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Which Transformer for homebrew GS-31B

Discussion in 'Amateur Radio Amplifiers' started by K5JCT, Dec 25, 2011.

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  1. WA7PRC

    WA7PRC Ham Member QRZ Page

    You could call MFJ/Ameritron and ask them what the actual specifications are. Or, you could ping on Tom/W8JI for info.

    I understand your concern about size, weight, and cost. But, for me, a piece of equipment that compromises performance because of [fill in the blank] is a piece of equipment that won't get much/any use.

    In my case, my 160m GS-35b project will use a Heath SB-220 outer case and I won't have room at all for the 45# plate xfmr or the 35# 1H/800mA choke. So, the plate supply will be housed in a separate chassis that I'll fabricate. The RF deck will be lighter than my SB-220. I may also build amplifiers for 6m and/or 2m so, the separate PS works out to be a very good idea. You might consider that, especially if you come upon the deal of the century on a behemoth xfmr! :D
     
  2. K5JCT

    K5JCT Ham Member QRZ Page

    Thanks all.

    I just ordered the Peter Dahl/Magcap PT-220 from Harbach.

    Jimmy, K5JCT
     
  3. WA7PRC

    WA7PRC Ham Member QRZ Page

    That'll just about do it...
    1170VAC @ 1.3A through a doubler yields 3300VDC @ 650mA (2145W). Assuming 55% efficiency, you should realize approximately 1180W RFO. :)

    The above assumes no sag in the EO. Minimize sag with a stiff AC source.
     
  4. K9FV

    K9FV Ham Member QRZ Page

    Good deal Jimmy - That should be a very good transformer for the GS31b tube. Is that the $335 transformer?

    BTW, did you ever mention what band (s) you are planning for?

    Ken H>
     
  5. K5JCT

    K5JCT Ham Member QRZ Page

    Its the PT220 transformer on the Harbach SB220-221 page. It's $340.00. I know the other one was listed at $335.00. It's the same transformer. Maybe I could have saved $5.

    It will be 160-10.

    I would have rather spent the $63 dollars more and gotten the Ameritron AL-12 series transformer, but I could not make it fit. I think this one will work out fine.

    The 650 mA rating is CCS so hopefully it will do the job.

    If I had an extra inch I would have certainly gone with the Ameritron iron. You really can't beat their price on that one. $403.00 for 2570vac @ 800mA.

    If I don't get the performance I want, I'll sell the Harbach SB220 one and "make" the Ameritron one fit.

    I'm already building my next amp in my head...Maybe 2xGS-31B.

    Jimmy
     
  6. AF6LJ

    AF6LJ Ham Member QRZ Page

    This is going to be a very Cool project.
     
  7. K9FV

    K9FV Ham Member QRZ Page

    I agree with your thinking on the transformers Jimmy.

    Why the focus on GS31b tube vs the GS35b? Solely based on cost? That was my reasoning, and I'm not sure there is that much difference in the two tubes other than the nice copper anode cooler on the GS35b. I think the GS31b is pushed much less at a KW each than the GS35b is at 1500 watts each.

    Keep us posted on your progress and build. I wish I'd built my amp with power supply in a seperate box.

    73 de Ken H>
     
  8. WA7PRC

    WA7PRC Ham Member QRZ Page

    You're OK as long as you don't run any high D/C modes (FM, RTTY) and have sufficient airflow past the xfmr.

    I did, by a bunch, by rewinding an old xfmr that came to me free. Total cost ≈ $150 for materials; output > 4KVA. :D

    There ya go. Consider going with a separate HV supply. That allows you to use the HV supply with more than one RF deck (not simultaneously, of course). It also removes significant weight from the RF deck, making the RF deck easier to handle.

    I like the GS-35b over the -31 'cuz the cost not much more but the PDISS is 50% higher. I've read that this rating is conservative. Also, generally, a single larger device behaves better than multiple devices in parallel.
     
  9. K9FV

    K9FV Ham Member QRZ Page

    Actually the cost is just about twice as much for only 50% more rating - and the 50% rating increase comes at the expense of half the rated life per datasheets.

    GS31b at $95 shipped (I have purchased two from this seller)
    http://www.ebay.com/itm/31-GS-31B-R...ultDomain_0&hash=item3a6e281661#ht_661wt_1159

    GS35b at $167 shipped (OK, not hardly twice as much - and I sure like the looks of that copper anode cooler)
    http://www.ebay.com/itm/Russian-POW...tronics_R2&hash=item4160dd2592#ht_3801wt_1159

    I don't think you can go wrong with either tube - and at times I sorta wish I'd went with the GS35b..... but I also sorta wish I'd build the power supply separate. I had planned separate, but got to thinking "this will be my last tube type amp so not reason for separate"..... I sure hope it's not my last one to build:)

    73 de Ken H.
     
  10. WA7PRC

    WA7PRC Ham Member QRZ Page

    I seem to recall that, at MF/HF, the GS-35b can handle closer to 2000W PDISS. If you're using solely cost, that tilts the numbers the other way. Even if it didn't, the cost difference isn't much. My primary reasons for using one tube are electrical performance, and simplicity of amplifier construction. The cooler on the GS-35 outweighs the tube itself. A glance at the -31b and -35b coolers indicates the cooler for the -35b has MUCH more surface area, and has the potential to cool better.

    I'd like to get on 6m and 2m (SSB & CW), to do some DXing and contesting. I may build amplifiers for those band(s); a separate power supply eliminates that work and expense. I already have a spare GS-35b w/o cooler.
     
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