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Old 3rd November 2009, 12:54 PM
Richard Richard is offline
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Join Date: Dec 2005
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Default Re: Phono 3 with 5751 valves

Quote:
Originally Posted by Greg. View Post
Hi Richard,

Thanks for the up date. 5751's have been discussed before in this application but I've not tried them to date. What valves are you using? Are they nos or new buys? Jerry or anyone else like to make recommendations?

I'm seriously considering a rebuild of Phono II, hard wired and to incorporate the latest upgrades. That leads me on to a question. I've done the RIAA tweak as per the original Phono II FAQ thread although I'll have to check resistor value is actually 14.3K (it may be very close but not exact). If I incorporated C9/10/9a/10a changes to the standard Phono II 220pF, without access to a scope, can I set 30pF on 9a/10a out of circuit with my DNM (it has the farad measuring function) prior to fitting and expect a correct outcome?

Regards,

Greg
Hi Gerry and Greg,

Thanks for your exp. I thought some folk would have tried them by now but that I'd better wait till I was familiar enough with the sound to both listen and measure. Snap with Gerry, I'm using the GE Jan 5751 green print, fairly common 2 mica '75 date codes.

They are a near rather than exact equiv to ECC83 and do have an effect on frequency response that can be seen on the scope. (The addition of bypass caps to the first stage has no effect on f response that I can see.)

That said all versions of Phono do roll off at the very top end slightly and using 5751 lifts this without causing a lift past flat.

I took some pics to show how my trimmer caps ended up, then measured a spare at the similar position, which comes out at 42pF near as I can tell so will update that circ. That would make 222pF so I'd not touch yours at all Greg, just wack the valves in and have a listen as you won't do better by guesstimate due to differences in pcb. wiring, etc. It will have a little more top end but that's not the whole story by any means - and do give the bypass caps a go





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