01a preamp build

MrEd

Senior Nobody
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I started on 01a preamp today.
My second DHT pre, first was a 2p29l.
This one is the recipe from AL Mogliaa @ Bartola Valves.
The circuit uses Ale's Gyrator board and Rod Coleman filament regulators.
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MrEd

Senior Nobody
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I would strongly suggest not starving the filaments on those tubes. This will diminish tube life on a valve that is getting rather scarce.
View attachment 45306
Many have written that when using thoriated filaments is actually increases their life span.
I will try with starved and normal to see if there really is a sonic benefit.
 

mhardy6647

Señor Member
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I would strongly suggest not starving the filaments on those tubes. This will diminish tube life on a valve that is getting rather scarce.
View attachment 45306
@paulbottlehead have you/you all ever traced the original source of that graph? I learned of this in a discussion some years back about the 12SN7 (if memory serves). It's easy to find the "contemporary" source, which was (IIRC) a DIYAudio thread*. Said source claims the graph was originally published by RCA -- but I have yet to track the original reference down.

It's been long enough ago, now, that I looked for it that it might be worth some sleuthing @ worldradiohistory -- but, since you brought it up ;) I figured it wouldn't hurt to ask!

* Heater Wiring - the Good the Bad and the Ugly

There are tonnes of hits on a search on starved filaments on teh webz, with somewhat conflicting information -- as I am sure most folks reading this thread would already know! ;)
 

MrEd

Senior Nobody
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I guess we will differ on this application and we will get past it. 😊
I respect your knowledge and experience Paul.
I do not see this published piece for Emission Labs having as much to do with a 100 year old 01a as with later tubes with different filament materials.
I'm not going to lose sleep worrying at this point.
I'll plod along and see how it works.
 
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Fran604g

Just Call Me Junior
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I have everything wired up.
Tested my filament regulars and my gyrator voltage with dummy loads today.
All look good.
Next up plug in some tubes and light the fuse...
I have 4 strong testing 01A's sleeping in a c.~1926 ERLA - it might be time for me to wake them up. The radio's interstage transformers are open, and although I could replace them with alternate circuitry and fully restore the cabinet, I've elected to not.

The chassis board could possibly be repurposed to build that preamp, but of course I wouldn't want to do anything to it that couldn't be reversed to restore the radio. How cool would it be to house the preamp in this old radio cabinet?

What are you planning on driving with it? I'm looking forward to your impressions, and I wonder if this preamp might be fun to drive my 6B4 or 1626 SET amps?

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MrEd

Senior Nobody
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Okay, I'm an idiot! They're UX201A... same thing, though, right?
Yes preamp , have another cup of coffee 😊
Same tubes. If I don't work too late today I might get to power it up and see if I have noise maker or a preamp.
I have an older version of the gyrator boards I bought about 5 years ago. Some the FETS are now obsolete. It may oscillate with newer type FETs so so no holding to much hope at this point.
 
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