Vinylcafe
Linvin' the Dream
Found an old barn stored 800C and decided to rebuild and give it to my daughter this Christmas.
Was an ugly duckling with a little more corrosion than I'd like, but went ahead.
One metalbone kit later and 3 replaced can caps and I can't get anything but a faint whisper out of the left channel.
Tubes are all good, checked and double checked my wiring. Voltages for the 7591s good (drawing about 28 milliamps per tube)
Channel is dead in aux, phono and FM (AM I think is dead).
I am loking for a strategy to find the problem.
Reading the schematic it looks like the best way to go is work backwards from the left channel outputs and compare readings to the working right channel.
So V12, half of V16 and half of V17 seem dedicated to the Aux level preamp.
I am assuming that the high voltage side is good (but maybe I shouldn't).
I'm confused around the heater pins and voltages around V12 (left side) and V15 (right side)
Looking at the schematic for these tubes there is no heater voltage given (I believe 12AX7s can run 6 or 12v depending on series or parralel).
V15 and V12 show pin 9 to ground and pin 4/5. I assume this is because they are notsplit to separate channels.
Readings are as follows- both tubes have Pins 4&5 jumped together.:
V15 pin 4/5 0 volts
pin 9 0 volts
V12 pin 4/5 0 volts
pin 9 0 volts
Does this mean for these heater voltages I cannot just gound my meter to the chasis, but must run it across pins 9 and 4/5?
Clearly both tubes are getting warm, though I am not sure the voltages are correct.
They pretty well match readings on each pin of the two tubes, and I get a nice loud crackel on each channel as I move my probes from pin-to-pin (this make me believe its a problem before th 7591s).
On V16 and V17 here are the readings, again the schematic does not give any voltages for pins 4 and 5.
V-17
Pins
1 182v (should be 167 - out of spec resistor)
2
3 1.05v
4 -24.6v (?)
5 -11.5v (?)
6 180v (bad resistor)
7
8 1.07
V16
Pins
1 190v (should be 167 - out of spec resistor)
2
3 1.0v
4
5 -11.56v (?)
6 192.7v (another bad resistor)
7
8 .972v
If pins 4 and 5 are heater pins, how do you get negative voltages there?
Cleaned and measured voltages out of both phase pots, they look similar.
Any thoughts would help.
Hoping to get at least the amp portion done so I can deliver this Christmas!
Was an ugly duckling with a little more corrosion than I'd like, but went ahead.
One metalbone kit later and 3 replaced can caps and I can't get anything but a faint whisper out of the left channel.
Tubes are all good, checked and double checked my wiring. Voltages for the 7591s good (drawing about 28 milliamps per tube)
Channel is dead in aux, phono and FM (AM I think is dead).
I am loking for a strategy to find the problem.
Reading the schematic it looks like the best way to go is work backwards from the left channel outputs and compare readings to the working right channel.
So V12, half of V16 and half of V17 seem dedicated to the Aux level preamp.
I am assuming that the high voltage side is good (but maybe I shouldn't).
I'm confused around the heater pins and voltages around V12 (left side) and V15 (right side)
Looking at the schematic for these tubes there is no heater voltage given (I believe 12AX7s can run 6 or 12v depending on series or parralel).
V15 and V12 show pin 9 to ground and pin 4/5. I assume this is because they are notsplit to separate channels.
Readings are as follows- both tubes have Pins 4&5 jumped together.:
V15 pin 4/5 0 volts
pin 9 0 volts
V12 pin 4/5 0 volts
pin 9 0 volts
Does this mean for these heater voltages I cannot just gound my meter to the chasis, but must run it across pins 9 and 4/5?
Clearly both tubes are getting warm, though I am not sure the voltages are correct.
They pretty well match readings on each pin of the two tubes, and I get a nice loud crackel on each channel as I move my probes from pin-to-pin (this make me believe its a problem before th 7591s).
On V16 and V17 here are the readings, again the schematic does not give any voltages for pins 4 and 5.
V-17
Pins
1 182v (should be 167 - out of spec resistor)
2
3 1.05v
4 -24.6v (?)
5 -11.5v (?)
6 180v (bad resistor)
7
8 1.07
V16
Pins
1 190v (should be 167 - out of spec resistor)
2
3 1.0v
4
5 -11.56v (?)
6 192.7v (another bad resistor)
7
8 .972v
If pins 4 and 5 are heater pins, how do you get negative voltages there?
Cleaned and measured voltages out of both phase pots, they look similar.
Any thoughts would help.
Hoping to get at least the amp portion done so I can deliver this Christmas!
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