Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: g-man on April 06, 2016, 08:35:18 pm

Title: PA conversion finished – odd plate voltage reading
Post by: g-man on April 06, 2016, 08:35:18 pm

(https://lh3.googleusercontent.com/-3waeKIohMns/VwWtprecZQI/AAAAAAAABvg/_CRjuVREJw0u_XKtnqHXRj4He_nKoJZrwCCo/s800-Ic42/FINAL%2BFender%2BPro%2B6g5%2Bmodified%2Bschem%2B%2528cathode%2Bbias%2529-B.jpg)
(https://lh3.googleusercontent.com/-cGULggBs9us/VwWl3WMzS7I/AAAAAAAABu4/OCNyYethYlkh1z3pubo0zeVy7p9IU2Z5wCCo/s640-Ic42/DC%2Breadouts.jpg)(https://lh3.googleusercontent.com/-xIxfdrQDig8/VwE-ubRZRqI/AAAAAAAABu0/xS3KHxPrIkslJZpOi_RC4a6DNLOAMM13QCCo/s800-Ic42/IMG_2711-GNDS.jpg)


 

Title: Re: PA conversion finished – odd plate voltage reading
Post by: g-man on April 07, 2016, 05:49:55 am

(https://lh3.googleusercontent.com/-t_nP4BTt4MA/VwZIXSgfC0I/AAAAAAAABwE/VMyr_3rwY7kyHF095zjM9i4h-aohM1hCwCCo/s640-Ic42/IMG_2730.jpg)

Title: Re: PA conversion finished – odd plate voltage reading
Post by: HotBluePlates on April 07, 2016, 06:56:38 am

Quote from: g-man on April 07, 2016, 05:49:55 am

Now I'm thinking my regular meter probe was unable to get a good reading on V5 because it was closer to the phase inverter, NFB wire, OT? Does that seem likely?

Normally, no.

You have something wired to pin 1 of your sockets. What is it?

Title: Re: PA conversion finished – odd plate voltage reading
Post by: sluckey on April 07, 2016, 07:26:34 am

Quote

You have something wired to pin 1 of your sockets. What is it?

I believe pin 1 is connected to the PI coupling caps and there is a grid stopper mounted between pin 1 and pin 5, Fender style.

Title: Re: PA conversion finished – odd plate voltage reading
Post by: g-man on April 07, 2016, 07:35:27 am

Deleted

Title: Re: PA conversion finished – odd plate voltage reading
Post by: sluckey on April 07, 2016, 07:50:59 am

I've see the same thing happen  a couple times while testing plate voltage on the output tubes. Each time it was caused by a poor connection between the probe and the socket. The poor connection would even cause a high freq oscillation that could be heard through the speaker. Using needle tipped probes or gator clips gave a reliable connection and reading. Maybe this was happening with you?

Title: Re: PA conversion finished – odd plate voltage reading
Post by: g-man on April 07, 2016, 08:22:56 am

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Title: Re: PA conversion finished – odd plate voltage reading
Post by: jojokeo on April 07, 2016, 10:53:10 am

Hi Stu! I replied last night then removed it but was thinking the "odd" photo was correct and the "normal" one was not. If you don't recognize the "." placement holders then the 423 vdc looked much more normal than only 9.25volts on a plate reading!

Title: Re: PA conversion finished – odd plate voltage reading
Post by: g-man on April 07, 2016, 09:12:17 pm

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Title: Re: PA conversion finished – odd plate voltage reading
Post by: g-man on April 07, 2016, 09:17:27 pm

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Title: Re: PA conversion finished – odd plate voltage reading
Post by: DummyLoad on April 08, 2016, 12:29:59 am

on volt chart: V5-6 pin 7 should be V5-6 pin 8 column?


--pete

Title: Re: PA conversion finished – odd plate voltage reading
Post by: g-man on April 08, 2016, 06:12:33 am

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