2m amplifier "upgrade" 4cx1000k to a GS-35b?

Discussion in 'Amateur Radio Amplifiers' started by TF3T, Dec 4, 2011.

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  1. TF3T

    TF3T Ham Member QRZ Page

    Hi all

    last year I built a 2m amplifier for EME operation, It was based on a old RF deck from Telefunken that I acquired by chance. it had a 4CX1000k (different from the 4CX1000A) . I have one 4cx1000k - and I have no clue what the status of it is.
    It uses the GM3SEK tetrode boards for control and has a big blower for cooling.

    pictures: http://www.tf3cy.is/2m-linear

    The current amplifier has one very important feature.
    - Very high gain - I have a K3 with the internal transverter - so 10w in 1Kw out.
    - It's very stable - it has a neutralization circuit.

    Problems:
    - It uses this rare and expensive tube - 4CX1000K has a solid screen ring
    - "low power" - for EME work (match all the GS35's and 8877's)- it would be good to have bit more available. I have not been able to get more than 1KW out of it and I have noticed the tube starting produce less and less- filament voltage is correct. The efficiency is around 60%

    so I'm probably going to have to replace the current tube - and that's going to cost.

    I now have a HV power supply that can supply voltages from 2,5kv - 4Kv at 1,5A ICAS. (using a P.D. ARRL-02-002)

    so I'm working on a GS35b hf/6m amplifier - so naturally I think I should perhaps look at GS-35b for the 2m amplifier.

    The GS35b has littlebit less output capacitance - but that should be no problem, but I fear the big heatsink will produce more stray capacitance as the RF deck is bit small. not 100% if that matters.

    if I'm running a GS-35b on 4KV - how much drive will I have to use to fully load the tube ?
    (I know 10w does not do it, but 100w? more?)

    and ---any concrete thoughts on this ?

    Is there another tube I should consider ?

    - will a 4cx1500 fit into the current socket ? (I'm not keen on that as I already spent $300 on the grid/screen transformer and the 1500 has much higher screen supply demands)

    73, Benni TF3CY
     
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