Not yet. I'm using a variac to set the AC line to 117. My AC line varies from 120 to 124, So I will buck the heater when I get everything else worked out.Did you connect the extra heater winding to act as a buck winding as shown on the schematic?
Dave
That's correct. Ideally it is good to get the two channels within at least 10% of each other, which you're a ways away from.
One of the excellent things you can do now that you've installed EFB(tm), is to use the amplifier to match the tubes for you in a way that you never could before. This is because with EFB installed, that amplifier can operate safely with just one output tube installed -- which could never be done with the stock design, as it would burn up the tube. To match your tubes:
1. Remove all four tubes, and select one tube socket to use as the test socket.
2. Install the first tube to test in the socket, and with your meter connected across the appropriate 10 Ohm resistor, adjust the bias control for .22 vdc on your meter. Once stabilized at that reading, record it as the value for that tube.
3. Now, power the amplifier down, remove the first tube tested, and without touching the bias control, install the second tube to be tested into the same socket. Turn the amplifier on, and record the reading that the tube stabilizes at.
Proceed with the same process for all tubes to be tested. In this way, you can match your tubes rather closely under quiescent condition. Once you find four that have readings within no more than a 10% difference (5% is really good), then you've produced a set of tubes that is much more closely matched, than if you just shoot in the dark.
I hope this helps!
Dave
I'd expect it to come down once all the tubes are biased properly. Looks like its set a little low currently, so the voltage will be high.So 414V B+ is OK?
I have the V2 amp with 4 separate test points. If I remember correctly, they are supposed to be set to 20mA on each tube.I'd expect it to come down once all the tubes are biased properly. Looks like its set a little low currently, so the voltage will be high.
I hope I'm correct...but it's been my understanding that moving up is not the problem. If the OPT's are rated for 4 ohms, you can drive 4, 8, or 16 ohm speakers. But you wouldn't want to move in the other direction (i.e. driving 4 ohm speakers with an 8 ohm OPT).
The original OPTs were 7600 Ohm units, while the Z-565s measure 7800+ Ohms. Not a big deal, but enough to change the output slightly.
Dave
I'm finally getting around to finishing my 9304-20, I've decided to incorporate the Dave's modifications to my rebuild.
As far as upgrading OPTs. Edcor offers a 7600 Ohm OPT. In theory, could you sub these in for the original stock units without needing a scope to reset the NFB resistor values. Plug them into Dave's "modified" version to get the advantage of his improvements and the improved bandwidth, etc,..., of th newer OPTs.