My old schematic of this unit correctly states the upper number is the "operating voltage", while the low number is the "standby voltage". Other than that, I have no literature, with a schematic that isn't even as good as yours.
My information dates to June of 1980 when I came across one of these sans power transformer. My notes show I called Executone at the time, and through a discussion with one of it's representatives, was told that it was rated at 75 watts.
The OPT is strange however. At the time, I measured a turns ratio from the primary at the 20 volt secondary of 21.73. based on a 75 watts rating, that makes this tap a 5.333Ω tap, with a reflected impedance of 2518Ω. The 70 volt secondary had a turns ratio of 7.01, with a 75 watt rating making that tap a 65.333Ω tap, with a reflected impedance of 3214Ω. I could never tell from my poor copy of the schematic what the 3 volt winding was (3.3Ω? 3.5Ω?), but it has a turns ratio of 182.08. If it is a 3.5 volt secondary, that makes it a .16333Ω tap (appropriate for 50 8Ω speakers in parallel), with a reflected impedance of 3777Ω. But all of these are too low for KT88 tubes under100 watt operating conditions. Just to make things even more confusing, I show that the transformer in my unit had UL taps at 26.6% of the winding as well. But that was all a long time ago.
Remember that even when 6550/KT88 tubes are operated in "100 watt" mode, assuming that all the power supply voltages hold up, you'll still only get about 81 watts of power into a secondary load due to OPT losses. So, it is a certainty that the unit is not a 100 watt unit.
If you could specify what the heck that 3 volt winding is actually rated at from your schematic, I could at least put that mystery of this unit to bed -- after what, 37 years??
Dave
Hi Rick -- If I may, I think you're indicating the voltage on either side of the heater winding center tap at the power transformer. What I was hoping you could clarify is over at the output terminal strip -- the one labeled "Installation Connections". I show that terminal:
1 = 70 volts output.
1A = 20 volts output.
2 = Mystery Figure. It appears to be 3.something volts output, but I can't make it out to be sure. This is what I was hoping you could clarify for me.
2A = GND.
If you can, thanks in advance for checking!
Dave
Hey Dave, "My information dates to June of 1980 when I came across one of these sans power transformer. My notes show I called Executone at the time, and through a discussion with one of it's representatives, was told that it was rated at 75 watts.Thanks so much!!
Dave
Hey Dave, "My information dates to June of 1980 when I came across one of these sans power transformer. My notes show I called Executone at the time, and through a discussion with one of it's representatives, was told that it was rated at 75 watts.
Dave I had though that as well about the bias current but when I checked them, the last tube set the bias pot was set to give me 24ma on one tube and 27ma on the other I adjusted the DC balance pot and they nearly squared off at 25ma each, the note on the schematic does say 50ma as you said I was thinking that was the total for both. Well I will later this week up the bias curent to 50am as you suggested and see what I have then as the volume of the amp at 25ma each tube was pretty loud can't wait to see what I have when I bump it up. I post back after adjusting and let you know. I been busy building a maggie 8603...Nice Job! You would want each tube to draw 50 mA, for a total output stage quiescent current of 100 mA.
Dave
Did you ever get a decent copy of the schematic to pdf. made for this?Sorry no