EL34 Mullard Xf2 pair NOS/NIB branded Tungsram 1968/1969 V21/22

Description

Here is a pair NOS/NIB Mullard Blackburn EL34 valves branded TUNGSRAM. 

Description

The Mullard Blackburn Xf2  EL34 valve is legendary.  Introduced after the metal base EL34 in the early sixties, this was the second version and many say the best sounding Mullard EL34. They are never used The tubes have NOS appearance and test values. These tubes are King of the EL34. 

Sonics

The Mullard Blackburn Xf2 EL34 is the worlds most musical; EL34 tube known for its pronounced liquid midrange.  I refer to the many reviews on the web. And they seem to last forever.

Note: my tubes are often not the cheapest.  But is very hard to find better tubes !

Test results*

Valve 1 V21	Ia (plate current): Transconductance (Gm): Gas test, Shorts test:	103 mA       11,8  mA/V OK	=  NOS = NOS
Valve 2 V22	Ia (plate current): Transconductance (Gm): Gas test, Shorts test:	113 mA 12,1  mA/V OK	= NOS = NOS

Telefunken measuring values for new unused tubes:

• The rated emission value for a new EL34 is:  100 mA. 
• The rated transconductance value for a new EL34 is:  11 mA/V . 

For Telefunken specs info see last picture 

Test condition & equipment:

Mutual transconductance, plate current, gas and shorts test equipment: AVO Mk IV (Dutch army tester) , AVO Valve Data Manual 23rd edition 1981, RFT stabilised mains, Utracer3+, Philips PE 4832, 2x Korad KA3005P programmable power supply, 2x Keithley 2700 and 2x Fluke 145. Test conditions: Ua (plate voltage) = 250 Volts, Us (screen voltage) = 265 Volts, Ug = -13,5 Volts and Uf = 6,3 V ± 3% (factory conditions). Please read our test page.

Summarized description