[Amps] Equalizing Restistors
Sat, 2 Mar 2002 20:55:36 -0800
>If I understand you, I can remove the swinging choke leaving just the 25mfd
>cap as the hv filter.
>If the high voltage then rises to about 3kv instead
>of the normal 2.2 kv, I would have to change the screen voltage and the
>grid voltage proportionally to maintain the proper operation of the 2
>4-400's. Is this a correct assumption?
Sort of. The proper screen potential is c.800v for AB1. Grid bias
should be adjusted for c.75mA of ZSAC. This will be c. 120vdc.
Screen V is can be obtained from a zener-string. Since the screen
current required for two tubes is c. 26mA, 35mA of zener bias would be
enough. Thus, 33v, 5w (rated @25ºC case) zeners will do the job. Thus,
one needs 25 of such zeners in series mounted on a perfboard with some
air flowing. One means of zener bias current is the anode supply.
Roughly 60 - 70 k‡s @ 75w is indicated.
>BTW....I understand that the 4-400's would run better with 3kv
Indeed. With the tetrode config., 4000v is even better. For SSB. some
guys use 4800v. In AB2-GG, 3500v is good.
>Thanks in advance,
ur welcome, Bill. have fun.
>At 09:07 AM 3/2/02 -0800, you wrote:
>> >Thanks for the replies folks. I should have figured the power rating of the
>> >resistors myself......i use ohms law, must have been a "senior moment"!!!
>> >As for the swinging choke input filter, Im stuck with it unless I
>> >completely re-do the whole Thunderbolt. If I go to a capacitor in put
>> >filter, the HV will rise and this will cause all sorts of headaches I
>>€ Switching to C-input and removing the swinging-choke should raise the
>>anode-V to about 3kVDC, which is c. the same as a SB-220 and TL-922. My
>>guess is that the extant tank components will withstand the increase.
>> >My main reason for changing the hv cap is to increase the
>> >capacitance from the stock capacitance of 8mfd to about 25mfd to help the
>> >regulation on ssb.
>>€ To compensate for the transient unregulation produced by rapidly
>>changing current on SSB/CW through the swinging choke, it might take
>>considerably more C. I would start off with c. 0.1F and check it with a
>> >Any other suggestions will be greatly appreciated.
>> >Bill Russell
>> >Amps mailing list
>>- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
>Amps mailing list
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,