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Trying to go through alignment procedure for HP412A that I rebuilt, having trouble with first step lol

 

Hello all, I am finishing up on a restoration of a HP 412A VTVM. ?It¡¯s quite accurate from the get go after the restoration. ?
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I replaced every capacitor minus ceramics, I replaced pretty much every carbon composite resistor with 1% metal film of good quality, installed nos tubes that tested quite strong. ?I¡¯m not sure if I¡¯m doing the hum balance correctly. ?
It says to connect a scope to the amplifier terminals which happen to be on the back of the meter and adjust for minimal 10 hz signal. ? I¡¯m not seeing any 10 hz, only seeing stuff in the kHz.
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If I adjust the hum balance pot it does change the waveform seen and it does lower the frequency, but I get nowhere near 10 hz and the frequency is jumping all over the place. ?
I did also notice that the hum balance adjustment also affects the zero point of the meter fairly greatly. ?After playing around with it I had to zero the meter using the small screw directly below the meter face.
How do I do this correctly? When adjusting hum balance in a tube amplifier I would adjust for lowest noise/hum. Would adjusting for the lowest point where the needle sits on the meter work? Equating that the needle is higher due to noise, this is a total guess here. ? I¡¯m sure there are others that have aligned this meter so I¡¯m hoping for some help.
Thank you,
Dan
 

I apologize, I have a duplicate thread. I didn¡¯t realized the post had to be authorized before being posted. It can be deleted, use this thread for help.?

Thank you,
Dan
 

On 11/30/24 18:04, Dan via groups.io wrote:
I apologize, I have a duplicate thread. I didn¡¯t realized the post had to be authorized before being posted. It can be deleted, use this thread for help.
No problem. I saw the two messages in the moderator queue and it was pretty clear what happened, so I just put both through not knowing if you'd have a preference as to which one went.

Keep in mind, though, that this is not a web forum, it is a mailing list that also has a web interface.

-Dave

--
Dave McGuire, AK4HZ
New Kensington, PA
 

Okay, I really appreciate it Dave. ?So what¡¯s the difference really? Do they kind of function the same, but each message and response puts an email in your email account?
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Thank you again,
Dan
 

it might actually be better to eliminate this one, I already have a couple responses on the other posting I have, and nothing here, except for you letting me know you saw that I had put two listings on. Thank you

Dan

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