[Amps] Thoughts after a weekend with my SB-200 during CQWW SSB

W5CPT w5cpt at bellsouth.net
Mon Oct 29 21:26:07 EST 2007


Here are some thoughts after a weekend using the SB-200 during CQWW SSB. 



Firstly I will never get over the difference it made. I started with the amp in standby (I built my rig to amp interface and included a bypass switch in it rather than in the amp itself) thinking that I would only use it if NECESSARY. When the first station I called did not answer after 3 tries I tuned it up and flipped the switch. BANG, he came back to me on the first call with the amp.  I tried the same thing a few more times with exactly the same result so the amp stayed in the contest till the end.  I will have to upgrade the TV cabling as the bride says it puts lines in the TV and makes the picture BLOOM sometimes. I think an S-Video cable from the satellite box to the TV should cure that and I had been planning to do that anyway.

 

The amp is really tolerant during tuning. The TUNE control has WAY more effect on the output than the LOAD control does. In fact, while I have not gone through and built a TUNE/LOAD chart for the different bands I would be willing to wager the LOAD control is always between 4 & 7. The peaks are rather sharp with very little gained after the first tune up on a frequency.  I am using an old Heathkit HM-102 as an output meter, so I really don't know how much power it really is putting out. I will borrow a Bird and run a calibration between them to see how close the HM-102 is, (I am not counting on it, but it is a good relative reading of power).

 

To tune the amp, I am running into a cantenna and putting the radio in RTTY and using the TX button to key the radio and amp. The GRID CURRENT rarely gets over mid scale requiring me to turn down the power. I am running about 50 to 70 watts during tune. I did crank the radio back up to 100 watts when I noticed that the GRID CURRENT (I leave the meter switch in that position since I think it is the greatest indicator of how I can damage the amp) was barely moving during SSB TX.  I imagine that would not be true for CW and RTTY.  During tuning I watch the HM-102 for max and the GRID CURRENT for max center of meter scale.  

 

I resorted to using a headset for the contest as the fan is noisy. Not really bad, but annoying enough to want to block it out when trying to dig my callsign out of the noise and the pile up.  Harbach sells a replacement. Should I get one of those or would a muffin type fan be better and quieter?  I might consider two muffins, one top and one on bottom to get the air flow without the noise.

 

Since I am going to open up the amp should I consider changing the RCA jack input to an SO-239? I have a RCA to SO-239 adapter into an L connector to feed the RF to the amp.  I do not use ALC since two hams whose opinion I respect have said it is not necessary. One went so far as to say ALC stands for "Automatically Limits Contacts". Also there is no adjustment for the ALC on the SB-200 so the set up with my IC-756 would be problematic.

 

As always I invite comments, suggestions and answers to my questions are always welcome.

 

Clint - W5CPT

 

 


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