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>> -----Original Message-----
>> From: Jim Thomson
>> Sent: Wednesday, July 31, 2002 04:19
>> To: 'stevek@jmr.com'
>> Cc: 'w6frmarv@dslextreme.com w8JI@contesting.com'
>> Subject: diode strings...bias
>>
>> steve/rich/marv/Tom
>>
>> I got the same results as Rich did, varying the current from
>> 100ma to 1.2A Also tried 40ma to 800ma, and also 350ma
>> to 3A. regulation was in the order of abt 14%. Got the same
>> results whether using 1N5408's or using 6A10's. The 6A10's are
>> rated at 1kv-6A-400A surge, and are double the diam of a 5408.
>> Same length and wire leads.
>>
>> I also tried sticking a 1000 uf - 50v rubycom electrolytic across
>> the entire string. The DYNAMIC reg was then WAY less than 14%
>> on ssb/cw.
>>
>> 6A @ .8V = 4.8 Watts. Hot as hell if CCS.
>>
>> I use 10 x 1N5408's with a 1000 uf 50V lytic in all my 3 x
>> L4B's. The drake L4B ran zero bias (240ma idle on ssb
>> position-2600V) This mod dropped the idle down to 100Ma on ssb,
>> and 40Ma on CW(1900V) I used a 3 position center off toggle,
>> spdt-center off to give me 3 positions of bias.
>>
>> Funny, with 40ma of idle on 1900v cw position, zero imd
>> results, as measured 1/2 mile away on ssb. Drive requirements
>> went up by 6-8 watts.
>>
>> Also tried grounding with some strap, just ONE grid pin of each
>> 3-500Z. Drive requirements dropped on all bands by 20 watts.
>> Drake had used 3 x 200pf caps + 1 choke on each tube socket.
>> Heath later copied same ckt. I mentioned this to my buddies
>> with TL-922's + SB-220/ SB-221's.
>>
>> They also tried the grounding just one grid pin of each socket
>> and all reported the same 20w reducrion in drive power.
** Frequency didn't matter?
>> The fellows with the SB-221's also reported that their output power
>> on 10M shot up from 700-800 watts to 1350-1400 !!
>>
** 10m is the band where 600pF of grid bypass [XC=9.4-ohms] is
seemingly enough. Since a typical "Zero-inductance" 3-500Z
grid-grounding strap has c. 15nH of XL at 10m, a 600pF grid-bypass will
put the grid closer to ground than a strap.
>> The fellows with the TL-922's reported that they could now
>> remove the AG6K nichrome suppressors, and the TL-922's were now
>> rock stable.
>>
** 922 / rock stable . . . I own one and that's laughable. They are
[factory-fresh] squirrelier than a SB-220 or an AL-1200 with
"neutralization".
>> On the big metal triodes, I use a 12 position rotary switch
>> and 50 x 6A10's + 1 lytic across the entire mess. I tap right
>> after diode #10, then every 3rd diode after that.
>>
>> ...
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
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