SSE FRED diode Fairchild ISL9R8120P2 alternative? - diyAudio
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Old 2nd October 2014, 08:33 PM   #1
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Default SSE FRED diode Fairchild ISL9R8120P2 alternative?

Hi All,

I am making my plans to built a simple SE amplifier. At this point I am in the process of trying to understand the available information and based on that built my parts list.

So far I have been able to 'find' most parts on Mouser and Digikey but the one part I cannot find is the 'Fred diode' or the advised alternative Fairchild Stealth ISL9R8120P2 that all seem to be out of production.

What would be a good alternative?

Thank you and best regards,
Jock
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Old 2nd October 2014, 11:03 PM   #2
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8Amps at 1200Volts? why such a high current? Use a 1N4007.
That will give you a good Amp.
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Old 3rd October 2014, 12:21 PM   #3
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Quote:
Originally Posted by JonSnell Electronic View Post
8Amps at 1200Volts? why such a high current? Use a 1N4007.
That will give you a good Amp.
Hi Jon, from you websites I see you know you business. I wish I could answer your question because that would mean my knowledge on building a tube amplifier would have boosted with 10.000 points LOL.

The reason I am looking at the simple SE is because of the very good reactions, my current amp is way overpowering my speakers, and the fact that I think I can built it following a the step by step explaination from the tubelab site.

In this thread Mr George Anderson talks about the voltage of the diode. Maybe this helps?
FRED diode change for Tubelab se

Best regards,
Jock
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Old 3rd October 2014, 02:53 PM   #4
Spica is offline Spica  Canada
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If you use the tube rectifier you don't need the diodes. Below is a quote from one of George's posts that I saved.
Simple Simple SE questions post #12. Might be a good thread to look at

3) The old IXYS parts work fine. The newer ones (made in the last 3 or 4 years) will fail in this circuit. The Fairchild Stealth Diode # ISL9R8120P2 will work just fine. The FRED diodes are only needed if you want to use a solid state rectifier, and may be omitted with a vacuum tube rectifier.

Last edited by Spica; 3rd October 2014 at 03:04 PM.
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Old 3rd October 2014, 04:11 PM   #5
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Quote:
Originally Posted by Jockaruba View Post
Hi All,

I am making my plans to built a simple SE amplifier. At this point I am in the process of trying to understand the available information and based on that built my parts list.

So far I have been able to 'find' most parts on Mouser and Digikey but the one part I cannot find is the 'Fred diode' or the advised alternative Fairchild Stealth ISL9R8120P2 that all seem to be out of production.

What would be a good alternative?

Thank you and best regards,
Jock

This thread should answer your question....

Fairchild Stealth ISL9R8120P2 diode not available

Many questions can be answered by searching the forum.

As the poster above mentioned you can skip the solid state diode and go
with tube rectification only, for this the 5AR4 rectifier is what Tubelab
recommends.
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Old 3rd October 2014, 04:24 PM   #6
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Quote:
Originally Posted by spendorite View Post
This thread should answer your question....

Fairchild Stealth ISL9R8120P2 diode not available

Many questions can be answered by searching the forum.

.
And I have and also found this thread but am not under the impression that the Fairchild RHRP15120 is a generally 'accepted' alternative yet like the ISL9R8129P2 that is mentioned in a lot of threads. Maybe I'm wrong.

Learning here: What is the difference between using solid state diode and tube rectification? What will I be missing by skipping the solid state diode?

Thank you,
Jock
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Old 3rd October 2014, 04:56 PM   #7
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Quote:
Originally Posted by Jockaruba View Post
And I have and also found this thread but am not under the impression that the Fairchild RHRP15120 is a generally 'accepted' alternative yet like the ISL9R8129P2 that is mentioned in a lot of threads. Maybe I'm wrong.

Learning here: What is the difference between using solid state diode and tube rectification? What will I be missing by skipping the solid state diode?

Thank you,
Jock
At least one user attest the Fairchild RHRP15120 is working fine in his SSE.

You wouldn't miss anything by skipping the solid state diode, but you would
gain something by going with an indirectly heated tube rectifier like the 5AR4.

With a solid state rectifier your B+ voltage comes up immediately on switch-
on and zaps your output tubes before they've had time to warm up which
can potentially shorten the life of these tubes. With a tube rectifier like the
5AR4 you would get a soft start, that is, the rectifier gradually heats up and
brings up B+ slowly to the required voltage.
There are some people who claim that the tube rectifier sounds better than
solid state but I don't detect a difference.

Of course you can go with both solid state and tube rectification using a
switch to go between the two. I think the George, the designer, added solid
state as an alternative to tube rectification, you can go with either one or
both.
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Old 3rd October 2014, 08:03 PM   #8
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Thanks for explaining Spendorite,

I was a bit worried that the diodes could have a large effect on the overall sound quality but learned now that is not the case and that they are not used in tube rectification mode at all.
I think I'll fit the RHRP15120 in with a switch and expect to be running the tube mode mostly.

Best regards,
Jock
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Old 6th January 2015, 03:27 AM   #9
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Just happened across this thread. We have hundreds of the ISL9R8120P2 diodes in stock...and will be on sale sometime this week:
Fairchild Stealth Diode 8A/1200v, Sonic Craft
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