Oscillation in new Trainwrek express build

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Oscillation in new Trainwrek express build

Postby ep1966 on Sat Sep 10, 2016 11:36 pm

Hello,
Thanks for reading my post. I built a Trainwreck Express kit from Triode Electronics. I must say this amp really surprised me. I have always been the type to plugin and play. Dime the tone and volume on the guitar and just jam you know keep it simple. These amps are very touch sensitive and it let me know real quick what I have been missing. But I am having an issue with it. With the bright switch (or that is what I call it) is switched to the 500pf cap a faint parasitic oscillation can be heard out of the speakers. Also if you switch it to the 100pf same thing a small parasitic oscillation. When the switch is in the middle where the 500pf or the 100pf is switched out the oscillation goes away , however when turning up the presence control say halfway or more the oscillation comes back. Any thoughts on this or how to correct the Issue.
Link to the kit
http://www.triodeelectronics.com/twtubeampkit.html
Link to the pdf layout
http://site.triodestore.com/TWEXPRESSLAYOUT.pdf
ep1966
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Re: Oscillation in new Trainwrek express build

Postby Unit_1 on Sun Sep 11, 2016 12:23 am

Well the first thing I noticed is there is no obligatory 68k resistor between the input and the tube, started looking around on the web to see if this was indeed supposed to be, found a layout on Ceriatone showing a 2k2 resistor instead

Image
Line to this layout:
http://ceriatone.com/images/layoutPic/t ... iatone.jpg

Then I found this by someone else who built one:
Noise: surprisingly, it’s got very decent noise level. No oscillations at any volume levels. Trainwrecks are notorious for being noisy and prone to oscillations, but I’m very happy with this build in that compartment.


You can see the rest of this article at:
http://diy-fever.com/amps/ax84-4-4-0/

Perhaps you could ask this gentleman for his layout, and compare to see any differences. The answer to why his has no problems could perhaps be found..

:highfive:
Image
The ability to play/make music is a gift that not everyone gets. Those of us who have it should use it.

Asimov:Individual science fiction stories may seem as trivial as ever to the blinder critics and philosophers of today — but the core of science fiction, its essence, the concept around which it revolves, has become crucial to our salvation if we are to be saved at all.
Unit_1
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Re: Oscillation in new Trainwrek express build

Postby ep1966 on Sun Sep 11, 2016 3:10 am

Thanks, Unit 1 for the response. Yep no 68K grid stopper in this one. I would think if one was placed there it would alter its touch response some. But how ever it was one of the first things I notice when I began the build. Really as for noise the amp is very quite. Train wreks are very noisy but I was floored when I seen how quite this amp was. except for the oscillation issue. At first I thought I had the plate wires on the power tubes out of phase but with all the amps I have had that happen to the oscillation would start as soon as you start rolling the presence up. This amp you can get it 1/2 up or better with the bright caps switched off before the oscillation starts. guess I could try it though I've seen more crazy things happen.
ep1966
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Re: Oscillation in new Trainwrek express build

Postby Unit_1 on Sun Sep 11, 2016 3:41 am

How about a few pictures, maybe someone can spot something.

How's the wire dressing? Make sure there's no parallel wires? When they cross the closest to 90 degrees is the best to reduce one wire picking up the EM from another...

Interesting design!!!
Image
The ability to play/make music is a gift that not everyone gets. Those of us who have it should use it.

Asimov:Individual science fiction stories may seem as trivial as ever to the blinder critics and philosophers of today — but the core of science fiction, its essence, the concept around which it revolves, has become crucial to our salvation if we are to be saved at all.
Unit_1
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Re: Oscillation in new Trainwrek express build

Postby ep1966 on Sun Sep 11, 2016 8:46 pm

Well cant take pics at the moment it at a friends house and I want be back over there until next weekend.
I found the spec's document on the tranny. I read somewhere that the dot on tranny doc's show the tranny
phase.

Image


If this is correct and I if I understand this correctly, If you compare it to the layout of the amp
the power tubes are out of phase.

Image

The amp is wired just like the layout.
ep1966
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Re: Oscillation in new Trainwrek express build

Postby ep1966 on Fri Dec 09, 2016 1:22 am

UPDATE!!!!

Well work is killing me and not giving me time for the amps. Thought I'll drop an update and let all know what the issue was.
it was picking up some out side interference. After shielding the bottom of the chasse the oscillation was gone. This amp is a great amp but can be very temperamental. Wire dressing and component placement is very important. With that said its a blast to play over. Would I build another? You Bet!
ep1966
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Re: Oscillation in new Trainwrek express build

Postby Unit_1 on Fri Dec 09, 2016 9:52 pm

:cheers:
Image
The ability to play/make music is a gift that not everyone gets. Those of us who have it should use it.

Asimov:Individual science fiction stories may seem as trivial as ever to the blinder critics and philosophers of today — but the core of science fiction, its essence, the concept around which it revolves, has become crucial to our salvation if we are to be saved at all.
Unit_1
Prince
 
Posts: 3713
Joined: Mon Oct 03, 2011 3:29 pm
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