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Old 20th October 2009, 08:15 AM   #41
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Don't know how the 26 compares with the 10Y in a preamp yet, but can easily find out since with a few resistor changes I can use a 10Y in my preamp. I currently have a 30sp (VT-67) in it but I have nice big heatsinks for the DC filament and for the IXYS active loads so I can experiment a bit. I built this preamp as a bit of a test bed. With a more robust power supply I can take the voltage up. Early days yet, but will report!

andy
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Old 21st October 2009, 07:47 AM   #42
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Kevin,
I know that you have been working with the 26 DHT and line output transformers. I understand that the output level is fairly low due to the output transformer step down ratio. Would it be possible to use a high quality 1:2 input transformer to remedy this, or will this result in overload/clipping since the tube will have to swing more volts?
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Old 21st October 2009, 08:44 AM   #43
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Hi Bequerel,

Do you actually need a step-down transformer in the output? The LL1660 is a good sounding option in 1:1. I've used it and so have colleagues. Are you going into a tube amp or a solid state one? If tube, does it matter?

andy
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Old 21st October 2009, 09:05 AM   #44
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Originally Posted by andyjevans View Post
Hi Bequerel,

Do you actually need a step-down transformer in the output? The LL1660 is a good sounding option in 1:1. I've used it and so have colleagues. Are you going into a tube amp or a solid state one? If tube, does it matter?

andy
If I have understood it correctly a 1:1 transformer will give an output impedance of approx the same as the Rp, a high 8k or so. I have a Yamamoto A08 SET, but I feel that a lower output impedance would give me more flexibility/compatibility with other amps, and reduce the interconnect cable influence as well.
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Old 22nd October 2009, 01:07 AM   #45
kevinkr is offline kevinkr  United States
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An input transformer will work, but linearity will be compromised at some point due to the high signal levels present.

If you need more gain a 2:1 step down on the output will give a source impedance of about 2K with about 12dB of gain.. A good trade off I would say.
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Old 22nd October 2009, 07:26 AM   #46
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Originally Posted by kevinkr View Post
An input transformer will work, but linearity will be compromised at some point due to the high signal levels present.

If you need more gain a 2:1 step down on the output will give a source impedance of about 2K with about 12dB of gain.. A good trade off I would say.
Good idea, Kevin!
I am sure that Mr. Eliano or Mr. LeFavre can wind me a suitable transformer when I am ready to take the plunge.

Speaking of DHTs, this might be a good candidate for a parafeed linestage:

EML-20A-20B-30A Datasheet. By Emission Labs.

Click the image to open in full size.
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Old 22nd October 2009, 05:14 PM   #47
CFT is offline CFT  United States
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How different do they sound? I mean : output transformer vs. LC vs. RC vs. CCS
And how would parafeed come in?

smps for the filament sounds like a good solution, did you find any sonic deficiency using it?

Thanks!
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Old 24th October 2009, 06:29 AM   #48
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Originally Posted by CFT View Post
How different do they sound? I mean : output transformer vs. LC vs. RC vs. CCS
And how would parafeed come in?

smps for the filament sounds like a good solution, did you find any sonic deficiency using it?

Thanks!
SMPS filament sound was less refined I felt but great relief over hum. I tried all sort of filament schematics I got hold of but only the SMPS gave me the hum free sound after all.
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Old 24th October 2009, 12:37 PM   #49
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Just an update on my 26 preamp. I've now fitted IXYS 10M45 active loads (available from Digikey). So setup is 190vDC HT (choke input) into a 150v glow tube (0D3), cascode IXYS active load with a 1.1k sense resistor set for 3mA. Cathode resistor is 2.4k wirewound. The sense resistor for the glow tube is 2.4K, 5watts. Bypass is .056 Russian teflon. Filament supply for the 26 is 6v secondary on transformer, Schottkys into 22,000uF into a LM1084 with a 1.2 ohm sense resistor, 7watts. Heatsink about 3ins square and 2ins high - needs to be a decent size.

Sound is exceptionally clear and nice! Enjoying this preamp a lot. Silvery fast sound with lovely timbre and liquid female vocals.

Not quite sure where I go from here - this is the best yet. I still have to try it with a hotter operating point, and then in goes the majestic 10Y! But for now this is more than good.

andy
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Old 24th October 2009, 02:39 PM   #50
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Originally Posted by andyjevans View Post
Just an update on my 26 preamp. I've now fitted IXYS 10M45 active loads (available from Digikey). So setup is 190vDC HT (choke input) into a 150v glow tube (0D3), cascode IXYS active load with a 1.1k sense resistor set for 3mA. Cathode resistor is 2.4k wirewound. The sense resistor for the glow tube is 2.4K, 5watts. Bypass is .056 Russian teflon. Filament supply for the 26 is 6v secondary on transformer, Schottkys into 22,000uF into a LM1084 with a 1.2 ohm sense resistor, 7watts. Heatsink about 3ins square and 2ins high - needs to be a decent size.

Sound is exceptionally clear and nice! Enjoying this preamp a lot. Silvery fast sound with lovely timbre and liquid female vocals.

Not quite sure where I go from here - this is the best yet. I still have to try it with a hotter operating point, and then in goes the majestic 10Y! But for now this is more than good.

andy
Andy,

175V on plate/-9V on Cathode gave me the best sound on my 26 so far.
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