CAS voltage not the same

bqc · 11924

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Offline Paul Birkeland

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Reply #30 on: December 28, 2020, 07:22:00 AM
The next step would be to play your 100Hz tone into the amp through both channels.  Measure the AC voltage between 5 and 10 on each transformer, then also measure the AC voltage at the speaker binding posts.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline bqc

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Reply #31 on: December 28, 2020, 08:09:27 AM
question on measuring at the speaker terminal, do I need to have speaker or dummy load or should it be left open?



Offline Paul Birkeland

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Reply #32 on: December 28, 2020, 08:17:44 AM
I would leave it open.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline bqc

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Reply #33 on: December 28, 2020, 08:38:16 AM
So with the source at full volume, the AC voltage across 5 and 10 of left transformer is 52V  and right transformer is 122 V
AC voltage across speaker terminal left 2 V, right 8 V
BTW I also measure the inductance of the 16 ohm secondary (which is what I am using)  Left transformer 0.2 mH  ,  right trans  37mH



Offline Paul Joppa

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Reply #34 on: December 28, 2020, 09:17:27 AM
The photos show a wire connected to transformer terminal 6, and none connected to transformer terminal 8. This is not consistent with the 16 ohm wiring. I can't see the rest of the secondary wiring well enough to say more, but the voltage and inductance data suggest a short across a portion of the secondary.

Paul Joppa


Offline bqc

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Reply #35 on: December 28, 2020, 09:31:32 AM
Sorry, the pictures were old and were taken when I had it wired for 8 ohm, I will retake pictures



Offline bqc

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Reply #36 on: December 28, 2020, 09:40:54 AM
The photos show a wire connected to transformer terminal 6, and none connected to transformer terminal 8. This is not consistent with the 16 ohm wiring. I can't see the rest of the secondary wiring well enough to say more, but the voltage and inductance data suggest a short across a portion of the secondary.



Offline Paul Birkeland

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Reply #37 on: December 28, 2020, 10:22:59 AM
One of your short red output transformer jumpers looks to be touching the chassis.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline bqc

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Reply #38 on: December 28, 2020, 10:39:54 AM
Do you mean the jumper between 1 and 2 of the transformer ? I lifted the amp and look  at it from the side and see that there is a 1/2 gap between the jumpers and the chasis so they are not touching.



Offline bqc

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Reply #39 on: December 28, 2020, 11:57:43 AM
So what to check next  to find out why there is a short in the secondary



Offline Paul Birkeland

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Reply #40 on: December 28, 2020, 01:28:41 PM
Take all of the jumpers and leads off the transformer you believe is bad, but leave the wires on 5 and 10, then recheck the AC voltage across 5 and 10.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline bqc

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Reply #41 on: December 28, 2020, 03:50:21 PM
with all leads and jumpers removed except at 5 and 10 on the left transformer, with input at full volume, the AC voltage across 5 and 10 on the left transformer is 55V while the AC voltage across 5 and 10 on the right transformer is 120 V



Offline bqc

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Reply #42 on: December 28, 2020, 06:24:01 PM
So can we conclude that there is a short inside the transformer on the secondary winding? If so what are my options? Is the transformer still under warranty ? if not how much would it cost to get a stock replacement transformer and how can I order it?



Offline Paul Birkeland

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Reply #43 on: December 29, 2020, 04:56:16 AM
Now lift the wire off terminal 10 on the output transformer, then measure the AC voltage between this wire and terminal 5 on the output transformer.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline bqc

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Reply #44 on: December 29, 2020, 07:12:59 AM
with wire on left transformer terminal 10 lifted, AC between wire and terminal 5 on left transformer is 140V, a jump from 55V to 140V, while the AC voltage between 5 and 10 on the right transformer remains at 120V