replacement transformer installed resistance check problems [resolved]
- Thread starter tipatina
- Start date
8 is connected by hardware directly to the chassis plate. If this isn't 0, then terminal 3 probably isn't zero either, and you'd have a loose black wire somewhere. I would triple check that you have OL there and not at 3, as those results are improbable.tipatina said:
22 can be brought to zero by tightening your power transformer mounting screws.
If all the power transformer screws are tight they will all make contact with the metal of the transformer cover and pick up the earth reference for the one screw that is tied to the safety ground.tipatina said:
Whatever you do, do not try to force this connection by adding extra wires or removing hardware. 22 can be OL and the amp will function just fine without any safety concerns if necessary.
OK, noticed that the resistor 12 -13 L was adherent he terminal strip near 12L/U and a wire so I heated 12L and backed it out slightly and then resistance checked on all. Passes voltage although 8 had drifting voltage below 1VDC. LEDS and tubes lit up. Music sounds fine but cracking when touching base plate and level hum. Hum and cracking disappear with volume at lowest or highest positions-silent then.
DO NOT turn on an amp that doesn't pass its resistance checks. DO NOT listen to an amp that doesn't pass its voltage checks. An amp that doesn't pass these checks isn't working and can destroy your headphones or possibly shock you.
You cannot turn this amp on until the resistance value at terminal 8 is correct.
You cannot turn this amp on until the resistance value at terminal 3 is correct.
Terminal 3 is the anchoring point of the power supply to the chassis. Your power supply is not referenced to earth properly, and this is likely from a loose black wire. We find very frequently that one of the black wires at the headphone jack will be loose and cause this problem.
Please track down the loose/unsoldered black wire and verify that 3 and 8 (and the outside metal of the RCA jacks) all show 0 ohms of resistance with respect to terminal 12.
You cannot turn this amp on until the resistance value at terminal 8 is correct.
You cannot turn this amp on until the resistance value at terminal 3 is correct.
Terminal 3 is the anchoring point of the power supply to the chassis. Your power supply is not referenced to earth properly, and this is likely from a loose black wire. We find very frequently that one of the black wires at the headphone jack will be loose and cause this problem.
Please track down the loose/unsoldered black wire and verify that 3 and 8 (and the outside metal of the RCA jacks) all show 0 ohms of resistance with respect to terminal 12.
OK, thx. Backed up and went back to work.
Reflowed some more black wires and used a solder removal gun to get rid of excess from the previous refl;ows. Lightly sanded the bell around at transformer screw holes and retightened, sanded the plate surface around and tightened the screw holding 8 and the ground tab in the back. Reflowed the bus wire at the IEC, safety ground lug and 16L
All resistance checks passed/all voltage checks passed.
Hooked up to power, LEDs and tubes light up.
Music-no more scratching/popping, silent volume adjustment and music sounds fine. No noise between tracks.
Think it may be done now...
Reflowed some more black wires and used a solder removal gun to get rid of excess from the previous refl;ows. Lightly sanded the bell around at transformer screw holes and retightened, sanded the plate surface around and tightened the screw holding 8 and the ground tab in the back. Reflowed the bus wire at the IEC, safety ground lug and 16L
All resistance checks passed/all voltage checks passed.
Hooked up to power, LEDs and tubes light up.
Music-no more scratching/popping, silent volume adjustment and music sounds fine. No noise between tracks.
Think it may be done now...
When you need a 5+ watt resistor, that's generally the most available option. You could get four 540 Ohm 3W metal film resistors and parallel them if you wanted to, but they probably wouldn't reach across between the 6 lug strips. Ultimately the power supply dropping resistors aren't exactly in the signal path, so durability and thermal capability are most important. For the 3K/10W plate loads, those are simply place holders for the larger Speedball PC board.tipatina said:
A lot of people like the 5998, but they have gotten insanely expensive and they don't offer substantially better performance (the output impedance drops slightly, but it's only by about 10-20 ohms). Also don't get sucked in by the people on the internet who say a 12AT7, 12AX7 and 12AU7 are interchangeable.tipatina said:
If the amp worked for a while and then started crackling, I would suggest getting a wooden chopstick and poking around the amp while it's running with a pair of cheap headphones plugged in so you can hear if there's a specific joint or region of the circuit causing the issue. It would also be a good idea to describe the noise, is it totally random or periodic?
OK, I got prepared for the chopstick test and think I found the issue. Before starting with the chopstick I had the cheap headphones hooked up and was listening and tapping my fingers on the top of the facplate and getting the scratchy/static noise. I noticed that the 9 pin tube could be pushed further in, when I did I noticed that the tube socket/ring was loose and created lost of noise with moving but could be silent in just the right position. . I turned everything off and tightened the socket and back on-no noise and good sound on the HD 650. I guess the loose socket was the culprit-possibly interfering with a solid grounding.
That may well be a loose connection around the 9 pin socket as well. If the noise comes back, I'd start poking around in that area. (Also double check where the black wires meet on the headphone jack, that has been a persistent place over the years where soldering is an issue, and one black wire not captured well by solder will cause all sorts of problems)
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