>Rich Measures wrote:
>>
>> >The question from Dave triggered my interest since I now am in the phase
>> >of starting building a linear myself. ...snip...
>...... the 1500B is what I have and can get more (surplus and cheap)
>so I will stick to that one. However is there any special worries, and
>if so what are they ?
>
- Zener-string shunt regulation for the screen is important. The c. 25mA
constant-current source for the screen regulator should be via a suitable
resistor to the anode supply.
- Providing a low-Z path between the grid and RF-ground is important.
- Operate the heater within Eimac specifications. An extra 1/2 minute of
warmup time might be a good idea.
>> >(Can I avoid
>> >input tuning ?
mostly
>I forgot to mention that I mean only all the ham bands in that range,
>Do you mean I can (simplify) the input by using a 12,5 Ohm grid
>termination below 20 Mhz
- The 12.5 ohm GTR - and the 4 /1 bifilar step-down transformer that
drives it - is not switched in and out. The 12.5 ohm termination needs
to be there at all frequencies to provide stability and to load the radio
that drives it. . . If you have a radio that can make 144w pep, you can
use a 12.5 ohm grid termination R and -60v of grid bias. At the higher
frequencies, you might need to switch in some shunt L to cancel the grid
C.
- If you have a radio that can make 36w pep, you can use a 50 ohm GTR and
-60v of bias. However, with 50 ohms, the input SWR is going to need some
shunt L sooner than would be the case with a 12.5 ohm GTR, as frequency
increases.
....
>If I go for 4Kv anode voltage, what est. output would you assume ?
>
The 4cx1500B is rated at 3000v max. and 900mA max.
>The marine type one gives min. 1500 W out with 2,9 Kv.
>
This sounds reasonable.
good luck, Harald
Rich---
R. L. Measures, 805-386-3734, AG6K
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