--- In ham_amplifiers@..., "badgerscreek" <qrp73@...>
wrote:
There is a nice article published in the latest QEX. Its for a
filament voltage regulator. Its Titled " A high Efficiency
Filament
regulator" K8LV. It uses a PIC and some pass resistors. It seems
any size tube is accomodated by increasing pass transistor sizes,
including bumping up heatsink sizes. It also has a ramp up
feature. My guestimate suggests that it would be cheaper building
this regulator than buying 2 X 50 or 100 watt rheostats.
Greg
### Greg.... how would 2 x 50/100 w rheostats regulate fil
V ?? Or are they using pass transistor's in a regulator ?
### 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.
### 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.
### I have the fil xfmr, and associated variac for it.. + a
sola constant V xfmr.. in a shelf... below RF deck.... so RF deck
is in top of rack... fil stuff is below... in same rack. HV supply
is in a separate rack.
### another method is to use a sola constant V xfmr. These are all
of the ferroresonant type. Mine has input taps for
118....208....236 v. The output side is a constant 236 /118 V
It regulates very well. You can swing the input Voltage a huge
amount on either side of a particular input tap... and output side
remains constant. These things are HEAVY though.... my 750Va unit
weighs 65lbs. I have seen em in 250-500-750-1000-2000 va. Fair
radio had tons of em.... some brand new in the box.... dirt cheap.
### A SS regulated method might be the ticket....would be lighter.
How much fil POWER can these things handle ? Are they RELIABLE ?
The last thing anybody needs is a regulator to crap out... and fil
V increase... even a few percent.
### Another related issue is seasonal line V regulation. I have
seen mine as high as 247.2 V at 1 AM in the summertime [122.2 +
125 =247.2] Usually , in the dead of winter, at dinner time,
it's 240v, or 239.9v. Last week, it's 234V [117+117]... and that
was at 2 pm on a sunday afternoon... go figure.
Point here is the variation is from 247.2 v... down to 234V... and
that's just measuring the V with HV supply OFF... no big load.
With a big load on thr plate xfmr.. it's going to get sucked down
even more. Changing taps on a plate xfmr is one thing... having to
constantly be tweaking a fil variac is a real pain... and impossible
to do between RX/TX. 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
