16-11-2022, 05:37 PM
(This post was last modified: 16-11-2022, 05:51 PM by Murphyv310.)
Ok.
Looking at the PDF I assume this is a PC generated circuit?
There's a few anomalies IMHO, the EF91 V1 anode load is too low a value, the cathode resistor of 680 I'd say is low but ok if you stick with the 33k which I personally wouldn't, C2 should be a higher value as a 0.1uf will boost HF not a good idea as you want roll off above 3kHz for an amateur radio TX. It also might be better to strap the G3 to ground, you want more swing to the phase splitter and replace the ECC83 with an 81 if you leave in the 83 then the anode load resistors will need to have unequal values, ECC83s don't make good phase splitters.
Valves 3&4 may need a lower cathode resistor to achieve 5 watts drive, the EC90 gm is quite low, I'd use EL84s which will have loads of headroom.
Other than that Id say the circuit is good.
EDIT: V1 could be replaced with a 6BR7 or an EF86 and run in starvation mode with an anode load of 1 meg, this will give you a large peak to peak drive to the phase splitter, the EF91 might work in that mode but they I've never tried it. You want plenty of drive to the phase splitter and, less gain in that part of the circuit.
Also it's possible to directly couple the anode of the first stage to the grid of the phase splitter and retain the. ECC83, have a look at the Mullard 5-10 circuit.
Looking at the PDF I assume this is a PC generated circuit?
There's a few anomalies IMHO, the EF91 V1 anode load is too low a value, the cathode resistor of 680 I'd say is low but ok if you stick with the 33k which I personally wouldn't, C2 should be a higher value as a 0.1uf will boost HF not a good idea as you want roll off above 3kHz for an amateur radio TX. It also might be better to strap the G3 to ground, you want more swing to the phase splitter and replace the ECC83 with an 81 if you leave in the 83 then the anode load resistors will need to have unequal values, ECC83s don't make good phase splitters.
Valves 3&4 may need a lower cathode resistor to achieve 5 watts drive, the EC90 gm is quite low, I'd use EL84s which will have loads of headroom.
Other than that Id say the circuit is good.
EDIT: V1 could be replaced with a 6BR7 or an EF86 and run in starvation mode with an anode load of 1 meg, this will give you a large peak to peak drive to the phase splitter, the EF91 might work in that mode but they I've never tried it. You want plenty of drive to the phase splitter and, less gain in that part of the circuit.
Also it's possible to directly couple the anode of the first stage to the grid of the phase splitter and retain the. ECC83, have a look at the Mullard 5-10 circuit.
