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G8MNY  > TECH     13.05.19 10:15l 89 Lines 3769 Bytes #3 (0) @ WW
BID : 4631_GB7CIP
Subj: Power Factor of Drake L-4B PA
Sent: 190513/0808Z @:GB7CIP.#32.GBR.EURO #:4631 [Caterham Surrey GBR] $:4631_GB

By G8MNY                                   (Updated Oct 10)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
넬컴커    _    _  납       
냅컴켸   (_)  (_) 납       
넬컴커    _       납       
냅컴켸   (_)    膨       
 o            [|]납       

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
L훟-o컴컴o/o컴쩡컴컴컴컴컴컴컴컴컴\ o컴컴컴컴컴커_
 Fuse 1   on                       oSSB        __)|| _
                 200VA                   TUNE__ ||(
              ____    __           _____________)||(  850V on
 Heaters, Fan  110V)||(__ 5V        |          __ ||(  TUNE mode
  & Relay PS   ____)||(__ 25A       |             )||(  or 1.1kV
 Transformer  ____ || __           |         110V)||(  in SSB Mode
  is in the   110V)||(  18V        |        _____)||(  @ 2A to
   PA unit.  FAN   )||(__0.5A       |       [o-o__ ||(  the Voltage
              쳐컴켸           16uF===   Fuse 2   )||(  Doubler
                              400V |         110V)||(_
                               AC  |            _)||  2.2kW Peak
N컴컴컴컴컴컴컨컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴켸      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!

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.

컴쩡횴T 2.8kV             컴컫컴 HT 2.8kV
       @1A                 68k
 50W                        68k  REPLACMENT
     ORIGINAL              68k  All  
 50W                        68k  10W WW
                      Neon (:)
  쳐컴 +120V ALC             쳐컴 +120V ALC
 5k    & Cathode            27K    & Cathode
 5W    Rx Bias              5W     Rx Bias
컴좔 0V                  컴컨컴 0V

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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