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previous: Trace q{If/When you add you touch to this... -- 9/27/2000 2:59 AM View Thread

Re: Trace, please post your results.

9/27/2000 8:12 AM
Steve A.
Re: Trace, please post your results.
Trace:  
 
    So what B+ voltages were you running? Best reports indicate that the real Expresses run about 405vdc. Did you use the same power supply resistors spelled out in the basic schematic? I'm asking those questions because the voltages throughout the amp seem to be very critical to a good sound. Especially if you are trying to get the power tubes to distort before the PI (and the PI to distort before the preamp tubes).  
 
    The preamp can be tricky to work on... it wasn't until I wired the EL84's up as triodes that I was really knocked out by the sound. Once I got that sound I then reworked the preamp so that I would get similar results with the EL84's wired as pentodes, with both cathode and fixed bias modes. (I haven't experimented with EL34's for a more authentic Express yet.)  
 
    The Callaham clones are probably pretty close in design to at least some of the amps Ken Fischer built (he reportedly fine-tuned each of his amps so that no two Wrecks were exactly the same). But the Callahams don't have KF's custom OT's so they don't sound the same.  
 
    Now from what I have heard some of the Allesandro amps sound more like a Wreck than the Callahams, although the circuits have a lot of tweaks that KF evidentally didn't use. Maybe you have to do stuff like that to get a Wreck sound from off-the-shelf trannies (like bypassing one of the plate resistors with a poly cap and experimenting with lower gain tubes like the 12AU7).  
 
    And don't forget Aron's report of the Dirty Little Monster... one of the early prototypes KF built on a Fender Princeton chassis with stock trannies and cathode-biased EL84's (possibly wired as triodes). The amp is supposed to be absolutely killer.  
 
    Were you asking about the 820 ohm resistor between the vol pot wiper and the 2nd stage grid? I don't see what effect such a low value resistor would have... if a resistor was actually used in that location in some amps my guess is that it was actually supposed to be an 82k resistor. Maybe Callaham read the value wrong and wired his amps with the wrong resistor...   ;)    
 
Steve Ahola  
 
P.S. "I haven't really decided if I want to go much further to be honest." As had been said here before, it takes a day to build a Wreck and a week or two to fine-tune the sucker...  
 
    So was that a Liverpool, an Express or a Rocket that you had played? 3 different animals there...

 
Replies:
Trace q{So what B+ voltages were you runn... -- 9/27/2000 12:59 PM