[Amps] PSU design question

[Ian White GM3SEK]

Craig wrote:
>
>What is "safe"  practice in a grounded screen tetrode amplifier where 
>the requirement is that the power supply negative rail is left 
>"floating" ?
>
>It always makes me nervous poking around a grounded screen amplifier 
>when some parts of the circuit is below chasis potential and the 
>negative of the power supply is left floating.
>

Me too. I don't think there is any wonderfully safe way, as all three 
power supplies - HV, grid and screen  - are only connected to chassis 
through the G2+ connection. In particular it needs a fully floating HV 
supply with a very well insulated negative side.

DC grounded screen isn't a configuration I would ever choose willingly. 
The only exception would be in a UHF tetrode amplifier using concentric 
coaxial cavities where the screen has to be grounded for reasons of 
mechanical construction. (Gerald K5GW is the local expert on that.)

At lower frequencies I would much prefer to tackle the problems of RF 
bypassing the screen grid, and operate with the cathode DC grounded in 
the normal way.


-- 

73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek