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Re: Trainwreck amps


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4/14/2000 2:32 PM
peter Re: Trainwreck amps
Excellent, thanks for that.  
 
Something I ought to have mentioned for  
Nathan's benefit is, don't be put off the  
amp by my experience, there are so many  
variables (guitar, speakers, output  
transformer etc etc) that my amp  
may not be "representative".
 
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4/19/2000 2:02 AM
rob
Peter, what did you use for a power supply? cap values and resistors. I've built one of these and am in the final tweaking stages.
 
4/19/2000 3:04 PM
peter
Unfortunately all I had was a hammond 270bx,  
which gives a plate voltage of 495 volts,  
but I used a tube rectifier and added  
three 15 volt zeners, so that the final plate voltage is 430 volts, dropping to about 390 at  
full output. Can't remember the filter cap  
values off hand, but I started smallish and  
then made them bigger cos I didn't like the ripple.  
 
A choke of 2 henries supplies the screens.  
 
Following that I had a 10k resistor to feed the  
PI. The PI supply was then about 380 volts.  
I increased the 10k to 22k, dropping the voltage  
to 330 or so. This also reduces the preamp supply  
voltages, and I noticed a significant improvement in  
sound this way.  
 
So how would you describe the sound you are getting  
out of yours?  
 
peter
 
4/19/2000 3:29 PM
rob

Give me your email and I'll email you direct your voltages are to high.Mine sounds alot like the Van Halen first record distortion wise.
 
4/19/2000 3:39 PM
Bruce

Check that 270BX... there is no way that tranny can deliver 495vdc in this amp!!  
You either don't have a 270BX or you have no tubes in the chassis.  
Bruce
 
4/19/2000 4:20 PM
peter
Right you are, Bruce, I made a typing  
error, it is a 273BX, 350-0-350 at 175 mA,  
weighs 8.8 lbs.  
 
Now did you look that up, or did you just happen  
to know that a 270BX is a wee thing, or is there  
some code to understanding these numbers, that I don't know?  
 
peter
 
4/19/2000 5:03 PM
Mark Kane

When you guys got your TW's put together did you have any oscillation problems, as in squeals when you cranked the treble and mid controls? thanks! Mark
 

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