Help! Sunn Set!

[Fred Cook]

I was playing through the mighty Sceptre when the sound went fuzzy and the fuse blew!  

-- I replaced the fuse. New fuse did not blow.

-- Amp works, but there is decided 60hz hum.

-- Amp sounds OK, maybe some treble loss, but when running up the volume the sound turns fuzzy and sounds like classic "transistor" distortion, as opposed to tube overdrive.

-- Once before, when I had hum, I replaced the 6AN8 and the hum went away.

-- First preamp tube is a 12AT7 vice a 12AX7.

Any thoughts or recommendations?

[Fred Cook]

Trying to run down the problem I found the following:

-- Swapped out the 6AN8 - no change
-- Replaced the first tube back to a 12AX7 - no change, except, as you would expect, the problem comes in at a lower number on the volume knob.
-- Altering the bias has no effect. (Of course the JJ KT-88s don't seem to care how much (or how little) bias you give them.)
-- No signs of distress from the amp, transformers are cool, no burning smells, etc.

Right now the amp sounds great, solid bass, "growling" distortion, up to about 3.5 on the volume knob. Then there is a distinct "klunk" sound and the amp sounds papery and transistory. The bass turns flabby.

Ideas anyone?

[Fred Cook]

Swapped the rectifier tube on principle. (The original is ORIGINAL - 1959) Bass may be a bit firmer, the the symptoms are the same: Amp sounds great up to 2.5/3 on the volume, then there is a "pop" and the sound turns flabby.

A bit like the hop's post on a muddly low end on his 200.

All thoughts welcome as I won't have access to an amplifier tech until I return to the US.

[Anonymous]

Fred;
Could be an intermittent in the power supply. I'd check the multi-section can filter cap and the dropping resistors. Also check the 50uf bias caps.

Good Luck!
Ryan