fetrons... what to do with them?

Discussion in '"Boat Anchor" & Classic Equipment' started by K7WXW, Jun 11, 2019.

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  1. W2WDX

    W2WDX Subscriber QRZ Page

    One of the reasons for Fetrons emergence was the potential lower noise and lower distortion vs. tubes. Scarcity of tubes, not so much. (Contrary to what was written in most amateur literature at the time). But of course it depends greatly on the circuit topology and application it's used in. Fetrons came into being for submarine sonar applications where low-noise low-distortion circuits were crucial to improving performance in existing tube electronics of the day.

    Today they are an interesting esoteric vestigial remnant of the era where hollow state was giving way to solid state. How practical they are or whether they have any useful application over more modern equivalent circuits that can be built today is dubious at best.
    Last edited: Jul 15, 2019
  2. K7WXW

    K7WXW Ham Member QRZ Page

    Based on what I have been able to find on these devices, I'd agree. They offered "as good as" performance and better specs for noise, distortion, and reliability. As far as using them for some project around here now, practical wouldn't be on my list of requirements. But then, very little of what gets built on my bench would qualify as practical. Most of it probably wouldn't even pass for useful. Interesting is usually reason enough for me.
  3. N8FVJ

    N8FVJ Ham Member QRZ Page

    What is a Fetron?
  4. W7UUU

    W7UUU Super Moderator Lifetime Member 133 Administrator Volunteer Moderator Platinum Subscriber Life Member QRZ Page

    A solid-state replacement for many common tubes using FET devices along with resistors to handle voltage compensation and capacitors as needed to make the solid-state replacement have more-or-less the same specs as the tube they were replacing. They were billed as "lifetime tube" replacements but of course that's not true.

    "Tubesters" was another brand of the same thing

    Collins S-Line and Drake rigs seem to have been the primary target for them.

    I had a Collins S-Line receiver with "Tubesters" that worked well - but no idea if it still does today, after all the years of the parts slowly failing inside each "Tubester".

    Same story with "Fetrons"

    IMO: both were a novel idea but just a novelty in the long term.

  5. K6LPM

    K6LPM Ham Member QRZ Page

    Fetron's Huh? I was unfamiliar with such a device. Seems a very interesting curiosity to me.
    I am curious to know what these things priced like to comparative tubes that they were replacing?
    Were these devices a direct device for tube replacement? In other words a 12ax7 could be replaced by a direct Fetron 12ax7 substitute?
    A previous post seems to indicate that wasnt quite the case and each application was a bit different depending on how the tube was applied in what type of circuit.
    Very interesting.... I wonder given the modern technology of today, what kind of direct plug and play tube substitution could be designed and how close could the performance mimic that of tube technology as well as how much different performance behaviour could be expected.
    Obviously much of solid state has far exceeded the performance of tubes, however in some esoteric applications (mostly nostalgic audiophile) the shortcoming of tubes is actually a desirable trait.
    I wonder just how closely we can actually mimic a tube in a drop in replacement device?
  6. KX4OM

    KX4OM Ham Member QRZ Page

    I just came across a QST article on replacing several tubes in a Drake T4X-B with homebrew FET circuits mounted on tube bases. It has info on replacing 12AT7, 12AU7, 12AX7, 6AU6, 12BA6, 12BY7A, 6CL6, and 6EV7 types. The replacements are grouped in 4 basic characteristics. A table shows voltage, transconductance, etc for the schemes. For example, one of the tubes is V9, the 12BY7A PA driver tube.

    The article is in the April 1977 QST, "Solid-Tubes-a New Life for Old Designs". A follow up is in Technical Correspondence in the September 1977 QST.

    Ted, KX4OM
    Last edited: Jul 19, 2019
    K6LPM likes this.
  7. WB2GCR

    WB2GCR Ham Member QRZ Page

    FETRONS were an implementation as a hybrid circuit (like a hand-made IC) of the Western Electric "HIN"
    devices. (see earlier in the thread?)

    A short while back I plugged a FETRON into the hole where a 6AK5 was sitting as the RF front end on an
    R-388 (51-J) receiver. I have to take some time to explore it further. Initially, seems like on the BC band,
    both the FETRON and the 6AK5 have the same gain. I think I saw lower gain on 75m for the FETRON.
    That is somewhat surprising, but it would pay to tweak the alignment of the RF stage, just to see if it turned
    out to be an impedance difference or not. I'll also need to look higher up the bands. But it does work.

    This was compared to a "hot" 6AK5, btw.

    Since there are various "incarnations" of the "6AK5" (about a dozen or so) as FETRONs, others may or
    may not perform the same.

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