My first TW Express "variant" is up and running!

[Rick]

I fired up the Trainwreck Express variation today. Once the electrolytics were charged into submission, it started to work pretty well.
I was quite impressed for a first time startup performance. The only shielded wire is the short input jack piece. Everything else is teflon or PVC stranded wire 22 or 20 AWG. Filaments are 20 ga. solid wire. It is amazingly quiet for using no other shielding. (Good design )

The transformers are Hammond, the 6V6's are Russian 6n6c's. It is a pretty close rendition of Nik's (Ceriatone) layout with a few modifications, like the power supply (which I greatly compacted) is 2-1N5408s instead of 4-1N4007s, and the cap substitutions for radial leads where convenient, etc. It really rocks with a more intense tone than any of my 18 or 36 watt TMB builds. I think I'm really going to like it, especially once I learn more how to use and control it. I will like to try EL-34s in it too when I can spare the change for a nice pair.

www.laserampchassis.com/trainwreck/twe1.jpg
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www.laserampchassis.com/trainwreck/twe6.jpg
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www.laserampchassis.com/trainwreck/twe8.jpg

[joe6v6]

Sweet deal Rick! yea it takes some time to dial it in, diffrent gutars like diffrent settings. Like yours my first didnt follow a traditional circuit layout & it works just fine. I havent tried 6v6's yet but plan to soon.

JOE

[UR12]

Looks Great!!! Congrats

[Rick]

Thanks guys. I noticed the 6n6cs were really running hot, the second matched pair I tried was idling low as I could go at 140 mA, wowser! I remembered I had a new matched pair of EH 6V6s I got for a 5E3 a while back, so in they went and now it's idling at very acceptable (I think) 40 mA. I notice one starts to red plate a vertical stripe in the center with the lights off when jamming while the other has a little purple glow off and on. The 6n6cs have black glass, so it's a bit harder to tell what's going on, but they were definitely running hot (2nd pair). Maybe it was just that 2nd pair, cuz the 1st pair biased around 40 ma also, but they weren't as well matched, go figure.

Anyway, it really sounds great, I'm very happy. I'm beginning to wonder if I will ever build any more 18w or 36w TMB amps. This seems to be all that, and a lot more. It's all true, these are awesome amps.

[joe6v6]

idling at very acceptable (I think) 40 mA.

With the lower plate dissipation of 6v6's (12 watts vs 25 for an EL34) you should bias closer to 30ma or below. If you have say 400V on the plates at 40ma you are about 30% above max plate dissipation of 12 watts. Red plates will ensue. There is a good artical here that talks about biasing in a manner that is understandable. http://www.duncanamps.com/technical/lvbias.html

Joe

[Rick]

Thanks Joe, I got to thinking about that last night. I'm going to have to change some resistors since the trimmer is all to the right low as it can go and I'm still running about 40 mA. I'll look at changing the resistors in the bias circuit and see if that will get me there. thanks again, Rick

Problem solved, I added 470K in parallel with the 220K before the diode, that brought the net resistance to about 150K, maximum bias voltage came down to about -68 volts, and idling at around 24 mA.

I guess I spoke too soon, it's not sounding so good any more. It is really fizzy and buzzy sounding at low volumes. At higher volume, it's so distorted and electrical, metallic sounding, it's hard to tell if it's supposed to sound that way, or if something is wrong. My guess, something has gone wrong on the board section and maybe the negative feedback loop is causing trouble. I have no idea on this kind of amp, since I don't know what it's supposed to act like. It may go to the recycle heap. I can still use a lot of the pots, trannys, switches for something else. My patience for ironing troublesome amps has worn short. If anyone wants the chassis, let me know. I may strip it.

[Buschman]

Rick, troubleshooting a build is just part of it. Don't give up yet. Post some voltages for all to see.

[joe6v6]

It may go to the recycle heap.

This seems kind of drastic & you may be jumping the gun a bit. I have spent hours & days trying to figure out a bad sounding build only to find a 100K resistor where a 100 ohm should have been. It could be a very simple problem that just needs to be found. . . If it worked better with the EL34's put it back that way & do like Bushman said & post some voltages. These are pretty touchy amps & just moving a wire can make a big diffrence.

JOE

[brownnote]

You're definitely more in the bias range at 24mA, I was going to suggest 20-22mA, but 24 is close enough.
BTW...that red stripe doesn't sound like red plating, but more like the fillament glowing hotter....I believe most any power tubes will do that when you drive 'em hard, yes?

[dehughes]

Yeah Rick, stick with it....usually it is just a simple little issue that can be easily resolved once you determine what it is. I spent about 1/4 of my total build time just "troubleshooting" the last amp...and it turned out to not even really have a problem! It was just my own incorrect perception and incorrect assumption as to what was "normal".....not saying that's true in your case, but sometimes we just get too close to a build and loose objectivity and troublehooting ability. You'll fix it, man.....just give it time.

[Rick]

Yeah, I know. This is not my first build. Believe it or not, this is my 10th finished, working amp. I've built 3-36W TMBs, 3-18W TMBs, and 3-5E3 Deluxe variations before this making it my 10th. I'm just getting sloppy or burned out. I went back and found at least 2 solder joints I didn't even solder, 1 whisker short, a tube pin terminal short, and moved a ground wire.

It was humming really badly, I moved the bias ground wire off the tranny star ground to a separate stud and away from the OT primary leads, the hum went completely away!! It's working quite well now. I have to run the 6V6s at about 30 mA idle or it gets a little barky and the presence control starts to sound like old Sparky on low levels. I think it's time to just leave it alone and play on it for a while.

Thanks a bunch for the encouragement guys!!

[dehughes]

Sweet! Good job man! Way to stick with it and get it working correctly. Bravo.

[Rick]

Thanks.