johnson tr switch

[w5tmg]

ive used this tr switch for several years with out an issue. recently i got my rca bta1r on the air on 160, and all of a sudden my tr switch went belly up. i read on the front of it 3.5 to 27mc... well i know what happene dto my tr switch now, is there a mod to make that thing do 160 meters???

[WQ9E]

First thing is to determine what failed in your T/R switch.  Within its power ratings it should be OK on 160 but depending upon the peak output of your new rig and the match (or better mismatch) of the antenna there could have been a power related component failure.  This is one of the places where PEP output of an AM rig is important and it is at its limit with a 1 KW carrier output 100 percent modulated AM rig into a perfectly matched load.

I can see where it will have some receive loss on 160 compared to the higher bands but it shouldn't have component failure. . 

[ke7trp]

Yep, Its a simple schematic.  Check the tubes first, Then check the voltages. The unit itsell will take the power of the BC rig so that is not what killed it.

C

[KM1H]

Is that rated for 1000W DC input? If so thats 700-750W carrier.

I havent run either of mine or the B&W that high yet.

[WQ9E]

Broadcast rig power level should be OK as long as the antenna is perfectly matched.  But high SWR, or a momentary antenna or rig glitch, will exceed the peak voltage limit of the TR switch when running at its power limit.   The stated Johnson rating is 4 KW pep but I am pretty sure they are referring to input power so they probably assume around 3 KW PEP to the switch when used with a typical legal limit AM rig of the time (like the Desk KW).  One would expect there is a little leeway in this limit but at 4 KW PEP out from a 1 KW output broadcast rig you have used up any slack in the rating so there is no room left for increased SWR or other problems.

For me personally the only reason I would use an electronic switch is if I wanted to run full break-in CW.  Otherwise I much prefer a good quality regular or vacuum relay.  I have a Johnson TR switch that came with a Globe Chief/HQ-129X setup from a good friend's estate.  But my main AM rigs use a vacuum relay (Desk KW and Viking 500) and regular cube type relays for the rest.   Simple with less chance of receiver damage.  Of course the Johnson TR switch does make an excellent coffee cup warmer

[ke7trp]

They take a transmitter with 4000 PEP input and a BC rig is not going to run that much.  At least most wont and most operators wont.  If worried, Dont use it. 

Use a relay.  But most of use a Dowkey and they are not rated for a BC rig either.

two advantages to the TR switch is you get 2 to 6 DB increase in RX performance and instantly switching with no arcs or relays to chatter or fail. 

The last advantage is that the TR switch has a probe jack on the front for your O scope or mod monitor.

I have two, Used one briefly and will probably rebuild one soon to use with the J500.

 

[Opcom]

How much power and peak power did you use? That switch may say 4K peak but it's old and unless someone can say otherwise those are ham (ICAS) ratings and from the KW input days, so you could have been pushing it.

I have used that TR switch with a 500W output amp, but for bigger stuff like actual transmitters I always use a contactor like the kind that goes in the a/c condensing unit.

Could it have just blown out the coupling capacitor and let the RF get into the tube? There is not much to break in it.

If the tube's grid is not conducting, all the voltage on 56K resistor R2 might reach its 1/2W rating in a 50 Ohm situation at about 590 Watts.

input-> 0.005uF -> 56K -> 0.005uF ->GND

(in the above I didn't consider the reactances of the caps but it is low.)

[Pete, WA2CWA]

If you read the initial post, it's not clear what the issue is (belly up means nothing to me).

I tried my Johnson TR Switch earlier this evening and on 160M, it acts like a very good receiver attenuator. The receiver output side of the TR Switch was not designed to go down to 160 meters.

[w5tmg]

it was a tube, and yes it is a simple layout. the power rating on the old thing is at 4000 pep. it was just its time  to give up the ghost... and im back on the air.. thnxs for all the replys...