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Old 16th January 2019, 06:23 PM   #11
McQuaide is offline McQuaide  United States
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Originally Posted by takitaj View Post
md_Stryker is correct. The F5 requires a dual rail supply of +24v and -24v with a common ground. The 760VA secondary is the only one useful here. If you were to use that transformer you could only use a pseudo ground type power supply, which will divide the voltage, ~12v going to the positive rail and ~12v to the negative rail. It's not going to work for the F5.

You need to use either a 24v-0-24v center tapped (3 wire) or 24v + 24v dual secondary (4 wire) transformer.

Have you read through any of the F5 threads yet? Perhaps 6L6's build guide would answer a lot of your questions and point you to the path of success.

That board isn't a Pass design so you may have to translate part numbering between the genuine board schematic and your board, and may affect the support you receive because of that. FYI.

One other thing to consider is where you acquired the JFETs and if they are genuine. They've been obsolete for quite a while and since there is still demand from DIY'ers they are often faked/re-marked.


18v secondaries for 24v rails.
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Old 16th January 2019, 07:11 PM   #12
Attila I is offline Attila I  Germany
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With the given xformer you could take the high power secondary and run it into a voltage cascade to gain 46V only to divide it with a virtual ground later on to +23/0/-23.
dunno if this works with class A amps - it does work with light bulbs (200W).
But then you might also consider the single rail powered F5 iteration.
where there's a will, there's a way

Last edited by Attila I; 16th January 2019 at 07:14 PM.
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Old 16th January 2019, 09:51 PM   #13
adason is offline adason  United States
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I hope fred0 did not left the building
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