Being primarily a Marshall/Fender guy, I was surprised to see that the Express screen grid supply was about 8-12 Vdc lower than the plate supply (based on reported voltages) due to the use of a 1K resistor vs. a choke. Does this effect the distortion characteristics of the Express ?
Also, while I'm at it, whats with the diode in the "Asteriod" amp power rail ? Is this some 'gimmick'...if so, it appears never to have caught on cause I've never seen this in any other amp.
Express Screen vs. Plate supply Voltages
Moderators: pompeiisneaks, Colossal
Re: Express Screen vs. Plate supply Voltages
I don't know I just built it the way I see it. 
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Re: Express Screen vs. Plate supply Voltages
Try a search for 'compression' in the Trainwreck forum as the 1K resistor and the resultant power supply compression has been discussed a few times before, and that search term should bring them up.
The diode in the K60 is an anti-sag diode for the preamp power supply, so exists to combat power supply compression.
It allows the plate and screen voltages to sag under load as usual, but stops the preamp filter chain (which could be at a higher voltage than the screens when the power tubes are working hard) from dumping charge back into the screens filter to stabilise the voltages and therefore drag the preamp voltages down.
The Concorde, which dispenses with the tube rectifier, also foregoes this diode. It won't have the same amount of power supply sag without the tube rectifier so it may just be that the diode was unnecessary for this model, or it may be that a level of preamp power supply sag was desirable since this is the 'Marshall' model in their line.
The diode in the K60 is an anti-sag diode for the preamp power supply, so exists to combat power supply compression.
It allows the plate and screen voltages to sag under load as usual, but stops the preamp filter chain (which could be at a higher voltage than the screens when the power tubes are working hard) from dumping charge back into the screens filter to stabilise the voltages and therefore drag the preamp voltages down.
The Concorde, which dispenses with the tube rectifier, also foregoes this diode. It won't have the same amount of power supply sag without the tube rectifier so it may just be that the diode was unnecessary for this model, or it may be that a level of preamp power supply sag was desirable since this is the 'Marshall' model in their line.