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Old 27th October 2011, 09:56 AM   #511
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Thanks Fran and Salas for your instructive comments. Salas's comments about the PS might be the ticket as they aren't marked with their voltage rating. I've taken note of your other comments and will tackle them as I go along.
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Old 27th October 2011, 10:35 AM   #512
Salas is online now Salas  Greece
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If they are the typical axial clear plastic wrap type they are 160V most likely.
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Old 27th October 2011, 11:44 AM   #513
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Correct Salas, that's the type, so at 160V as you say they are being pushed to their limit.
Do you think changing the coupling cap C4 to 47n teflon will have a positive effect? The smoothing cap C7 is an SCR 4.7u PPE MKP FC as per Rev1.1.
Thanks and regards.
JA
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Old 27th October 2011, 12:12 PM   #514
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Good point Salas, lately I loaded with several resistors values my Partridge 977 finding 10K the best one so it's very important for final sound.

Sonata149 as Salas, Ricardo & many others pointed the best for RIAA caps is accuracy.

Last edited by merlin el mago; 27th October 2011 at 12:14 PM.
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Old 27th October 2011, 12:24 PM   #515
Salas is online now Salas  Greece
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Quote:
Originally Posted by sonata149 View Post
Correct Salas, that's the type, so at 160V as you say they are being pushed to their limit.
Do you think changing the coupling cap C4 to 47n teflon will have a positive effect? The smoothing cap C7 is an SCR 4.7u PPE MKP FC as per Rev1.1.
Thanks and regards.
JA
Sort out the Riaa curve caps first. And if its still heavy in tone, the 0.047u couple may help you if its partly due to rumble.
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Old 28th October 2011, 06:34 PM   #516
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Hi Salas and all, I changed the riaa caps with cheap but matched film thingies rated at 250V. The result was a noticeable, if not dramatic, improvement and I am now much happier with the overall sound. The tubiness is gone and vinyl surface noise very low. I measured the voltage from the upper cathode of the first stage which is 169V and 172V from a B+ of 285V.

I am now waiting for the riaa caps GB organised by Merlino which will replace the cheapie caps I'm using now. I will also install 0.1uF 200V FT-2 teflon coupling caps which I already have. I suppose that this voltage rating is adequate. Next step will be the building of a SSHV Mosfet shunt-regulator which I am confident will further improve the Itch.

Meanwhile, thanks Salas and all contributors to this interesting and very competent design. It is not complicated to build and I encourage others requiring a phono stage to tackle it.
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Old 28th October 2011, 08:17 PM   #517
Salas is online now Salas  Greece
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Got any pictures as it is now?
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Old 28th October 2011, 08:31 PM   #518
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oh yes pics please!!

Apart from anything else, its good inspiration for others!
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Old 28th October 2011, 08:43 PM   #519
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Yes of course; Woodturner's pics in particular and his build descriptions inspired me to take on the project. Salas's prompt and continued support to various builders (Merlin + RCruz among others) was equally important in instilling a sense of confidence in case problems cropped up during the build process. Pics to be posted in due course.
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Old 29th October 2011, 12:21 PM   #520
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Here are a couple of pictures. Nothing fancy aesthetically. Mainly used materials I already had. Blank space on underside of amp is for SSHV and heater regs which will replace the present eBay Chinese regulator which supplies only 285V at B+. Used tagstrip/boards for component layout. Valves are russian 6n2p-ev and 6H8S. Even with no boutique components I like the sound a lot. No hum or background noise whatsoever. A satisfying project all round (despite the hitches).
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File Type: jpg Sal_Valve-Itch present setup.jpg (690.7 KB, 263 views)
File Type: jpg Salas Valve Itch_Wiring.jpg (695.3 KB, 250 views)
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