yours is going too low. Check to make sure pin 1 of the VRM pot isn't accidentally shorted to ground. It should connect to ground through a 220K resistor.

Hank, maybe you can check your Tramps and see what the B+ measures with the VRM set at max and min.


That's is a great idea, I will check this, thanks Mitch. I did read through the forms and noticed someone else had posted a vrm range, for the life of me can't find that post again. However from what I recall it was 60v at idle.

I agree that the range does seem to be bunched up the being of the pot travel and does go very low. Could one effectively adjust the range of adjustment so that the vrm is more useful in its entire travel?


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PostPosted: Wed May 06, 2020 11:00 pm 
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Here are the voltages from my Tramp: B+ VDC; measured at 1st cap (C12)on Tramp are:

Idle: 88.8
4: 100.3
5: 111.6
6: 120.4
7: 130.7
8: 144.6
9: 255.7
10: 363.5
Max: 402.3

Hope they help. :hmmm:

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PostPosted: Wed May 06, 2020 11:10 pm 
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Hankules wrote:
Here are the voltages from my Tramp: B+ VDC; measured at 1st cap (C12)on Tramp are:

Idle: 88.8
4: 100.3
5: 111.6
6: 120.4
7: 130.7
8: 144.6
9: 255.7
10: 363.5
Max: 402.3

Hope they help. :hmmm:


This is an immense help. Thank you Hank!


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PostPosted: Wed May 06, 2020 11:14 pm 
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sounding more and more like the MOSFET is shot.

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PostPosted: Wed May 06, 2020 11:17 pm 
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Any time I solder something solid state, I try and put a heat sink on it :bugeye: I'll try and research it and check the build guide, too :!:

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PostPosted: Thu May 07, 2020 1:08 pm 
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Hank,

I am seriously starting to think that. Found the MOSFET on mouser and will order a few. Going to check the vrm potentiometer as well. As it could be suspect. Checking over the things Mitch suggested as well. So far it's sounding good.

This may seem like a dumb question but is it normal for a bit of a pop when engaging tude or the fat switches?

I might look into the preamp boost option as well, granted once everything else is working correctly.

Thanks again for the help!

As for now I have been rocking the tramp cranked with a boss pq-4 providing healthy boost and a touch of mids (only pedal I own, besides my tuner). :) using my heavily modified squire jazzmaster, or my custom res o glas guitar I built if I am feeling lofi.


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PostPosted: Thu May 07, 2020 2:50 pm 
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Yes, the engaging the 'tude/thin switch will produce a pop. Normal.

Have you tested the MOSFET per Stephen's instructions, on pages 65 and 66 of build guide? I know it's PITA, but you will still have to pull the board anyway. If you do have to install a new MOSFET, try this when you install the new one: bend the leads and install VRM chip on the chassis per instructions and set the board on it and standoffs, then solder the two outside leads of chip, unscrew the chip and carefully remove chip and board . Then you can solder the PITA center lead of the chip and reinstall board and chip. If at all possible, put heat sinks on chip leads when you solder them. I found some of the aluminum ones on Amazon with bent tips https://www.amazon.com/H-2SL-Goot-Heat- ... 195&sr=1-3, kinda pricey for two, but solid state components don't play nice with heat :!: It works pretty good in tight space. Bent tip surgical forceps do, too.

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PostPosted: Thu May 07, 2020 8:33 pm 
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Thanks Hank for clarifying the tude/fat switches.

I actually happen to have medical grade forceps for this very thing. I am holding off till I get the new MOSFETs I ordered. For now I will keep rocking. Out of curiosity what do you roll in your tramps? I want to order a 6L6 and El34 or KT66. Might get another 12ax7 while I am at it. My budget is pretty tight with not working unfortunately.

Cheers,
Kim


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