I have an Audio Research SP10. It was working fine. I took about the power connector on the preamp to fit resistors to the cables to drain off high frequency interference. When I put it back together however, only half of the tubes powered up.
Attached is the schematic, see page 5 for the power umbilical pinout.
The tube pairs that are not working are: 3,4, 5,6, 11,12. All show no voltes (<100mv) across the tubes.
The tube heater common lines return to one of two pads, which then return to the power supply using one of two wires. As stated in the manual, one wire is the return for 1,2, 5,6, and 9,10, while the other handles 3,4, 7,8, 11,12. However that is not how the pads are wired in practice. The actual wiring is 5,6, 7,8, 11,12, and 1,2, 3,4, 9,10.
If I connect my probes between one of the non-working heater connections to the opposite pad, I get ~14v (as opposed to 12.6 for the working pairs).
Swapping the power wire for 1,2 with the wire for 5,6 caused 1,2 to stop working, but 3,4 and 5,6 started working, leaving only 1,2 and 9,10 off.
I'm utterly confused, since I didn't actually change any wiring. All pins have connectivity to the power supply. It feels like it must be some kind of grounding/return issue, but I can't think what.
EDIT: I'm sorry, manual didn't get uploaded first try, it's attached now!
Attached is the schematic, see page 5 for the power umbilical pinout.
The tube pairs that are not working are: 3,4, 5,6, 11,12. All show no voltes (<100mv) across the tubes.
The tube heater common lines return to one of two pads, which then return to the power supply using one of two wires. As stated in the manual, one wire is the return for 1,2, 5,6, and 9,10, while the other handles 3,4, 7,8, 11,12. However that is not how the pads are wired in practice. The actual wiring is 5,6, 7,8, 11,12, and 1,2, 3,4, 9,10.
If I connect my probes between one of the non-working heater connections to the opposite pad, I get ~14v (as opposed to 12.6 for the working pairs).
Swapping the power wire for 1,2 with the wire for 5,6 caused 1,2 to stop working, but 3,4 and 5,6 started working, leaving only 1,2 and 9,10 off.
I'm utterly confused, since I didn't actually change any wiring. All pins have connectivity to the power supply. It feels like it must be some kind of grounding/return issue, but I can't think what.
EDIT: I'm sorry, manual didn't get uploaded first try, it's attached now!
Last edited:
Gah, sorry. Tried to upload schematic and failed. See original post, schematics are now attached.
Absolutely, I wont deny that. I just can't figure out what I broke.
Absolutely, I wont deny that. I just can't figure out what I broke.
Start ohming out all of the filament connections.
Verify all connections to each node in the filament supplies from the tube socket pins.
Verify all connections to each node in the filament supplies from the tube socket pins.
Every reading I took started high and fell, slowing as it got lower. I'm reporting the values settled near.
Measuring from the tube to the corresponding pad on the power supply, I got <2 ohms, and <20 ohms on other pads with the same common.
Measuring from return to power supply common I got < 6 ohms for all wires.
Measuring from the tube to the corresponding pad on the power supply, I got <2 ohms, and <20 ohms on other pads with the same common.
Measuring from return to power supply common I got < 6 ohms for all wires.
For each filament regulator circuit:
Measure directly from the regulator IC output pin to the correct tube socket pin.
Measure directly from the regulator IC common pin to the correct tube socket pin.
Make sure you include all parts of each entire loop.
If you have verified all points for the proper continuity, then look for ohmic shorts across each series filament.
This is much less likely.
Measure directly from the regulator IC output pin to the correct tube socket pin.
Measure directly from the regulator IC common pin to the correct tube socket pin.
Make sure you include all parts of each entire loop.
If you have verified all points for the proper continuity, then look for ohmic shorts across each series filament.
This is much less likely.
That’s what I did. The only thing between me and the regulator was a 7.5 ohm resistor when I redid the measurements from behind this resistor, the values were the same, just 7.5 ohms higher.
I could believe my shoddy plug job could have shorts. I don’t know how to test for them, because I wires connect at different points and I don’t know what readings to trust.
My guess is you extracted the power plug pins and did not put back to its actual position.
I have removed the modifications, and I’ve check and rechecked and over checked. I’ve been going around in circles.
That does mean I’ve plugged and plugged these wires many times, some are worn. If a wire looses 50% of its strand connections, I would think that would result in partial power failure, not complete.
That does mean I’ve plugged and plugged these wires many times, some are worn. If a wire looses 50% of its strand connections, I would think that would result in partial power failure, not complete.
You have a perfectly good working power amp.
You ****** up the mains cable. The amp doesn't work correct anymore.
You think there's something wrong with the amp?
What is this, logic 2.0?
Jan
You ****** up the mains cable. The amp doesn't work correct anymore.
You think there's something wrong with the amp?
What is this, logic 2.0?
Jan
I saw a sign in a garage once ...
"These are our hourly rates:
If we did the work, £20.
If you did the work, £40"
"These are our hourly rates:
If we did the work, £20.
If you did the work, £40"
Another free advice (amazed that nobody mentioned it): get another, non-improved mains cord and see it it works OK.
(I won't comment on the utter BS to 'add resistors to drain off RF - you can't make this stuff up!)
Jan
(I won't comment on the utter BS to 'add resistors to drain off RF - you can't make this stuff up!)
Jan
Those are CPC connectors and removing the pins requires a special tool. They’re crimped and not soldered.