TW clone problems.. pics, clip.

  • Thread starter Thread starter HilltopExplosion
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HilltopExplosion

HilltopExplosion

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Hi guys, I bought a T-Wreck expression clone from a dude. It's a Ceriatone build, but the transformers have been changed to Classictone (correct #'s for the model) and the filter caps have been upgraded also. The amp sounds great at low volumes. For example I can run the amp volume at noon, but the guitar volume low. As I turn up the volume on the guitar, the amp has a (for lack of a better term) phase issue. When I strike a string or hit a chord, there is a PEEOOOWWNN sound to it.. I have checked resistors, voltages with the output tubes in and out. I pulled the output tubes and flipped the amp on, no hum. pulled the PI.. no hum. Pulled v2, no hum. When I pulled v1 there was a noticeable hum, but I finally got rid of it after changing some preamp tubes and replacing the 2200 pf cap with a new one.

When I replaced the output tubes, I measured 400 volts across pins 8 and 3.. I started at 40 ma with EL34s, and now it has EH6CA7's in it. When I would hit a chord, the bias would go high on one side, but try to go in the negative on the other tube. I had never seen this before, and asked a few people both here an on another site. They think this is normal, but I'm throwing it out there just for other opinions.

Like I said, the main thing is the attack of this amp has a real strange phase going on with it, if anyone has experienced this, or might know the cause I would appreciate some advice.

I added a youtube vid, a clip and pics/layout .


https://www.youtube.com/edit?o=U&video_id=q4_GmgwdpYc

In the clip I turned everything to noon, cycled the bright switch, then left it in middle position and used my guitar volume knob for volume/gain. this problem persists no matter what tubes/cab/guitar/ combination I use. Thanks!

https://soundcloud.com/user-437728583/t ... sh/s-Xo4nd



 
What are the bias feed resistor values (far top/right on circuit board in pic)? They look red-red-green which would make them 2M2. They should be red-red-yellow (220k).

EDIT: and if they are 2M2 don't crank the amp, I wouldn't even play it.
 
SpiderWars":b069hn5y said:
What are the bias feed resistor values (far top/right on circuit board in pic)? They look red-red-green which would make them 2M2. They should be red-red-yellow (220k).

EDIT: and if they are 2M2 don't crank the amp, I wouldn't even play it.
Click to expand...

Thanks for taking a look, I appreciate it! The resistor is red-red-yellow-gold.

 
Not that one, the two resistors that form a V at the top right of the main circuit board.
 
SpiderWars":33yjcrng said:
Not that one, the two resistors that form a V at the top right of the main circuit board.
Click to expand...

Thanks again! They are red-red green gold
 
Damn, there is a 100K plate resistor right there close by and the yellow band looks yellow. The 3rd band on the bias splitters is very dark green in the pic. These are the two resistors right in front of the Presence control with the red and yellow wires that go to the power tube sockets.

But if that's not it then I don't know. Was hoping it could have been something that simple.

Where is the blue NFB wire going after the 100K NFB resistor? It should only connect to the resistor there but it looks like it continues...to somewhere.
 
HilltopExplosion":3nwdv5hk said:
SpiderWars":3nwdv5hk said:
Not that one, the two resistors that form a V at the top right of the main circuit board.
Click to expand...

Thanks again! They are red-red green gold
Click to expand...

So instead of being 220k they would be 2200k, right? And that would be... wrong.
 
Yes, very wrong. 220k is actually ALREADY over the recommended spec on the tube sheets. The Express (Expression) is low-ish voltage and doesn't really stress the tubes much at all so that's prob why it has gotten away with it. In many amps that are close to the limits I'm pretty sure the tubes would have been toasted already.

It would explain the bias going wonky too, those big ass 2M2 resistors make it difficult for the bias supply to remain at a constant voltage at the tube pins.
 
SpiderWars":3copxkd4 said:
Yes, very wrong. 220k is actually ALREADY over the recommended spec on the tube sheets. The Express (Expression) is low-ish voltage and doesn't really stress the tubes much at all so that's prob why it has gotten away with it. In many amps that are close to the limits I'm pretty sure the tubes would have been toasted already.
Click to expand...

WOW!! Thanks! I'm waiting on photobucket to upload a pic and I will post it.. I appreciate your help!! I will get some resistors and change these out and see if that clears everything up! I really appreciate it! :thumbsup: :rock:
 
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