trying to fix broken reduction part 2

lesouthern · 3024

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Offline lesouthern

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on: April 02, 2023, 11:48:18 AM
Hi-

Continuation of this topic that I resolved:
https://forum.bottlehead.com/index.php?topic=14615.0

From the previous posting, I installed a new resistor, now all the resistances and voltage readings are correct according to the manual.

Now there is no sound coming from the left (black) channel. Have switched cables, tried a different turntable, consistently no sound.

Is it possible I have a bad tube? How do I check that?

thanks

Larry Southern



Offline Paul Birkeland

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Reply #1 on: April 02, 2023, 02:29:56 PM
Very frequently an issue like that can be solder that drips out of the center pin of an RCA jack and bridges the center pin to the shell, which will short out a channel. 

If the voltages are all correct, the tubes are working.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline lesouthern

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Reply #2 on: April 03, 2023, 06:46:46 AM
Thanks Paul.

Tried to clean up these areas the best I could. I'm still getting a very weak signal from the left (black) channel

See attached pictures. I'm not seeing solder to remove from base anymore. And the side that works looks similar. Do I need to remove more?

If so could you show pictures of what looks correct, and tools you would recommend to scrape away and remove solder in areas like this?

thanks

Larry Southern



Offline Paul Birkeland

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Reply #3 on: April 03, 2023, 06:55:58 AM
In the first photo you posted, the wire going through pin 5 on the tube socket is bent sideways.  If that touches pin 6, you'll get smoke.  I would trim that ASAP.

If you have solder shorting an RCA jack, you will not be able to measure the 47K or 475K resistor that spans the jack with your meter (it will measure closer to 0 ohms).  So you can put one probe on the center pin and the other probe on the shell and check those resistances.

I also see plenty of leads that aren't bent up and around terminals, and lots of solder joints that need more heat to flow out properly.
« Last Edit: April 03, 2023, 07:00:19 AM by Paul Birkeland »

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline lesouthern

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Reply #4 on: April 03, 2023, 07:40:00 AM
Trimmed up the wires around the tube socket
The resistance on the 220 olm (red red brown gold) measures about 218. The 47.5k measures exactly that, when I measure them from the jack
Are there some other specific resistances I can measure to isolate my issue of weak left signal?
thank you



Offline Paul Birkeland

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Reply #5 on: April 03, 2023, 07:44:18 AM
How about the output jacks?

If the 220 ohm resistors are bad, your DC voltages will not be correct, so don't worry about those.


Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline lesouthern

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Reply #6 on: April 03, 2023, 07:59:13 AM
Trying to understand- there are no resistors as you can see on the output

What resistances should I be measuring?

Are there specific places I should be confirming connections?

I did trim the output, you can see from the photos I posted.



Offline Paul Birkeland

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Reply #7 on: April 03, 2023, 08:08:03 AM
Measure the DC resistance across the output jacks.  It should be about 475K.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Doc B.

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Reply #8 on: April 03, 2023, 08:52:23 AM
If the preamp used to work and went dead I'm going to suggest reflowing pretty much every joint. If the left channel works but is weak the issue could be a bad connection in the RIAA components on that side.

Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.