3-400 tubes in the SB-220

Discussion in 'Amateur Radio Amplifiers' started by W1BR, May 13, 2014.

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  1. WA8UEG

    WA8UEG XML Subscriber QRZ Page

    I have a early Swan MKII that came with 3-400's but had the bias added for 3'500's with a jumper that can removed for using the 3-500's. I purchased it around 1980 and use it almost daily plus a few weekend contests a year. The original 3-400's still have close to full output. I purchased 4 3-400's that were new about 5 years ago for $150.00 (they were advertised as new and as far as I could tell were). 3 were good one was gassy. I rotate the 3 every year and the fourth made a cool lamp for the shack. No doubt the 3-400's are going to out live me!!!!!
  2. W2VW

    W2VW Ham Member QRZ Page

    Original 3-500Z had mu of 200 just like the 3-400. It was reduced to 160 and was no longer zero bias at 2500 volts. See original spec sheets.

    Installing 3-400s into an SB-220 would require a small bias change if used on ssb. It also may be less stable in terms of parasitics due to the higher gain.
  3. KM1H

    KM1H Ham Member QRZ Page

    The early SB-220's were shipped with the high mu Eimac graphite 3-500 and didnt give any problems nor did several 220's with the hi mu Amperex graphites.
  4. W1BR

    W1BR Premium Subscriber QRZ Page

    At least one commercial AM 5kW transmitter used a 3-500Z, Collins used the tube in their PDM modulated transmitter back in the 80s. I'd bet a lot of those rigs are being retired as the source of reliable NOS American made tubes dries up.

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