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G8MNY > TECH 25.08.20 07:45l 114 Lines 4597 Bytes #999 (0) @ WW
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Subj: 4CX250B PA Timing & Control
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Sent: 200825/0642Z @:GB7CIP.#32.GBR.EURO #:3008 [Caterham Surrey GBR] $:3008_GB
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Corrections May 13)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
PTT Timing
The PTT relay should connect the power to the valve to turn the valve on for
TX. It is recommended that this relay operates after the aerial C/O relay, but
releases before the aerial C/O. Suitable diode steered CRs can do this.
Also note that the screen power (PTT RELAY) should not be connected if the
valve...
1/ has No Anode supply.
2/ has no air flow.
3/ has no bias supply.
4/ has not warmed up. (takes 1 min),
5/ has no 12V Control voltage.
MY SOLUTION
Again simple transistor & relay inhibit electronics can do all this (e.g. no
PICS or gate arrays). Here is one way I have used for a contest K2RIW 70cm PA.
It uses the negative bias supply for the relays as I had some different voltage
but similar current relays to power up in sequence.
N1 SW1 No Air Flow
+2kV>ÄM33ÄM33ÄM33ÄM33ÄÄ<´Ã>ÄÂÄÄM56ÄÂÄÄÄÄÄÄÄÄÄÄÄ/oÄÄ¿ Vane micro switch
EHT Hazard Neons³ ³ 33uF 160V ³
ÚÄ<´Ã>Ä<´Ã>ÄÙ ÃÄÄ´ÃÄÄÂÄÄ´>ÃÄÄÄ´
_³_ N2 N3 +160V ³+ C1 ³ D1 ³
M68 ÀÄ2M2ÄÄÄÄ´
/Á\ Neon _³_
\Â/ N4
+12V>ÄÄÄÄÂÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄ)ÄÄÄÄÄ¿
³ ³1u C2 \³ ³ ³
³ === T2 ÃÄÄÄÄÄ´ ³
4k7 ³ C3 n1 e/³ ³ 100k
³ ÃÄÄ´ÃÄÂÄÄ´<ÃÄÄÅÄÄÄ´ÃÄÄ´ ³
³ ³ ³ D2 ³ C4 ³ ³
³ ³ ³/e 1k n1 ³ ³
PTT>Ä5k6ÄÁÄÄÄÁÄÄÄ´ T3 _³_ \³ ³
³\ OK \_/ T1 ÃÄÄÄ´
3k3 LED ³ e/³ ³
ÚÄÄÄÂÄÄÄÄÂÄÄÄÄÄÄ)ÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄ´ ³
_³_ 68 _³_TX ÃÄÄÄÂÄÄÄÄ¿ _³_ ³
/_\ ³ \_/LED ³ ³ 3k3 180k
D3 ³ ÀÄÄÄÄ´ 1k ³ ³ ³
³ \³ ³ ³ ³ ³ GRID BIAS
³ T4 ÃÄÄÄÄÙ +³2u2 ³ ÀÄ<TEST -25V
³ e/³ C5 === ³
ÚÄÁÄÂÄÄÄÄÄÄÁÄÄÂÄÄÄÄÄÄÄÁÄÄÄÄÙ
33k _³_D4 _____³______
³ /_\ |_FAN_RELAY__| e.g. 12V First to
ÀÂÄÄÙ _____³______ Operate
+³ |AERIAL_RELAY| e.g. 36V & Last To
=== _____³______ Release
C6³100u |DRIVE_RELAY_| e.g. 24V
³100V R1
ÃÄÄÄÄÄÄÄÄÄÄÄÄ´
_³_D5 _____³______ Last to Operate
\_/ |__TX_RELAY__| e.g. 12V & First To
+ÚÁÄ¿ ³ Release
=== M47 ³
ÀÄÄÁÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄ< -100V UN-REG SMOOTHED
C7 1mF BIAS SUPPLY @ 30mA
T1 & T2 NPN BC107, T3 PNP XTX541 high voltage, T4 NPN high voltage BFX84
D1-5 1N4003, N1-N4 wire ended neons.
R1 Sets relay current. If relays require different currents then parallel Rs
across the lower current relays until all relays have adequate voltages.
HOW IT WORKS
Protection.
On power up wire neons N1 N2 N3 are lit from EHT. After the fan pressure vane
switch SW1 goes open, the 150V across N2+N3 charges up C1 through D1 from the
EHT in about 1 min time, set by C1 & M56. With the discharge through the 2M2 it
also mimics the valve temperature & shortens the warm up time is the valve is
already warm. (1 & 2)
If GRID BIAS is OK it opposes the 12V rail & turns off T3, that would otherwise
inhibit T1 from being able to turn on. (3)
When the voltage on C1 is > 90V the warm up delay, N4 neon strikes & turns on
T1. This light up the OK LED. (4 & 5)
Timing.
On PTT earthing, T3 is now able to be turned on, after a small delay to stop to
fast a PTT/Rig mic contact bounce, & some RFI filtering etc. T4 turns on NPN
emitter follower T4 after more slight delay circuit.
T4 operating immediately powers up the 3 "first to operate" relays, these
prepare the circuits for the PA RF path & valve cooling speed up etc. When C7
is charged up via steering diode D5, "TX relay" is operated, putting HT on G2
of the PA.
On PTT unearthing the reverse happens. But this time the "TX relay" releases
first & the now charged up C6 via steering diode D4 holds the FAN AERIAL,
AERIAL & DRIVE relays for a fraction of a second.
These features ensure there is no welding/splashing of RF contacts on the
relays that is easy to do with QRO PAs, as well as chancing a PA stage
flashover by powering up the valve into no load, or possibly unstable key
up/down RF oscillation.
See Tech Bul "4CX250B PA Regulated Supplies"
Why Don't U send an Interesting Bul?
73 De John, G8MNY @ GB7CIP
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