From: Michael Tope <W4EF@dellroy.com>
Subject: Re: [Amps] L-4/L-7 Power Supply
Hi Ed,
What you refer to as bleeder resistors are really part of a voltage
divider that provides cutoff bias for the 3-500Zs. There are two 50 kohm
x 50 watt resistors in series on the top side of the supply which are in
turn in series with a 5K resistor on the bottom side. Each of the 50k
resistors dissipates around 30 watts when the mode switch on the amp is
in the SSB position.
### Drakes ancient idea of using the V drop across the 5 k resistor
was not a smart move. 2650v /105k ohms = 25.2 ma .
.025 x 5k = 126 vdc [ used to cut off tubes on RX] On the lower
V CW position, it's now 1900V / 105 k ohms = 18 ma.
.018 x 5 k = 90vdc [which also cuts the tubes off on RX]
## the 2 x big 50k bleeders diss 62.5 watts between em [31 w each]
on ssb pos... and only 32.4 watts between em [16.2 watts each],
when on CW position.
## I tossed ALL 3 x resistors, you don't need em! OK, now you lost
the 130/90 v cut off bias. Better method is to just wire a 100 k
[or 2 x parallel 100k, for redundancy] 3 watt, mof resistor's in the
CT of the fil xfmr. You will see the yellow wire, that's the CT.
## OK, now use the center pole of the stock 3pdt T/R relay, and wire it
over to the newly installed pair of 100k 3 watt mof's. [COM + NO]
2 x wires required. Ok, now when on RX, idle current flows through
the pair of 100k 3 w mof's.. and resulting V drop, CUTS THE TUBES OFF.
## Total DISS in the parallel 100 k 3 w mof's is virtually zero watts.
## the drake method is silly imo. When T/R relay is in ..'mid air' , the
Cathode is momentarily open for a split second. Any time you open
the cathode, the cathode will try and rise to full B+ potential.
## U also end up with the center pole of the T/R relay, burnt
to a crisp, from hot switching the 130/90 V.. 'cut-off bias'
## Pole #1 used for 100w input. Pole #3 used for kw output.
## presto, you just eliminated 62 watts of heat in the L4PS,
and now the B+ supply runs stone cold, instead of blazing hot.
## I installed a 50 ohm 50 watt WW for a glitch R in the L4B itself,
one end mounted directly to the red Millen, using SS internal tooth lock
washer, flat washer, etc. Top end of same Glitch R is unsupported, does
not budge. New 5 kv rated red belden wire run from top of new glitch.. to
base of plate choke. In this case, the HV interlock was tossed as well.
[ to make room]. All 4 x L4B's were modified like this, zero problems.
glitch diss with 800ma cxr = 32 W. On ssb,it's 8W [400 ma average]
V drop across glitch = .8 x 50 ohms = 40 v
## In retrospect, the 50 ohm ,50W WW glitch could have been located
in the L4PS, outboard power supply. [ since both 100 k's were tossed]
My No load B+ is still exactly 2650 vdc.. with the 2 x 100k bleeder's
removed ! I was expecting it to rise, but it doesn't budge. [RX]
The 8 x 100 k 3 watt MOF EQ resistors, across the 8x lytics is plenty,
and does the EQ and the bleeder function.
Later... Jim VE7RF
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