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Old 26th November 2012, 01:46 PM   #91
spurlte is offline spurlte  United States
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Default Transformers

Quote:
Originally Posted by kevinkr View Post
Pass tube requires a minimum of 200V for proper operation, it is a series pass after all. I actually get transformers built to spec for most of my designs. Based on ongoing listening experience I still find I prefer this design sonically to some more recent designs. I have not tried the shunt yet..
May I ask, who makes your transformers? I live in U.S.A. also--Chicago really. I have looked several diy phono preamps and I like yours the best as I am a novice diy-er. I am currently building the Krell KSA-100, Jim's Audio clone power amplifier for my european albums I purchased in Germany back in the early 1970s, U.S. Army PX. I like the fact that the tubes are plentiful and cheap!!!
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Old 26th November 2012, 04:19 PM   #92
kevinkr is offline kevinkr  United States
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Hi Spurite,
The plate power transformer was made by Edcor, and I generally buy an off the shelf antek toroid for the filament supplies in my designs.

The plate chokes are Magnequest EXO-001 100H/20mA chokes.

I will post the part numbers for the filament and plate supply transformers soon.
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Old 20th December 2012, 03:28 AM   #93
kevinkr is offline kevinkr  United States
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I've received a couple of requests that I post the final schematic as built rather than asking people to take the original and modify it with the various options listed in later posts - so here it is.

Note that I have removed the recommendation for the 6S3P-DR from the latest schematic as the samples I had access to were not nearly as uniform from sample to sample as the 32 6S3P-EV I purchased in several batches.

The chokes (L1 in below schematic) are Magnequest 100H type with a DCR of ~910 - 1000 ohms aka EXO-001, note that the winding resistance is important within the context of this design since the operating point of the upper triode is determined by the voltage impressed between its cold end and the grid. Target current is approximately 10 - 11mA.

Edit 2013-05-12: This is the final version of the audio circuitry.
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File Type: png 6S3P_Phono_Final_2012-12-27.png (57.6 KB, 469 views)
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Old 27th December 2012, 05:43 AM   #94
kevinkr is offline kevinkr  United States
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Checking prices of the 6S3P-EV on eBay tonight was interesting - last time I checked they were selling for $1.50 each, these days they seem to be going for between $3 and $7 each depending on quantity, maker, and seller. Still a pretty good bargain compared to the 5842 which is relatively similar in terms of its performance. (They are not exact equivalents)
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Old 28th February 2013, 11:08 AM   #95
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Looking for a poor mans solution for L1. Which is more important the DCR or the Inductance?
I have a Edcore 5W, 5:1 when wired primary with secondary in series equals 967 ohms not sure of the inductance but I'm sure it is less than 100 H.
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Old 1st March 2013, 04:45 PM   #96
kevinkr is offline kevinkr  United States
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I'd give the Edcor a shot, the DCR determines the operating point of the stage, and the inductance determines at what point the gain at the LF end of the spectrum starts to drop off.
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Old 12th May 2013, 06:57 PM   #97
kevinkr is offline kevinkr  United States
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Default Audio Chokes

Note that MagneQuest is on Facebook here: https://www.facebook.com/pages/Magne...21507687917410 - should be able to query Mike and probably order the chokes.

Note that the Lundahl LL1668 / 25mA choke with the windings wired in series with a 221 ohm resistor will provide both the required inductance (100H) and proper dc resistance for biasing the choke augmented mu follower second stage.
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Old 12th May 2013, 11:31 PM   #98
kevinkr is offline kevinkr  United States
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Default Edcor HV Transformer And Choke

Power transformer part number is: XPWR228-120

120V 60Hz to 800 volt (400-0-400) @ 100mA,
6.3 volt @ 2A, 6.3 volt @ 1A,
5 volt @ 2A
With Vertical Blue End Bells
Class X Power Transformer

Set up charge has already been covered so the price should be quite reasonable.

Choke P/N is: CXC100-5H-200mA

5H Inductance, 200 mA DC current,
58 ohms DCR with leads, Gapped Core
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Old 13th May 2013, 12:08 AM   #99
kevinkr is offline kevinkr  United States
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Default Filament Transformer

AnTek AS-0509 50VA 9V shielded toroid with dual secondary.
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Old 31st July 2013, 03:35 AM   #100
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Hello!
I beg you to read carrefully all what I wrote if your time is forgiving because I have a problem and I am not too good in mathematics so I will be as objective as possible to make you understand what I want to tell.
For quite a while (allmost 1 years of intensive readings all over the net) I am looking for the best possible phono preamp solution only through theoretical and net research and I found some worrying texts on the internet.I thought for a while that a design like FVP5A of allen wright or Toccata with their split riaa "have the touch", only to find later that those who replicated the fvp5a experienced instability with the original values because of the high voltage on some 6922 tube.
I have enough siemens e88cc and others good tube and I bought even some siemens e810f and philips d3a, e282f e280f (etc) too, and now I am troubled about hearing that 6c3p is better in terms of stability or microphonics than d3a...I have only one 6c3p-ev, but I will find the truth.

Now i don't know what to choose between :
1--split riaa a la toccata with battery bias, and all the good stuff ,although 200v dc on a 6922 is a bit too much,
2-- another design prety much as yours with triode strapped e810f and e88cc cascode as front stage, rc riaa and kimmel mu follower with 6j9-pe and 6n6p (or other western combination-I have hundreds of tubes) for the output stage inspired by Patrick Turner and others-you included
and
3-- a lcr design with transformer coupled after the first cascode and kimmel mu-follower final stage.

My question would be, if you are kind to answer to a so much unexperienced designer as myself:
is it possible to couple a 1henry-390 ohms-primary winding dc resistance of a double-c core transformer with 1 square cm and 9 ohms dc secondary dc resistace 13:1 coupling ratio in your cascode anode muscovite design for driving a 600 ohms lcr filter?
I think the reflected impedance in the primary winding would be about 90k ohms.Is it too much for couplind directly as cascode anode load, or better would be to make a cathode follower after cascode with some 12at7 and place the transformer in the cathode?I have two transformers like these from some farmaceutical quipement and they are very well built with multiple screens internal and external and two separate sections for windings.I saw some designs with lundahll anode loads and d3a as pentode and those Lundahlls are 30 henry at only 250 ohms dc resistance which makes me think that my 1 henry 390 ohms dc resistance, 1 square cm surface, double c core will not be too dc current forgiving,
I will first try the rc riaa network to be sure it's worth lcr but can you clarify about my problem?
Why I can't believe it's worth to give lcr a chance as bigger dinamics and ****.I built about to years ago a simple srpp design with 12ax7 and 12at7 like Patrick Turner first preamp and it sounded prety good to y years(a bit dark and resolute sound)in terms of dinamics.Why to bother lcr when I didn't even tried cascode and mu-folllower?
I have the best capacitors and resistors for rc and coupling(silver-mica, mkv siemens, mkp1841 and mmkt1813 ero, low miller styroflex ero and another 100 killos of good passive components so I can experiment.I even built some 30 kilograms power source for 8 different dc rectified and regulated filament rails, simetric and regulated anode voltages between minus-plus 120v dc to 375 v dc and all good stuff for this project.Then the preamplifier chassis is allmost done and contains 7 possible to be used tubes per channel.I just need some theoretical advices from an experienced builder because in my country nobody realised something so extensive in that aria.
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