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G8MNY > TECH 05.03.09 01:35l 71 Lines 3056 Bytes #999 (0) @ WW
BID : 19717_GB7CIP
Read: GUEST
Subj: Power Factor of Drake L-4B PA
Path: IZ3LSV<IK2XDE<DB0RES<ON0AR<GB7CIP
Sent: 090304/2325Z @:GB7CIP.#32.GBR.EU #:19717 [Caterham] $:19717_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (Updated Jul 08)
(8 Bit ASCII Graphics use code page 437 or 850)
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 mode 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_____________)||(
110V)||(__ 6.3V | ³__ ||( 850V TUNE
Heaters, Fan ____)||(__ 25A | )||( or 1.1kV
& Relay PS ³____ || __ | 110V)||( SSB @ 2A
Transformer ³110V)||( 20V | _____)||( to the
FAN )||(__0.5A | [o-o__ ||( Voltage
ÃÄÄÄÄÙ 16uF=== Fuse 2 )||( Doubler
³ 400V | 110V)||(_
³ AC | _)||
NÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ 2.2kW Peak HT Transformer
For 110V mains, all the windings are put in parallel not series.
Wired in this location it is effectively about 10uF when on tune mode & 16uF
when on SSB mode. In the UK on 50Hz, the transformer is heavily saturated in
SSB mode with the mains TUNE tapping bypassed. The 16uF does the best it can to
tune the heavily saturated HT transformer core (all 3rd harmonic) in SSB mode.
Results were PF of 0.97 in tune mode (up to 600W PEP on good mains), & 0.7 in
SSB mode (up to 1200W PEP), 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 etc) before the generator trips out when
/P.
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 neon
is visible through the meshing cover.
I used the freed up space to mount the mains 16uF capacitor.
ÄÄÂÄÄHT 2.8kV ÄÄÄÂÄÄÄ HT 2.8kV
50k 68K
50W 68K
³ 68K
50k 68K
50W 68K
³ Hazard 68K
³ Neon (ù)
ÃÄÄ +120V ÃÄÄÄÄ+120V
5k Rx Bias 27K Rx cathode Bias
5W ³
ÄÄÁÄÄ 0V ÄÄÄÁÄÄÄ 0V
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 the other side!
Why Don't U send an interesting bul?
73 de John, G8MNY @ GB7CIP
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