Message-ID: <1D890D2AF7A34E7E847559C8EE4921A4@AGB>
From: "Graham" <g8fzk@g8fzk.fsnet.co.uk>
To: <rsgb_lf_group@blacksheep.org>
References: <CAKvcm2d8JffcrF9E7MojDPtEZVaJGTwxiX6yU0dWUUs0tYYuWQ@mail.gmail.com><20121218092921.Horde.h2yZX_rSz0VQ0BtRPVIC2uA@posti.anvianet.fi><CAKvcm2cgFMiw2fkhCXvh+op-35cxQX65F3GsNM7bBEgKee_3QQ@mail.gmail.com><20121218100332.Horde.2ASBc_rSz0VQ0CNU8mNkBhA@posti.anvianet.fi><CAKvcm2cwH8j7yVD2p+Qd+EcrMbzURfzbYFe_0K688-F75vBTjQ@mail.gmail.com><20121218152622.Horde.XfcUIerSz0VQ0G7_VqKUnlA@posti.anvianet.fi><CAKvcm2evEerTZqS07BZTUD8acksEv34vLApYU3wnCOGEDHSYMQ@mail.gmail.com><83EEBFC65ED94B0880138E0637A84E24@AGB><CAKvcm2emxJUnTXkVGUs-PjPbapzATU=9H2Xrc51BWHw4H+m6bQ@mail.gmail.com><9E879884664540C8BC7A08377EAFC51C@AGB> <CAKvcm2dg=Dmh5HZDx-DNSNh5rm2=DUYknKn-adqTi6bSLSr0Ng@mail.gmail.com>
In-Reply-To: <CAKvcm2dg=Dmh5HZDx-DNSNh5rm2=DUYknKn-adqTi6bSLSr0Ng@mail.gmail.com>
Date: Wed, 19 Dec 2012 10:00:32 -0000
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Subject: Re: LF: Better picture of the 807 based 500kHz TX
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Ok D

I ran a  AM screen  modulated  807 long  ago  , with a  resistive   divider 
for the  screen  voltage ,  mod  transformer  [ output transformer , with 
speaker  winding  as  the  input from  small  amp]  to  tune  open cct 
[switch]  the  earth of the  divider ,screen volt = max ,  tune for  max  RF 
out, shallow dip   , then  switch -on- dropped the  screen  to  50% volts  , 
gave  good  upward mod , had a  8 ? uF  cap at the  tapping to take audio to 
ground ..

73-G.



--------------------------------------------------
From: "Dimitrios Tsifakis" <dtsifakis@gmail.com>
Sent: Wednesday, December 19, 2012 12:47 AM
To: <rsgb_lf_group@blacksheep.org>
Subject: Re: LF: Better picture of the 807 based 500kHz TX

> That is not the final schematic, this is one I drew as a starting
> point and there have been many changes (including a cathode resistor
> to provide some of the bias and a resistor with a few turns on it on
> the plate for avoiding parasitic oscillations). It's not quite
> class-c, it's somewhere between class-c and class-b by the way. The VR
> valves were not used when I configured this for AM, but I am only
> using CW now, so I thought the regulated screen voltage is not a
> problem... Need to revisit that I guess...
>
> 73, D.
>
>
> 2012/12/19 Graham <g8fzk@g8fzk.fsnet.co.uk>:
>> lol  well  that config is  for  linear  service  , you should  have the
>> screen  fed  via  something like   6.8K  from the  plate  supply  , with 
>> a
>> 0.1 uF decoupling  cap , no regulation  for  class C as  the  screen 
>> voltage
>> will  vary as the  anode amps / secondary emission changes [ negative
>> resistance type of thing] , you need   a   100 ohm  2 watt  resistor ,
>> shorted   with a over wound  8 turn 10 mm id  coil  directly  to  the 
>> anode
>> as   acp , would  normally  have 50/100 ohms  in series  with the 
>> cathode
>> as  auto  bias , should  the  drive  fail, or  IA = inf  very  quickly 
>> ...
>> starts  off  with  orange anodes  by the  wire supports  , then  yellow ,
>> then  sparks  inside  , then  white anodes  , then  glass  shatters / 
>> melts
>> = game over   , with  cathode keying  , looking  at  a  big  gap  cw  key 
>> !
>>
>> Happy  days  : )
>>
>>
>> G..
>>
>> --------------------------------------------------
>> From: "Dimitrios Tsifakis" <dtsifakis@gmail.com>
>> Sent: Tuesday, December 18, 2012 11:46 PM
>>
>> To: <rsgb_lf_group@blacksheep.org>
>> Subject: Re: LF: Better picture of the 807 based 500kHz TX
>>
>>> 2012/12/19 Graham <g8fzk@g8fzk.fsnet.co.uk>:
>>>>
>>>> Why the  stabilised  screen  supply ?
>>>> G..
>>>
>>>
>>> It's embarassing. I like the glow of VR tubes! :-)
>>>
>>> 73, Dimitris VK1SV
>>>
>>
>