Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old January 19th 16, 05:13 AM posted to sci.electronics.repair
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Default Peavey Classic 60 questions

John Heath wrote:


Your idea of monitoring current on a scope opens up new possibilities.
I could see how the ESR of the main filters condenser could be guessed
at by monitoring the inrush current from a cold start.



** The way you tell is when running the amp into a load there is some, or a maybe lot of test frequency visible in the AC current wave.

Normally you see only half sine pules of about 3mS duration at double the supply frequency with no higher frequencies visible if the electros are good.

If you then go inside and scope the electros, there is excess ripple voltage and lots of test frequency visible on the main DC rail/s.

You can also spot bad rectifiers ( valve or SS) if alternate current pulses are missing or weak.


..... Phil











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Old January 20th 16, 04:05 AM posted to sci.electronics.repair
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Default Peavey Classic 60 questions

On Tuesday, January 19, 2016 at 12:13:05 AM UTC-5, Phil Allison wrote:
John Heath wrote:


Your idea of monitoring current on a scope opens up new possibilities.
I could see how the ESR of the main filters condenser could be guessed
at by monitoring the inrush current from a cold start.



** The way you tell is when running the amp into a load there is some, or a maybe lot of test frequency visible in the AC current wave.

Normally you see only half sine pules of about 3mS duration at double the supply frequency with no higher frequencies visible if the electros are good.

If you then go inside and scope the electros, there is excess ripple voltage and lots of test frequency visible on the main DC rail/s.

You can also spot bad rectifiers ( valve or SS) if alternate current pulses are missing or weak.


.... Phil


Interesting. There are always easier ways if you think about it long enough.. Well done. Just thought of another one . Is the degassing coil working on a TV. Put an AC meter on a degassing coil in front of the TV then turn it on. If there is a burst of AC measured then the degassing coil is okay. The problem is they no longer make TVs that have degassing coils , ah.


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