EMRFD Message Archive 2186

Message Date From Subject
2186 2008-10-04 19:37:56 Hari G 4cx250 heater
Allison ,

Here we have serious variations in voltage, iam right now in a part
collection phase for a 2M linear. I thnking if its ok to use an old PC smps
as the heater supply with slight mod.

73
Hari


On 10/4/08, Allison Parent <kb1gmx@arrl.net> wrote:
>
>
2187 2008-10-05 19:16:17 Allison Parent Re: 4cx250 heater
Harri define serious...?

Here is the deal, yes, you can run a 4cx250 at 6.3V and likely it
would run that way for hundreds of hours but not the 10s of thousands
they were designed for.

The goal would be to nominally be at 6.0V Now at that at 230V line
level (primary of a transformer) about a variation of 4V. We see
that here in the USA all the time (typically more like 10-15V).
The tube will work fine at 5.8 or 6.2 but if you don't try to hit 6.0
initially and use 6.3V +- your already .3 high and if the line goes
higher well tube like and stability will suffer. For high power
amplifiers here some hams will include a variac (variable transformer)
so they can adjust as needed.

You can use a regulated 6V DC source but that may be over doing it.

The other voltage that has to be regulated is the screen (g2)
and that does affect performance greatly. But that can be regulated
using Zener diodes or gas regulator tubes. The exact voltage is
somewhat dependent on anode voltage but will be around 300V.

Running high power tubes[valves] like that also require metering for
voltages and currents on a constant basis for both tuneup and
establishing it continues working as it should.

High power tubes have their likes and dislikes for best performance.
the 4cx250 treated right will produce a very strong and clean signal
mistreated the signal quality will have hams in the region hunting
for you with the goal of making yo stop. The reason for that is all
the distorti
2191 2008-10-06 10:12:16 Hari G Re: 4cx250 heater
Allison ,

The palce where i stay now, voltage will will be in the range of
180-230.Most of the time will be 200/210 but will change.There are places
where it will go down to 180 and climb up to around 240. I have never seen a
230 till now !.

Right now iam using 3x807 and giving me around 150W max, very happy with
that.Iam using shunt regulator for the screen grid which is adjustable.I
think the the original design was by G3SEK.

First i used series pass with BU508 it ended in a disaster and i had to
replace the device and the zeners three times.

The plan to use 4cx250 is only for VHF fo about 100W+ of power so that its
easy for me to access the repeater which is around 400Km from my palce.

Getting a PC SMPS is easy and mod will take only few minutes to do to get
6V, i will take that route and will report how i progress.

73
Hari



On 10/6/08, Allison Parent <kb1gmx@arrl.net> wrote:
>
> Harri define serious...?
>
> Here is the deal, yes, you can run a 4cx250 at 6.3V and likely it
> would run that way for hundreds of hours but not the 10s of thousands
> they were designed for.
>
> The goal would be to nominally be at 6.0V Now at that at 230V line
> level (primary of a transformer) about a variation of 4V. We see
> that here in the USA all the time (typically more like 10-15V).
> The tube will work fine at 5.8 or 6.2 but if you don't try to hit 6.0
> initially and use 6.3V +- your already .3 high and if the line goes
> higher well tube like and stability will suffer. For high power
> amplifiers here some hams will include a variac (variable transformer)
> so they can adjust as needed.
>
> You can use a regulated 6V DC source but that may be over doing it.
>
> The other voltage that has to be regulated is the screen (g2)
> and that does affect performance greatly. But that can be regulated
> using Zener diodes or gas regulator tubes. The exact voltage is
> somewhat dependent on anode voltage but will be around 300V.
>
> Running high power tubes[valves] like that also require metering for
> voltages and currents on a constant basis for both tuneup and
> establishing it continues working as it should.
>
> High power tubes have their likes and dislikes for best performance.
> the 4cx250 treated right will produce a very strong and clean signal
> mistreated the signal quality will have hams in the region hunting
> for you with the goal of making yo stop. The reason for that is all
> the distorti
2199 2008-10-06 16:54:24 Allison Parent Re: 4cx250 heater
UHi Hari,

If going to a used PC power supply is convenient good, never really
considered that myself. The valve doesn't care that it's DC.

For VHF, use as high a voltage but not exceeding 2000V and run the
screen at 300-350V, the key is not the exact voltage but making
stiff with operational changes. At 250mA per tube you can see
about 300++W at 6M. At 2M maybe 250W. Being grid driven the power
must be kept below the level that causes grid current to flow or
typically less than 2W. A pair in parallel is serious power,
typically 600W or more.


Allison