>
>Leigh wrote:
>>
>>I guess the biggest question I have is in regards to the
>>requirements of the screen supply. There appears to be no screen
>>by-pass resistor in the RF deck so I'll assume the builder (have
>>no idea who it was) included that in his screen supply. The
>>Eimac data sheet states 70mA for this resistor so I guess its
>>value should be around 5k ohms? What is the recommended size of
>>this component. I would guess 5 watt would be large enough but
>>maybe I am not considering possible failure modes? Some
>>references I have seen state that HV should be applied before the
>>screen voltage so I'll assume it is a good idea to apply screen
>>voltage with the TR relay activated. Any thoughts on a
>>recommended screen supply circuit. I wouldn't think with the
>>screen bleeder that regulation is required and I was thinking of
>>using a choke input filter (anyone have a ~4-5 HY 350mA 400VDC
>>filter choke lying around?).
>>
>The Eimac advice assumes that you are not using a regulated screen
>supply,
? Eimac 8660 specification sheet dated 6-1-1967, page 4, "The screen
voltage must be maintained constant... ...".
'
>...only a "dumb" bleed resistor - but for good linearity and tube
>protection you MUST regulate the screen voltage closely.
>
>When you use active regulation of the screen voltage, you no longer need
>a 70mA bleed. 10mA is plenty, and its only function is to clamp the
>screen voltage while the T/R relay contacts are actually changing over.
>
? Typical screen current is stated to be Negative 14mA.
cheers, Ian.
- Rich..., 805.386.3734, www.vcnet.com/measures.
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