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1. Ok,assuming all the valves are lighting up ok and you have swapped valves around and found it makes no difference and you have used other diagnostic means to proves the valves really are ok then we can look elsewhere.
Which pair of valves is at fault? The left pair of pins on the Molex connector control the valves 8 & 7 and the right pair control valves 5 & 6. The valves are numbered left to right when looking into the back of the amp 1,2,3,4,5,6,8,7. (8,7. It's not a typo)
You say that you have no reading at all????
This could indicate that one pair of valves is pulling no current, or they are but there is a conection problem on the Biasing PCB, or connector CON 11 of the mother board JCM-60-00. ( get this schematic off the net)
So check the voltage across R54 & R68. The results should be the expected bias values. Also check R61 & 59. These supply the bias voltage to each pair of grids.
If you are sure that the supporting resistors are good then measure the anode / plate voltage. If this is not around 500VDC. Then look for bad joints, burnt / fused track and finally check the integrity of your output Transformer. (The 1/4" spade tab and recepticle connexions on this model are notorious for plagueing your day and some people have had issues with these transformers, although, it is usually other problems which cause transformer failure to occur).
2. Only 50mV on the other side?????
This should be nearer 90 if all is well. If one of this pair isn't conducting then you would get a reading of about 50.
Remove one and measure, then try the other and measuse (power down each time first of course) and determine which socket isn't performing. Then just narrow it down to the blown component or dry joint.
It sounds like your amp could have more than one issue going on here.
Finally, with respect, these amps contain lethal voltages.
Go steady.
Which pair of valves is at fault? The left pair of pins on the Molex connector control the valves 8 & 7 and the right pair control valves 5 & 6. The valves are numbered left to right when looking into the back of the amp 1,2,3,4,5,6,8,7. (8,7. It's not a typo)
You say that you have no reading at all????
This could indicate that one pair of valves is pulling no current, or they are but there is a conection problem on the Biasing PCB, or connector CON 11 of the mother board JCM-60-00. ( get this schematic off the net)
So check the voltage across R54 & R68. The results should be the expected bias values. Also check R61 & 59. These supply the bias voltage to each pair of grids.
If you are sure that the supporting resistors are good then measure the anode / plate voltage. If this is not around 500VDC. Then look for bad joints, burnt / fused track and finally check the integrity of your output Transformer. (The 1/4" spade tab and recepticle connexions on this model are notorious for plagueing your day and some people have had issues with these transformers, although, it is usually other problems which cause transformer failure to occur).
2. Only 50mV on the other side?????
This should be nearer 90 if all is well. If one of this pair isn't conducting then you would get a reading of about 50.
Remove one and measure, then try the other and measuse (power down each time first of course) and determine which socket isn't performing. Then just narrow it down to the blown component or dry joint.
It sounds like your amp could have more than one issue going on here.
Finally, with respect, these amps contain lethal voltages.
Go steady.
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