[Amps] SB-220 6M conversion

Alek Petkovic vk6apk at bigpond.com
Fri Jun 5 23:28:53 EDT 2020

 From what I know on the subject, stick with the flat coil.

Also, there is a quite finnicky, incremental and precise tuning procedure.

I remember being with a local ham friend, when we fired his converted 
amp up for the first time. We were similarly disheartened but we 
persisted and followed a specific tune up procedure and bit by bit, with 
each step, the output inched upwards. So much so, our final result was 
the 1500W we were hoping for at the outset.

Once that sweet spot was found, we logged it and left the knobs right 
where they were. That was a few years ago and the knobs have not been 
touched and the amp still produces the goods.

Talk to Lou, W1QJ, the guru on this subject.

Your plate volts sound a bit low but probably the metering resistors 
have drifted.

73 and good luck, Alek, VK6APK

On 6/06/2020 11:10 am, 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
> manuals at artekmanuals.com

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