James -
Sounds like you have the basic idea. The only thing I would mention is
that the 3-500Z tubes are rated for I believe 120 mA max grid current
(each) - so keeping the grid current to 240 mA or less for 2 tubes will
help insure long life. I have a Drake L-4B that also uses a pair of
Eimac 3-500Z tubes, and they are still going strong, and meeting spec
after almost 40 years of operating. The dual 3-500Z design is a
winner, that's for sure. I get about 1300 watts out of my amp on 80
meters, which falls to about 900 watts on 10 meters - surely enough for
anything I need to do.
Tuning the amp for max forward power while not exceeding allowable grid
current has worked for me for years, and your comment about leaving the
tuning alone once it is set for max output then reducing the drive to
produce whatever output power you need at the moment is also correct.
However, you can also remember that the 3-500Z tubes are true
transmitting types, not wimpy sweep tubes, so taking a few extra seconds
to tune up won't hurt them.
When using the amp on continuous duty modes like FSK or FM, the plates
will run a nice red-orange color. This is perfectly normal, and not a
sign of problems. Don't let them get as far as yellow though - that's
too much. Unfortunately, the SB-220 doesn't have as robust a plate
transformer as the one in the L-4B, so be a little careful with
continuous duty modes. Other than that, you're good to go. Have fun,
and I am sure you will enjoy the amp. .
- Jim, KL7CC
K3JPS wrote:
> Well, I finally figured out how to tune this SB-220 using what Elecraft gave
> me for now. FSK-D at 50W is a good place to start; quickly peak tune and
> load while keeping an eye on lg and lp seems to work well. That portion of
> the tuning takes me about 5 to 7 seconds to do. I then bump power up to
> 100w and then tune for max smoke which is another 3-5 seconds. Afterwards,
> I drop exciter power to whatever output I want while leaving the SB-220 at
> its current tune settings. As a result, 100 watts out of the K3 and a good
> tune registers about ~790ma lp and about ~250mA lg. It seems like a 10-1
> ratio with the 220 on CW/Tune mode; i.e. 10 watts out of the K3 gets me 100w
> out of the SB-220... 100w out of the K3 gets me 1000watts out of the amp. I
> think all is well at this point!
>
> 73 de James K3JPS
>
> On Thu, May 28, 2009 at 11:20 PM, Bob Garrett <
[hidden email]> wrote:
>
>
>> Jim,
>>
>> Let's not make this complicated. Set the K3 to say 10 watts out and tune
>> up the SB220. Increase the output from the K3 and adjust the SB-220 for
>> the output you desire keeping in mind the plate and grid current limits.
>> BINGO, you are good to go.
>>
>> 73, Bob K3UL
>>
>>
> __
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