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November 28, 2022, 11:12:45 PM

Author Topic: Low Kreg Both Sides [resolved]  (Read 73 times)

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Offline AllenS

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Low Kreg Both Sides [resolved]
« on: November 22, 2022, 02:19:02 PM »
I have the following readings (rightmost number) resulting in low kreg on both sides. Been reading through a few threads and focused on the center board. Cleaned a couple of not so shiny solders but nothing bad was standing out or other shoddy jobs on the boards or terminals. I am deducing this is low heater voltage which I picked up from one of the threads but that is pure speculation speculation since I am able to adjust bias to 145v on both sides. All leds and tubes are lit and validated that IA IB OA OB are within tolerances.

Thanks for any insight where to check.

1   39.7KΩ 39.9k
2   0Ω
3   0Ω
4   0Ω
5   39.7KΩ 39.9k
6   0Ω
7   0Ω
8   0Ω
9   0Ω
10   0Ω
11   0Ω
12   *
13   0Ω
14   *
15   210Ω-220Ω 208
16   0Ω
17   *
18   0Ω
19   * 212k
20 *
21 0Ω
22 * 211K
23 0Ω
24 *
25 210Ω-220Ω 207.5
26 0Ω
27 *
28 0Ω
29 *
30 *



+275vDC on the Power Supply Board    275V 279.9
+6.3vDC on the Power Supply Board    55-65V 58.9
-6.3vDC on the Power Supply Board    50-60V 52.9
IA on the A side C4S Board    275V 275.7
IA on the B side C4S Board    275V 275.5
Breg Regulator Board (both sides)    220V a 217.4 b 215.8
-reg Regulator Board (both sides)    0V
Kreg Regulator Board (both sides)    8-12V a 5.4 b 4.98
« Last Edit: November 23, 2022, 11:28:20 AM by Paul Birkeland »

Offline Paul Birkeland

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Re: Low Kreg Both Sides
« Reply #1 on: November 22, 2022, 03:02:17 PM »
I wouldn't worry about seeing 5V at the Kreg terminals, especially if you can dial in the 6C45P plate voltage as expected.  Your heater voltage is 6V, so there's nothing to address there.

You may find that the 12AU7 needs a few days of running in to awaken and reach full emission, and that these Kreg voltages may creep up a bit as that particular tube gets some more run time.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline AllenS

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Re: Low Kreg Both Sides
« Reply #2 on: November 22, 2022, 04:45:30 PM »
Ok. I am not getting in sound out unfortunately.  I have tried two input devices on 1 and 2 and tried both output jacks.

There is something in the ears however (dead quiet and no hum, wow!) as I can hear a near by wifi click.

Offline Paul Birkeland

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Re: Low Kreg Both Sides
« Reply #3 on: November 23, 2022, 05:41:37 AM »
If you change the coarse/fine level switches, you should hear a little high frequency ringing as the internals of the tubes vibrate, are you hearing that?

I would recommend posting some build photos.  Also if you don't have a meter with a 2V AC scale, I'd go buy one and I can help you trace signal through the amp (Harbor Freight has a very decent meter for about $25 that can do this).

-PB
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline AllenS

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Re: Low Kreg Both Sides
« Reply #4 on: November 23, 2022, 06:27:07 AM »
No, not hearing a ringing when switching the settings. There is a faint white noise so something electrical is reaching I think.

AC meter readings can be handled by my Klein MM1000 I would expect:
ac Voltage Measurement
range resolution accuracy
400mV ˜
 400V 0.1mV ˜
 0.1V ± (0.75% + 5 digits) 40Hz ˜ 400Hz
1000V 1V ± (1.0% + 8 digits) 40Hz ˜ 400Hz


When you say trace the signal, I am assuming from RCA in through to the switches and then to the output jack posts... Correct?

Photos attached. Let me know if you need some zooms.

Thanks as I have retraced most wiring build steps, shorts with 25x work lamp and looked at my solder joints over. I have also measured voltages out of the transistors (tracing the kreg voltage previously) which are consistent across all four.


Offline Paul Birkeland

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Re: Low Kreg Both Sides
« Reply #5 on: November 23, 2022, 06:51:53 AM »
Find an old phone or tablet with a headphone jack and use an 1/8" to RCA adapter cable and a tone generator amp to play 60Hz into the amp with the volume on the device all the way up.  You can do this initially with the amp powered off to test the input wiring. 

With the black meter lead attached to terminal 7, you should be able to measure the AC signal voltage on the RCA jack pins, and that same voltage on each end of each red and white wire leaving the input selector toggle switch.  This would be the first step!
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline AllenS

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Re: Low Kreg Both Sides [Resolved]
« Reply #6 on: November 23, 2022, 11:07:11 AM »
OMG...  :-[  :-[ I can't believe the schoolboy mistake & excuse I have for you Paul... It became very obvious as I put the tone signal signal on and walked the wire that there were no center wires on the Input switch!

Page 55 was "stuck" with a sticky glue thing perhaps from shipping material or something... never noticed while flipping pages in the wire check that I had missed the 4 center pin wires. oops... Kinda explains no sound since it had nowhere to go.

Everything is up an running! Thank you so much for the pointers.


Offline Paul Birkeland

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Re: Low Kreg Both Sides
« Reply #7 on: November 23, 2022, 11:28:12 AM »
Well I'm glad it was something easy! 
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man