I agree with Tim. Also, seems to me the grid current is too low. I’m
going by memory, but for two 3-500Zs, shouldn’t it be above 200mA?
Possibly the drive is too low?
73,
Jim w8zr
Sent from my iPhone
> On Jan 1, 2022, at 9:01 PM, Tim Duffy <k3lr@k3lr.com> wrote:
>
> So two 3-500Z tubes give about 50 ohms feedpoint Z. W1QJ can correct if need
> be.
>
> So take OUT the tubes - put IN a 50 ohm non inductive resister there. You
> know where it goes?
>
> Then use the RIGEXPERT and find the match on the input - get it to 1:1 (you
> can do this easily with the core).
>
> Then you will have over 1 KW on 10 meters output.
>
> 73
> Tim K3LR
> -----Original Message-----
> From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Sam Ferris
> Sent: Saturday, January 1, 2022 3:54 PM
> To: amps@contesting.com
> Subject: [Amps] FW: SB220 - 10 Metre input coil adjustment
>
> Hello Gudguyham. I am seeing an input SWR of 1.4:1 at 28.005 and it rises to
> about 3:1 at 28.700. On the input side it is above 1.5:1 staring at 28050
> MHz. No input SWR dip between 28005 and 28050 – just rises all the way.
> Have not tried beyond 28700. As far as I know and by the looks of the amp
> the tank coli has never been touched for tuning. The latest trial yielded
> about 520W at the HV setting, in comparison with the very first setting based
> on physical depth measurements alone.
>
>
>
> Thanks
>
> Sam
>
>
>
>
>
> From: gudguyham@aol.com <mailto:gudguyham@aol.com> [mailto:gudguyham@aol.com]
> Sent: Saturday, January 01, 2022 2:45 PM
> To: Sam Ferris <ve5sf@sasktel.net <mailto:ve5sf@sasktel.net> >;
> amps@contesting.com <mailto:amps@contesting.com>
> Subject: Re: [Amps] SB220 - 10 Metre input coil adjustment
>
>
>
> 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
> <https://apps.apple.com/us/app/aol-news-email-weather-video/id646100661>
>
> On Saturday, January 1, 2022, 3:04 PM, Sam Ferris <ve5sf@sasktel.net
> <mailto:ve5sf@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
>
>
>
>
>
>
>
>
>
>
>
> _______________________________________________
>
> Amps mailing list
>
> Amps@contesting.com <mailto:Amps@contesting.com>
>
> http://lists.contesting.com/mailman/listinfo/amps
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|