Unidentified B7 base power beam tetrode ? - UK Vintage Radio Repair and Restoration Discussion Forum

trobbins · 1st Jun 2019, 9:14 am

Can anyone help identify a B7 base power beam tetrode as shown below, with anode top-cap. Just got from HRSA swap meet.

Cathode exits from top and then linked down to base via two outermost rods, with getter cup on one rod. Internal beam plates linked to cathode at top.

It looks like the first grid has the beefier rods and radiating end-loops top and bottom.

Heater to pins 4,5, but can't quite see other pin associations.

Plate not as long as an EL34, and same length as KT66, but not as wide and winged as KT66, and internal beam plates allow the grid and screen to be seen. So likely under 20W pate dissipation.

Ta, Tim

barrymagrec · 1st Jun 2019, 9:38 am

Kt44?

trobbins · 1st Jun 2019, 11:30 am

I just measured heater - it stabilised at 1.3A with 2.0V, so I guess it could go to 2.5V, but unlikely to be 4V heater.

Hartley118 · 1st Jun 2019, 12:01 pm

Could it be an N43, introduced in 1936?

Found it in the valve museum:

http://www.r-type.org/exhib/abo0022.htm

"The N43 is an output pentode suitable for both audio and video use. The load impedance required is 5,400Ω. The cathode resistance is 90Ω and in single ended configuration the output is 4.5 Watts."

Heater is 4V @ 2A, which tallies with the measurement.

Interesting that the anode is brought out to a topcap, implying high voltage and perhaps high frequencies. Looks like a step on the road to the 807.

Martin

Mr Moose · 1st Jun 2019, 1:03 pm

Hello,
I think it is a Mazda AC6/Pen or its naval equivalent NR74.
https://www.radiomuseum.org/tubes/tube_nr74.html
Yours, Richard

trobbins · 1st Jun 2019, 1:29 pm

Thanks gang - yes that Mazda AC6/Pen enlarged image clearly shows the same anode structure, and the lower radiators under the mica, and the correct getter position.

Much appreciated as I wouldn't have found that.

1st Jun 2019, 9:14 am	#1
trobbins Heptode Join Date: Oct 2009 Location: Melbourne Australia Posts: 901	Unidentified B7 base power beam tetrode ? Can anyone help identify a B7 base power beam tetrode as shown below, with anode top-cap. Just got from HRSA swap meet. Cathode exits from top and then linked down to base via two outermost rods, with getter cup on one rod. Internal beam plates linked to cathode at top. It looks like the first grid has the beefier rods and radiating end-loops top and bottom. Heater to pins 4,5, but can't quite see other pin associations. Plate not as long as an EL34, and same length as KT66, but not as wide and winged as KT66, and internal beam plates allow the grid and screen to be seen. So likely under 20W pate dissipation. Ta, Tim Attached Thumbnails

1st Jun 2019, 9:38 am	#2
barrymagrec Octode Join Date: Dec 2017 Location: Morden, Surrey, UK. Posts: 1,560	Re: Unidentified B7 base power beam tetrode ? Kt44?

1st Jun 2019, 11:30 am	#3
trobbins Heptode Join Date: Oct 2009 Location: Melbourne Australia Posts: 901	Re: Unidentified B7 base power beam tetrode ? I just measured heater - it stabilised at 1.3A with 2.0V, so I guess it could go to 2.5V, but unlikely to be 4V heater.

1st Jun 2019, 12:01 pm	#4
Hartley118 Nonode Join Date: Aug 2015 Location: Cambridge, Cambs. UK. Posts: 2,198	Re: Unidentified B7 base power beam tetrode ? Could it be an N43, introduced in 1936? Found it in the valve museum: http://www.r-type.org/exhib/abo0022.htm "The N43 is an output pentode suitable for both audio and video use. The load impedance required is 5,400Ω. The cathode resistance is 90Ω and in single ended configuration the output is 4.5 Watts." Heater is 4V @ 2A, which tallies with the measurement. Interesting that the anode is brought out to a topcap, implying high voltage and perhaps high frequencies. Looks like a step on the road to the 807. Martin __________________ BVWS Member

1st Jun 2019, 1:03 pm	#5
Mr Moose Octode Join Date: Jul 2008 Location: Gloucestershire, UK. Posts: 1,043	Re: Unidentified B7 base power beam tetrode ? Hello, I think it is a Mazda AC6/Pen or its naval equivalent NR74. https://www.radiomuseum.org/tubes/tube_nr74.html Yours, Richard Attached Thumbnails Last edited by Mr Moose; 1st Jun 2019 at 1:09 pm.

1st Jun 2019, 1:29 pm	#6
trobbins Heptode Join Date: Oct 2009 Location: Melbourne Australia Posts: 901	Re: Unidentified B7 base power beam tetrode ? Thanks gang - yes that Mazda AC6/Pen enlarged image clearly shows the same anode structure, and the lower radiators under the mica, and the correct getter position. Much appreciated as I wouldn't have found that.