Message 24070 in TECH.WW
From: G8MNY
Date: Fri, 12 Jun 26 07:10:00 Z
Newsgroups: TECH.WW
Subject: Power Factor of Drake L-4/4B PA
Message-ID: <62214_GB7CIP>
Path: N2MH4|GB7BED|EI2GYB|GB7CIP
R:260612/0713Z 32323@N2MH4.#SENC.NC.USA.NOAM LinBPQ6.0.24
R:260612/0712Z 12773@GB7BED.#21.GBR.EU LinBPQ6.0.25
R:260612/0711Z 55214@EI2GYB.DGL.IRL.EURO LinBPQ6.0.25
R:260612/0710Z @:GB7CIP.#32.GBR.EURO #:62214 [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)
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 and SSB modes where the mains tap on the HT transformer is changed
by 30%.
CW/tune
& Relay PS ____)||(__ 30A | )||( or 1.1kV
PA unit. FAN )||(__0.5A | [o-o__ ||( the Voltage
For 110V mains, all the primary 110V and tune windings are each put in parallel
not series.
Wired to the above, the correction is effectively about 10uF when on tune mode
and 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), and 0.7 in
SSB mode (up to 1400W PEP with odd order mains harmonics!), UK now has a 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 and
120V DC tap chain, for 6x 68K 10W + 27K 5W, and with a series HT warning neon,
all on a smaller tag strip. The wasted power is much less and 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.
50W 68K REPLACMENT
50W 68K 10W WW
5K & Cathode 27K & Cathode
5W Rx Bias 5W Rx Bias
HT CAP STACKS
I also cleaned and 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, and 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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