KT61 6P25 EL33 CV1438 CV2938 N147 OM9 AUDIO BEAM TETRODE

beam tetrode octal based valve
Manufacturers: Mullard , GEC Valves , Marconi , Osram , RCA

OK, let's get this straight right from the start, I do know that the Mullard EL33 is actually a pentode but it’s both pin and electrically equivalent as well as being easier to drive whilst showing lower intermodulation distortion and was introduced at the same time as the KT61 in 1939.

An interesting alternative and the youngest of this type being introduced during 1948 is Mazda's 6P25, a beam tetrode just like the KT61, it  having slightly higher mutual conductance gm and with it's outer envelope screening whilst it may not be as pretty as a KT61 some say it is a better performer.  But, who knows, why not tube roll with a couple of each and decide for yourself.

The KT61 proper, also introduced during 1939,   is an  audio output beam tetrode valve, part of a family of similar valves from the Marconi-Osram Group and   finds use in many classic hifi amplifiers, the Leak  TL10 being one such example, the benefits of beam tetrodes also transfers well to guitar amplifiers where KT61 are seen as a useful modification in replacing 6V6 as the valve of choice to give a distinctive but desirable sound.  But watch out, the KT61 is prone to heater-cathode shorts so make sure you test regularly and buy carefully - preferably from us!!!!!!!!

Picture of OSRAM BROWN BASE KT61 FROM FEB 1958
OSRAM BROWN BASE KT61 FROM FEB 1958
On offer today we have a beautiful Osram device. It tests as 100% emission as you can see from the attached test data label courtesy of our AVO VCM163. The envelope carries the etched ellipse cartouche and the brown micanol base is tight to the envelope and shows clean uncorroded pins - a simply super device.
Stock Code: u12
Availability: 1 in stock
Delivery date: 1 week
£45.00
Picture of OSRAM BROWN BASE KT61 FROM FEB 1957
OSRAM BROWN BASE KT61 FROM FEB 1957
On offer today we have a beautiful Osram device. It tests as 100% emission as you can see from the attached test data label courtesy of our AVO VCM163. The envelope carries the etched ellipse cartouche and the brown micanol base is tight to the envelope and shows clean uncorroded pins - a simply super device.
Stock Code: u35
Availability: 1 in stock
Delivery date: 1 week
£45.00
Picture of  OSRAM BLACK BASE KT61 FROM NOV 1953
OSRAM BLACK BASE KT61 FROM NOV 1953
On offer today we have a beautiful Osram device. It tests as 100% emission as you can see from the attached test data label courtesy of our AVO VCM163. The envelope carries the etched ellipse cartouche and the black micanol base is tight to the envelope and shows clean uncorroded pins - a simply super device.
Stock Code: A106
Availability: 1 in stock
Delivery date: 1 week
£45.00
Picture of OSRAM BLACK BASE KT61 FROM JANUARY 1952 MISSING SPIGOT
OSRAM BLACK BASE KT61 FROM JANUARY 1952 MISSING SPIGOT
On offer today we have a beautiful Marconi - Osram device. It tests with good emission as you can see from the attached test data label courtesy of our AVO VCM163. The envelope carries the white inked cartouch showing a date code for January 1952 and the black base is tight to the envelope and shows clean uncorroded pins BUT the central base spigot is missing - a simply super device but be careful when mounting for use.
Stock Code: y44
Availability: 1 in stock
Delivery date: 1 week
£40.00
Picture of OSRAM BROWN BASE KT61 FROM JANUARY 1956
OSRAM BROWN BASE KT61 FROM JANUARY 1956
On offer today we have a beautiful Marconi -Osram device. It tests with good emission as you can see from the attached test data label courtesy of our AVO VCM163. The envelope carries the white inked cartouch showing a date code for January 1956 and the brown base is tight to the envelope and shows clean uncorroded pins - a simply super device.
Stock Code: 3/6/2
Availability: 1 in stock
Delivery date: 1 week
£45.00
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