[ARC5] AM linear amplification

[Richard Knoppow]

    I have a copy  of the 4th edition of the RSGB handbook The circuit 
shown as a push-pull zero bias Class B audio amplifier to be used as a 
modulator. The control grid is connected to the screen grid through a 
22K resistor so it is essentially a triode. Grids are driven from a 
transformer. Might be adaptable to RF. I looked in both a very old RCA 
transmitting tube manual (1938) and also the HB-3. Both contain 
operating conditions for Class-B RF linear as a tetrode but not zero 
bias (wants - 40V).  Output at standard CCS ratings is 12.5 watts. I 
have a couple of other places to look. I think I have seen the same 
circuit elsewhere.
     FWIW, the 807 is not a pentode but a beam power tetrode. Makes no 
difference here.

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


-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL