HRO help
I have been trying to figure out a problem with my HRO-5 (was restored by another but not able to obtain assistance) but not getting very far.
The HRO-5 appears to have 'lost the secondary grid voltage' on the 6K7 valves which is my simple description but I cannot seem to locate the fault. This is obtained by division of the input voltage B+ but the R all seem to be fine so scratching head ... (I could wholesale replace them all just in case but seems a bit like overkill)
I have managed to check the voltages on the pins on both my faulty HRO and a working one (at RAF Duxford) and pin Pin4 ( Screen Grid?) on many of mine are at 0V (2nd IF V6 (6K7), 1st IF V5 (6K7), 2nd RF V2 (6K7), 1st RF V1(6K7)) when on the working HRO-5 are at about 138V DC. And Pin 5 & 8 are at 0V on V5 1st IF (6K7) and V2 2nd RF (6K7) whereas on working are at 4.33V DC. Anode voltage on these valves are all c230V so the B+ is working.
R10 is fine and is 15K
R32 appears to be fine 1K (168V at R30 end, 158V at other feeding R10)
R30 is a 2K2 1/4 watt and is fine.
R11 is 3K (a 2K7 is fitted and was there when I got the set)
R15 is 33K
One end of R10 is at 158V DC the other connected to pin 4 V6 is at zero volts.
I tried with all the 6K7 valves removed V1, V2, V5, V6 but no change in the voltage values.
Pin 6 of V7 which comes from the same B+ source initially is at 168V through R18 which is a bit high at 53K not 47K.
The AF stage V9 is working fine as I can inject a signal into it and get plenty of amplification.
Anyone got any idea what might be the problem or suggestions?
72
Dom
M1KTA
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