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Re: BDT preamp details

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John Swenson

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In Reply to: Re: BDT preamp details posted by smoking-amp on July 09, 2004 at 10:00:14:

Thanks for the tip on the demagnetizing, the spec sheet does mention keeping away from magnetic fields, I was going to try a mu-metal tube but I never thought of the tube itself getting magnetized.
Any hint on where to get ahold of those 50s and 60s articles? I did a fairly thorough search and only came up with TV and RF applications.
John S.

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Re: BDT preamp details - smoking-amp 16:46:10 07/09/04 (7)
Hi John,
One of the articles I just found here, it is titled "Audio Applications of a Sheet - Beam Deflection Tube" by J. N. Van Scoyoc of Armour Research Foundation in Transactions I.R.E. PGBTR circa 1960, pages 3 thru 7. Mentions applications such as phase splitter, variable gain control/AGC, tone control, stereo balance control, audio compressor, input signal selector. I have a scan of Fig. 6, a variable gain preamp/amplifier if someone can show me how to include it in the forum post or put it on their website. (I could scan the whole article too.) I believe I have another similar article somewhere too, but can't find it at the moment.
Don
- smoking-amp's scan - Bas Horneman 00:09:49 07/10/04 (6)
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  To infinity and beyond!!!
  - Allen Wright is gonna love that circuit ... :-)) - Eli Duttman 05:34:02 07/10/04 (5)
    That's kinda cool. The design is balanced end to end. Even the O/P trafo secondary and NFB circuitry (sic) are balanced.
    
    Eli D.
    - Yeah - except for the interstage and the NFB... (nt) - Allen Wright 11:07:32 07/10/04 (4)
      - NFB, etc. - Eli Duttman 11:54:50 07/10/04 (3)
        
        In Reply to: Yeah - except for the interstage and the NFB... (nt) posted by Allen Wright on July 10, 2004 at 11:07:32:
        
        Allen,
        NFB I can live with, IF it's done right. I have my doubts about a circuit, like the 1 shown, with an interstage trafo inside the loop(s).
        IMO, hackers (including yours truly) should keep NFB loops short and have no more than 2 caps. in the loop. Phase shift oscillators are FUGLY.
        FWIW, I thought you would appreciate the TOTALLY balanced circuitry, even if it has features you don't favor.
        
        Eli D.
        
        I thought you would appreciate the TOTALLY balanced circuitry... - Allen Wright 03:56:00 07/11/04 (2)
        
        In Reply to: NFB, etc. posted by Eli Duttman on July 10, 2004 at 11:54:50:
        
        Sure do - and a recent policy decision here at VSEI has resulted in the deletion of our unbalanced FVP5A preamp fromour product lineup, to be replaced with a (much) lower cost differential preamp, making all our amplication products balanced/differential. Way to go!
        Allen
        
        TOTALLY balanced circuitry - Triode Kingdom_ 12:41:38 07/12/04 (1)
        
        In Reply to: I thought you would appreciate the TOTALLY balanced circuitry... posted by Allen Wright on July 11, 2004 at 03:56:00:
        
        Allen, does this mean you will be eliminating all single-ended operation in your designs? Everything will be differential/push-pull, including low-level stages?
        
        Yes... - Allen Wright 04:18:04 07/13/04 (0)
        
        In Reply to: TOTALLY balanced circuitry posted by Triode Kingdom_ on July 12, 2004 at 12:41:38:
        
        > does this mean you will be eliminating all single-ended operation in your designs? Everything will be differential/push-pull, including low-level stages? <
        No great change as the only SE stages I've ever used or shown (since 1980) are in the FVP range of preamps - I've never used a SE driver stage in a P-P poweramp for example.
        The latest FVP5A is a great sounding preamp and it's map will stay up on my site - but commercially we can now do a fully balanced product (kit or completed) for less, it sounds even better and interfaces optimally with the growing trend for disc players etc to have balanced outputs, and manypoweramps to have balanced inputs.
        And good phono cartridges have always been "balanced"...
        Allen

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