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G8MNY > TECH 12.09.06 21:46l 68 Lines 2744 Bytes #999 (0) @ WW
BID : 33720_VK2DOT
Read: DL1RX DL1LCA DL8FBH GUEST OE7FMI
Subj: 4CX250B PA Timing & Control
Path: DB0FHN<DB0RGB<OK0PPL<DB0RES<DK0WUE<7M3TJZ<TU5EX<IW8PGT<CX2SA<VK2DOT<
VK2DOT
Sent: 060905/1826Z @:VK2DOT.CC.NSW.AUS.OC #:33720 [Niagara Park] FBB7.00i
\_/ 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/ C5 === ³
ÚÄÁÄÂÄÄÄÄÄÄÁÄÄÂÄÄÄÄÄÄÄÁÄÄÄÄÙ
33k _³_D4 _____³______
³ /_\ |_FAN_RELAY__| eg. 12V First to
ÀÂÄÄÙ _____³______ Operate
+³ |AERIAL_RELAY| eg. 36V & Last To
=== _____³______ Release
C6³100u |DRIVE_RELAY_| eg. 24V
³100V R1
ÃÄÄÄÄÄÄÄÄÄÄÄÄ´
_³_D5 _____³______ Last to Operate
\_/ |__TX_RELAY__| eg. 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 my C1 & M56. With the discharge though 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 &
DRIVE relays for a fraction of a second.
These features ensure there in no welding/slashing of RF contacts on the
relays that is easy to do with QRO PAs, as well as chancing PA stage flashover
by powering up the valve into no load or possibly unstable key up/down RF
oscillation.
Why Don't U send an Interesting Bul?
73 De John, G8MNY @ GB7CIP
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