SB-200 No Joy

Discussion in '"Boat Anchor" & Classic Equipment' started by KG5EN, Jun 9, 2012.

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  1. KG5EN

    KG5EN XML Subscriber QRZ Page

    Well Gary, There's really only one antenna I plan an buying in the near future, that being a Cushcraft Ten-3 10 meter monobander. Geez, the spellchecker suggests that monobander should be spelled moneylender! After last weekend I could use one of those! There's no hurry on the antenna until I get the garage cleaned out and find my Ham II rotor and control cable. If the antenna will give me <2:1 SWR on 28.3 to 28.6 I'll utilize the Bypass coax output on the Dentron tuner. The next buying frenzy will be a little different. Soon I'm going to start my own swap meet and it will be called "AMPS 4 RIGS" One or two rigs, of 21st century vintage will be the goal, with several amps as my wampum. You heard it here, first on channel QRZ! Huh? What's that? Whatcha got buddy?
  2. KG5EN

    KG5EN XML Subscriber QRZ Page

    Just a couple comments on the FL2100B. It was pretty tricky to get it loaded up correctly on 10M, and those tubes really get hot with a lot of RTTY level tuning. Basically what I get is 450W into a dummy load and 400W to the antenna (R5 vertical). I get the max with 50-55 watts of drive. If I try to increase drive past 55W out, it seems to reduce output from the amplifier. I'm thinking that must be a function of the ALC? The plate and load settings are right exactly on where the manual says. From what I've read, 450W isn't bad for 10M with these amps. All in all I guess I couldn't expect much more from this oldie! I have no idea how old the tubes are, but if they're not broke, I ain't gonna swap em out.
  3. G4FUT

    G4FUT XML Subscriber QRZ Page

    This is the most amusing and educational thread I've read in a long time... Hope all goes well C.R. you deserve a break....
    Now about this new AA society...can I join as I have a problem with my home-made, 2 X 813s which keep blowing fuses when I apply 2,500v HT.....;)
  4. KG5EN

    KG5EN XML Subscriber QRZ Page

    Hi Mr "Brit"
    Glad to edify and amuse! Actually, Gary is the funny one and I'm stumbling around trying to re-learn what I knew 30 years ago. I bit the bullet and ran the acid test this evening. I knew I was putting out 400-500 watts but had to know if the signal was clean and audio good. I tuned up and found some gents in northern Calif chatting and asked for a radio check with the linear. The guy said go ahead and turn it on! Well I did and he and a couple others said it sounded great, no problem. My report was about a 57 barefoot putting out 70 watts and a 59 plus 5db with the FL2100B putting out 500 watts. I'll go ahead a leave it connected up until the Ameritrons start arriving. Between Mon and Thu next week all 3 should be delivered. Now that I'm comfortable with the fact the Yaesu is a perfectly good amp, the decision of which ones to sell will be difficult. I'm going to really go through the SB-200, changing out the tubes, inspecting the T/R relay, tweaking the input coils and in general looking for anything that's not right. When (not if) I get the Heathkit amp going, I believe I'll put it and the Yaesu on the block, probably along with the AL-811. They should generate enogh cash to get me a nice late model rig, like a FT-950 or IC-7400. They should do a much better job of playing with Ham Radio Deluxe. The 751A's UX-14 and CI-V connection will only run at 1200baud. That was fine 20 years ago hi hi. You know what? There's a little part of me that wants to keep all five amplifiers. I know, it's the disease! Meds pls.
  5. W4BOH

    W4BOH XML Subscriber QRZ Page

    Should we consider an open circuit in the grid, like the sense resistor?
  6. KG5EN

    KG5EN XML Subscriber QRZ Page

    Definitely Wilson,
    The limited amount of drive I was able to give it, never produced any grid current. I will definitely add that check to my list. Thank you sir!
  7. K6CPO

    K6CPO Ham Member QRZ Page

    What mod on the 751A? I also am using an IC-751A, only barefoot, and I'm interested in mods that will improve the performance.
  8. KG5EN

    KG5EN XML Subscriber QRZ Page

    A big improvement to the 751A is replacing the plastic trimmers with ceramic in vco's and PIN diodes in the rx HPF filters. Randy Starace KK7TV did hundreds of the mods, but retired before I got around to having him do it. It's a 2-3 hr job. The original trimmers can cause you to have a dead radio below 8.000 MHz. So far, my only problem is a burned out (I guess) S-Meter lamp!
    73, C.R.
  9. KG5EN

    KG5EN XML Subscriber QRZ Page

    Well Folks,
    Another day, another DOA. The AL-811 came today. Had to go to the post office to get it as the carrier lady wouldn't come up and knock on my door. She was afraid there might be dogs around was the story later....there were none! Anyway, got home unpacked the box and everything looked fine. A separate box held the 3-572B's he said would be included. I opened up the unit, ostensibly to install the 3-811A's I assumed were wrapped safely inside. My heart sank as soon as I took the top off. He had shipped the amp with the tubes installed! All three tubes were loose (completely out of the sockets) and one was smashed to pieces. I took pics of it all and then proceeded to clean out all the glass from the chassis. I made a call and verified the 572B's could be installed and were better anyway. I noticed how loose fitting the tubes were in the sockets, compared to my earlier tube installation in the SB-200 and FL2100B. They probably came out the first time the box was jostled in shipment. I then connected up everything for testing. Tuned up on 40M, set the dials and switches per the manual and proceeded. Power on...plate V 1700... Great! Switched to operate and keyed it up. Red xmit led lit up, but no idle current (supposed to be 60ma). Repeated everything several times to no avail. NO plate current and NO grid current. No good to a matched ant or the KW Kan dummy load. So that makes three first run-thrus with amps and zero success. At least I did get the FL2100B going after correcting the jumper setting in the Ameritron ARB-704. In a few I'm going to pull the ALC line and rout the relay direct to the amp from the 751A. It should still key fine and I can't get over 100W out anyway. It might have something to do with what's going on.
    Even though I'm o for three, I still have a chance of batting .400 before it's all over. The 4th amp, an AL-811H is scheduled to arrive Tue the 3rd, and no. 5, the ALS-600 on Fri the 6th. Think there's a chance one or both will actually work, first try? I'll either be very happy or "comfortably numb." Meds please!!
  10. KG5EN

    KG5EN XML Subscriber QRZ Page

    Welcome back QRZ.COM!!
    That must have been a heck of a storm. The DOA arrival of the AL-811 and subsequent lack of concern from the seller (Jeep_hunt) kicked me in the butt to open up the SB-200 and try to find the main problem. I FOUND A COUPLE! The tubes were weak, so I replaced them with the matched pair of Chinese 572B's. Inspection of the grid cct resistors and t/r relay didn't show any problems, so I ran the resistance tests for anode cap to chassis and pin 3 of tube socket to gnd. The latter was in tolerance but one tube had an open anode to gnd instead of the spec 180K ohm. I unsoldered the cap clamp assy with the parasitic suppressor. It checked out ok so I resoldered it in place with a good hot re-flow of everything tied to that lug. Shazaam! It now checked out at 162K ohms (is there an ohm sign in the character set??). After all this, the input Z I thought was a problem went away! Fired it all up and guess what... The amp was loading up on every band, but still no grid current (so the meter said) and only about 400W on average per band with 10M being the lowest at 300W. I accidentally found that if I turned off the amp and increased the rf output of the exciter to 70-100W, then turned on the amp and keyed it, I would get well over 500W out. The any fine tuning would return it to limiting the drive in some cases to 50W or less. At that point, 3 things entered my diseased mind (you understand Gary)... ALC, meter switch (already repaired to restore HV reading) and the Ameritron interface. My first go around with the SB-200 was with a buffer setting (by factory) which keyed the relay but that was it. So that's one different factor. Since my rig won't put out over 100W CW (RTTY) and I want to be super gentle on my amplifier tubes, I'm pulling the ALC cable. After that I was able to load up the amp to 500W or more CW on every band and only running about 350ma plate current! Stting my rig at 70W out gives me a solid 400W CW and 500-600W PEP on SSB. Well, I ain't the smartest kid (72yo) on the block but it was now obvious the lack of any grid current was strictly in the mind of the meter switch. This may end the saga of the SB-200 No Joy thread but I do wish to thank everyone that made constructive comments along the way and folks like Gary that injected a modicum of levity along the way.
    73 de KG5EN
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