Transverter - ran too much power to it, now what?

Discussion in 'Radio Circuits, Repair & Performance' started by K9OO, Feb 11, 2018.

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  1. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    If you find an old Hallicrafters HA-2 transverter (it uses tubes and is from the 1960s), they are pretty easily modified to 222 MHz by changing a crystal, a few coils, a few capacitors and cutting down the P-P plate lines (mechanical work). They do not have a built-in AC power supply and normally used the same power supply as the Hallicrafters transceiver it was connected to; however many "tube transceiver" power supplies from different manufacturers will work.

    Downside is it's old and also fairly "large."

    Upside is these things never die, and the P-P 5894 output stage runs about 75W output power on 222 MHz once converted, so it's often enough to make a lot of contacts without another amplifier; also, I have seen them for $150-$200 on the used market often enough to know they're not terribly rare.

    [​IMG]
     
    K3XR and K3RW like this.
  2. KB2E

    KB2E XML Subscriber QRZ Page

    QUOTE="WB2WIK, post: 4555426, member: 274916"]What would have been taken out instantly would be Q5.

    Possibly also RV1, L14-L15 and maybe C43-44-45 and the input swamping resistor (I can't read its designation on this screen but looks like 180 Ohms across the 28 MHz input just prior to the low-pass input filter).[/QUOTE]

    But might the attenuator have survived? My reasoning, which is not always based on all the knowledge necessary but on only what I have, is that if something in the attenuator opened then the power would not pass to the XVTR board. Sort of like if there's a pressure spike in a pipe the weak point breaks and no more flow occurs downstream. Here's how my head works. I typed that and realizd that the theory is not neceessarily true. Some flow may still appear, just less. But in the case of the attenuator more "flow" perhaps than the XVTR could handle unless here was a complete opening on the input instantly, which obviously didn't happen.
     
  3. K7TRF

    K7TRF Premium Subscriber QRZ Page

    It's a different set of parts and troubleshooting flows to get your head around but if you can troubleshoot motors and get to the root cause then you can learn to do the same with electronic circuits.

    Here's the schematic with a red line added to show where the higher than expected power from your rig entered the circuit. It's either voltage across components (e.g. Q5) or current through components (e.g. RV1) that would do damage when you applied excessive power to the input of the transverter. Take a look at the diagram and where that red line leads and match it up to the components Steve listed and it's pretty easy to see why he picked those out as the most likely to be damaged.

    Certain things help like knowing that dual gate FETs (Q4 and Q5) show a very high input resistance on their gates but are also prone to over voltage damage and the switching diode VD2 should block the receiver circuitry to lower voltage signals (which is likely why the receive chain still works in the transverter) but apply a big enough signal to VD2 and it will act like a power supply rectifier and send some of it backwards into Q4. And if JP2 was opened up (you were using a separate receive input) then the high transmit signal wouldn't even have reached VD2 or those portions of the circuitry.

    upload_2019-8-9_13-42-27.png

    BTW, Q4 and Q5 are the receive and transmit mixers respectively and they're what do the bulk of the transverter's functions by mixing the incoming receive signal (Q4) and outgoing transmit signal (Q5) against the 116 MHz output of the oscillator (Q2 and CR1). The rest of the circuit is filtering, some amplification, power regulation and the circuitry to handle transmit receive switching. Take a look at where that 116 MHz line runs and it's easy to see where the mixing (transverting) occurs.
     
    Last edited: Aug 9, 2019
  4. K9OO

    K9OO Ham Member QRZ Page

    Followup:

    So I ended up purchasing a new attenuator and a new transverter board. I don't believe this was necessary. The extra power had not done anything to the board that I could tell. It may have, but I took the hf antenna port out of circuit. When I replaced the transverter board (my assumed area of issue) it still didn't work. So I ordered an attenuator board. When I was playing with it, I noticed it worked sometimes, but not always. When I examined it, nothing looked off where I was looking. Then I saw it... At some point, the power positive came into contact with the board in the attenuator. It shorted the board at the part and the soldered part lifted up slightly. When I pushed down on the part, I could make it all work together, otherwise it was intermitant. The end result was running a separate wire to another part of the board to fix the broken trace - and insulating the power input. It is all good now.

    TLDR, I assumed it was the transverter board, it was the attenuator board and a preventable problem.
     
    K7TRF likes this.
  5. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    The Hallicrafters HA-2 and HA-6 actually had a specific power supply that connected to both units. It has a circuit that allows only 1-transverter to be "on" at the same time. If both transverters have the power switch in the "on" position, the AC mains is disconnected from the power supply and will immediately be connected when one of them is turned off. I do have this power supply connected to my HA-2 / HA-6. Frankly, running the transverter from the same power supply as the exciter would be too much for most tube-type transceiver power supplies.

    For 222 MHz, I also modified another HA-2. For the power supply, I use a home-brew equivalent of the Heath HP-23A power supply. That power supply uses the power transformer from a Heath SB-400 transmitter which is the same transformer as was used in the HP-23A.

    Glen, K9STH
     

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