--- In ham_amplifiers@..., Tony King - W4ZT <w4zt-
060920@...> wrote:
I'd be interested in the article (wonder why ARRL puts good
technical articles in QEX instead of QST?) but I don't see huge
rheostats for filaments either.
### I wonder the same thng.... probably to promote sales
of .."QEX". They have one too many publications imo.
### Fil V can be of concern...esp when sucking vast amounts of
current for the plate xfmr. On a set up where the fil xfmr pri
V
is derived from the same 240 V source as the plate pri....
under a
full bore load... the fil V can be affected.
Especially with indirectly heated cathodes. They are much more
likely to
be damaged by changing filament voltages, especially low voltages.
#### agreed.,
### One way out of this mess, is to run a separate, smaller 240
V
line... just for the fil xfmr pri. That might not solve all
the
fil sag problems... but at least the separate fil 240 v
supply...
will only have the v drop on your drop wires coming into your
home, to contend with. If anybody goes this route... make
sure
you label.. "more than one live circuit present". You are
gonna
have to kill TWO sets of breakers to completely kill all 240
v
coming into the amp. In cases where the RF deck is totally
separate from the HV supply, it may not be an issue.
And if you have line voltage variations that are common,
especially in areas where high air conditioning loads are the norm,
even separate circuits wont help.
### You are probably right. My buddy's 3x6.... between no load
and dead cxr... is 241 v..... down to 236.5 v... a 4.5 v instant
drop. Until we measure how much of that is from the 2 ga wire from
HV /fil supply to main 200A panel... and how much is from drop
wires coming from the street... will determine if a separate 240
v line... just for the fils, will actually help.
### another method is to use a sola constant V xfmr.
And they get hot! That means they waste LOTS of power... and that
is not a good thing. If you're going to consume lots of power,
let's convert at least half of it to RF ;)
#### Unloaded... they get hot after 1-2 hrs. But so does my Dahl
fil xfmr... with no lod on it either. One night, I left the dahl
on for several hrs.. forgot abt it... and it was HOT. With a full
bore 70-79 A load on it... it's barely luke warm ! The sola's
are sorta the same way... they run cooler with a load on em..... so
if used... you don't want to oversize em. A 500 va sola is fine
for a 375 va fil... and a 750 va sola is fine for a 560 va
fil. You want at least a 40-50% load on a sola.
### The absolute ideal scenario is to use a separate 240 v line...
[separte from the 2 ga wire to the HV supply]... directly to the
SOLA.... then to variac... then to dahl filo xfmr.
## I don't use the variac for step start
either. The variac.. once set.. stays put. A 25 ohm 100/150
w metal finned resistor in one leg of the 240 V, feeding the fil
xfmr primary.. and a 8 second delay, is used.
Later... Jim VE7RF
Jim, isn't 8 seconds a bit long for your step start? That's 480
cycles at 60 Hz. Even with the huge capacitor bank and a good step
start, it should be up to snuff long before then shouldn't it?
#### The 8 seconds was the step start on the FIL. We used a 0-30
timer... and arbitrarily 5-10 seconds for the FIL. The 25 ohm
resistor in one leg limits the fil V to exactly 75%. I'm
wondering if we should be limiting the V to 50-60% ?? We could
have just used the fil variac as a step start each time. But, the
fil variac was carefully dialled in, to give full bore out... with
the least fil V... and in this case... after 200 hrs... the fil V
was reduced from 7.0 down to just 6.1 V. Another concern was
IF the power went out from the power co in winter.... then when it
came back on... and IF fil variac still cranked up.... there would
be No step start....../ hence the 8 second delay circuit.
### Now, per this latest PDF from Reid Brandon on the YC-243....
it's saying all these big metal tubes are designed for commercial
service.... one on and one off cycle per day..... and don't keep
cycling the fil on/off several times a day. With either step
start.. and /or a variac... that shouldn't be a problem... esp bring
up a variac real slow. The 25 ohm fil step start just slams the
juice on.... it's not like charging caps up in a hv supply. It's
75% fil V... now.
### The big HV supply has a 14-18 second delay... 7900v + a 135
uf filter. You can bring it up pretty good in 5 seconds.... but
the extra 10 seconds keeps bringing it up.. slowly. When step start
finally activates... minimal secondary surge. We were in no big
rush. 1/2 V is only 1/4 charged up on hv caps. Energy storage
goes to the square of the V. You need the V on the caps to almost
70% ... just to get em 1/2 charged up.
### BTW... I saw ur sub mounted socket scheme for the russian
tube .. superb.. now I get it. Pix was obvious.
Later... Jim VE7RF
73, Tony W4ZT
