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G8MNY > TECH 30.04.21 09:26l 89 Lines 3769 Bytes #999 (0) @ WW
BID : 32434_GB7CIP
Read: GUEST
Subj: Power Factor of Drake L-4B PA
Path: IW8PGT<IZ3LSV<I3XTY<I0OJJ<GB7CIP
Sent: 210430/0724Z @:GB7CIP.#32.GBR.EURO #:32434 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Oct 10)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
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For /P work this USA made Drake PA has a very poor mains power factor, on 50Hz
it is only 0.5 lagging, this means in standby it draws 2x the mains current it
needs to.
Exactly where to put a PF correction capacitor is not straight forward, as the
PA has Tune & SSB modes where the mains tap on the HT transformer is changed by
30%.
CW/tune
LÄo-oÄÄÄÄo/oÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ\ oÄÄÄÄÄÄÄÄÄÄÄ¿_
Fuse 1 on ³ oSSB __)|| _
³ 200VA ³ TUNE³__ ||(
³____ __ ³_____________)||( 850V on
Heaters, Fan 110V)||(__ 5V | ³__ ||( TUNE mode
& Relay PS ____)||(__ 25A | )||( or 1.1kV
Transformer ³____ || __ | 110V)||( in SSB Mode
is in the ³110V)||( 18V | _____)||( @ 2A to
PA unit. FAN )||(__0.5A | [o-o__ ||( the Voltage
ÃÄÄÄÄÙ 16uF=== Fuse 2 )||( Doubler
³ 400V | 110V)||(_
³ AC | _)|| 2.2kW Peak
NÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ HT Transformer
For 110V mains, all the primary 110V & tune windings are each put in parallel
not series.
Wired to the above, the corrrection is effectively about 10uF when on tune mode
& 16uF when on high power SSB mode. In the UK on 50Hz 230-250V, the transformer
is heavily saturated on SSB mode, when the extra mains TUNE tappings are
bypassed. The 16uF does the best it can (high 3rd & 5th harmonic currents!) to
tune the heavily saturated HT transformer core in SSB mode!
Results were PF of 0.97 in tune mode (up to 700W PEP on good mains), & 0.7 in
SSB mode (up to 1400W PEP with odd order mains harmonics!), in the UK there is
no need to use the SSB mode with a 400W licence! Or in other words I saved at
least 1 Amp at 240V, so there is more available for other loads (lights &
rotator etc.) before the /P generator's 10A mains trip goes!
HT BLEED CHAIN
I reworked the PSU, changing the 2x 50k 50W (was broken) + 5k 5W HT bleed &
120V DC tap chain, for 6x 68K 10W + 27k 5W, & with a series HT warning neon,
all on a smaller tag strip. The wasted power is much less & the light from the
new hazard neon is visible through the mesh cover.
I used the freed up space to mount the mains 16uF capacitor above.
ÄÄÂÄÄHT 2.8kV ÄÄÄÂÄÄ HT 2.8kV
³ @1A 68k
50k ³
50W 68k REPLACMENT
WW ³
³ ORIGINAL 68k All
50k ³
50W 68k 10W WW
WW ³
³ 68k
³ Hazard ³
³ Neon (:)
ÃÄÄÄ +120V ALC ÃÄÄÄ +120V ALC
5k & Cathode 27K & Cathode
5W Rx Bias 5W Rx Bias
ÄÄÁÄÄ 0V ÄÄÄÁÄÄ 0V
HT CAP STACKS
I also cleaned & remounted the 2 stacks of 4 electrolytics, this time avoiding
the need for HT crossover wires, by putting the +ve multiplier stack near the
+ve output cable mount, & the -ve stack on the other side!
See my Tech bul on "ALC line for Drake L-4B PA", "PTT Line for Drake L-4B PA" &
"Valve Heater delay Drake L-4B PA".
Why Don't U send an interesting bul?
73 de John, G8MNY @ GB7CIP
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