[ARC5] Switching the dreader B+ line.

[Tom Bridgers]

Another option to do the following:

o  key an unmodified  SCR274N or ARC-5 Tx

o  provide a spot freq function

o  provide an RX-TX antenna relay function (such as BC-442)


and to provide regulated oscillator voltage to the VFO, do this:


o In addition to the power supply to deliver specified voltages

needed (575vdc,  275 vdc, 210 vdc (preferably regulated),

and 28 VDC for fils and relays) to power on and transmit CW

using an unmodified TX, include a separate power supply on

the power supply chassis for the regulated 210 VDC for the VFO.

It will be toggled on when the transmit switch (see below) is

turned on. (I also provide a separate 28 vdc power supply for

the Stinson keying relay.)


o Put a separate spst "Select Tx" switch for the K53 relay

on the power supply chassis. It completes the circuit for K-53

to operate.


o  Use a DPDT "Transmit switch:".  One switch segment toggles

on 120 VAC to the primaries of the HV Xfmr (for the PA B+ and

SG) and the separate primary of the Xfmr for the 210 VDC p/s.


The other switch segment delivers 28 VDC to an antenna relay,

such as a BC-422.  Or a different voltage if not using a BC-442.


o Given the above, here's how this lash up works to provide a

spot function, transmit function and antenna TX-RX relay

function:


(1) To begin operating, turn on the main power supply with a

separate spst switch.  This switch instantly delivers 120 VAC to

two (2) separate 28 VDC supplies. One is for the transmitter

filaments, and makes that voltage also available for use by K53

when the select switch is toggled on.  The other 28 vdc supply is

the source voltage for the keying relay. This switch also delivers

120 VAC to the "Transmit Switch", which when turned on, is used

by the primaries of the HV and VFO power supply xfmrs.


(2) Now, toggle on the "Transmit Switch" which does the following
   a.  turns on the HV power supply and it delivers 575 vdc and 275

to the TX "keying relay".

   b.  turns on the 210 VDC regulated power supply and it delivers

this voltage to the set of K-53 contacts that go to the 1626 VFO tube.

   c.  delivers 28 vdc to the RX-TX antenna changeover relay.


(3) To spot the TX's frequency, toggle on the "Select Switch". This

switch in turn toggles on K-53, which grounds the 1625 cathodes AND

turns on the VFO.  Note that the Tx does NOT transmit on the air,

however, because the keying relay has NOT been toggled on by your

morse key.


When you are satisfied that your TX is on the desired frequency, leave

the select switch toggled on.


(4) Using your morse key or a bug, begin sending CW signals.  You're

on the air.


(5) To receive, toggle off the "select switch" and the "transmit switch."


(6)  The select and transmit function could be simplified into one switch

if you used a 3PDT switch instead of separate SPST and DPDT switches.


Admittedly the above is old school.  But then at 75 years old, that's pretty

much all I know right now.


I hope you all find this lash-up useful.  Suggestions/changes?

-Tom  KE4RHH

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