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G8MNY > TECH 21.01.18 12:29l 88 Lines 3732 Bytes #999 (0) @ WW
BID : 6494_GB7CIP
Read: GUEST
Subj: Power Factor of Drake L-4B PA
Path: IZ3LSV<I0OJJ<GB7CIP
Sent: 180121/1013Z @:GB7CIP.#32.GBR.EURO #:6494 [Caterham Surrey GBR] $:6494_GB
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, 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
110V)||(__ 5V | ³__ ||( TUNE mode
Heaters, Fan ____)||(__ 25A | )||( or 1.1kV
& Relay PS ³____ || __ | 110V)||( in SSB Mode
Transformer ³110V)||( 18V | _____)||( @ 2A to
is in the FAN )||(__0.5A | [o-o__ ||( the Voltage
PA unit. ÃÄÄÄÄÙ 16uF=== Fuse 2 )||( Doubler
³ 400V | 110V)||(_
³ AC | _)|| 2.2kW Peak
NÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ HT Transformer
For 110V mains, all the primary windings are 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 to tune the heavily saturated HT
transformer core (all 3rd & 5th harmonics) 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 + 5k 5W HT bleed & 120V DC tap
chain (was broken) 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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