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#26 pre amp
#26 pre amp
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Old 21st July 2021, 05:39 PM   #5131
Susan_Parker is offline Susan_Parker  United Kingdom
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Hope everyone is keeping well.
Alternative ways of generating the HT...
The Mallory Elkonode
Whilst one might not want a spark-gap transmitter as part of the circuit, some judicious component choices could keep this "traditional" in appearance if not in form.
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Old 11th October 2021, 03:07 AM   #5132
rchamber is offline rchamber  United States
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Default ??? Which preamp is on first ???

Quote:
Originally Posted by andyjevans View Post
Here's a simple 26 preamp I built not expecting too much, but it sounds very nice, nicer than I expected. ...
Hi Andy,

So, this is the preamp du jour. How does it compare to your 10Y/VT25 preamp du jour of 21 November 2017 in message #4508? And this one has no plate choke(s), how come? Did I miss any between then and now?

Best, Robert
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Old 11th October 2021, 06:33 AM   #5133
andyjevans is online now andyjevans  United Kingdom
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Quote:
Originally Posted by rchamber View Post
Hi Andy, So, this is the preamp du jour. How does it compare to your 10Y/VT25 preamp du jour of 21 November 2017 in message #4508? And this one has no plate choke(s), how come? Did I miss any between then and now? Best, Robert
Hello Robert. First thing to say is I never use a preamp. I only use a 2 stage amp. So these "preamps" are vapourware, they don't exist except as transient builds. I do build 26 preamps for others in a very limited way. For my own use a 26 or 10Y stage would only be useful for driving a high gain final like EL38 or EL12. I flirted with that combination last year but this year I'm using and very much enjoying 6C4C/6B4G finals. The driver stage needs a mu of 30 at least, so no place for a 26. So my stocks of 26, 01A, 46 and 10Y are basically part of my pension fund. I never use them.

Yes, I prefer plate chokes, even a humble Hammond 157G. But a resistor load can sound good in a basic design. I'll always prefer a 10Y or a 46 to a 26, but once you're using a good DHT the sound will be there.
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Old 14th October 2021, 12:29 AM   #5134
rchamber is offline rchamber  United States
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Default Andy, How do you Test Your Preamp Design/Builds?

"Hello Robert. First thing to say is I never use a preamp. I only use a 2 stage amp. So these "preamps" are vapourware, they don't exist except as transient builds. ..."

Hi Andy,

Well, I'll start by saying that it's good that we all do it differently.

How do you configure your system to test - and then report on the sound of - your new designs that popup with some frequency - of preamps you "never use"?

Also, why design and test *briefly*, preamps you will never use long term? Some of your design evaluations indicate that you've been listening for 15 minutes, and then...poof!

I'm just looking for a missing link to solve the AndyJEvans preamp mystery.

I will admit to having in my saved files a Documents/Audio/Andy Evans file with a 2P29L entry, two 26 entries - one with SiC diode bias, and a 10Y entry. And they all inspire me to think about where to go next. Although it seems you've dumped SiC bias, if I am up to date.

My system has many sources so I need a preamp in-systeme to deal with: 1. phono LP collection that I've been building since 1958, 2. FM radio, 3. Tape, and 4. CD. My current line preamp is a 5687WOT (LL1660/10), and my phono pre is Diego Nardi's Phi 42 from Sound Practices long ago. Power amps are either: 1. 24A/45/James 6123H, or 2. EL84/2A3C/FS030, both Loftin-Whites. Loudspeakers are Lowther PM2A A.T. Spezial spec'd in front firing Fidelios, with Edgar midrange horns in front of the PM2As.

I need to try some new things and I am inspired in that direction by contributers here too numerous to mention...thank you all!

Cheero and Best, Robert
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Old 14th October 2021, 08:29 AM   #5135
andyjevans is online now andyjevans  United Kingdom
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Quote:
Originally Posted by rchamber View Post
How do you configure your system to test - and then report on the sound of - your new designs that popup with some frequency - of preamps you "never use"? Also, why design and test *briefly*, preamps you will never use long term? Some of your design evaluations indicate that you've been listening for 15 minutes, and then...poof! Although it seems you've dumped SiC bias, if I am up to date.
In 2020 I was using EL38 outputs for several months in what I called my "Inverted DHT Amp" where the DHT was in the input, not the output. So there I was indeed using an input stage which was 10Y (excellent) or 26 (good). Sounded very good too. So that was months, not 15 minutes. The DHT was a driver stage not a preamp, though the circuit was the same as always - plate choke and FT-2 teflon cap. The DHTs were in filament bias, so no SIC diodes. This is still a viable amp design, and the EL38 is excellent, even better than EL12.

Later in 2020 I switched back to 300b outputs which required a higher gain IDHT tube on the input, so the DHT went back into the output stage. This Autumn I've switched from 300b outputs to 6B4G outputs (6C4C) and loving them. So one of the ways of configuring the input tube is one or two SIC diodes together with a resistor. The resistor feedback takes a bit of the slight edge off the diodes alone.

So no place for a preamp or a 26 stage. I build one or two to sell. I suppose you could say "poof and they're gone", though it takes me several days to build them. I do use a modular system which allows me to endlessly recycle parts. I use 19" sub rack parts so everything screws together. I actually never used a "preamp" as such. All the DHT stages I built and experimented with were driver stages, originally for PSE 4P1L outputs. All my source material is on my Mac Pro, so volume is in software.
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