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Author Topic: SB200 amp.  (Read 6430 times)
KD2DYY
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Posts: 45




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« on: June 04, 2013, 04:57:15 PM »

 on the Heathkit SB200.......
I cannot "Tune" the darn thing
I tuned the input tuned coils.(Using the SWR approach ). Mission accomplished on that. My grid voltage was at -134VDC. Ok so far,so good.....Filament voltage(ac) was fine,both sides of CT. I did change out the caps in the HV PS.... I did apply the "soft start" kit and that works fine...I also installed a real rf input connector. (239).
When I fire it up I cannot get much grid current OR plate current. The plate current does respond to my increase in drive from my exciter. (Kenwood TS520S) but no where near the levels that the manual states.. I barely get 100 mills. The grid ,similarly, has very low current.
My dip is so-so  but in accord with the band switch position but the load control might as well be fixed because it does not" pump" up the power level at all.
I did try to find a tube tester for the 572's but that was impossible around my location Camillus NY(near Syracuse NY)..
I have been on E-Bay looking for decent prices but whew!. Could I go with 811's and keep the loading down...? They are half the price of the 572's.......(I know this question will bring the wrath of god)
I have tried to get on the air with the amp. and it DOES pump up my signal  but I know I can do better. (Oh, by the way, I do show a remarkable increase in my output indicated by my wattmeter..It is not accurate ,however, so that is subjective.
Anybody out there have any ideas (other than tube change?) I'm kind of in limbo right now..... I am itching to go at it with the 500 pound gorillas on 20m but I am cooling it till I find the answer to the "tune" problem.
Thanks ,in advance, for any help on this issue......
                                                                                                                                    Mike KD2DYY
 
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K2DC
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« Reply #1 on: June 05, 2013, 02:22:37 AM »

Mike,

  No you can absolutely NOT use 811A's in an SB-200, you will destroy them.  The nominal plate voltage (no load) of an SB-200 is around 2300V.  The maximum rated (ICAS) plate voltage for an 811A is 1500V.  You can always use a 572B in place of an 811, but never the other way around.  Unfortunately I no longer have an SB-200 (I'm in Lafayette) to test the tubes, but there must be several around because I bought both the one's I've had locally.  You should check around some more, and maybe ask around at the RAGS Hamfest on 7/14.

73,

Don, K2DC
 
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W1QJ
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Posts: 1515




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« Reply #2 on: June 05, 2013, 03:20:46 AM »

You asked to give reasons for problems but don't say tubes.  Maybe it is the tubes.  If so you are on a fools mission if that is the case.  Also RF tubes like the 572b don't test well on tube testers.  The only real way to test a tube used for rf is to put it in a known good amp and try them.  I would be more than happy to test them in my amp for you.  Don't chase your tail looking for a problem if you close your eyes to all possibilities.  PLUS your 520 needs to be readjusted when looking into the input of the amp.  What is the idle current when the amp is keyed with no drive?
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WX7G
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« Reply #3 on: June 05, 2013, 03:28:32 AM »

572B tubes are $40 each at RF Parts. $80 for two tubes will fix the problem or allow you to move to the next step.
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KD2DYY
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Posts: 45




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« Reply #4 on: June 05, 2013, 04:21:10 AM »

Yup, Thanks guys, I KNOW I will have to get new tubes but I was hoping that there was one little step that I was overlooking. Ok on the 811's I will NOT try that . I did not know they could not handle the voltage....
As to the adjustments to the Kenwood 520s.............Huh? That concerns me . I did NOT crank up the drive too much to try to get the plate current to proper level. Did I miss something there?Huh???I don't want to hurt the little girl. I like her a lot(Kenwood)...
As always, thank you very much guys(girls) for your input so far. I will carry on and guess I will bite the bullet and buy those darn tubes.
 When you try to run with the big dogs you have to pay the price,. Right???

Any more info on the Kenwood adjustments would REALLY be appreciated..... Thanks,,

                                                                                                                           Mike..KD2DYY
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WX7G
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« Reply #5 on: June 05, 2013, 06:02:33 AM »

http://www.rigpix.com/linears/heathkit_sb200_manual.pdf

The amp idle current should be 90 mA. Increase the exciter RF power until the SB-200 plate current is 500 mA per the manual. The drive power will be around 35 watts. 
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KA5N
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Posts: 4380




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« Reply #6 on: June 05, 2013, 07:47:54 AM »

The bias voltage when the relay is keyed should be around -4 volts.  It sounds like
you have the cutoff voltage on which would cause hardly any plate or grid current
to be present.  So you have to measure the grid voltage when the relay is keyed.
If the voltage is more than -4 volts then you have a bad componet(s) such as R18
R16, R 23, R15,R23, R21, R22.  There might be a problem with the relay. The soft start kit doesn't have anything to do with grid voltage.
Good Luck
Allen KA5N
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KD2DYY
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Posts: 45




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« Reply #7 on: June 05, 2013, 03:13:06 PM »

Thanks ,again, to all that are helping me. I really DO appreciate........
Addressing KA5N.... I just looked at the grid voltage while turning on the "send" key on the 520s.... My voltage is reading approx. -1.35 on each tube..... That is higher than the -4  you recommended but close to the -2 volts in the Heathkit build manual. Think a pull out of the resistors is in order?Huh?
As to WX7G.... I can't get close to the 500 ma at the plate reading no mater what power output I try with the 520s exciter....
100 ma is all I can get on the plate .... I'm still thinking tubes but want to hear KA4N,s take on the grid current I am observing.
Thank you guys. Please stick with me. I was looking at ordering those tubes but I have the nagging doubts that they will cure my problem. (I'm a cheap sob, too. LOL)
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WX7G
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« Reply #8 on: June 05, 2013, 04:39:02 PM »

Are you able to measure RF output power?
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W1QJ
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« Reply #9 on: June 05, 2013, 05:03:15 PM »

If the amps load and tune are way off perhaps you won't obtain much plate or grid current.  Try this before you go too crazy.  With the amp in bypass adjust the drive level of the 520 to say 20w output.  Set the amp's meter function switch to forward rel. pwr.  Now key the amp with the 20 watts drive and adjust the load and tune on the amp for maximum reading on the rel pwr meter.  After you do that then go back to the 520 and while keying the amp and 520 adjust the load and tune on the 520 also for maximum output on the rel power meter.  Then increase drive from the 520 to about 60 to 70 watts and again adjust load and tune on the amp for maximum power output, lastly tweak up the load and tune on the 520 once again.  If the tubes are good and all is well you should be getting around 600 or so watts output on 80 or 40 meters.  You might not have any problem at all just that the amp may be way out of tune trying to drive it to a said plate current.  I think you are better off setting the drive to about 20 watts and loading the amp up regardless of what the current reading is.
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KD2DYY
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Posts: 45




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« Reply #10 on: June 05, 2013, 05:41:53 PM »

Hi guys and my continuing THANKS for all your help...In response to WX7G..... Yes I show MUCH more output using the amp than just the barefoot . My wattmeter is woefully out of calibration but I can determine that the amp. is,INDEED, putting out much more than the little 520s can deliver by itself. I just want MORE power "Scottie".
In response to W1QJ   I will try to back off the drive from the exciter to ,around, 20 wats to see if that might be the trick....
I DID buy new 527's.  They will be arriving in few days. Darn it!  Grrrrrrrrrrrr!
Thanks,again, guys. I continue to be in awe as to the amount of help my fraternal friends have shown me. I AM happy to be back among you after all these year of absence from the hobby.....I was WA2AMZ about 50 years ago....... My, how time did fly.....

                                                                                                        Your grateful friend and 73's, MIKE
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KH2G
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Posts: 341




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« Reply #11 on: June 11, 2013, 09:36:08 PM »

Just curious and would like to confirm your tuning in CW or FM? I trust your tuning into a dummy load as load matching problems can give some really bizarre EgIp indications.
73,
Dick
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KD2DYY
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Posts: 45




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« Reply #12 on: June 12, 2013, 05:24:47 PM »

Darn it. EgLp?HuhHuhHuh?? Another language I'll have to learn.
No, my tune ups are using CW into dummy and then ,and only then , into open frequency (after calling to see if frequency is being used). Short follow up "live" try tune...
Like I said , previously, I have ordered new 527b's and will hold on the problem until I check all this with "fresh" new tubes. (Still awaiting delivery of the tubes)
I just used the amp this afternoon and previously on several QSO's  and it DOES increase my signal output.I use the old Kenwood 520s barefoot and then ask my contact if I could try the amp. and see if they can tell a difference. YES is the answer.... however I am concerned that I am not getting the full 600 watts out, hence my nagging doubts.
Thank you, Dick on your question. I look at the forum from time to time to see if someone, like you, has tried to help. I DO appreciate very much....So I go on.......

                                                                                                                               Mike
                                                                                                                             KD2DYY
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K6AER
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Posts: 3535




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« Reply #13 on: June 13, 2013, 08:21:32 AM »

Unless you are using a peak reading watt meter under normal conditions a 600 watt peak signal on a normal meter movement has an inertia lag and will only show about 150 watts out.
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KH2G
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Posts: 341




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« Reply #14 on: June 13, 2013, 03:31:12 PM »

Hi Mike and just a FYI Eg Ip is Grid voltage / Plate current which you see on the tube data sheets and is needed for Amp design
(It relates to plate impedance) Guess it doesn't get discussed much anymore in our solid state world world- hi
73, Dick
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