05-10-2021, 04:21 PM
(This post was last modified: 05-10-2021, 04:27 PM by Mike Watterson.)
Yes. Seem to be very rare and quickly replaced by other models.
The filament current is interesting compared to these models:
(My own measurements)
It's about 1/2 of a 1p24b and about twice a 1j29b or a 1j37b. But the 1p24b and 1j29b are really dual rod pentodes, that's why they both have two filaments with a common at the top to give the illusion of a centre tap. The 1j24b is extremely efficient, but the the 1j29b is about twice the power rating of the 100mA DL94, but at about 1/2 the filament current. Thus the 1j29b has about 4 times the filament efficiency per mW as the DL94. The DL92 is miserable at about half the output power of the DL94 and thus the 1j29b is 8 times it's efficiency, if you used enough DL92's in parallel for the same power.
So I suspect the 1j26a is a bit like half of a 1j29b or 1p24b in construction using a similar filament to the 1p24b, which has two and thus three g1 plates:
Top View
| . | . | The control grid plates and filaments on all dual filament, thus "centre tapped" tubes, 1j29b, 1p22b, 1p24b
And single filament tubes:
| . |
Not shown: g2 and g3 being pairs of rods.
At least one rod tube has a single anode, thus is 1/2 a regular rod pentode.
I suspect the few applications where it was used the 1j26a was replaced by the also rare 1j36 and more commonly by the high power 1j29b or massive power 1p24b.
The 1j36b, quoted as the replacement is about 74mA filament current vs 130 mA.
The filament current is interesting compared to these models:
(My own measurements)
It's about 1/2 of a 1p24b and about twice a 1j29b or a 1j37b. But the 1p24b and 1j29b are really dual rod pentodes, that's why they both have two filaments with a common at the top to give the illusion of a centre tap. The 1j24b is extremely efficient, but the the 1j29b is about twice the power rating of the 100mA DL94, but at about 1/2 the filament current. Thus the 1j29b has about 4 times the filament efficiency per mW as the DL94. The DL92 is miserable at about half the output power of the DL94 and thus the 1j29b is 8 times it's efficiency, if you used enough DL92's in parallel for the same power.
So I suspect the 1j26a is a bit like half of a 1j29b or 1p24b in construction using a similar filament to the 1p24b, which has two and thus three g1 plates:
Top View
| . | . | The control grid plates and filaments on all dual filament, thus "centre tapped" tubes, 1j29b, 1p22b, 1p24b
And single filament tubes:
| . |
Not shown: g2 and g3 being pairs of rods.
At least one rod tube has a single anode, thus is 1/2 a regular rod pentode.
I suspect the few applications where it was used the 1j26a was replaced by the also rare 1j36 and more commonly by the high power 1j29b or massive power 1p24b.
The 1j36b, quoted as the replacement is about 74mA filament current vs 130 mA.
