[Amps] SB-220 6M conversion

[Artek Manuals]

Shack is dark ...will post pixs tomorrow

The old "tune" cap is now the load cap

The "new" tune cap measures 7-55pf and it is about 1/2 way meshed at 
resonance...getting a nice sharp dip in plate current at resonance

Using about 2 1/2 turns ( going from memory that might b +/-  turn 
played with a lot of "taps"  with no real difference)

Have not done the short the grids to ground yet ...Did that on my TL-922 
last year didn't change power out noticeably.But will try that tomorrow 
if I don't get a better suggestion

Dave
NR1DX

On 6/5/2020 11:22 PM, Jim wrote:
> Did you directly ground the grids with short wide straps? (best not to 
> use braid).
>
> What did you change on the 10/15 meter coil to use it on 6 meters?� 
> What are you using for tune and load caps? What is the minimum 
> capactiance of the tune cap?
>
> Post some pictures so we can take a look at your layout, tank circuit, 
> and the tuned input.
>
>
> Thanks
> 73
> Jim W7RY
>
> On 6/5/2020 10:10 PM, Artek Manuals wrote:
>> I have enough HF amps here (four at last count) One of them is an 
>> ancient SB-220 , so I thought what the heck I would "hack" it and 
>> turn it into a 6M single band. I have a folder� full of articles on 
>> how to from the last 20 + years.
>>
>> All done "physically" but try as I may I can not get more than about 
>> 600w out .
>>
>> 1) Two different tank circuits , one with a section of the original 
>> 10/15� coil from the SB220 and a 2nd one with a a piece of flat 
>> copper strap ...no difference
>> 2) Changed the parasitic chokes
>> 3) Tried� "T" input match. Pi input match , straight through ...no 
>> difference
>> 4) Plate voltage is 2400 unloaded and about 2050 loaded in CW position
>> 5) Bias measures 6V
>> 7) Has new Hardbach bias and diode and metering board
>> 8) Older set of Eimac 3-500Z and newer set RF Parts 3-300ZG ...no 
>> difference
>>
>>
>> What am I missing, ?
>> What else to try?
>>
>> Dave
>> NR1DX
>> manuals at artekmanuals.com
>>
>
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-- 
Dave
Manuals at ArtekManuals.com
www.ArtekManuals.com


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