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G8MNY  > TECH     06.02.07 10:00l 42 Lines 1771 Bytes #999 (0) @ WW
BID : 1630_GB7CIP
Read: DL8FBH GUEST DL1GMC OE7FMI
Subj: PTT line for Drake L-4B PA
Path: DB0FHN<DB0FOR<DB0MRW<DK0WUE<DB0RES<TU5EX<ON0BEL<GB7CIP
Sent: 070206/0817Z @:GB7CIP.#32.GBR.EU #:1630 [Caterham] $:1630_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To  : TECH@WW

By G8MNY                                           (Updated Aug 06)
(8 Bit ASCII Graphics use code page 437 or 850)
THE PROBLEM
If wired directly to a IC735 Tx send connector, the IC735 relay contacts weld
up with the linear relay's back emf.

            L I N E A R                               I C  7 3 5
 14V            S4  _____                             SEND PTT
())))Ä´>ÃÄÂÄÄÄÂÄ/oÄ´relayÃÄÂÄ´>ÃÄÄo                  o)ÄÄ \  Tx
=====    ===  ³     ~~~~~  ³    PTT                   ³    ³ reed
      100u³  2k2       10n===   GND                   ³    ³ relay  
        ÄÄÁÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄo                   ÀÄÄÄÄÁÄÄÄ

This old large valve HF PA used an inductive 12V PTT relay that is run on 18V.

MY CURE
Not wishing to modify either pieces of kit, I chose to find a simple fool proof
solution in the inter connecting lead.

To stop the back emf & inrush current to the IC735's reed relay SEND contact,
I added a 35V 4u7 in series with a 100ê across linear's PTT 2 pin plug.

             L I N E A R                              I C  7 3 5
 14V            S4  _____            P L U G                 SEND PTT
())))Ä´>ÃÄÂÄÄÄÂÄ/oÄ´relayÃÄÂÄ´>ÃÄÄÄo ÄÄÂÄÄÄÄÄÄÄÄÄÄ(o o)ÄÄ \  Tx
=====    ===  ³     ~~~~~  ³     PTT  100ê        ³   ³    ³ reed
          ³   ³            ³           ³+         ³   ³    ³ relay
      100u³  2k2       10n===    GND  === 4u7     ³   ³    ³   
        ÄÄÁÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄo ÄÄÁÄÄÄÄÄÄÄÄÄÄÙ   ÀÄÄÄÄÁÄÄÄ
                                            L E A D

The added operate & release delay is not detectable (1mS?), & there is no
longer a spark & shocking back emf if U manually earth the phono plug etc. 


Why Don't U send an interesting bul?

73 de John, G8MNY @ GB7CIP


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