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August 10, 2020, 01:56:39 AM

Author Topic: Speedball voltage, B+ low on the big board [resolved]  (Read 98 times)

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Offline rat3hat

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Speedball voltage, B+ low on the big board [resolved]
« on: August 01, 2020, 08:19:20 AM »
Hi. I have one voltage check outside of the target range  for the big board:

Targets from the manual:
OA  75-100V
OB  75-100V
G    0V
B+  170-195V

My voltage readings:
OA    90.7V
OB    77.4V
G      0V
B+    114.5V

B+ should be higher. It is probably the usual suspects (crappy joint somewhere), but I thought I'd ask where was likely.

Best,
Chris
« Last Edit: August 02, 2020, 09:28:12 AM by Paul Birkeland »

Offline Paul Birkeland

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Re: Speedball voltage, B+ low on the big board
« Reply #1 on: August 01, 2020, 08:21:19 AM »
B+ connects back to terminals 2 and 4, as well as IA and IB on the big PC board.

How are the voltages on the small board?  Does B+ pop back up if you run the amp without the 6080?
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline rat3hat

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Re: Speedball voltage, B+ low on the big board
« Reply #2 on: August 01, 2020, 08:38:34 AM »
Small board Measurements
OA 75V
IA 120V
B-A/B 0V
IB 120V
OB 75V

It did pass checks after mounting small board earlier

Large board without 6080 B+ is 225V


Offline rat3hat

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Re: Speedball voltage, B+ low on the big board
« Reply #3 on: August 01, 2020, 08:41:53 AM »
Also, perhaps the heat sink closer to the 6080 is hotter than the heat sink closer to the 12au7 socket. Not sure if this means anything.

Offline Paul Birkeland

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Re: Speedball voltage, B+ low on the big board
« Reply #4 on: August 01, 2020, 10:13:26 AM »
Are the TIP50 transistors properly mounted?  Be sure B+ to the big board is not connected to terminal 2 or 4 by accident.

If all else fails, you can post photos of the build and we might be able to spot something.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline rat3hat

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Re: Speedball voltage, B+ low on the big board
« Reply #5 on: August 01, 2020, 11:24:10 PM »
OK. My 15 y/o was sharp enough to point out that I was missing an LED on the big board at D2....  :o >:(

Once I put that in, it all seems to be measuring in range. On the big board OA, OB are measuring ~110V each. That is around 10% above the high - I am assuming that is OK - or is that just too high?

« Last Edit: August 02, 2020, 04:00:00 AM by rat3hat »

Offline Paul Birkeland

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Re: Speedball voltage, B+ low on the big board
« Reply #6 on: August 02, 2020, 06:13:52 AM »
Yes, that's OK.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline rat3hat

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Re: Speedball voltage, B+ low on the big board
« Reply #7 on: August 02, 2020, 06:34:50 AM »
Thank you, again - for being a patient and excellent guide. Great kit.