I am using the Salas HV shunt board with great results!
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Here's a simple 26 preamp I built not expecting too much, but it sounds very nice, nicer than I expected. I used back to back transformers in the PSU because I had some. Values are mostly correct, but I've done some tweaking since writing down the circuit.
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Hi Andy,
I used a 22k resistor on the anode of my 26 pre for quite a few months. I can’t say for certain that it wasn’t my favorite iteration so far. Simple, cheap and it works wonderfully as long as one has an amp with a fairly high input impedance.
Has your 6R2 cathode resistor stayed the same? Or was that changed in the tweaks?
Regards,
John
I used a 22k resistor on the anode of my 26 pre for quite a few months. I can’t say for certain that it wasn’t my favorite iteration so far. Simple, cheap and it works wonderfully as long as one has an amp with a fairly high input impedance.
Has your 6R2 cathode resistor stayed the same? Or was that changed in the tweaks?
Regards,
John
Here's the actual circuit and voltages. The HT is lower than I'd like and needs to be looked at. Alternatively a plate choke could be used with the HT as it is. With the resistor the current is 4.3mA and it would be better to raise this to 6mA. However, it does actually sound pretty nice as it is.
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Hello Rod. It is indeed my ingenious junk-box build, not that transformers are cheap! What I've used, however, is easily available at good prices from CPC, Farnell, RS, Rapid etc. Doesn't need special transformers for tube gear, just the common items.
Can you estimate the extent of the noise coupling? Are you suggesting something audible?
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.
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.
??? Which preamp is on first ???
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
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.
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
"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
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.
Another Improvement to These Schematics would be...
Andy, You've posted PSU schematics in messages 5122, 5124 and 5128 and in none of them can I figure where the connexions are located. How about some *black dots* where there are connexions? Otherwise...vapour.
Cheero,
RC
Andy, You've posted PSU schematics in messages 5122, 5124 and 5128 and in none of them can I figure where the connexions are located. How about some *black dots* where there are connexions? Otherwise...vapour.
Cheero,
RC
I should not really have posted my power supplies - I was just using up parts I had. Since most builds will use a "normal' small mains transformer with the right HT, I leave it up to builders to work out their power supplies in a more conventional fashion.
The only thing I'm building these days is 2a3/6B4G amps.
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