[AMPS] The Emtron DX2 amp: A 50ohm 50 Watt resistor in B+?

[Phil Clements]

At 09:30 AM 10/17/97 EDT, you wrote:
>
>On Fri, 17 Oct 97 03:15:03 -0800 Rich Measures <measures@vc.net> writes:
>>> at 10:00 PM 10/16/97 -0700, you wrote:
>>>>I question the resoning on a high value such as the 50ohm 50 Watt
>>>>resistor in their amp. Seems a little off to me.
>>>>
>>>>Comments?
>>>>
>>>
>>>That is Svetlana's recommended value for that tube.
>>
>>Which tube, Phil?
>
>
>For the 4CX1600B as used in the Emtron the "real" Svetlana recommendation
>is 25 Ohms or more. This would then lead to the assumption that the tube
>manufacturer feels a 110-120A surge is acceptable at a nominal
>2700-3000VDC.

I do not! I have to pay "retail" for my tubes.

>See my other post for the spec sheet quote. 
>
>Again assuming around a 3KV Ep in the Emtron (Tube max is 3.3KV) the amp
>designer is being quite conservative with a 60A rating. 

It is always best to be conservitive. Most modern day designs are hanging
on the
ragged edge on component parts at the 1500 watt level.
>
>>>You never want this resistor to open during an event.
>>
>>good point -- or sustain any type of damage.  
>>
>>>10 ohms is ok up to about 3 kv. I am running 20 ohms
>>>on my Alpha 77SX with good results.
>>>
>>Does  'good results' mean that you shorted the anode supply and the 20 
>>ohm glitch resistor was able to handle the resulting current without 
>>sustaining damage?

That is correct...I use 2 10 ohm 12 watt glass wirewounds in series due to a
space constraint. Flashovers in the Alpha 77SX RF compartment have been so
intense that some users have reported that internal parts in the blower
were even destroyed. It is imperative that a glitch resistor be added in
the Alpha 77 series. I put the resistor right next to the HV crowbar.


(((73)))
Phil, K5PC

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