I left you last having completed the installation of the vertical. I'm pleased to say, it's still up! And yes, I'm having a blast being back on the air. Here's what I've been up to.
After getting the vertical up, I set to putting the SB-200 back on the air as well. Last time I shared SB-200 stuff with you guys was when I just about killed myself by sticking my hand in the chassis with the HV power applied. I definitely learned my lesson and took many extra precautions this time around. Getting the SB-200 out of storage and converted back to 120v (no 240v in the new shack) I noticed the softkey circuit I had was not working, there was no keying action. The circuit was powered by a 3v lithium coin cell so its no surprise. I thought while I was in there, I'd rework the 12VDC power rectifier I built for the PC fans I put in there in our last blog post.
I decided to go full hog and just throw a 12v transformer, as well as cut out the case for better air flow. This turned out to work a lot better than the way I had it hooked up before and I didn't have to worry about the filament voltage from being impacted in any way. Unfortunately I did find out that you can't ground the DC side of the transformer to the case. It took a while to find out why the fan would stop when transmitting. In investigating all of that, I ended up going down to just 1 fan and I can definitely tell it works really well with just the one to keep the tubes cool.
Since I was running the amp on 120v I wondered if I could improve the performance with the lower source voltage. With the exception of the soft key and the fans, I'd made zero modifications or updates to the amp. Surprisingly the amp was totally untouched and working great all things considered. And yet, I had picked up replacement capacitors for the power supply when I bought the amp at Hamvention so I figured it was time to just replace the aged ones in the amp. You've probably seen pictures like the one below on the internet and I always thought, "oh that's a blown up cap," but it turns out that's just the glue that goes in the paper covers! All 6 of the caps in my amp, did end up being absolutely fine, but I did find a bad diode which I also replaced.
Everything else checked out and once it was all buttoned up everything looked great! I got the amp back on the air and it didn't take long until I reached the limit of the 15 amp circuit to the shack and that was about it. It became painfully obvious that I was just not going to be able to run an amp in the new shack without a more worthy circuit. And, do be honest, in all these years, I've not really enjoyed using the amp on CW. Friends will tell you, I'm a little extreme about having a quiet shack and once you get rid of the fan noise, the SB-200 is silent...until the T/R switch goes off. And man is it loud! I seriously considered adding QSK but it turns out there's no "drop in" boards available anymore so I kind of went off the deep end...
After I left you on the last post I had decided I was going to run a 240v AC line to my shack as well as a secondary 120v, 20A line for my computer and radio stuff. The idea was to get all this on line before the IARU HF Championship contest over the weekend so I got up early Friday (before my wife got up and complained that the power was off) and got to work. It took a whole lot longer than I had planned but the finished product is pretty clean and runs the SB-200 really well. My idle HV now sits at 2500v instead of 2400v and only sags to 2100v instead of 1800v.
In my last post I mentioned that I had planned to try out those Svetlana tubes I got at Hamcom last year in my SB-200. I swapped them out before the contest started and they seemed to tune up just fine, providing about 500W out on all bands with 80w of drive. I ran the whole contest with this setup.
The conditions were not very good until around local grey line when EU started coming in on 40m and 20m. Up until then, I was working almost exclusively NA stations which is pretty boring for a DX contest! Operations were pretty tame and according to N5EIL, the Reverse Beacon Network was reporting only 800 some unique calls operating in the contest which is pretty small number. None-the-less, I really enjoyed operating with the amp and the new antenna and got about 73,000 points from 440 contacts. I'm really finding this Gap Titan to work really well on 40, filling in several slots for DXCC on the band. Until now, I've never had a decent 40m antenna. Even the dipole I had up in Iowa was too short for any effective operation on the band.
The only thing that bugged me during the contest was the louder-than-ever AC cooling fan in the SB-200. Sunday I decided I'd look at fixing it. It's pretty trivial to remove the fan, just remember to shut the power off and let the amp sit for a while to bleed off the HV. I took the fan out, oiled it a bit and put it back but in all that, I actually made the fan louder. I needed a better solution. I ran to Fry's and picked up a few 80mm 12v computer fans and set to wiring them in. The easiest way to get 12v DC in the amp is to tap off the filament voltage (6.3v AC) and rectify it. (see image below) I used double sided foam tape to stick the fans on the inside of the tube chamber where the old fan sat and ran the wires through the mounting holes for the old fan. I hooked up the rectifier on the bottom of the chassis and measured about 15v DC on the output. Looks like I'll be over-volting the fans a bit but I have spares so if they fail, no big deal.
Keep in mind, in order to measure all this stuff I've had to move the amp to the operating position, plug it in, and power it on. There are LETHAL voltages present inside the cabinet. I had the fans hooked up and they were spinning. They were very quiet. I thought, "hmm how much air is moving now?" and made the (nearly) fatal mistake of sticking my hand inside the chassis to feel the air flow. I must have let my finger hit the filament clip (+2,500V) because in a moment I saw a flash of plasma, the undeniable sound of arcing, and that scent of lightly burnt flesh. My left arm went numb for about 10 seconds but I walked away from that incident with a few 2nd degree burns on my middle, and index fingers, and my thumb. BE CAREFUL AROUND HIGH VOLTAGE!!!
I almost didn't want to share this bit because it's probably the most stupid thing I have ever done but maybe my tale can help keep someone else from making the same mistake.
After I left things for a couple hours to nurse my hand (and my mind) I went back (with proper precaution) and luckily the amp survived the event. I put the Centron tubes back in and buttoned everything up, applied power, and was happy to see that the amp had not been destroyed. The breakers had tripped which probably prevented the whole thing from being far worse. Even more, I was happy to see that the Centron tubes were working far better than the Svetlana ones, providing 100w more output on all bands, at half the grid current, which meant I could drive the amp with 100w instead of 80w. Looks like the NIB tubes will go back on the shelf for backup. I let the amp sit for an hour or so and I was very pleased with the reduced noise - the amp is no louder than my computer fans now - and cooling performance. With the old fan, the top of the case would be quite warm to the touch, even when idling and now its only a few degrees over ambient.
The last thing to do before everything is perfect is to figure out how to keep the room cool. During the contest, my shack got up to 85 F quite a few times while the rest of the house was in 79 F range. Unfortunately the only thermostat in the house is in the bedroom, on the other end of the house. Running the furnace fan helps some but I think I need to balance the vents some more to make it really effective. Just new house things I guess!
I ran by HRO after work yesterday and picked up the 2kw gas tube for my Alpha Delta lightning protection in anticipation of firing up my SB200 for the big IARU contest this weekend. The little amp has not been powered up since we moved from Iowa and I was a little apprehensive about turning it on again for the first time. Luckily my fears were unfounded because it fired right up without any issue.
I made a few new pieces of coax to get me QRO handling capability - I was only using RG58 from my radio to the entry panel - and got everything hooked up. I started tuning the amp on 20m, and watched the power meter go up...up....up....to almost 700w. I thought, "Oh wow! This antenna loads up better than my hex beam!" And then I adjusted the meter for SWR and saw the failure in my ways. I was getting 5:1 SWR, something had gone wrong! I grabbed the antenna analyzer and saw my 20 and 40m SWR were both very high, while the other bands seemed OK. Connectors on the new coax all seemed fine so it must have been the antenna...
So I went out to inspect and it only took a moment to see what had happened.
This wire was attached to the bottom of the 20m element on the antenna, dangling between the spreaders for the 40m radial loop. Apparently this little bitty stuff (and its insulation) can't handle a few hundred watts while touching other metal parts! The insulation had burned off and caused the 20m element to short out to the 40m element. I'm lucky I didn't burn anything else up! I replaced the wire with some much, much heavier stuff with nice thick insulation and rotated the loop a bit so it fell evenly between 2 spreaders, maximizing the space between them. It shouldn't happen again but I'm going to look into a more sturdy solution that doesn't rely on a flexible wire.
With that all fixed up, the amp was showing me 400w out on 20 and 40, just in time for the 0300z CW Ops mini CWT. I ran most of the time and walked away with 52 contacts, mostly on 40. I've been really happy with this antenna on 40m.
I still have those 527b tubes I got at Hamcom last year I'd like to throw in and test so I may do a little post on that tonight or tomorrow if I remember.
So I guess the station is primed and ready for the big contest this weekend. I hope to hear you all on the air!
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I decided to go full hog and just throw a 12v transformer, as well as cut out the case for better air flow. This turned out to work a lot better than the way I had it hooked up before and I didn't have to worry about the filament voltage from being impacted in any way. Unfortunately I did find out that you can't ground the DC side of the transformer to the case. It took a while to find out why the fan would stop when transmitting. In investigating all of that, I ended up going down to just 1 fan and I can definitely tell it works really well with just the one to keep the tubes cool. 
