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Old 6th October 2019, 04:07 PM   #21
donkeytrousers is offline donkeytrousers  United Kingdom
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I mean the rectifier diodes which are different one amp to the other and measure differently too.
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Old 6th October 2019, 05:00 PM   #22
indianajo is offline indianajo  United States
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Well, the power supply rectifier diodes are nothing special. Forwards voltage can vary from .450 to .770 on the DVM without meaning anything. Modern ones tend to be lower voltage, that is more efficient and not possible in 1970. Just be sure if one is defective, don't buy schottky, fast recovery or ultra-fast recovery diodes. These make more RF from the sharp cutoff edge to interfere with the amp circuit. Sharp edges can cause 100 hz (Europe) buzz. Designers bypass the rectifier bridge with a .01 or .1 us ceramic 500v cap to reduce the buzz. There are more sophisticated tricks involving a cap series a 10 to 100 ohm resistor across the bridge.
To buy diodes, I use the selector table on farnell, select semiconductors, select diodes, check stock only, then select standard recovery diodes, then minimum 400 PIV and current 3 to 6 A. Select leaded parts. That got me 1n5404 in August; you may come up with different stock in the UK.
Factories tend to save money by buying different rectifier diodes each run. I paid $.11 each for the 1n5404, whereas generic diodes from a "no free catalogs no salesmen" supplier like GI or hang seng are probably $68 for 10000.
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Last edited by indianajo; 6th October 2019 at 05:19 PM.
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Old 6th October 2019, 08:21 PM   #23
donkeytrousers is offline donkeytrousers  United Kingdom
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Thanks again, Indi. I have really appreciated everything.

On ther subject of component price...you've got to allow for the cost of picking and mailing 5 to 10 components at a time. You pack, bill and post 10,000 as fast as you post 10. Handling cost is identical.
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Old 11th October 2019, 09:31 PM   #24
donkeytrousers is offline donkeytrousers  United Kingdom
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Just wanted to post a big thank you to both of you for your help. I finally fired up the MA50's and they are utterly fabulous. If you get the chance to hear a pair that have been rejuvenated with love and determination you will not regret it. Massively pleased. I put on a record andsat there with a smile "like a Cheshire cat" as we say over here.
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Old 11th October 2019, 09:34 PM   #25
indianajo is offline indianajo  United States
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Congratulations. Glad your project reached a successful end.
Off the internet until the 23rd.
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Old 11th October 2019, 09:54 PM   #26
MarcelvdG is offline MarcelvdG  Netherlands
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Thanks for the feedback, I'm glad to read that the amplifiers work as intended now!
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