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I've got a Silverface Deluxe Reverb in for some work. It has an enormous PT fitted and it looks like this was done in 1990 by the note inside the amp. There's no bias tap off the transformer and the standard bias circuit is connected to one side of the heater supply. So a bias voltage of just over -3v.
If it had just been done like that, it would be one thing. But it's been in use, red-plating away with its mismatched Phillips and Ferranti tubes for years. There's a floating HT fuseholder that someone has nicely bridged with 20g to prevent the 500mA fuse from blowing.
How this amp has stood up to this beats me.
A straightforward fix - change the 470R series resistor in the bias circuit to 100K and the divider resistor to ground from 10k to 22k, then move the feed to one side of the HT AC, just like a Princeton Reverb.
There are numerous other bodges, but I've not seen one has bad as this for a good while.
If it had just been done like that, it would be one thing. But it's been in use, red-plating away with its mismatched Phillips and Ferranti tubes for years. There's a floating HT fuseholder that someone has nicely bridged with 20g to prevent the 500mA fuse from blowing.
How this amp has stood up to this beats me.
A straightforward fix - change the 470R series resistor in the bias circuit to 100K and the divider resistor to ground from 10k to 22k, then move the feed to one side of the HT AC, just like a Princeton Reverb.
There are numerous other bodges, but I've not seen one has bad as this for a good while.
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