EL34 Mullard Xf3 branded Valvo same date code V293 296

Description

Here is a pair NOS testing Mullard Blackburn Xf3 EL34 valves branded Valvo.

Description

The Mullard Blackburn Xf3 black base EL34 valve is introduced as a successor of the famous Xf2 EL34 in the late sixties, this was the third EL34 version made by Mullard Blackburn. The Xf3 type EL34 was the first version with stapled plate, after this type finally came the Xf4 which ended production in Blackburn in the 1970s. The tubes are used but have NOS test values. Both tubes are produced in the same week: second week of may 1975.

Please note that the plate of one tube shows some colouration; this effects the aesthetics but doesn’t influence the performance. 

Sonics

The sonics of the Xf3 EL34 is typical for the Mullard Blackburn sound character and is among 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.

Test results*

Valve 1 V293	Ia (plate current): Transconductance (Gm): Gas test, Shorts test:	101 mA       11,8  mA/V OK	=  NOS = NOS
Valve 2 V296	Ia (plate current): Transconductance (Gm): Gas test, Shorts test:	115 mA 12,9  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