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-   -   Phono 3 with 5751 valves (http://www.world-designs.co.uk/forum/showthread.php?t=5404)

Richard 2nd November 2009 01:41 PM

Phono 3 with 5751 valves
 
I've been trying 5751 valves in Phono 3 this past week. Lovely. I used them a few years ago instead of ECC83 in my 5-20 monobloc poweramps, thought they were good then, and have been meaning to try them in here for a while.

They have a little less gain than ECC83 with mu of 70 instead of 100. With the first stage bypass cap mod fitted, gain is now just a little more than standard (ECC83 and no bypass caps). The sound though is better than the 3 ECC83 types I'd tried before. Natural, transparent and airy are the words that come to mind. I'm not saying they're better than everything else, just that they're another flavour that can be tried without any problems :)

I checked RIAA response after fitting and there was a slight lift from 10KHz to 20KHz. Square wave confirmed an overshoot. This tells us the high frequency output was greater. A small adjustment of the trim caps corrected this easily (for anyone not using test gear the trim caps end up just past middle of the adjustment range - see pics later). Once this is done the response is ruler flat. The reason for this lift is the slightly lower plate resistance of 5751 compared with ECC83.

http://homepage.ntlworld.com/richard.../RichPhono.gif

Gerry 2nd November 2009 08:01 PM

Re: Phono 3 with 5751 valves
 
Richard

I use them in my Phono II and wouldn't go back.....so I can well believe they work well in the III.
The drop in gain has never worried me, in fact I saw it as a benefit as the noise floor(hiss) dropped.
I didn't make any adjustments to the circuit or components, but it looks as if the III is somewhat different with a trim pot for 3.18uS RIAA equalization?

Anyway interesting reading...many thanks.

bearded fiddler 2nd November 2009 08:14 PM

Re: Phono 3 with 5751 valves
 
Hi Richard,

I'm planning to order Phono 3S without the XL kit but with 5751 valves, as I have a pair in the phono stage I'm using now and love their sound.
Is the first stage bypass cap just a means of increasing gain (which I, like Gerry, don't need), or is it necessary for a good sound with these valves? What type of capacitor do you use?

Greg. 2nd November 2009 08:59 PM

Re: Phono 3 with 5751 valves
 
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

Gerry 2nd November 2009 09:32 PM

Re: Phono 3 with 5751 valves
 
Greg
Hope all is well with you.
I use the GE 5751 JAN NOS tubes which are probably the best out there without getting into the vintage stuff (when I did my research). Not sure what the Philips JAN 5751 are like.
As a valve they are not very microphonic which is an added bonus.

I did the RIAA tweak and really did notice a difference, really worthwhile IMHO.

Richard 3rd November 2009 11:13 AM

Re: Phono 3 with 5751 valves
 
Quote:

Originally Posted by bearded fiddler (Post 67014)
Hi Richard,

I'm planning to order Phono 3S without the XL kit but with 5751 valves, as I have a pair in the phono stage I'm using now and love their sound.
Is the first stage bypass cap just a means of increasing gain (which I, like Gerry, don't need), or is it necessary for a good sound with these valves? What type of capacitor do you use?

Hi Jan,

Try with and without the bypass caps. You will find a sound quality difference :) Yes you'll get more gain and using the 5751 it will be reduced a little. The net result is a little more overall gain than the original no-bypass/ECC83 combination. It's only a little more though (making phono level about the same as CD into a preamp) and the sound, to my ears, is vastly improved with the bypass caps on either valve type. I'm using Soniqs coupling caps as in pics later, black 0.1uF 630v and blue 2.2uF 250v.

bearded fiddler 3rd November 2009 11:40 AM

Re: Phono 3 with 5751 valves
 
Thanks Richard. It's becoming clear now, except for the caps. I meant the 220 uF bypass caps. What type should I use? As my knowledge is rudimentary every detail has to be explained to me at great length:)

Jan

Richard 3rd November 2009 11:54 AM

Re: Phono 3 with 5751 valves
 
Quote:

Originally Posted by Greg. (Post 67015)
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 :)

http://homepage.ntlworld.com/richard...s/P3GE5751.jpg

http://homepage.ntlworld.com/richard...ages/P3pcb.jpg

http://homepage.ntlworld.com/richard...P3TrimCaps.jpg

Richard 3rd November 2009 11:58 AM

Re: Phono 3 with 5751 valves
 
Quote:

Originally Posted by bearded fiddler (Post 67019)
Thanks Richard. It's becoming clear now, except for the caps. I meant the 220 uF bypass caps. What type should I use? As my knowledge is rudimentary every detail has to be explained to me at great length:)

Jan

Ah, Oscon 220uF 10V RS 176-8347 http://uk.rs-online.com/web/search/s...duct&R=1768347

Greg. 3rd November 2009 08:09 PM

Re: Phono 3 with 5751 valves
 
Hi Jan,

If you want to read up on the full thread about the bypass caps, read here.

http://www.world-designs.co.uk/forum/showthread.php?t=5305&highlight=Phono+cathode+bypa ss+caps+Jekyll+Hyde

Regards,

Greg


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