sound city 50R problem

[chief mushroom cloud]

still there...w/either transformer (other Partridge is known tested and good by MM)

[JazzGuitarGimp]

Are the output tubes matched? Dissipating the same amount if power at idle?

[martin manning]

I'm still not surprised that there is some ripple on the B+, which the OT will cancel- it if it is the same on both sides. So JGG has a good idea! Measure the DC resistance of each half of the OT, then measure the DC voltage across each side with the standby on, and calculate current.

[chief mushroom cloud]

ok, OT:
DCR across p-p is 90ohms.
Almost a perfect 45ohms per side.
No DCR short measured to secondaries.
most definitely 3.4k determined from winding ratio measurement.
Tubes are brand new EH only about 5mA apart...the Svet's that were in there are matched even better.
Voltage across primaries is same ~460V...maybe about 1V difference
bias is ~-41V on both pins 5....no bias ripple present on pins 5

Like I said, I subbed in known good OTs (A470 and an original, tested Partridge)......ripple still there at output

I'm done w/ amps. I'm buttoning it up and giving it back to owner. This cost me too much in time and extra parts...hrs of my life I will never get back or get paid for...fuck this shit.

Thanks to all for the help, tho....good bunch here.

[chief mushroom cloud]

I'm still not surprised that there is some ripple on the B+, which the OT will cancel- it if it is the same on both sides. So JGG has a good idea! Measure the DC resistance of each half of the OT, then measure the DC voltage across each side with the standby on, and calculate current.

That's how I measure bias

[Firestorm]

Phase inverter? Supply cap and grounds (especially the grounded grid side).

[sliberty]

Even if you solve this one, the amp will still hum. SC's hum, loudly, period. I've had half a dozen of the 50's on my bench for everything from minor maintenance to mid-level surgery. They all hum. I believe it is caused by the shitty wire routing and overall workmanship. They may have some things in common with a HiWatt, but at the end of the day, a SC is no HiWatt. And I have never turned up any Internet posts that claim to have quieted them down - they all just complain about how much they hum. Shame.

Good luck. I hope the OT is not bad since I doubt the hum will go away even after a rewind.

[JazzGuitarGimp]

What is the distance from the OT to the PT? And is the long side of the PT facing the OT, or the short side?

[overtone]

Even if you solve this one, the amp will still hum. SC's hum, loudly, period. I've had half a dozen of the 50's on my bench for everything from minor maintenance to mid-level surgery. They all hum. I believe it is caused by the shitty wire routing and overall workmanship. They may have some things in common with a HiWatt, but at the end of the day, a SC is no HiWatt. And I have never turned up any Internet posts that claim to have quieted them down - they all just complain about how much they hum. Shame.

Good luck. I hope the OT is not bad since I doubt the hum will go away even after a rewind.

Back in the eighties in London they were known as Sound Sh*tty.
Life is too short.

[martin manning]

I was thinking magnetic coupling too, but then the OT's that were sub'ed in probably weren't close to the PT.

[selloutrr]

Even if you solve this one, the amp will still hum. SC's hum, loudly, period. I've had half a dozen of the 50's on my bench for everything from minor maintenance to mid-level surgery. They all hum. I believe it is caused by the shitty wire routing and overall workmanship. They may have some things in common with a HiWatt, but at the end of the day, a SC is no HiWatt. And I have never turned up any Internet posts that claim to have quieted them down - they all just complain about how much they hum. Shame.

Good luck. I hope the OT is not bad since I doubt the hum will go away even after a rewind.

Really? I have 1-100, 2- 120R, 1- 120, 1-50, 1-50r, and a concord. As well as several classic hiwatts. The SC are silent studio useable amps. Only the SC 100 is close to a hiwatt 103. If anyone is wondering the R = reverb the tank is a short spring and pretty sucky. If you love the tradition fender or Ampeg verb but great if you are using the amps for heavy layering.


As for fixing the amp. Can I assume you are testing the amp on an isolated circuit?

[Cameron]

ok, OT:
DCR across p-p is 90ohms.
Almost a perfect 45ohms per side.
No DCR short measured to secondaries.
most definitely 3.4k determined from winding ratio measurement.
Tubes are brand new EH only about 5mA apart...the Svet's that were in there are matched even better.
Voltage across primaries is same ~460V...maybe about 1V difference
bias is ~-41V on both pins 5....no bias ripple present on pins 5

Like I said, I subbed in known good OTs (A470 and an original, tested Partridge)......ripple still there at output

I'm done w/ amps. I'm buttoning it up and giving it back to owner. This cost me too much in time and extra parts...hrs of my life I will never get back or get paid for...fuck this shit.

Thanks to all for the help, tho....good bunch here.

Did you look at the heater supply and grounds?

[chief mushroom cloud]

Really? I have 1-100, 2- 120R, 1- 120, 1-50, 1-50r, and a concord. As well as several classic hiwatts. The SC are silent studio useable amps. Only the SC 100 is close to a hiwatt 103. If anyone is wondering the R = reverb the tank is a short spring and pretty sucky. If you love the tradition fender or Ampeg verb but great if you are using the amps for heavy layering.


As for fixing the amp. Can I assume you are testing the amp on an isolated circuit?

yer in so cal...cmon over...i'm ready to take a sledge hammer to it
1070 Hastings Ranch Dr Pasadena
get the fuck over here...I have beer
ENLIGHTEN ME!

oh, and yes..isolated circuit....PI coupling caps are shunted...nothing coming in from pre or reverb circuits

[chief mushroom cloud]

Did you look at the heater supply and grounds?

That's next and last thing....unless I can get selloutrr over here to show me god

[Cameron]

Really? I have 1-100, 2- 120R, 1- 120, 1-50, 1-50r, and a concord. As well as several classic hiwatts. The SC are silent studio useable amps. Only the SC 100 is close to a hiwatt 103. If anyone is wondering the R = reverb the tank is a short spring and pretty sucky. If you love the tradition fender or Ampeg verb but great if you are using the amps for heavy layering.


As for fixing the amp. Can I assume you are testing the amp on an isolated circuit?

yer in so cal...cmon over...i'm ready to take a sledge hammer to it
1070 Hastings Ranch Dr Pasadena
get the fuck over here...I have beer
ENLIGHTEN ME!

oh, and yes..isolated circuit....PI coupling caps are shunted...nothing coming in from pre or reverb circuits

Im in just down the 5 in sun valley if you want to bring it over.