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SB-206
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NI5L
Good morning, all. I recently acquired a converted 6-meter amp that is named the SB-206. It was converted by KM1H in 2006 from an SB-200 and it actually works very well. I have been very carefully tuning it with the max output method, which is the only way I can do it. The "manual" is a single sheet of paper with minimal instruction. I have tried to contact the builder, but his email bounces and his phone is disconnected.
Has anyone on this reflector had one of these? If so, I would like to know how you tune your amp properly. I am trying t avoid killing it with improper tuning. 73 Warren / NI5L |
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On 2023-12-20 8:12 am, NI5L wrote:
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Carl hadn’t been in on the various groups since before Covid. ?Reports say he’s ok but probably got tired of fighting on the groups and is pounding sand somewhere else.
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On Wednesday, December 20, 2023, 12:10 PM, Don Roden <donroden@...> wrote:
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NI5L
OK. Thanks for the replies, guys. I am getting 600 watts out at 18 watts of drive with the load backed off CCW ~25 watts from peak (per the instructions). The grid current is at 500 mA. The plate current is 650 mA.
Are these acceptable numbers to help the tubes live longer??? Thanks for any input. Warren / NI5L |
开云体育If his license expired that long ago , his e-mail is not valid any longer, and his phone is disconned... that doesn't bode well. If I still lived in Mashachewzits, I'd take a drive up there to see whether it looks like he still lives there; but my guess is he's gone, for one reason or another. He wasn't exactly the type to have a close compadre with whom he would leave "final words" about whom to let know whether something happened to him; so I'm not surprised we haven't heard anything whatsoever from or about him. Somebody with access to the local newspapers might check the obituaries, going all the way back to before the start of the pandemic. Steve, K0XP
On 12/20/2023 11:33 AM, Louis
Parascondola via groups.io wrote:
Carl hadn’t been in on the various groups since before Covid. ?Reports say he’s ok but probably got tired of fighting on the groups and is pounding sand somewhere else. --
See my QRZ.com page at |
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The grid current?isn’t 500, it’s has?nothing to do with the scale reading. ?As long as it’s in the white area it’s ok. ?With the 572b tube it’s the temperature of the plates that is the driving factor, not so much grid or plate current. ?The572b has a very robust grid and plate structure. ?As long as the plates don’t glow bright red and stay relatively dark,you are fine. 700 watts on 6 meters is about the safe level but not for digital modes!! ?SSB 800 pep is fine.
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On Wednesday, December 20, 2023, 6:30 PM, NI5L <ni5l@...> wrote:
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开云体育Something doesn't sound right... you shouldn't be able to get 500 mils grid current and still have working tubes, ESPECIALLY with only 18 watts drive... That's a RIDICULOUSLY-LOW amount of drive; most of us are proud to get 650 mA plate current from a pair of new 572Bs with 65 watts drive power on the HF bands! For the most part, follow the Heath SB200 manual tuning instructions; except that you will undoubtedly find you get much more output power by peaking the plate tuning rather than dipping the plate. Try increasing the loading capacitance to reduce the grid current
below half-scale, as you peak output with the plate tuning. SLOWLY
increase drive, keeping grid current at or below half-scale,
increasing loading slightly again (grid current should decrease
slightly as you increase loading capacitance), then peaking output
power with the plate tuning. My guess is you aren't reading the grid meter right; I can't believe Carl would have messed up the grid current meter scale that badly. Let's put it this way for now... keep the grid current reading below about half scale on the grid meter, whatever that may be. You can increase drive until the output does not also increase
but by then, you may be running the tubes real hard. I'd keep them
down to no more than 700 watts output under "rare DX pileup"
conditions, and more like 600 watts when working common schtuff
like North Carolina or Arkansas. For Nieu Yawk/Nieu Joisey/Pennsy,
I'd turn the amp off? 8-D 73, Steve K0XP On 12/20/2023 3:30 PM, NI5L wrote:
OK. Thanks for the replies, guys. I am getting 600 watts out at 18 watts of drive with the load backed off CCW ~25 watts from peak (per the instructions). The grid current is at 500 mA. The plate current is 650 mA. --
See my QRZ.com page at |
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NI5L
Lou,
I am tuning it to keep the grid current at 500 mA or less. The white area tops at 500 mA so that is what I have been referencing. This is a very touchy tank circuit! The amp came with some pencil marks (!) for reference when tuning so I used them. The final tune points are not off from those marks by much at all. I don't plan on running anything over 600 watts to help preserve the tubes as much as possible. I guess the only meter function that is relevant is the HV.? :) Thanks for the insight. Warren / NI5L |
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NI5L
Steve,
With no REL PWR function, I have just been peaking everything up using a watt meter. Like you, I am a little bit curious as to why it only takes 18 watts of drive to get 600 out. I just wrote it off to this being a 6-meter VHF amp.? It has a VERY narrow bandwidth... 50.000 to 50.500 according to the plate on the amp's face., which is perfect for me. I have tried peaking the grid and dipping the plate but I come up with some pretty hairy plate current when I do that. I'm just really nervous about killing the tubes or the tank circuit. After reading what Lou said, now I am even more puzzled as to what references to use when tuning this thing. Carl said that once it is tuned, leave it alone and that the frequency range would be covered if tuned at 50,200 or so. I will try what you said next time i get the amp online. Currently it is going to be an off-desk amp when I need power on 6 meters since we have very few 6 mete DX openings like the east coast does. Spotlight openings are few and far between out here in southeast Arizona. Thanks and 73 Warren / NI5L |
开云体育This is interesting…was this amp modified for grid drive instead of grounded grid?? ? Another possibility is that there could be a bit of positive feedback, not enough to cause self oscillation but enough to generate more gain. ? Agreed, 18W for 600 W out isn’t possible for a normal functioning grounded grid amp with 572B’s.? Their gain at best in GG is perhaps 12 dB. which would yield maybe 270 watts with 18W drive.? An unintentional positive feedback of 3+ dB would do it though….and the tuning would be VERY sensitive. ? -Chuck ? From: [email protected] [mailto:[email protected]] On Behalf Of NI5L ? Steve, |
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NI5L
Chuck,
The grid question is a good one and there is NO schematic of the conversion. It is written on the "manual" page in big script that there is no schematic. That is part of the reason I am puzzled about this amp. The "manual" claims between 10 and 12 dB gain in this configuration. As everyone probably figured out, I am not much of a technician and am trying to figure out what is going on with this unusual amplifier so that I don't kill it. I could pull it out of the cabinet and see if the grids are still grounded. I may do that just to try and get some more info to work with. 73 Warren / NI5L |
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Warren, at 50 mhz the neutralization on 572b tubes?is way out in outer space. ?It’s bad enough on 10 meters let alone on 50mhz. ?That said, you can’t expect a dip in the plate at maximum output’. So the proper way to load it is to peak the load and tune for maximum output then try to reduce the grid current a bit and repeak the plate fo maximum output. ?You came much too late to late to this party. ?Both myself and Carl converted many of those SB200’s to 6 meters. ?The trick is to?make it stable at the maximum output point and as Carl said, LEAVE?IT ALONE. ?As long as the plates keep?from getting cherry red you’ll be fine. ?There’s quite a bit of regeneration but the skill in?building them was to keep them from taking off when loaded for maximum output. ?Carl kept his recipe for getting SB200’s to work on ?6 meters as much of a sectet as Mrs. Paul’s cheesecake. ?I’ve probably converted?half as many as Carl did and 18-20 watts gave you?about as much output as you’d dare. ?Keep the output peaked and the plates dark and you’ll be fine. ?This is just another mystery of faith. ?Lou
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On Wednesday, December 20, 2023, 7:55 PM, Chuck Neal <cdoneal@...> wrote:
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Skip, he is reading the grid current wrong!!!!!! ?THE SB200 amp does not have a graduated scale for grid current!!!!!! It only has a white area as a safe zone. ?The last mm of the white zone is 100 ma. ?But it’s NOT on the scale.
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On Wednesday, December 20, 2023, 7:03 PM, Steve <k0xp@...> wrote:
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NI5L
Thanks for that, Lou. And I re-read the meter explanation in the Heathkit manual and saw what you said. The end of the white range is 100 mA.
?This may or may not be an issue but I do not show any idling plate current. Is that a problem? If it is, is there an adjustment like on the SB series radios? I will tune it up like you said and be happy with it. I have a friend about 130 miles from me with a nice 6 meter array ad I am going to see if the audio is clean. If it is, I'll just leave it alone.? :) Thanks, guys. 73 Warren / NI5L |
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There should be about 70-90 ma. ?of idle current. I’d leave it alone.
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On Wednesday, December 20, 2023, 9:39 PM, NI5L <ni5l@...> wrote:
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Yup! Leave well enough alone.
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On Wednesday, December 20, 2023, 10:47 PM, NI5L <ni5l@...> wrote:
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On 12/20/2023 6:18 PM, Louis Parascondola via groups.io wrote:
........... There’s quite a bit of regeneration but the skill in?building them was to keep them from taking off when loaded for maximum output. ?Carl kept his recipe for getting SB200’s to work on ?6 meters as much of a sectet as Mrs. Paul’s cheesecake.Yup; he was never real open about how he did some of the "successful" schtuff he was able to accomplish. I’ve probably converted?half as many as Carl did and 18-20 watts gave you?about as much output as you’d dare.So, Lou: are you saying that you believe Carl converted this "SB-206" to full grid-driven instead of grounded grid?? If so, that certainly does help explain why tuning seems so touchy; I wouldn't have believed that if you hadn't mentioned it. Tell us, Lou... did you modify yours to grid-driven, or were yours grounded grid?? 73, Steve K0XP |
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NO NO NO. Not grid driven. ?Cathode driven! Neither?Carl or myself did grid driven! ?It was cathode driven. ?Yes I know 20?watts drive sounds crazy but handling the bit of positive feedback with the gain at proper loading kept it stable. ?He said to find the right spot and leave it alone else you might find yourself in trouble. ?It could have been even better with solidly grounded grids rather than floated but hey.
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On Wednesday, December 20, 2023, 11:11 PM, Steve <k0xp@...> wrote:
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On 12/21/2023 5:31 AM, Louis Parascondola via groups.io wrote:
NO NO NO. Not grid driven. ?Cathode driven! Neither?Carl or myself did grid driven! ?It was cathode driven. ?Yes I know 20?watts drive sounds crazy but handling the bit of positive feedback with the gain at proper loading kept it stable. ?He said to find the right spot and leave it alone else you might find yourself in trouble. ?It could have been even better with solidly grounded grids rather than floated but hey.OK, thanks for clarifying that, Lou, as it wasn't clear before. 73, Steve K0XP |