[AMPS] Amp using 833A

[jeff millar]

Tom's probably got the best point about high IMD without the cathode
negative feedback.  He's also right about high gain, instability, long leads
and oscillation at HF.

That being said, it's fairly easy to create a step up grid circuit.
According to my handbook, in class B service, 3000V on the plate
requires -70V on the grid and 400V of p-p drive (because class B mean grid
current).  This tube wants to operate in push-pull.  If you're lucky you may
find some BC-610 output tank coils that were used in a plate modulated c1940
transmitter that ran a pushpull pair of 833 modulated by 810's (? before my
time).  The BC-610 tank used a nifty swinging coil output link coupling.

Some suggestions to consider...

- use two in pushpull
- drive the grid with broad band step up from 50 to about 800 ohms, requires
a 4:1 turns ratio.
- resistive load the grids with 400 ohms
- less than 70V negative bias for AB...don't know if AB2 required for decent
output
- Drive with a bit less than 100 Watts
- Neutralize with cross coupled plate to grid capacitors
- Suspend the tubes in the middle of the box, design for best look
- Don't worry about lead lengths, the tube designers didn't
- Best just accept single band operation
- Make sure you can see the plates in operation
- Use a low speed fan...quiet has a cool factor all it's own
- Keep the operating frequency below 15 -20 MHz
- Operate 3 - 3.5 kV and 750 ma and expect 1500W out

----- Original Message -----
From: "Phil (VA3UX)" <phil@vaxxine.com>
To: "jeff millar" <jeff@wa1hco.mv.com>; <amps@contesting.com>
Sent: Monday, September 18, 2000 9:09 PM
Subject: Re: [AMPS] Amp using 833A


> Not to worry Jeff.  I pretty much ignored the reply you refer to below.
> Grounded grid never even entered my mind with respect to this tube.  It
was
> Rich that chose to reply in a one-sided manner regarding g-g, despite
being
> fully aware of the other driving/operating configurations for tubes like
> this.  Pay close attention to this trait of his.
>
> I'm curious about this tube since being given 2 of them this past weekend.
> I'm a bit of a nostalgia buff (antique radios - oscilloscopes - test
> equipment and anything else with valves).  I've already received a couple
> of offers for assistance with information for 833A amps and I intend to
> follow them up.  Maybe there'll be some pics of a newly minted 833A amp on
> the Amp Pix page in the not too distant future - who knows.
>
> Phil
>
> At 08:14 PM 9/19/2000 -0400, you wrote:
> >This is a sad day in amateur radio.  Here we are in a mail list for the
high
> >end of the amateur radio building community and we're reluctant to use a
> >tube that requires bias!?  4-1000's look ok when glowing orange but an
833A
> >is gorgeous with that bright red region in the center of the plate (not
> >anode, plate).
> >
> >jeff
> >
> >----- Original Message -----
> >From: "measures" <2@vc.net>
> >To: "Mark S Graalman" <wb8jkr@juno.com>; <phil@vaxxine.com>
> >Cc: "AMPS" <amps@contesting.com>
> >Sent: Sunday, September 17, 2000 10:25 PM
> >Subject: Re: [AMPS] Amp using 833A
> >
> >
> >>
> >> >
> >> >  I'd make a lamp out of it.
> >> >
> >> sound advice, Mark  The Mu is too low for g-g service.
> >> >
> >> >On Sun, 17 Sep 2000 21:24:05 -0400 "Phil (VA3UX)" <phil@vaxxine.com>
> >> >writes:
> >> >>
> >> >> Anyone ever build or use an amp employing the 833A ?
> >> >>
> >>
> >>
> >> -  Rich..., 805.386.3734, www.vcnet.com/measures.
> >> end
> >>
> >>
> >> --
> >> FAQ on WWW:               http://www.contesting.com/FAQ/amps
> >> Submissions:              amps@contesting.com
> >> Administrative requests:  amps-REQUEST@contesting.com
> >> Problems:                 owner-amps@contesting.com
> >>
> >>
> >
> >
> >
>
>


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