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Anyone good at fault finding with amplifiers here?

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Joseph Noci 125/08/2019 07:28:16
543 forum posts
832 photos

Very Nice Neil! And with 'improvements'!

Am busy trying to repair a 4KW Phonic stereo amp at the moment...All transistors, some FET's, no IC's.

Uses split supply rails as usual, but dual rail, ±55volt and ±120volt. The output stage has 16 transistors - 8NPN and 8PNP in parallel. These receive the ±55 rail when running below 1KW / 4ohms and there are some big FETs that then switch the 55volt rail out and the 120volt rails smoothly in..gives almost 4KW into 2 ohms...

13 Transistors in the input stages, 4 long tailed pairs..and 12 transistors in the output stages, excluding the 16 power output tranny's.

No scoundrels way out on this one..

We also have tons of mica here - literally mountains of it. Maybe that's why it is often dull and grey here in Swakop...Any light entering is trapped inside sheets of Mica and can never leave - out own Hotel California for light..

Joe

XD 35125/08/2019 08:42:48
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1356 forum posts
113 photos

So now that you have it fixed will Stub be playing a few licks on YouTube?

Nicholas Farr25/08/2019 12:39:52
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1992 forum posts
950 photos
Posted by Neil Wyatt on 24/08/2019 20:37:56:

All now working and tested.

 

Also thanks to Horovitz and Hill who explain thermal runaway in FETs in language I could understand - after the primer of this thread I could actually understand what they were on about in detail.

Neil

Hi Neil, tut! tut!, fancy getting Paul's name misspelt.surprise Threw me there for a moment, good job you got Winfield's one right.thinking yes

book001.jpg

Glad you got it fixed anyway. smile d

Regards Nick.

P. S. sorry I couldn't resist a little banter.

Edited By Nicholas Farr on 25/08/2019 12:49:15

Neil Wyatt25/08/2019 14:05:06
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Posted by Joseph Noci 1 on 25/08/2019 07:28:16:

Very Nice Neil! And with 'improvements'!

Am busy trying to repair a 4KW Phonic stereo amp at the moment...All transistors, some FET's, no IC's.

Uses split supply rails as usual, but dual rail, ±55volt and ±120volt. The output stage has 16 transistors - 8NPN and 8PNP in parallel. These receive the ±55 rail when running below 1KW / 4ohms and there are some big FETs that then switch the 55volt rail out and the 120volt rails smoothly in..gives almost 4KW into 2 ohms...

13 Transistors in the input stages, 4 long tailed pairs..and 12 transistors in the output stages, excluding the 16 power output tranny's.

No scoundrels way out on this one..

We also have tons of mica here - literally mountains of it. Maybe that's why it is often dull and grey here in Swakop...Any light entering is trapped inside sheets of Mica and can never leave - out own Hotel California for light..

Joe

Sounds fun... and that's why you have such amazing night skies

Neil

Neil Wyatt25/08/2019 14:06:46
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Posted by XD 351 on 25/08/2019 08:42:48:

So now that you have it fixed will Stub be playing a few licks on YouTube?

duncan webster25/08/2019 17:49:18
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2255 forum posts
32 photos

Don't give up the day job!

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