01a preamp build

[MrEd]

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.

01a Preamp (Gen2)

Introduction The 01a preamp has a long history in my system. I played a lot with many DHTs in the past from 26 to 71a, 30sp, 112a, 46, 4P1L and 10 amongst others as preamp valves. I particularly fo…

www.bartola.co.uk

 

[prime minister]

Will Google Translate work on what you just wrote?

 

[MrEd]

Will Google Translate work on what you just wrote?

Most likely not...
I thought I was using English 🙂

 

[paul_b]

I would strongly suggest not starving the filaments on those tubes. This will diminish tube life on a valve that is getting rather scarce.

 

[prime minister]

Most likely not...
I thought I was using English 🙂

That’s not a version of English that I understand. Maybe some Amurrican variant?

 

[MrEd]

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.

 

[paul_b]

Many have written that when using thoriated filaments is actually increases their life span.

The engineers who designed these devices at RCA would certainly disagree.

 

[MrEd]

The engineers who designed these devices at RCA would certainly disagree.

Recon any of them are still alive ? 😊

 

[mhardy6647]

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]

Yes, what testing is this graph based on?

 

[MrEd]

This an interesting read.
I am not sure but I think written by Steve Bench

DHT with starved filaments.

 

[paul_b]

The graph is purportedly from RCA regarding lifetime of tungsten filaments. Based on how picky EML is with filament voltage tolerance, I would infer that this also applies to oxide filaments as well.
Emission Labs. Information about life time of electron tubes.

 

[MrEd]

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.

 

[MrEd]

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...

 

[Fran604g]

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?

 

[Fran604g]

Okay, I'm an idiot! They're UX201A... same thing, though, right?

 

[MrEd]

That's a beautiful radio

 

[MrEd]

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.

 

[MrEd]

I got this playing music last night.
One channel at a time with an old 6x9 automotive speaker I use for testing. 😊
Some noise as expected with the way things are laid out.
Sounds promising and worth continuing.

 

[MrEd]

A glow shot... I have gotten rid of 90 % of the noise at idle. Made a change in the gyrator board of one of FET devices. I guess it is ready to try in the main system next.