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Heathkit sb200 issue

C

Crasher

Member
Apr 25, 2012
49
6
18
44
Norwalk, OH
Wondering if anyone has any insight. Purchased a clean sb200, RTO electronics went through the amplifier in 2012, replaced relay for newer transceivers. My issue is I cannot get more than 250w output. HV idle voltage is 2400, keydown 2100 volts. 10w drive give 200w out, 20w in and barely 250w, 40w in 250w. If I tune the amp at higher drive and back down the drive, seems like the ALC is cutting out all wattage as it will cut voltage down. Not sure what to look for or test.
Thanks
 

ALC has nothing to do with the Voltage. The voltage will drop normally when the amp is driven. ALC adjusts what the radio output is, so not to overdrive the amp.
What band is this 250 watts...10m? 80m?
Also did you check the SWR between the amp and radio (tuned Input slugs?)
Plate current? When showing 250w....could be soft tubes?
So let's go from there
All the Best
Gary
 
I will have to do some more testing and take readings later on. I was also thinking tuned input, need to check SWR between radio and amp. Readings were done on 10m and 15m, dummy load. From what I remember seeing, plate voltage was 500ma. Still has the Cetron 572b tubes, like I said was serviced in 2012 and everything was still in spec. I also let it sit idle for 4 hours before applying any RF.
 
SB200 has very bad input impedance on 10 and 15 meters, test it on 20,40, or 80 meters hopefully into a dummy load.

The input VSWR are decent on those bands.


Hopefully the tubes are not soft.

If you get decent output power on the lower bands just do a google search, there is a great sight for reworking the input tune on the sb200's.
 
All set, was the input tuning coil. SWR between radio and amp was way above 3:1 when fully tuned. Got the SWR down to 1.2:1 on 10m, works for me!
 
Great that should make a big difference...Follow the specs and drive her lightly. You run that at about 400w peak on SSB for 15/10m and around 500w 20m on down to 80m and she will last forever.
Don't overdrive those 572B's the good Ctron/RCA /Raytheon tubes are getting extremely hard to find...and going prices can reach $100 each...
Svetlana(white ceramic base) made good ones also but have been out of production now for a few years and prices have skyrocketed on those also...
Only option is China and buy (4) to get (2) good ones...:cry:
GL Enjoy
All the Best
Gary
 
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SB200

I have a SB 200 and if I put 50-60w drive into it instead of 100 I will lose about 200w in output so not sure about flat topping it at anything over 60w but it is first Heathkit I have ever owned so I am definitely no expert. Thanks Jimbo165
 

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