T-Rex help

[fusionbear]

Hello all, I recently purchased a Red Iron T-Rex, but it seems to always have a high frequency oscillation. The maker graciously offered to fix it, but I would prefer to fix it myself if possible and not have to re-ship. It uses 2-6SU7WGT's for the preamp and a 6SU7GTY for the PI. The power amp is 2 Cathode biased 6CA7's. I initially thought it was the tubes, but the maker sent replacements, but to no avail. Anyway, the amp sounds awesome, but the oscillation makes my ears hurt in about 2 minutes and I occasionally get a burst of "white noise" that goes away if I turn my volume knob down on my guitar. Sometimes it sounds as if the speakers are torn, but that sound goes away if I turn my volume knob down. Any ideas of where to start troubleshooting? Here's a gut shot:

[IMG768]http://i169.photobucket.com/albums/u223 ... 010100.jpg[/img]

[IMG768]http://i169.photobucket.com/albums/u223 ... 010094.jpg[/img]

[dartanion]

start here:

http://www.geofex.com/ampdbug/ampdebug.htm

[fusionbear]

Thanks, very helpful. I'll post when I figure it out.....

[fusionbear]

Found the problem: The connection out of the right cap out of the phase inverter to the strip by the power tubes was iffy. A little resoldering and now the amp is as queiet as a church mouse......yes!!!!

It sounds awesome. Not quite as much gain as a Trainwreck, but the touch sensitivity and rich harmonics are there in loads!!!!!

[dartanion]

EXCELLENT!!!

Never heard on of those before. Can you make some clips? I am planning an all octal wreck in the near future, so this is right up my alley.

[fusionbear]

I'll attempt to make some clips next week. I let some friends borrow it for the weekend.....

[ampgeek]

Well done! So satisfying to fix it yer'self!

I am very interested in hearing some clips. I must admit, this is the first time that I have heard of a T-Rex. Ok...ok..so I just got out from underneath that rock!

Any chance that someone has/can direct me to a schematic?

I, too, am partial to octals in the preamp. My very first amp build was a 5F6A with 5691's in all three pre-amp positions.

TIA,
Dave O.

[dartanion]

http://mhuss.com/18watt/schematics/

Thanks Mark!!

Although the the one pictured isn't quite like the schematics here.

[mhuss]

Yeah, I wonder if they share any commonality other than the name!

My TRex was a Richie Hall design from a couple years ago, with a normal 18w channel and a "trainwreck" style channel. Doesn't sound just like a true 'wreck, but still sounds pretty cool

--mark

[fusionbear]

When I get my T-Rex back, I'll attempt to make a schematic as the one referenced above seems different. One thing that it has in common with a Trainwreck is that it is loud! LOL! I think I'll add a PPIMV so I can at least use it at home without waking the neighbors......