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October 25, 2020, 11:53:08 AM

Author Topic: Assembly Question [resolved]  (Read 593 times)

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Online Paul Birkeland

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Re: Assembly Question [only partially resolved]
« Reply #15 on: April 27, 2020, 09:36:42 AM »
Your DMM.
Paul "PB" Birkeland

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Offline jjvornov

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Re: Assembly Question [only partially resolved]
« Reply #16 on: April 27, 2020, 09:56:31 AM »
Here it is
« Last Edit: April 27, 2020, 10:00:48 AM by jjvornov »

Online Paul Birkeland

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Re: Assembly Question [only partially resolved]
« Reply #17 on: April 27, 2020, 11:00:13 AM »
So the idea here is to download a tone generator app to your phone, then play that through the amp.  Your meter is autoranging and can resolve low AC voltages, so you have what you need to start. 

For the first measurement, the amp can be off, and all you need to measure is the AC voltage across the RCA jack, then post that here.

-PB
Paul "PB" Birkeland

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Offline jjvornov

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Re: Assembly Question [only partially resolved]
« Reply #18 on: April 27, 2020, 11:47:06 AM »
400mV from the iPhone headphone jack volume up all the way

Online Paul Birkeland

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Re: Assembly Question [only partially resolved]
« Reply #19 on: April 27, 2020, 11:54:31 AM »
OK, you can leave the black probe clip leaded to the shell (outside) of the RCA jack, keep the tone playing, then measure the AC voltage at terminal 10 with the amp running.
Paul "PB" Birkeland

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Offline jjvornov

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Re: Assembly Question [only partially resolved]
« Reply #20 on: April 27, 2020, 11:56:04 AM »
Terminal 10  (output transformer) is just bouncing around from nothing to OL and there's 61V of DC on it.
« Last Edit: April 27, 2020, 12:01:33 PM by jjvornov »

Online Paul Birkeland

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Re: Assembly Question [only partially resolved]
« Reply #21 on: April 27, 2020, 12:11:21 PM »
Terminal 10 by the 9 pin socket, not terminal 10 on the output transformer.
Paul "PB" Birkeland

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Offline jjvornov

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Re: Assembly Question [only partially resolved]
« Reply #22 on: April 27, 2020, 12:44:44 PM »
Okay. Terminal 10 reads 12.75 V

Online Paul Birkeland

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Re: Assembly Question [only partially resolved]
« Reply #23 on: April 27, 2020, 01:41:46 PM »
OK, so that rules out everything going on at the 9 pin socket.

Now check to be sure you also have 12V at pin 3 on the 4 pin socket.
Paul "PB" Birkeland

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Offline jjvornov

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Re: Assembly Question [only partially resolved]
« Reply #24 on: April 27, 2020, 01:47:40 PM »
Pin 3 is the same 12.75V

Online Paul Birkeland

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Re: Assembly Question [only partially resolved]
« Reply #25 on: April 27, 2020, 01:50:30 PM »
As much as we could continue following this around, I think you should post some build photos.  Specifically it would be good to see the area where the 47uF cathode bypass cap connects, as well as the cathode resistors.

The possibilities I see for what's wrong are:

1.  The 47uF cathode bypass cap isn't properly connected.
2.  The secondary wiring on the output transformers wasn't done correctly (in the manual where it says "to wire for 8 ohms, do blah blah blah).
3.  One of the wires going to terminal 5 or 10 on the output transformer is loose or missing.

-PB
Paul "PB" Birkeland

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Offline jjvornov

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Re: Assembly Question [only partially resolved]
« Reply #26 on: April 27, 2020, 02:11:32 PM »
Paul

So it was a miswire at the output transformer. It makes sense that it was playing but at low volume. Now they are matched in volume.

Thanks for your help. I've often said that half the fun of the hobby of kit building is the building, but the other half is troubleshooting and the satisfaction of getting the assembly working at the end.
« Last Edit: April 27, 2020, 02:25:09 PM by jjvornov »

Online Paul Birkeland

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Re: Assembly Question [only partially resolved]
« Reply #27 on: April 27, 2020, 03:07:11 PM »
I'm glad you found the issue, and I'm thankful it was something simple and accessible.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man