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sb220 Help

Discussion in 'Amateur Radio Amplifiers' started by N9DON, Dec 28, 2010.

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  1. N9DON

    N9DON Ham Member QRZ Page

    sb220

    I want to thank everyone for every suggestion.It helped to narrow it down to a filament to grid short.Put the extra tube in I had and she works like a champ!!This was only accoplished with all your tutorials THANK YOU Don:)
     
  2. WA7PRC

    WA7PRC Ham Member QRZ Page

    Once again, Tom/W8JI hit the nail on the head!
     
  3. W8JI

    W8JI Ham Member QRZ Page

    Don,

    What you found is by far the most common problem.

    The worry for me is you say the grid current meter did not read negative with the shorted tube in the amp. That is a major concern, because any time the tube has a grid-cathode short the grid meter should read negative.

    This means either you did not actually flip the meter switch to read grid current, you did not notcie the negative deflection but it was there, or you have a metering circuit problem.

    Does the grid meter work propery now? If not, you really need to find out why because it is the single most important thing to read. You really must have a grid meter that works, and you should use it. Do not run more than 300 mA or so on full power carrier or tune at full power!!

    That grid meter, if it is working properly and you check it, would instantly tell you many important things.

    73 Tom
     
  4. N9DON

    N9DON Ham Member QRZ Page

    sb220

    You're right I had inadvertently left the dial in the rel power position.Geez now the problem is solved but I only have part of the instrumentation readings used to get there.I'm a meter watching fanatic,I should have caught that.However I have learned much in this process! Don
     
  5. K4FNX

    K4FNX Premium Subscriber QRZ Page

    SB-2200 Loading Problem on 40 Meters

    I have an old SB-220 that I had not used in many years. In trying to get it back on the air, it does not load well on 40 meters. The Load capacitor is all the way to the right but the tune capacitor falls within the heathkit suggested range for 40 meters. When tuned in this way, the output is about 400 watts. Tuning on 20 meters is within heathkit's specs (including suggested ranges on the tune and load controls)- around 900 - 1000 watts with 100 watts drive. I have cleaned the bandswitch contacts and checked all connections.
    Any suggestions with this problem out there?

    K4FNX, Matt
     
  6. W8JI

    W8JI Ham Member QRZ Page


    Don't clean band switches except for dusting or removing some obvious film like cigarette smoke. If you clean a bandswitch, just use a soft brush and some light cleaner that totally evaporates like 100% alchohol or MEK.

    When you say the control is all the way to the right, is the LOAD knob set so this is minimum capacitance??? Plates wide open??

    Or is this fully meshed plates?

    Is the loading cap a single section variable, or is it the old multi-section broadcast style cap used in the very very early SB220??

    What is the grid current on 40 at maximum ouput, and what is the approximate drive power??
     
  7. K4FNX

    K4FNX Premium Subscriber QRZ Page

    SB-220 Loading Problem on 40 Meters

    Thanks for you comment W8JI,

    I made a mistake in my post. The Loading capacitor is all the way to the left (not right). The plates are fully meshed, so I suppose that is maximum capacitance. The loading capacitor is a two-section broadcast style cap. The grid current is 135 ma, which is within the expected range. The drive power is 50 watts from a FT-950. Power output as measured with a Bird wattmeter is approx 740 watts. Since the dc input is (.46 plate amps X 2300 plate voltage) 1058 watts and perhaps 66% efficiency plus drive feed thru, this is in the ballpark. Your are right, this is an old SB-220 (1970-73 vintage).

    K4FNX, Matt
     
  8. W9GB

    W9GB Ham Member QRZ Page

    Matt -

    What are you using for an antenna on 40 meters ??

    w9gb
     
  9. K4FNX

    K4FNX Premium Subscriber QRZ Page

    Hello w9gb:

    I am using a Hustler 4BTV vertical, ground mounted. It's an excellent performer, and works well with my transceivers (FT-950 and IC-7000). SWR is slightly less than 2:1.

    K4FNX, Matt
     
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