[Amps] gs35b on hf problem .

[Ian White GM3SEK]

Jerry Muller wrote:

>From: "Carlo Houben" <carlo.houben1 at pandora.be>
>To: <Amps at contesting.com>
>Sent: Thursday, November 10, 2005 4:43 PM
>Subject: [Amps] gs35b on hf problem .
>
>
>> Hi , i am building a hf amp around a gs35b (new old stock ) in a GG
>> configuration
>> g3sek triodeboard for control .
>> HV 3300V no load .
>> The following is my problem :
>> 1/  My glitch resistor  33 ohm  17 w passed out by measuring  zero signal
>> anode current .
>> first it was 20Ma and after i put the bias voltage to around 29 V it was
>> 100 Ma .
>> but after 3 times ptt the glitch resitor past out .
>> annyone an idea where i have to look for .
>> Thanks in advance .

>Is your glitch resistor a wire wound resistor? Your glitch resistor needs to
>be able to handle the full supply voltage for however long it takes to
>discharge the filter caps. Typically this isn't a long time and the wattage
>rating of the resistor can probably handle it. The key specification here is
>that the resistor needs to be able to handle the full supply voltage for a
>few milliseconds. Wire wound resistors don't cut it. They blow when a glitch
>occurs.
>
>Metal film or carbon comps are OK.

Sorry, I would say the exact opposite. Wirewound resistor CAN handle 
high-voltage surges, if they are the vitreous (glass) enameled type with 
a long body and terminals at opposite ends.

But normal wire-ended metal film and carbon composition resistors make 
very poor glitch resistors - they can not handle the power in normal 
operation, and they can not handle the high voltage in a current surge.

Carlo: Exactly what type of resistor were you using? Exactly what 
happened to the resistor? (Francais ou/of Vlaams OK)



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