How far can one reduce idle current before a degradation in sound at lower listening levels? I would assume that getting the current too low would put the tube in an operating range where linearity would be affected. I've now reduced the cathode current to 56 ma (required a bit of circuit change to get the bias voltage where it needed to be for the reduced current), and the amp still sounds great, though I'm sure my max power output is down, but still way more than I need. Reduced current to 65ma and noticed a reduced heat factor, without affecting the sound - plenty of power in my studio. The amp generated fair heat and the trannies would get fairly warm to the touch. Normal suggested bias for the 7591A pair is 70ma combined cathode current (35ma/tube). Question for you tube amp gurus: A bit of background before the question. I suspect I will be disappointed, but we'll see! I'll hook this amp up to my DAW in my sound studio to see how it compares to more modern stuff. At least they are the same physical size as the original tubes. I replaced the 7591A's with new, Russian made TungSol's. Don't know what I'll be getting for replacements of the 6u8's. Original 12ax7's and 6u8's were Telefunken's. Now I have to wait for a matched pair of 6u8's.
Hh scott stereo master lk 72 b generator#
I didn't have a scope or signal generator in my grade-school days! Once that was fixed, I started doing some power/distortion tests when I started seeing some very strange wave-forms on one channel on the scope. Found a slight wiring error in the preamp section that accounted for the slightly distorted waveform. Turns out I didn't do quite as good a job building as I originally thought. I noticed that the sine wave was slightly miss-shaped on one channel. I set bias and balance for the the 7591A's ( boy do those things generate heat!) and ran a sine wave signal through the amp. They look different but I'm looking for performance, not original appearance for this amp. I got a kit of lytics from Hayseed Hamfest. I had to add a bit of resistance to the the bias supply to compensate for the silicone rectifiers. I didn't re-stuff the old caps as the new caps were actually larger than the originals (physically), but they didn't look all that different anyway. Replaced all the tubular and lytic caps, several resistors that were actually within spec, but did it for grins and giggles cuz they were in bias and balanced circuits, one open power resistor, 4 matched output tubes, and one bias supply selenium rectifier. When this is finished, I'll tackle the tuner. When I get to this project, I'll re-stuff all of the capacitors, check all of the resistors, and replace the outputs with matched 7591's. I found the schematic on line and hopefully will find the rest of the info I should have.
Hh scott stereo master lk 72 b manual#
Not sure of the others as the identification markings are gone. Unfortunately, my sister lost the original assembly manual with the balancing instructions. The 12AX7's are Telefunken and the 7591's are branded as Scott. The output tubes, 7591s, are all very weak. I tested all of the tubes and the 12AX7's, the 5AR4 and the 6U8's test ok, if not very good. It rolls off the highs a bit and works best with speakers that accentuate the the high end. But, after close examination, I was fairly pleased with my layout and solder connections way back then! I read a review of this amp a couple of hours ago and they reported as being very warm but not very bright.
Before I opened the bottom of the amp, I had a bit of apprehension about my work as a teenager.
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