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Old 30th October 2011, 05:33 PM   #41
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Quote:
Originally Posted by Tony View Post
hi,

can you give more info like operating points, psu, and topology if you can please? thanks....i am also protyping a 1624 preamp.....
Tony,

I wished I could. The designer used to be a friend of mine. In fact it was just a couple of weeks after hearing how nice his all 6L6-based preamp sounded in my audio system when I had the designer and the present the owner of the 6394a/6L6-based preamp at my home to listen to tunes. As we listened the conversation changed to a triode tube the designer wanted to try in his 6L6 based preamp. So the opened a bag he had brought with him and produced the 6394a tube. We were all fairly excited with this new, triode that was previously unknown to all of us. As the tube was passed around and the conversation continued I turned and asked the designer ---{who I thought was my friend}--- "if" this new 6394a/6L6-based preamp sounds better than the 6L6-based preamp, would you make one of these instead of the 6L6-based preamps for me?

At the time he assured me he would, but as the build proceeded, I noticed I was being suddenly excluded from listening tests, emails I sent were answered in a harsh, condescending tone etc. Never was I told I changed my mind about building this preamp for you. In fact when I found a batch of eight NOS, Tung-Sol 6394a tubes for $200, I sent the designer an email explaining I wanted to buy these eight 6394a tubes so when he made my 6394a preamp I'd have plenty of spares. Even then when he was provided the opportunity to tell me "I'd hold off purchasing those 6394a tubes" the designer responded with "$200 was a good deal. You should buy the tubes if you could afford them!" To me it appears as if he deliberately tried to screw me over, by getting me to spend $200 on tubes he knew I would have no use for.

It wasn't until the 6394a-based preamp was finally completed and brought to the owner's home, that everything was revealed to me through the new owner. The new owner said, the designer told him he didn't want him to bring the 6394a-based preamp to my home and that he wouldn't be making me one of thes 6394a-based preamps! So I now I'm stuck with eight NOS, 6394a, Tung-Sol tubes I have absolutely no use for, I no longer speak to the designer ---{except to be socially exceptable when he attends some local audio events where we have mutual friends}--- and I'm unable to answer any of your questions about the 6394a-based preamps circuits.

Thetubeguy1954 (Tom Scata)
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Old 30th October 2011, 11:09 PM   #42
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Hi,

The only "raison d'etre" for using power beasts like that is when you want to drive a solid state amp with inordinate amounts of current (in a tube world) to bring it "alive" and make it sound as if it were a tube amp.

Other than that?

As for the 6336A as a rectifier? I guess the poor guy blew up a ton of power tubes due to grid inrush current taking out the grid at start-up.
Those guys like to have it come to them slowly which you eiher provide for (PS wise) or use use BIGgish gridstoppers like 100K or over.

Other than that, yeah, sure you can recycle any of those big bottle (from the humble Ruskie 6C19 up to a 6C33C) for rectification purposes. No genious there, it's pretty obvious. To me at least.

Ciao,
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Old 30th October 2011, 11:33 PM   #43
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Tom,

that was sad......but otoh, his loss, not yours......you can always sell those tubes....


i have used a 6as7 as rectifier in a hybrid fwb circuit in my 1624 it is still a wip.....

Click the image to open in full size.
Click the image to open in full size.

i will have to resort to ss filament supply, i can't get the hum issue to go away....
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Old 31st October 2011, 12:36 AM   #44
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Quote:
Originally Posted by Tony View Post
<snip>

i will have to resort to ss filament supply, i can't get the hum issue to go away....
Given the plate chokes I see near the power transformer are you certain that stray fields from the power transformer are not coupling into them? Note that your unfortunate choke orientation will provide excellent coupling between them and the power transformer - particularly the closest choke..

I have had problems with magnetic coupling into plate to line transformers and plate chokes in line stages which is why I now put the power supply on a separate chassis..
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Old 31st October 2011, 01:02 AM   #45
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kevin, i am beginning to think that a separate chassis psu is justified in this case....thanks....i think my problem stems from the fact that the B+ is not as stiff as it should be, the VR105 tube does not function as designed, this preamp uses the screen as plate btw, the real plate serves as a sheild.....but i may have to change that to real plate loaded....

i found some 1J6GT tubes to play with.....http://frank.pocnet.net/sheets/084/1/1J6G.pdf
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