replacement transformer installed resistance check problems [resolved]

[tipatina]

8-OL
22-OL
all others ok, build photos attached

[Paul Birkeland]

8-OL
22-OL

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.

22 can be brought to zero by tightening your power transformer mounting screws.

[tipatina]

I will check all the black wires again and reflow.
Dont understand how 22 has direct contact with ground since there is a black plastic washer between the metal flange and the chasis. Thanks

[Paul Birkeland]

I will check all the black wires again and reflow.
Dont understand how 22 has direct contact with ground since there is a black plastic washer between the metal flange and the chasis. Thanks

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.

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.

[tipatina]

I have checked wiring by going through the manual sequentially and reflowed all black (and most other) joints.
22-12 U OL
22-chasis-no resistance
8-12U OL
8-chasis-no resistance
12U and chasis OL
12U-3U no resistance

[tipatina]

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. 

[Paul Birkeland]

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. 

[tipatina]

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...

[tipatina]

Still getting great sound with no noise, thx Paul!
Couple of questions:
What is the purpose of the wire wound resistors (as opposed to the usual type)?
Was gonna try to tube roll in the future, any types to avoid?

[Paul Birkeland]

What is the purpose of the wire wound resistors (as opposed to the usual type)?

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.

Was gonna try to tube roll in the future, any types to avoid?

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]

Hello, Re;above
It worked for a while but the cracking/static noise is back. Id like to pursue sending it for flat rate repair. Im at the end of my abilities and would like to get the kit operational/figure out my mistake(s)
Pleas let me know how to proceed. Thanks

[Paul Birkeland]

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?