DX-60 PTT questions

[W2PHL]

Greetings: I will be adding a PTT relay to my beater DX-60B. There is one mod out there that recommends using a relay to simply switch the grid block keying circuit. Is it better to have the PTT relay switch the HV instead? The DX-60B PS has +600,+300 and -130v outputs. Should they all be switched by the PTT relay?

Thanks for the help!
Phil

[K5UJ]

Phil,  I'm going to offer something mainly to prime the information pump so someone who knows something will answer 

My HT20 T/R keys the h.v. primary winding and low voltage secondary but there is a choke filter on the 115 v. AC line into the power supplies which I understand is there partly to um, cushion(?) the keying demand.  There are two 1000 mmf 500 v. bypass caps to ground one from each side of the AC line followed by two AC line filter chokes one in series on each side of the AC line then two more bypass caps .01 mfd to ground like the first two.  Unfortunately this is all the component specification I can give because the manual doesn't provide any more information but the point is perhaps the DX60 needs some sort of similar circuit on the low voltage line in to do the keying you are asking about?  The HT20 runs the 4D32 with two moduator 807s so the h.v. is not that far off from the dx60 I think.

73
Rob
K5UJ

[W2PHL]

Hi Rob thanks for the reply, Tube type transmitters are kind of new to me. The function switch on the DX-60 enables the HV secondary in the tune, AM and CW positions. I'm wondering if inserting a PTT relay at that point in the circuit would be the best way to do it. Maybe a relay wouldn't last too long if there's a lot of arcing going on. The function switch on the DX-60 does have a reputation for zorching over. I'm not sure if leaving the HV on the plates is a big deal or not but the PTT mod that just keys the grid block circuit seems to do just that (HV constantly on). I'd like to do it the right way and maybe learn something while I'm at it!

Phil

[K5UJ]

Phil,

I guess we're the blind leading the blind hi hi; I know leaving the B+ on all the time is okay with amps; I have learned it is a different deal with transmitters (they're transmitters after all) but I don't know if low powered rigs can be keyed differently i.e. is method B okay, or is it just an el-cheapo design trick.  Re the arcing relay you could always use a vacuum relay but for this power level I'm not sure if it is over-kill or not.  You have pretty much exhausted my knowledge or lack thereof at this point 

73

Rob
K5UJ

[WQ9E]

I haven't added PTT to my DX-60 yet but I did add a relay to save the function switch contacts.  You can use an arc suppression circuit across the relay contacts which is simply a capacitor and resistor in series across the relay contacts.  The older handbooks and the web have a discussion of choosing values.  They aren't terribly critical and are chosen to minimize arcing.  Just make sure that the capacitor has a safe voltage rating and don't omit the resistor since it limits current through the capacitor.

Using the grid blocked circuit on AM is probably OK but I would want to investigate further to make sure that constantly leaving HV on the other circuits doesn't lead to excessive heating.  The original setup assumed that the HV was on only during transmit and once you violate that assumption you need to be sure that you are not building up excessive heat in other parts of the circuit when the transmitter remains with HV on for long periods of time. 

If I add PTT to mine, I will switch the HV as was done originally.

Rodger WQ9E

[W2PHL]

That's a good tip Rodger. I've used caps across contacts before but not with a current limiting resistor.
    I guess switching the HV is the way to go, just figured I'd ask for some opinions. No need to re-invent the wheel with all the expertise here on this board. Thanks for the suggestions so far!