[Amps] SB220 - 10 Metre input coil adjustment

[Jim W7RY]

With the SB220, a 6 foot cable (of 66% velosity coax, RG8, RG58 with 
standard dialectic, in other words non foam, non LMR type) between the 
amplifier and the radio is best.

73, Jim W7RY


On 1/1/2022 2:44 PM, gudguyham--- via Amps wrote:
> What kind of input swr are you seeing as you make these adjustments on the input coil?  10 meters is very touchy on these amps.  You also have to take readings at a set output power across the band to see if there is a marked increase somewhere.  This will tell you if you need to massage the 10 portion of the tank coils to bring the “ sweet spot” where you want it.  You should do that first off and then fine tune the input because it will make a difference!!
>
>
> Sent from the all new AOL app for iOS
>
>
> On Saturday, January 1, 2022, 3:04 PM, Sam Ferris <ve5sf at sasktel.net> wrote:
>
> Wonder if anyone can tell me how sensitive/sharp the 10 metre input tuning
> coil tuning is on a SB220.  I am repairing an SB220 for a fellow ham and
> when I received the amp the central tuning slug for the 10 meter input coil
> (part# 40-964) was in a bag of parts … seems the tuning slug had fallen out
> sometime in the past.  It was noted that the 10 and 15 metre input coils
> have the same part number so I measured the depth to the outer face of the
> slug to the outer edge of the 15 metre coil to get an idea of just where the
> 10 metre coil should be set initially.  On initial tune up I was not able to
> get more that about 450 Watts at 0.5A plate current and 110 mA grid current
> on 10 Metres into a 1:1 SWR at 28.600 MHZ (Sweet spot for my antenna).  I
> have tried one adjustment moving the coil slug in two turns which proved to
> be the wrong way to go.  Have taken another look and decided to return to
> the first setting plus about ½ turn out – then try again.  Can anyone advise
> just how sharp the tuning on these input coils is?  Would it be best to
> devote the time to making a temporary face plate that I can drill an added
> access hole through to access the tuning coil from the outside?
>
>   
>
> The amp functions fine on other bands with reasonable output on a set of
> EIMAC tubes.  Other repairs to this amp have included replacement rectifier
> board, new parasitic suppressors – old ones showed significant signs of
> heating, replaced broken bandswitch, soldered loose wires, general cleaning
> and check of components.
>
>   
>
> Thanks
>
> Sam
>
> VE5SF
>
>   
>
>   
>
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