Hello,
I'm new but I'm going to jump right in.
I have a H-K TA5000x that I’ve been slowing restoring. The only schematic I have found is in two parts, Part 1 has the right side cut off and Part 2 has the left side cutoff, which results in the phono preamp being shown on Part 1 and the power supply on Part 2. Unfortunately, while very similar, Parts 1 and 2 are not same version of the schematic. The specific problem I have is the phono preamp plate voltage feed from the power supply (Part 2) is listed at 190vdc, which I have measured to be 188vdc. This same supply is listed on at the phono preamp in Part 1 as 270vdc, which is then reduce to 170vdc and 120vdc before going to the plates. I have measured the plate voltages to be about 120vdc and 78vdc; this seems very low as these tubes are rated up to 300vdc plate voltage. It plays okay but I think it could be better. I definitely have much lower volume from phono then the radio or Aux and this receiver seems to have a little bit of low volume in general for the watt rating. I’m currently running reissue russian TungSol 12AX7/ECC803S gold pins and I have some used mismatched vintage tubes that work but strength is unknown; there are differences but in general new and old tubes work the same. Should I adjust the power supply voltage to the plates by changing resistor values and if I do what tube performance parameter should I being trying to achieve?
TA-5000X Radio Harman Kardon; New York, build 1965 ??, 9 pic
Thanks for reading and any input is welcome.
Bill
I'm new but I'm going to jump right in.
I have a H-K TA5000x that I’ve been slowing restoring. The only schematic I have found is in two parts, Part 1 has the right side cut off and Part 2 has the left side cutoff, which results in the phono preamp being shown on Part 1 and the power supply on Part 2. Unfortunately, while very similar, Parts 1 and 2 are not same version of the schematic. The specific problem I have is the phono preamp plate voltage feed from the power supply (Part 2) is listed at 190vdc, which I have measured to be 188vdc. This same supply is listed on at the phono preamp in Part 1 as 270vdc, which is then reduce to 170vdc and 120vdc before going to the plates. I have measured the plate voltages to be about 120vdc and 78vdc; this seems very low as these tubes are rated up to 300vdc plate voltage. It plays okay but I think it could be better. I definitely have much lower volume from phono then the radio or Aux and this receiver seems to have a little bit of low volume in general for the watt rating. I’m currently running reissue russian TungSol 12AX7/ECC803S gold pins and I have some used mismatched vintage tubes that work but strength is unknown; there are differences but in general new and old tubes work the same. Should I adjust the power supply voltage to the plates by changing resistor values and if I do what tube performance parameter should I being trying to achieve?
TA-5000X Radio Harman Kardon; New York, build 1965 ??, 9 pic
Thanks for reading and any input is welcome.
Bill
It is perfectly normal to have around 100V on the plate , read the datasheet and look at some schematics . That max Va rating is not for common cathode stage , the most used stage for amplification .
Probably that's how they made it , lower volume from RIAA is not unusual in many amplifiers ...
Probably that's how they made it , lower volume from RIAA is not unusual in many amplifiers ...
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Check the values of all of the plate and dropping resistors. If those are ok,
then it's likely to be the tubes.
then it's likely to be the tubes.
Funny you should bring up the RIAA. I lose Channel B when in RIAA but both channels work in NARTB (it has a switch). That was what I was working on when I discovered the schematic inconsistency regarding plate voltages. In regards to the phono tubes and associated circuits, to date I have verified all resistor values, changed the tubes, checked the switch, and replaced all the poly/electrolytic caps. Although I can't see why it would cause this problem, the plate voltages are the only thing that doesn't check out so far.
"I lose Channel B when in RIAA but both channels work in NARTB (it has a switch)."
Could be the EQ switch if the NARTB works, but check the selector switch just in case.
Hard to see how that happens, though. Maybe an intermittent loose connection on one of the switches.
Could be the EQ switch if the NARTB works, but check the selector switch just in case.
Hard to see how that happens, though. Maybe an intermittent loose connection on one of the switches.
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