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IDEAS: T/R for Central Electronics 600L w/Tranceiver??

Discussion in 'Amateur Radio Amplifiers' started by WB2GCR, Nov 26, 2019.

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  1. WB2GCR

    WB2GCR Ham Member QRZ Page

    Looking for ideas, schemes.

    Have a good (now that I fixed it) working Central Electronics 600L amp.
    Want to use it with a transceiver.
    It was designed for use with the CE Multi-Phase 20V exciter.

    The schematic is attached.

    The amp has "Input", "Output" and "Antenna".
    "Antenna" was intended to be used with a receiver.
    The tube is set up for grid block keying/control.
    There are no "T/R" relays internal.
    Stock, it would have been used with an external Dow Key relay going to
    the receiver...

    So, the short version of what it seems is needed goes something like this:
    (working backwards from the keyed up state)
    - drop exciter RF
    - dump in grid block (turn off tube)
    - switch "T/R relay" - transceiver for receive to Antenna (jack or coax)

    Keying up:

    - connect ("T/R") amp to coax/disconnect receive line from coax - transmit line to input
    - send RF from transceiver
    - unkey grid block (enable amp)

    Of course there are a few variations on the connection scheme.
    The transceiver could stay connected to the "Input" on the amp at all times,
    BUT the "loop back" from the Antenna jack or alternately direct to the coax
    (see schematic) must not arc, pass too much RF even on a transient, lest
    the amp oscillate and/or the receiver input get fried.

    Part of the circular nature of the thinking revolves around what keys what.
    As in, one could "key" the amp and have that key the transceiver, or key some
    sort of external relay, etc...

    Assume I have Dow Key relays, and electronic T/R, suitable open frame relays...
    but the idea is that the transmit jack and the receive port on the transceiver is
    the same, and likely switches WAY faster than the linear or the Dow Key can, and
    will NOT take abuse like a boatanchor rig.

    I'd greatly prefer to NOT have to buy a uproc operated "sequencer" and really would
    prefer some more basic approach. Transistors, and even some 555 timers or opamps
    seem more robust to me. Don't mind building a circuit with relays...

    Any ideas on how to make this go?


    Attached Files:

  2. K7TRF

    K7TRF Premium Subscriber QRZ Page

    I would definitely key the amp prior to sending it RF from the rig. I can't think of any good reason to intentionally hot key an amp. Assuming the amp is stable and doesn't oscillate there won't be any RF output out of a keyed amp that lacks drive signal so there's no reason I can think of to send RF from the rig prior to switching the amp into active mode.

    In terms of sequencing all of this the only real issue is when running VOX in voice or CW modes. If you run some version of PTT whether from the mic or from something like a foot switch in CW mode then it's easy to make sure you activate the amp prior to feeding it with RF. If you run phone and CW in PTT mode with either a mic switch or foot switch or something similar then you'd normally key everything at the same time but with an implicit delay to your first voice signals or CW characters.

    It's typical in commercial amps for the T/R relay and bias switching to be carried out via the same relay and therefore be simultaneous to one another when switching into or out of active transmit mode. But if you really want more sophisticated sequencing then it's easy enough to build an analog RC based or digital 555 or similar timer based sequencer with outputs to key the amp and to key the rig.
  3. WB2GCR

    WB2GCR Ham Member QRZ Page

    I understand all of your comments.
    My concerns include the idea that keying up and keydown (off) requires the reverse/inverse

    So, it's easy enough to (for example) delay the keying of the transceiver while the amp
    activates. Turning the excitation off and having the amp cease being able to output
    anything, and throwing a T/R relay so that the receiver now "sees" what was formerly
    the source of 500watts of RF is what I want bullet proof. Making delay in one "direction" is
    easy, not so easy to do it the other way... We're talking milliseconds, even microseconds making the difference
    between RF, RF bleed, and even hot switch arcing and not.

    Last edited: Nov 26, 2019
  4. K7TRF

    K7TRF Premium Subscriber QRZ Page

    It sounds to me like you're overthinking this. I'd do as just about every commercial amp on the market does and switch the RF path and the amp bias circuitry simultaneously using one or more relays to do that. Using fast vacuum relays for the RF path switching minimizes hot switching concerns but I'd set it up for a single keying line from the rig that does all the actual amp switching at the same time.

    If you also want to sequence your rig behaviors for instance to support VOX operation or CW break in keying (a form of VOX) then I'd tackle that as a separate project and not complicate your amp design for the purpose of making your rig behave differently.

    One possible variation on that idea is that if you do run a lot of QSK CW operation then you could either run a keyer like a K1EL that has built in PTT vs CW character sequencing or you could build an explicit CW QSK keying loop into your amplifier the way some Ten Tec amps are configured. Basically CW keying passes through the amp first and then back to the key input on your rig and there's a small time delay sequencer built into the amp so the amp gets keyed first and then the rig gets keyed via its key jack a tiny bit later. If you don't run CW QSK or won't use the amp while doing so then this isn't important.
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    What kind of rig are you using with the 600L?

    My rigs here have built-in "sequencing," which the user can set to whatever delay they wish, and the delay applies both in TX and RX; the amp key line closes first, then the TX output is delayed by however many mS you set; it works in reverse by unkeying the transmitter first, and then the amplifier by that same delay.

    These are Ten Tec transceivers which have that TX delay timing adjustable by menu. A lot of rigs have this, but obviously boat anchors don't.

    What are you using?
  6. WB2GCR

    WB2GCR Ham Member QRZ Page

    Good question. Nothing that supports that type of option.

    Considering running this with an early Anan, and likely a trusty TS-440.
    Nice that the Tentec does this internally.

  7. W2VW

    W2VW XML Subscriber QRZ Page

    Television surplus RF Transfer Switch A.K.A. Baseball Switch will handle all the RF switching and can be used to switch the exciter T/R along with blocking bias. TS-440 T/R speed is really fast, just ask Ralph.

    I have several in service. Ebay bargains for the patient thriftmeister (old skool) ham.
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Are you sure the Anan doesn't do this (I never owned one)? I think those are pretty software defined and have microprocessors and clocks and such in them, in which case the "capability" for timing almost anything should be there.
  9. WB2GCR

    WB2GCR Ham Member QRZ Page

    Even if it did, that would not transfer to another rig. So, I'd prefer a solution that stays with the
    amplifier and can be used with whatever transceiver is "de jour".
  10. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Do you want to load a sequencer board? I made a nice one that is about 2x5 inches. It has a little power supply on board and runs a few Clare mercury relays. Delays adjusted by pots.

    4 board minimum from the vendor and I used one.... about 30 bucks worth of parts to load. Works fab.

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