[ARC5] AM linear amplification

[Richard Knoppow]

    After a little though. The triode connection is somewhat unusual 
since normally one would see the screen connected to the plate rather 
than to the control grid. BTW, the RCA HB-3 tube handbook shows curves 
for a triode connected 807 but does not specify the connection (or 
perhaps I missed it). A casual inspection suggests its pretty linear but 
the curves may be different for the screen and control grid being tied 
together. This is a very intriguing idea.
    I will add just a little more. A controlled carrier transmitter 
varies the carrier so that the signal is essentially always modulated 
100% but the entire envelope varies with the modulation level. Usually 
there is a residual carrier at some fairly low level. The idea is that a 
linear amplifier will work about the same as it does for an SSB signal 
and does not need to dissipate the carrier power continuously.  The 
requirement for _peak_ power is not changed but the _average_ is 
substantially reduced.  There are commercial transmitters that put out 
controlled carrier AM such as the Drake T-4B and C. This is meant to 
allow them to be used with a standard SSB linear without having to cut 
the power way down. In receiving one needs either the same sort of fast 
attack, slow release AVC used for SSB or manual RF gain if the audio is 
not to "pump". I think there is probably a lot of material in the 
literature for controlled carrier systems.

On 12/19/2016 7:27 PM, AKLDGUY . wrote:
> Many thanks to those who have replied so far, all with interesting aspects.
> Use of a very large tube in order to get a worthwhile power output while
> not exceeding plate dissipation and Class B operation are of particular
> interest to me.
>
> I'm familiar with the 813 class of tube, being the owner of a RCA
> ET4332-B transmitter at one time which used a pair of them, and although
> they're sometimes available at swap meets here, the building of a 1500
> volt power supply is a bit further than I want to go (no suitable power
> transformers).
>
> Class B is interesting. It's not widely known that the 807 / 1625 is
> capable of Class B zero bias operation, with screen grid connected to
> control grid*. This configuration eliminates both the negative grid
> supply and the screen supply. A pair of these tubes requires about 5.5 W
> of drive power*, which the BC-230 can easily deliver.
>
> *RSGB Communication Handbook, Fourth Edition, 1968, page 9.21-22
>
> I'll look into this aspect. I had forgotten about 807s in Class B.
>
> 73 de Neil ZL1ANM
>
>
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL