So Ive purchased some go-no-further parts for the unit.
2x 100uf 450v caps
20/20/20/30 cap - I figured, if im gonna stay original.....
Since Im going no further till the parts arrived I though I might ask a few questions. In looking at the schematic...and wondering
1. The input terminals TIP/RING are tied together with a 470KOHM resistor. What is its purpose, and why 470KOHM
2. With the discussion about the 50uf caps:
The AC connection RD-BL supplies 50vAC to the rectifier with 65VDC out. The output after both Caps goes directly into
the 10K POTS to connections 6-21 onward to connections 1-2 and 22-23 to the EL34's pins 5-6. So any voltage
change with the larger caps can be offset by the bias pots. Correct? Also I imagine the caps are flipped around because the negative voltage is lower than the chassis....
3. What biases the 7199's? There is no negative value for any test points on the tube. Pin 2 plate of the 7199 connects to (A) 305VDC which is connection 19
after a further drop in voltage by a 270KOHM resistor but its also connects to the grid pin 9 on the triode side of the 7199. does that 82mmf cap stop the DC flow into pin 9?
4. Since there is no coupling cap between pins 9 and 2 of the 7199, am i to assume the DC Plate voltage from pin 2 is injected into the grid at pin 9
or is there some internal capacitor to separate the DC from the audio signal within the tube. It seems to me that the plate voltage of the pentode side[A] is
different from the plate voltage on the triode side [B].
5. Is a reliable way to test the choke C354 by measuring pin 8 on the GZ34 [435VDC] and expecting a 20VDC from on the output of the RF choke where it connects to the 20uf cap?
6. What is the purpose of the two 270K OHM resistors in series that connect the output signals to the EL34 grid after the .1mf coupling capacitors? Does this match the peak to peak size of the wave forms going to the EL34 after they are phase inverted?
7. what is the purpose of the 1K resistor before the input signal into the EL34. Is it to match the expected output signal to an appropriate input level for the EL34?
8. The pin 4 and pin 3 get a positive dc voltage from C power which is 415v i see that pin 3 is lower probably due to the resistance of the audio transformer coil
and should read 5 volts less as a result. Where is the return path for the primary side of the audio transformer, is it fed back into the EL34
sorry for all the questions, just curious
Last edited by jrubin on Mon Oct 05, 2015 8:45 pm; edited 7 times in total (Reason for editing : added pics)