[AMRadio] 807's triode connection question...

[ka1iic at prexar.com]

Hey thanks guys!!!  Even on the 4th AM continues FB!!!

Thanks for the input it helps quite a bit...  I'm going to try a modulator
with 807/1625 because I have quite a few in stock...  My other mod deck
uses 809's and they seem to be a FB tube but only have one pair of
spares...  of course I could use the standard 811 but hey... I got a few
fun tubes sitting around...  If I remember my 809 deck orginally used
5514's but for some reason I didn't like them...

BTW... I've got an VM-3 mod iron that I want to use... how could one limit
the power from the mod tubes to keep within the power limits of the tranny...
Don't care to take chances because it took me too long to find a good one
I plan to use std chokes for a mod reactor to keep the DC off of the
secondary....

any ideas on this one???

73
Vince
ka1iic
(PW stationary)

On Thu, 4 Jul 2002, Bob Bruhns wrote:

> Hi Vince,
>
> I have never tried these connections, but HLR-Timtron told
> me the RCA trick with drive to the screens and a 20K from
> the screens to the control grids was not ideal, and several
> experimenters tell me there's no way you get 120 watts from
> it at 750V.
>
> Tim said that when you bias this arrangement and drive it,
> first the plate current goes down at low audio levels, and
> then it rises at higher audio levels, and he didn't like
> that.  I forget whether he said there was distortion, but I
> think he would have overlooked the odd plate current effect
> if it sounded OK.
>
> Tim used a different circuit. If I remember, he grounded the
> control grids and drove the screens.  This makes sense to
> me, but as I said I never tried it.  It surely must take
> some serious drive levels, probably the screens run at
> zero-bias and peak at +500V.  In the end, this all does
> argue for 811As instead of 807s, if you have room for the
> tube envelope.
>
>   Bacon, WA3WDR
> ------------------------------
>
> (original message)
>
> Subject: [AMRadio] 807's triode connection question...
>    Date: Thu, 4 Jul 2002 06:01:53 -0400 (EDT)
>    From: <ka1iic at prexar.com>
>      To: <amradio at mailman.qth.net>
>
> Hi guys me again,
>
> I've been looking up all the info I can get about using
> 807's in triode connection....
>
> I have found 3 different cases and was wondering about the
> benefits of each....
>
> First off the older ARRL handbooks show connecting the grid
> to the screen through a 20k ohm resistor and driving the
> screen...
>
> Another publication shows connecting the screen to the plate
> directly and driving the grid as you normally would...
>
> And case three shows connecting the screen to the plate
> through a 100 ohm resistor and driving the grid as per the
> norm...
>
> Any guidance is welcome...  any comments welcome also...
>
> Thanks in advance
>
> 73
> Vince
> ka1iic
> -.--.
>
>
>
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