BP1 loud buzz in both channels, resistance check is off

Thijs · 1809

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Offline Thijs

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Hi all,

My dad was enjoying his original BeePre for about a year until it started developing some strange noises. Music sounding way softer in one channel, or sounding muffled, crackling sounds and so on. He doesn't remember if it followed the tube after swapping, but he did put in a new set. After a while it somehow seemed to operate just fine until a few hours into operation and it displayed symptoms again. Right now there's a loud buzz coming from both channels right after startup and the amp is unusable.

I had told him to redo the resistance measurements and that I would help him post it on the forum. Quite a few turned out to be out of whack, some more than others. Any suggestions as to which issues these readings would point to? Is it as simple as reflowing joints or is there more at play?

I'm copy pasting his data below.
If there more info needed, please let me know.

T4   9,1   300B   
T19   12,2   300B
T28   0,1       
T32   0,5       
T37   0,2       
T39   70 and rising
T42   0,4 Ω
T49   4 Ω

A1 increasing resistance, won't drop to 4Ω
B4 increasing resistance, won't drop to 4Ω

A1 and B4 won't drop at all.

Many thanks in advance to any and all who can help him out. Would be very much appreciated.

Cheers!

Thijs



Offline Paul Birkeland

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Reply #1 on: January 04, 2023, 10:43:09 AM
Take the two boards off that mount to the power transformers and look at the two 10,000uF caps underneath.  What is the condition of those caps?  Are the silver tops flat or bulging?

What are the DC voltages at POS-IN and POS-OUT on each board?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Thijs

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Reply #2 on: January 25, 2023, 10:29:59 AM
Take the two boards off that mount to the power transformers and look at the two 10,000uF caps underneath.  What is the condition of those caps?  Are the silver tops flat or bulging?

What are the DC voltages at POS-IN and POS-OUT on each board?

Thanks Paul! Sorry for the long wait. Today my dad finally had the time to take a look.

The electrolytics look to be in tip-top shape. No bulging.

DC at board are as follows:

#1
POS IN - 12.85V
POS OUT - 9.91V

#2
POS IN - 12.71V
POS OUT - 9.86V

Thanks so much in advance!

Cheers,
Thijs



Offline Paul Birkeland

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Reply #3 on: January 25, 2023, 12:43:13 PM
How about on that same board the three other labeled voltages that go to each EL84 socket?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Thijs

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Reply #4 on: February 07, 2023, 12:54:14 AM
Thank you so much!

He decided to just plug it in the system and see. It’s been running great for a few days so he’s really scratching his head now. Well, we’ll see for how long it functions correctly. Sounding great atm!

 Cheers,
Thijs



Offline Thijs

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Reply #5 on: February 22, 2023, 02:32:07 AM
Hello again!

The BeePre worked fine again, for a little while but started making noises in the end.
We flowed all solder connections and it's quiet again. We'll see for how long, I'll post here if noise shows up again.

He did get a chance to measure the EL84 voltages coming from the boards.
Maybe this tells you something:

C 144,3V
C 4,28V
C 0,01V

D 143,8V
D 4,29V
D 0,014V

Thanks so much in advance!

Cheers,
Thijs



Offline Paul Birkeland

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Reply #6 on: February 22, 2023, 04:50:20 AM
Those voltages look good.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Thijs

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Reply #7 on: February 22, 2023, 07:24:20 AM
Thanks for confirming, Paul!