June 24, 2006
I was still a teenager when I first got to play with Sunn.
I couldn't afford one but a CW band in Andalusia could. The Mavericks had 3 new
Sunn rigs when they hired me to play bass with them. I had to replace a power
transformer in their Sorado bass amp. That's when I fell in love with the simple
but rugged construction of these amps. I even built a Sorado as my first guitar
amp. I never had the good fortune to own one of these... until now. I bought
this 1971 Sceptre on eBay for $250.00. I replaced the 6AN8 tube, did a cap job,
and replaced the tremolo optoisolator. This thing has a very full, classic clean
sound and at 60 watts RMS, it can hang with a Twin Reverb any day. It's truly a
(I included a photo of these caps just
because I had a helluva time figuring out the color code.)
Update August 10, 2010
finally put a new set of SED Winged C 6550s in the amp. And I replaced the
stock bias circuit with a dual bias adjust circuit. The schematic has been
updated to reflect the changes.
Here's the original bias circuit. The test point simply
monitors the negative bias voltage fed to the grids.
The dual bias mod provides separate pots and testpoints
to measure cathode current for each output tube.
Locking pots and testpoints make bias adjustments and tube
matching a breeze.
Download the schematic
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