G8MNY > TECH 08.04.25 09:15z 90 Lines 3790 Bytes #16 (0) @ WW
BID : 29833_GB7CIP
Read: GUEST
Subj: Power Factor of Drake L-4/4B PA
Path: ED1ZAC<ED1ZAC<IZ3LSV<I0OJJ<GB7CIP
Sent: 250408/0900Z @:GB7CIP.#32.GBR.EURO #:29833 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Jun 24)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
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For /P work these 1960/65 USA made Drake PAs 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 115V)||(__ 5.5V | ³__ ||( TUNE mode
& Relay PS ____)||(__ 30A | )||( or 1.1kV
Transformer ³____ || __ | 115V)||( in SSB Mode
is in the ³115V)||( 18V | _____)||( @ 2A to
PA unit. FAN )||(__0.5A | [o-o__ ||( the Voltage
ÃÄÄÄÄÙ 16uF=== Fuse 2 )||( Doubler
³ 400V | 115V)||(_
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 correction 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 800W PEP on good mains), & 0.7 in
SSB mode (up to 1400W PEP with odd order mains harmonics!), in the UK now has
a new 1kW 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", "Drake PA 3-500 valve repair" & "Using 2
HF PAs".
Why Don't U send an interesting bul?
73 de John, G8MNY @ GB7CIP
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