I just got my 4-1k tube. It turned out to be a Sylvania brand.
I know Sylvania sold transmitting tubes.
But did Sylvania make them or buy them from another vender?

This one I got from ebay:
has a code date of 8806.

The history on it: was pulled from an AM
broadcast station in 1993, from the AM modulator.

And does anybody know the cold resistance or the filament?
I haven't seen any inrush current limiting circuits for the 4-1k.

73

n8zu

And does anybody know the cold resistance or the filament?
I haven't seen any inrush current limiting circuits for the 4-1k.

73

n8zu

I just put my home made amper on the filament. Actually a 2.80 amp
amper.
I couldn't find my 7805 I use for a constant current source. So I had
the 5 ohm resistor in series with my 14 volt regulated supply. My 5
ohm resistor is 40 ft of cat3 3 pair telephone wire for a total of 240
ft of 24 AWG wire. I put that in series with the 4-1k filament and
across 14.0 volt regulated supply it draws 2.80 amps.
The voltage drop on the filament was 0.100 volts and a filament
resistance at 0.100 volts is 0.0357 ohms. Funny because at 7.5VAC
it's exactly 10 times that resistance.
I can't afford peter dahl transformers. I has to use MOT's for the
filament screen and plate supplies. I have to use 2 MOT's to get the
power I need. This works out to my advantage because with 2 filaments
in series it gives me 7.5VAC CT, but at a current that is only limited
by the 14AWG wire they use for the winding. Two MOT's 14AWG wire would
limit the inrush current to about 150 amps of instantaneous current at
the peak voltage.


73

n8zu

On Aug 16, 10:52 pm, raypsi wrote:
And does anybody know the cold resistance or the filament?
I haven't seen any inrush current limiting circuits for the 4-1k.

73

n8zu

I just put my home made amper on the filament. Actually a 2.80 amp
amper.
I couldn't find my 7805 I use for a constant current source. So I had
the 5 ohm resistor in series with my 14 volt regulated supply. My 5
ohm resistor is 40 ft of cat3 3 pair telephone wire for a total of 240
ft of 24 AWG wire. I put that in series with the 4-1k filament and
across 14.0 volt regulated supply it draws 2.80 amps.
The voltage drop on the filament was 0.100 volts and a filament
resistance at 0.100 volts is 0.0357 ohms. Funny because at 7.5VAC
it's exactly 10 times that resistance.
I can't afford peter dahl transformers. I has to use MOT's for the
filament screen and plate supplies. I have to use 2 MOT's to get the
power I need. This works out to my advantage because with 2 filaments
in series it gives me 7.5VAC CT, but at a current that is only limited
by the 14AWG wire they use for the winding. Two MOT's 14AWG wire would
limit the inrush current to about 150 amps of instantaneous current at
the peak voltage.

73

n8zu

I almost forgot this thing draws more filament current at a lower
voltage
25 amps at 7.3 volts DC

On Aug 24, 9:12*pm, raypsi wrote:
I almost forgot this thing draws more filament current at a lower
voltage
25 amps at 7.3 volts DC.

Filaments like lamps are not ohmic, but I don't think they should ever
draw more current at lower voltage. That would mean "negative dynamic
resistance".

Seems more likely there's some measurement difficulties. Getting good
contact on the filament pins through thermal cycles is often an issue.

Tim N3QE