Help, my left channel has developed hum [resolved]

thunderfrenchie · 2752

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Offline thunderfrenchie

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on: November 02, 2018, 05:13:18 AM
Hi, total noob here. I assembled my Kaiju with zero problems, every test checked along the way. It worked perfectly at first. I was able to adjust the hum pots and the amp was 'quiet' at idle with no music. I left it on for 72 hours in a row to burn it in. It then developed a low level hum in the left/black channel. The pot is now out of whack. Turning it all the way to the left reduces the noise but meter still reads .123.

Some measurements.
Right (OK side):
53U: 57.6
IA: 504
OA: 297
32U: 174.2

Left:
65U: 23.1 [this seems a problem]
IA: 504
OA: 298
46U 174.0

Thoughts?

Thanks,

John
« Last Edit: November 04, 2018, 08:54:53 AM by Paul Birkeland »


Offline Paul Birkeland

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Reply #1 on: November 02, 2018, 06:45:18 AM
Can you post some photos of your build?

Is the 100uF axial capacitor oriented correctly on that side?  Are any of the legs of the hum pot touching the chassis?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Doc B.

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Reply #2 on: November 02, 2018, 01:44:11 PM
Also swap the 300Bs and see if the hum follows the tube and/or if you get different voltage readings

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

Offline Paul Birkeland

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Reply #3 on: November 02, 2018, 05:23:49 PM
Your pictures are teeny tiny, I can't see anything in there.  If the forum is bugging you about file size, you can put a couple on a post, then post the rest separately.   

The hum pot is the 10 ohm one with the 22 ohm resistors attached to it. 

-PB

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline thunderfrenchie

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Reply #4 on: November 03, 2018, 03:38:50 AM
OK, larger...


Offline Paul Birkeland

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Reply #5 on: November 03, 2018, 06:18:07 AM
10U doesn't look to be soldered.

What is the AC voltage between A1 and A4 with a 300B in the socket and the amp running?  (A pair of clip leads would be helpful to measure this)

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline thunderfrenchie

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Reply #6 on: November 03, 2018, 06:42:27 AM
On the affected side (actually B1 and B4) I'm getting 330v dc

On the unaffected side (A1/A4) I'm getting around 280.

Black lead was on the 1.


Offline thunderfrenchie

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Reply #7 on: November 03, 2018, 06:44:05 AM
Also desoldered 10U and 14-23U


Offline thunderfrenchie

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Reply #8 on: November 03, 2018, 06:47:24 AM
That's REsoldered


Offline Paul Birkeland

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Reply #9 on: November 03, 2018, 07:08:45 AM
Sorry, I meant to ask what the AC voltage is between B1 and B4, not A1 and A4. 

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline thunderfrenchie

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Reply #10 on: November 03, 2018, 07:18:45 AM
AC I get 0


Offline Paul Birkeland

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Reply #11 on: November 03, 2018, 07:20:37 AM
Be sure your meter is set to a very low range.  You can compare your values between B1/B4 and C1/C4.  I suspect you will find a difference between sides. 

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline thunderfrenchie

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Reply #12 on: November 03, 2018, 07:21:05 AM
In case it matters also notice I get a little transformer hum from PT9. All measurements with no speakers attached btw


Offline thunderfrenchie

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Reply #13 on: November 03, 2018, 07:29:31 AM
C1/C4 yields 4.92 V AC

Now getting about .003 v AC on B1/B4

My meter, Sperry DM-6250 is qutorange. Happy to buy whatever meter you recommend.


Offline thunderfrenchie

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Reply #14 on: November 03, 2018, 07:31:57 AM
B1/B4 now stabilizing around .007 v AC


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