Trainwreck Express Build

geetarpicker · Post by **geetarpicker** » Sat Mar 08, 2014 12:01 am

Yep, the 1k @ 25 watt resistor may seem like overkill but they do run hot in these amps!

Littlewyan · Post by **Littlewyan** » Sat Mar 08, 2014 1:03 am

Doesn't Ken run his on the PS board though? Then again I suppose he uses different material.

geetarpicker · Post by **geetarpicker** » Sat Mar 08, 2014 3:25 am

Yes he did, though it's up maybe 3/16-1/4" above the board so air can circulate under and around it.

Tillydog · Post by **Tillydog** » Sat Mar 08, 2014 9:05 am

Tillydog wrote:
Littlewyan wrote:Right an update. I move the HT CT to the cap can negative terminal but it didn't make a difference.
Hmm.... That's a shame!

I can't help but think that this still has something to do with it....

If you had the stomach for it, try the CT to the -ve on the 40/40uF can, but remove the ground wire between that -ve terminal and the chassis. Instead, connect the -ve on the 40/40 to the -ve on the 40/20/20/20 instead. (There will be a wire from the -ve of the 40/20/20/20 to the chassis as there is now.)

Littlewyan · Post by **Littlewyan** » Sat Mar 08, 2014 9:32 am

Could give that a go, replacing the ground leads for those caps later anyway.

Edit: Do you think its worth connecting the 40x20x20x20 to the back of the pots and leaving the 50x50 by itself?

Tillydog · Post by **Tillydog** » Sat Mar 08, 2014 10:30 am

Littlewyan wrote:Edit: Do you think its worth connecting the 40x20x20x20 to the back of the pots and leaving the 50x50 by itself?

FWIW, I'd connect the 40/20/20/20 to the chassis where you have it now, but run the -ve of the 50/50 (40/40?) to the -ve of the 40/20/20/20 (as I described above), rather than direct to the chassis, with the PT CT on the -ve of the 50/50.

It may be sacrilege, but I'd also disconnect the busbar from the backs of the pots, and ground it to the chassis at the input jack only.

Both of those points are on the assumption that the problem is coming from a grounding issue. As you didn't see any change when you tried moving the CT previously, this might not be the case - YMMV.

Good luck!

Littlewyan · Post by **Littlewyan** » Sat Mar 08, 2014 11:24 am

Well I had a few mins so I disconnected the bright caps completely, disconnected the bussbar ground wire and still no change. When I turn the amp off standby the buzz fades. I'll try what you said later on when I have more time to mess with the amp.

By the way when I'm moving wires about I think I'm hearing a change in the hiss more then anything. Will tinker later. I also found that the buzz didnt disappear completely until i grounded the grid of V2 or removed V1.

M Fowler · Post by **M Fowler** » Sat Mar 08, 2014 2:30 pm

Reminds me of a TW amp I built in which the buzz never went away no matter how many times I built it.

Turned out the Heyboer PT had been built incorrectly per Heyboer's inspection and they replaced it immediately. Caused me a month of work and I still have all the old parts on a shelf that I had removed and replaced trying to find the problem.

I guess if a guy paid attention to 60Hz verses 120Hz hum I would have been farther ahead back then. It was a raspy sound centered around the PI entrance on mine.

Mark

RJ Guitars · Post by **RJ Guitars** » Sat Mar 08, 2014 2:35 pm

The chassis mount resistors are intended to use the chassis as a heat sink. That is part of the reason why they can put it into that compact little package. When you mount it to a circuit board that reduces the amount of power it can dissipate... it might work fine but after you've used the amp for a while see if it looks like it's burning into the board. If so, move it to the chassis.

Have you done an isolation of the various stages to see you can identify where the hum is coming from? that is to say - start pulling tubes beginning at V1 and see what happens with the hum.

thanks,

rj

Littlewyan · Post by **Littlewyan** » Sat Mar 08, 2014 2:36 pm

I remember reading about that but I'm getting 50Hz and 100Hz Hum. Just redoing the grounds for the Cap Cans as we speak. By the way the 2 100 Resistors connect to the Bias Ground, would it make a difference if they went directly to the cap can ground?

Littlewyan · Post by **Littlewyan** » Sat Mar 08, 2014 2:38 pm

Hi RJ

Yes, now its a bit odd, if I remove V1 the hum disappears, if I ground the grid of V1a or b it gets quieter but doesn't disappear. If I ground the grid of V2 it disappears completely.

M Fowler · Post by **M Fowler** » Sat Mar 08, 2014 2:40 pm

Littlewyan wrote:Hi RJ

Yes, now its a bit odd, if I remove V1 the hum disappears, if I ground the grid of V1a or b it gets quieter but doesn't disappear. If I ground the grid of V2 it disappears completely.

Does it do this with any tube you install there?

Littlewyan · Post by **Littlewyan** » Sat Mar 08, 2014 2:46 pm

Yes but I've only tried 2 tubes. I'll try some more in a sec. Almost done with the grounding!

O btw the issue with the volume going quiet when on full only happens when all tone knobs are turned to 0 so I guess thats normal. Doh!

M Fowler · Post by **M Fowler** » Sat Mar 08, 2014 2:55 pm

V2 grid is connected to the junction of the .0022uf coupling cap and 150K.

What happens when that 150k resistor has a separate ground rather then to the ground buss on the pots?

Littlewyan · Post by **Littlewyan** » Sat Mar 08, 2014 2:57 pm

Ah good idea! That would make sense I'll give that a go. The Capacitor Grounding didn't seem to make a difference by the way.

The Amp Garage

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