View Full Version : Commander HF-2500 on 12 and 17m
i have an older Command technologies HF-2500 amp and read the manual. it claims to cover 10, 12, 15, 17, 20, 40, 80, and 160m. the band switch lacks 12 and 17m. no where in the manual does it say how to use the amp on 12 and 17, just that it will work.
i have tried to tune up the amp on 17m using the band switch on both the 15 and 20m setting but neither seemed to provide any output. i was driving the amp with only a few watts, but i was expecting to see some amount of plate current, but there was none. i just don't see how it will work since the tuned input does not provide for it, nor is the tank circuit tapped for it.
any suggestions on how to use this on 12 and 17m?
04-29-2011, 10:08 PM
I don't have one and never did, but I did a bit of Googling and it appears others have used or are using the HF-2500 on 12m and 17m, and evidently without modification.
For 17m, definitely use the 15m bandswitch position. For 12m, definitely use the 10m bandswitch position.
The output tank can evidently tune 17m and 12m okay and I didn't see any reference to people blowing up the plate RF choke so it's likely to work okay. The "problem" is that the input networks are tuned to 15m and 10m, and will be out of tune on the WARC bands. Usually, this means it will just take more drive to actually "work."
Have you tried applying full drive and then tuning the plate tune and load controls? Instead of "less" drive, you should probably use "more," and even 100W may not be enough if the input networks are sharply tuned.
Of course, you could also try re-tuning those networks, at the risk of losing normal operation on 15 and 10 meters.
In most amps I've used that use a single bandswitch setting for 15/17 and for 10/12, I was able to find an input adjustment that allowed them to work on all four bands, with a bit of mismatch on all of them (tuning for midway between the bands). I've done just this with my AL-80B, as an example, and that worked out well.
i'm a little shy with this amp after frying the choke in the 160 contest in December. it cost me two plates of brownies to remedy :) i was thinking it might take more drive, but it didn't want to push the choke or put too much mismatch on the tuning circuit - amp stages in the rig are not cheap. i learned that from the 30L1 days.
i mispoke - it's got plenty of plate current, just not much grid current. more input drive, more plate current. i'll have to mess with the tune and load to find the spot.