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diaz028 13th July 2007 03:31 AM

Peavey Heritage VTX - Schematics
Hi, I am looking for the schematics for this amp. I just want to know which tube sockets to use so I get to use only 2 tube sockets (65WATTS), instead of 4 tube sockets (130watts).

Also, my heritage seems not to be very loud. When I tried out a Peavey valveking 100 at the store, it sounded monstrous compared to my heritage... maybe because I am playing my heritage in a wide basement?


gingertube 13th July 2007 04:12 AM

Here are your schematics

Stuff below is from my looking at the schematic (I'm a qualified Electronic Engineer BUT I'm not beyond screwing up - proceed with caution)

Note that the output tube grids are connected to +15VDC and AC (signal) ground (via C67) and then are cathode driven by the Q6, Q7, Q8, Q9 circuit.

These transistors adjust the cathode voltage and hence the Grid 1 to cathode voltage such that the CURRENT through R155 and R159 develops sufficient VOLTAGE to follow the audio drive signal which is applied at circuit point "A" (Bottom left of schematic).

To use just 2 output tubes its probably best to use V1 and V4 since these tubes have small screen resistors (R3 and R6 = 100R 5W) whereas V2 and V3 do not.
Because of the way the cathode drive circuit works it will try to deliver exactly the same current from just one set of tubes as 2 sets which will cause the tubes to "cook". What you would need to do is change both R155 and R159 from 3 Ohms 5 watt to 6 Ohms 5 Watt so that it only tries to cause half the current to flow when using just 1 pair of tubes (Half the current will develop the same voltage through twice the resistance).

The schematic has some check voltages on it. Since it seems the amp is weak I would carefully check those voltages before embarking on modifications.
BUT (again)
NOTE: the amp has a HI/LO switch which switches the High Voltage to the output tubes between +525 V and +262 V respectively. Check that you are just not in the LO position before assuming the amp to be "weak". I would assume (could be wrong) that this switch would be on the rear panel. Do NOT change this switch with the amp running. Switch OFF before changing the HI/LO switch.

Hope this is off some help.


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