[Drake] Need PTT Relay for TX4C

[Garey Barrell]

Jim -

Unfortunately, it's not quite that simple in the T-4X.  The T-4X and 
T-4XB have "wired-in" relays rather than the plug-in type used in the 
"C".  They're quite reliable as long as no-one has been "adjusting" 
them.  :-)  Another cause of damage is operating into a poor load, that 
can cause sparking on the contacts.

Drake offered a small PC board to convert the older transmitters to the 
newer plug-in style relay if replacement became necessary.  John Kriner 
still has a few of those boards, I believe, and they use the same relay 
mentioned below.

That said, your problem is quite possibly related to the Bias supply in 
the AC-3/4.  Bias voltage is relied on to open the relay by cutting off 
the 6EV7 relay tube and if that voltage is low because of leaky 
electrolytics or ripple, the tube doesn't cut off as quickly.  Yet 
another possibility is that the 6EV7 is slightly gassy, which again 
causes tube to want to continue conducting after it is told to cut off, 
especially after long transmissions!  Another possibility is that the 
final tubes are dropping in emission, which requires you to set the bias 
voltage more positive to set the idle current to the proper value.

So...  Depending upon the condition of your power supply filter caps, 
(all AC-3/4 electrolytics exceeded their life expectancy about 20 years 
ago!,); or how old your 6EV7 and/or 6JB6s are, you can prioritize the 
possibilities!  The AC-4R power supply upgrade from the Heathkitshop is 
an excellent way to extend the life of your supply for another 30 
years.  The good news is, it's probably not the relay itself...

73, Garey - K4OAH
Glen Allen, VA

Drake 2-B, 4-B & C-Line Service Supplement CDs
<www.k4oah.com>



James Barrie wrote:
> Gary: does that apply to just the T-4XC's ?
>  I have a T-4X (serial 11901) and occasionally, I'll notice the relay 
> will hang for just a split second, before it will release. Not 
> often... just every once and a while.
>
> 73
> Jim - WA8SDF
>
>
> On Nov 12, 2007, at 10:41 PM, Garey Barrell wrote:
>
> Charlie -
>
> The "correct" replacement relay is the P&B (Tyco) R10-E1-Y4-V2.5k, 
> same relay used in the "late" T-4XC and TR-4C, which IS available from 
> Mouser and Digikey among others.   About $15.
>
> If your old relay is a Varley with a 15k coil, you need to add a 1.5k 
> 1W resistor in series with the coil, otherwise a drop-in replacement.  
> Look at the socket for V10, the 6FQ7 (or 6EV7).  If there is a 1.5k, 
> 1W resistor connected between Pin 6 and Pin 9, just plug in the new 
> relay.  If there is NO resistor, remove the wire connected to Pin 6 
> and move it to Pin 9, add a 1.5k, 1W resistor between Pin 6 and Pin 9, 
> and plug in the new relay.
>
> The 15k ohm coil relays were failure prone, primarily because of the 
> very fine wire needed.  The bobbin would swell,  especially in humid 
> conditions, stressing and breaking the wire.  This is why T-4XC's that 
> have been stored in the garage for a while often have a bad relay!  
> The 2.5k ohm coil of course uses considerably larger wire.