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December 14, 2019, 11:07:29 AM

Author Topic: Voltages 1/2 [resolved]  (Read 3291 times)

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Offline Paul Birkeland

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Re: Voltages 1/2
« Reply #15 on: October 25, 2015, 07:07:58 AM »
OK, well, this is a good indication. 

What DC voltage do you see on terminal 44 with no tubes installed?
Paul "PB" Birkeland

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Offline hbonilla

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Re: Voltages 1/2
« Reply #16 on: October 25, 2015, 07:54:17 AM »
Hi, thanks for the help. DC V terminal 44 is 464 without bulbs

Maybe you already saw this but here is an image of my last check. I am very off on terminal 7 with AC V 408 rather than 170-230

« Last Edit: October 25, 2015, 07:56:28 AM by hbonilla »

Offline Paul Birkeland

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Re: Voltages 1/2
« Reply #17 on: October 25, 2015, 12:12:57 PM »
OK, I seemed to remember you saying that all the voltage measurements were about half, but it looks like only 1 of the measurements is about half of what it should be.  This is a big difference.

408V at 7 can have many causes, one of which is the 12AT7 not getting heated (is it glowing?), a missing ground jumper to the middle of the adjacent 9 pin socket, an incorrect resistor value installed between the center post and pin 8 of that 9 pin socket, etc.

Can you post a photo of that region of your amplifier?
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline hbonilla

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Re: Voltages 1/2
« Reply #18 on: October 25, 2015, 12:49:09 PM »
Yes, everything was half when I started this process, it is only 7 that is off now.

Here are the pictures of 12AT7. Yes the bulb is glowing and heating.

Thanks

Offline Paul Birkeland

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Re: Voltages 1/2
« Reply #19 on: October 26, 2015, 07:58:32 AM »
Try reheating the center leg of the MJE5731 feeding those terminals.  Something is not conducting properly.

-PB
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline hbonilla

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Re: Voltages 1/2
« Reply #20 on: October 26, 2015, 09:40:59 AM »
I reheated both MJE5731. I also made a continuity test between the center of MJE5731 and terminal 7 and there is good connection, please see image.

DC V at terminal seven still 407.

Thanks

Offline Paul Birkeland

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Re: Voltages 1/2
« Reply #21 on: October 26, 2015, 11:41:03 AM »
Measure the voltage at pin 8 on the 9 pin socket of the offending side, then swap tubes and remeasure.

-PB
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline hbonilla

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Re: Voltages 1/2
« Reply #22 on: October 26, 2015, 01:26:55 PM »
Paul, I am back from my trip.

DC V on pin 8 is 12.2V

Thanks
« Last Edit: October 29, 2015, 08:41:31 AM by hbonilla »

Offline hbonilla

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Re: Voltages 1/2
« Reply #23 on: October 30, 2015, 06:43:11 AM »
Paul, I am back from my trip.

DC V on pin 8 is 12.2V, how does that sound?

Thanks

Offline Paul Birkeland

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Re: Voltages 1/2
« Reply #24 on: October 30, 2015, 07:32:09 AM »
Do you get that voltage with both 12AT7's on the offending side?
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline hbonilla

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Re: Voltages 1/2
« Reply #25 on: November 01, 2015, 01:12:20 PM »
I just checked with both12A7's and voltage is the same. However the voltage is now 440 rather than the 407 that I was getting a couple days ago. I have done nothing to the amp.

Thanks

Offline Paul Birkeland

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Re: Voltages 1/2
« Reply #26 on: November 01, 2015, 01:18:39 PM »
Measure the resistance of pin 8 on the offending 9 pin socket.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline hbonilla

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Re: Voltages 1/2
« Reply #27 on: November 01, 2015, 01:31:14 PM »
Resistance of pin 8 (against the center pin) is 366. Thanks
« Last Edit: November 01, 2015, 01:40:55 PM by hbonilla »

Offline Paul Birkeland

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Re: Voltages 1/2
« Reply #28 on: November 01, 2015, 01:41:29 PM »
12V over 366 Ohms is 32mA, which is way off target. 

Can you carefully check the DC voltage on pin 7 of the offending socket? 
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline hbonilla

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Re: Voltages 1/2
« Reply #29 on: November 01, 2015, 02:04:53 PM »
I have zero voltage, please see image

Was I correct in measuring resistance of pin 8 against the center pin? Or should I have done it against something else?

« Last Edit: November 02, 2015, 05:55:40 AM by hbonilla »