Which Transformer for homebrew GS-31B

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

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  1. K9FV

    K9FV Ham Member QRZ Page

    Bryan, there is one advantage to the GS35b tube I've not thought of until just now - cooling. With the much better anode cooler, it should take a bit less air flow to cool the tube at the same KW power rating. Less air flow means less noise from the amp. Those blowers sure do add to the noise level in the shack.

    You are correct in the small extra price - when you are talking $70 price difference in tubes of this power rating..... not much at all!

    Does that idea have any merit?

    73 de Ken H>
  2. K5JCT

    K5JCT Ham Member QRZ Page

    Got my tube from Russia today. Pictures don't do it justice. This thing is huge.

    Transformer should be here Monday.

  3. K9FV

    K9FV Ham Member QRZ Page

    Hey Jimmy - you are right, those GS31b tubes are pretty big. I saw one guy advertising silver plated tubes - from the photo it looked like the whole tube including anode cooler was silver plated. If so, that sure would look nice. I understand the GS35b tube/cooler is even larger than the GS31b tube. Heavier anyway with that copper anode cooler.

    I'd almost like to sell my GS31b 6 meter amp and buy parts to build another amp. I don't expect it would work any better, but it would make another nice project..... as if I needed another project:)

    73 de Ken H>
  4. WA7PRC

    WA7PRC Ham Member QRZ Page

    Groovy. :)

    The GS-35b is even bigger and more than twice the mass than the GS-31b, thanks to that BIG copper heat dissipator. ;)
  5. TF3T

    TF3T Ham Member QRZ Page

    I was very surprised when I held my first GS35b - it's huge and very heavy. compared to a 4cx1000/PL172.
  6. K5JCT

    K5JCT Ham Member QRZ Page

    I got the silver plated one. Looks very nice.

    The thing I don't like about this tube already is the air flow requirement. After I get it going good and work out the bugs, I want to buy an 8877 and convert it over to that. I really won't have to change all that much. It doesn't require near as much air flow. I think you had a good point in that the GS-35b could be used at lower power with a smaller blower because of the more efficient cooler. I just don't like the looks of the copper cooler. I almost wish that I had gone with 2 x 3-500z tube because of the much lower air requirements. I don't like noisy blowers. This amp will sit on my desk.

    What kind of blower did you guys use.
  7. K5JCT

    K5JCT Ham Member QRZ Page

  8. WA7PRC

    WA7PRC Ham Member QRZ Page

    I haven't gotten very far on my GS-35b 160m monoband "ample fire" project. I'm slowly collecting/fabricating parts. I don't see cooling requirements for the GS-31b. It'd be nice to have a starting point. FWIW...

    I've looked into cooling the GS-35b for my 160m monoband "ample fire" project. The GS-35b datasheet states it requires 2500 l/min (88 cfm) of airflow. Whatever you use to move the air, it'll move air easier if there is less restriction. I decided to use a Dayton pn 3FRF1 centrifugal blower (USD $88, 230VAC, 110cfm @ 0.5" SP). I expect zero cooling issues but, it might be a bit noisy.

    If you want/need to move air from below chassis, consider using the GS-35b "socket" and chimney design by Tony/W4ZT (SK). It has more crossectional area for air flow than you'll ever attain by making holes through a chassis directly under the anode. It also affords a low reactance path for the grid to ground (important if you're not driving the grid). The tube doesn't care which way you move the air, and blowing from above works -- you just need an electrically insulating fitting.

    Whatever you use for cooling, it's a good idea to verify the anode doesn't exceed 200°C. Temperature indicating paint, crayon, strips, or an IR non-contact instrument will do that. Omega Engineering is one source of such items.

    I don't know that I'd go with an 8877, based on the comparison to the GS-35b.
  9. K9FV

    K9FV Ham Member QRZ Page

    I used the Dayton Fan # 2C647 which is 134 cfm at zero SP, but still 79 cfm at .5 in SP. It does blow a lot of air, but sorta on the noisy side also. Seems like I remember the GS31b requires about the same air flow at 1,000 watts as the GS35b does at 1,500 watts? Not sure about that, but the larger anode cooler would help.

    Jimmy, I think you'll be happy with the GS31b tube..... BUT that long 3 minute warmup sure seems LONG when you're sitting there listening to a CQ you'd like to snag! The 3-500Z is almost instant on.

    73 de Ken H>
  10. WA7PRC

    WA7PRC Ham Member QRZ Page

    I haven't been able to find any data on cooling requirements fo the GS-31B. All I get from the GS-31b datasheet is that the maximum anode temperature is 200C. Not having flow data available is a pain. That blower might work... or not.
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