GuyNoir
Hallowed State
Good Evening ~
I'm working on a Sherwood S-5000. Per forum recommendations, I placed individual 10 ohm resistors between cathode to ground on the outputs for the purpose of measuring current. Initially, I mistakenly placed 10K resistors, reading the dull red band as black. Audio was garbled. I realized the error and ordered 10 ohm resistors. In the meantime, I had also removed the flimsy phenolic speaker terminal strip, and replaced it with a stout terminal barrier strip. I can screw in 8-32 threaded banana jacks, and they are rock-solid.
In the process of soldering up the new terminal block, I didn't put the DF (damping factor) ground terminal back in. I wired the respective OT black leads to the common terminals. In addition, there were two leads coming from the 7199 tube socket center pin, which I also soldered to the common terminals. The 4 and 8 ohm taps were straight forward, but the 16 ohm taps had leads coming from both the OT and smallish green wires coming from an area near the 7199s. There is just one black lead that isn't connected to anything now, and that's a single lead that went from a can cap negative terminal to the "DF" terminal.
Also, I replaced the 4.7K dropping resistor on the bias supply with a 3K, which gives me nearly -20 volts at the output tubes, as opposed to -17.5.
Now, I have no audio. The bias balance pot is working, and in test mode I get solid hum that can be nulled with the pot. I'm showing about -19.5 bias voltage to each of the four outputs. For current, I am reading 3.2 on the ammeter scale's second to lowest range, except for one tube that is nearly double that. I've ruled out anything on the amp's front panel - I know it by heart now, and everything is set as it should be.
One other thing is different now; the output tubes are seeing 460v on pins 7 and 9, whereas it was 438v not that long ago, both measured at line voltage.
Any ideas? (yeah, I know...stop mucking around) but other than that?
TIA,
Cary
I'm working on a Sherwood S-5000. Per forum recommendations, I placed individual 10 ohm resistors between cathode to ground on the outputs for the purpose of measuring current. Initially, I mistakenly placed 10K resistors, reading the dull red band as black. Audio was garbled. I realized the error and ordered 10 ohm resistors. In the meantime, I had also removed the flimsy phenolic speaker terminal strip, and replaced it with a stout terminal barrier strip. I can screw in 8-32 threaded banana jacks, and they are rock-solid.
In the process of soldering up the new terminal block, I didn't put the DF (damping factor) ground terminal back in. I wired the respective OT black leads to the common terminals. In addition, there were two leads coming from the 7199 tube socket center pin, which I also soldered to the common terminals. The 4 and 8 ohm taps were straight forward, but the 16 ohm taps had leads coming from both the OT and smallish green wires coming from an area near the 7199s. There is just one black lead that isn't connected to anything now, and that's a single lead that went from a can cap negative terminal to the "DF" terminal.
Also, I replaced the 4.7K dropping resistor on the bias supply with a 3K, which gives me nearly -20 volts at the output tubes, as opposed to -17.5.
Now, I have no audio. The bias balance pot is working, and in test mode I get solid hum that can be nulled with the pot. I'm showing about -19.5 bias voltage to each of the four outputs. For current, I am reading 3.2 on the ammeter scale's second to lowest range, except for one tube that is nearly double that. I've ruled out anything on the amp's front panel - I know it by heart now, and everything is set as it should be.
One other thing is different now; the output tubes are seeing 460v on pins 7 and 9, whereas it was 438v not that long ago, both measured at line voltage.
Any ideas? (yeah, I know...stop mucking around) but other than that?
TIA,
Cary