RF Amplifier Tubes- whats left & affordable for a RF Amp

Discussion in 'Amateur Radio Amplifiers' started by N8FVJ, May 4, 2019.

ad: L-HROutlet
ad: l-rl
ad: MessiPaoloni-1
ad: Left-3
ad: L-MFJ
ad: Left-2
ad: Subscribe
  1. W7RY

    W7RY Ham Member QRZ Page

    B&W (Viewstar) PT2500 has chimneys, Ameritron AL82 does as well, all Henry's do too. Drake L4 and L4B. Lots of marine amps of various brands that had 3-500 tubes also do.
    73
     
  2. W7RY

    W7RY Ham Member QRZ Page

    That may be, but folks on the amps reflector are looking for cathode input specifications. There are none on most of these types of tubes. The "4CX800" specs were made up by Svetlana.
     
  3. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    RY:

    The GI-7b, GI-7bT, and the GI-70, all exhibit very close to 100-ohms cathode input. As such, 2 of them in parallel exhibit very close to 50-ohms. I found that to be very close to what I am seeing with my 160-meter single band amplifier that has a pair of GI-7bT tubes in it.

    I am trying to remember just what the cathode input is for the GS-31b and GS-35b. If I remember correctly, it is close to 50-ohms but I may be mistaken. That information can be found, on the Internet, if one does a little looking. The reason that I am thinking they are close to 50-ohms is because I am slowly rebuilding a basket case Hallicrafters HT-33A replacing the defunct PL-172A with a GS-31b and the input will be un-tuned just like with the PL-172A. All but 1 of my exciters have a Pi-network output and can match a wide range of impedances. The remaining exciter has a built-in automatic antenna tuner and, if the impedance is far off of 50-ohms, it can still match the amplifier.

    Glen, K9STH
     
  4. W1BR

    W1BR Ham Member QRZ Page

    IMD can suffer if the tuned input is not as physically close to the cathode as possible. External remote tuner in the exciter or not...

    Pete
     
  5. KM1H

    KM1H Ham Member QRZ Page

    I use mine mostly on AM at 1000-1200W PEP, even on 10M, with a bias mod to run it deeper into Class B with barely noticeable distortion (cant hear it) on a spectrum analyzer. Currently running a mix of Chinese tubes for the past several years with some color on voice peaks which might keep them gettered.

    It is driven with one of the low power AM rigs here that I rotate with plate or carrier control screen modulation.
    Also improved 160 performance and added 12M with a plate choke mod as well as new parasitic suppressors of my own design which were copied by Ameritron with no "thank you". None expected considering who did it.

    Carl
     
    AC0OB likes this.
  6. KM1H

    KM1H Ham Member QRZ Page


    Agree, they are strictly a 600W PD USSR era military tube and there is little emission overhead for any serious ICAS or IVAS use which really cooks them. Svetlana will make a new run but I havent seen a price yet.
     
  7. KA9JLM

    KA9JLM Ham Member QRZ Page

    Medical pulls are going to get harder to find.

    They are rarely used now a days.

    Get them why you can.
     
  8. KM1H

    KM1H Ham Member QRZ Page


    If you want an eyeful just look at one of those little GI7 tubes on a SA! They are a low mu design and not suitable for SSB. But hams being hams love them for one reason: cheeeeeep.
    You might as well run 810's, 250TH, 304TL, etc or any number of older industrial heating tubes that are still cheap, 5867, TB3/750 and 5868, TB3/1250, etc. with very poor IMD. Great for CW, AM, and digital.

    The graphite 813's are still around, even NOS, stay far away from the later cost reduced sheet metal one, they light up similar to import 811's when barely pushed. Very good SSB IMD in GG.

    Want a low band amp, try the monster 803 with a "claimed 125W anode" which takes CCS to new heights. Ive had a pair at 1200W+ years ago up to 20M.

    The Russian GU-81M glass pentode is still a sleeper in the US, sockets can be expensive or make your own. Think 813 on serious steroids and good on HF. I have a pair in an AM modulator, havent finished the QB5/1750 amp yet...another sleeper in the USA

    OTOH the Russian GU-36B/4CX400A is still cheap and in production. Think a much more reliable/rugged 8122 using a 4CX250 socket or a cheap plain Russian/Chinese one. A fairly easy NCL-2000 swap in place of a single 3CX800A7 since prices went up and MRI pulls dried up. Also a plug in to the 144/222/432 MHz AM-6154/6155 surplus FAA amps.

    Other useable tubes such as the 4-250A and 4-400A are fine in GG and can even replace the 3-400/500Z in some amps.

    Tired of import 811A's that arent? Ready to experiment? Try the 814 aka VT154, still lots around real cheap, easy 150W each on SSB, I run 120W out on AM in a Hallicrafters HT9 for years. Can even be run horizontal.

    Carl
     

Share This Page