EL34 Mullard Xf2 test NOS no print same date V42 177 208 209

Description

Here is a matched Quad NOS testing Xf2 EL34 tubes. Pairwise same date code.

Detailed description

These Mullard Xf2 EL34 with single halo-getter and welded plate are from the Blackburn production site.The EL34 is a transmitting beam tetrode. The old Mullard Blackburn production from the past century is known as the ‘crème de la crème’ of the EL34. These tubes deliver superior sonics compared to the Chinese and Russian new production EL34. Sonically many prefer the old welded plate types above the later stapled plate versions.  I refer to the many reviews on the web

All four tubes have a Xf2 code. Both pairs have the same date code; so a perfect match!!

The print on the old Mullard tubes is very fragile; this quad does bears etch codes only. Please note that two of the tubes show some colouration on the plate; this is the result of a temporary overheating during use and has no effect on the proper functioning of the tubes.  

The Mullard EL34 Xf2 series is considered by many as an outstanding sounding EL34 tube; a lot better than todays production!

The quad has NOS test values. 

Test results

The measurement data below show that the tubes are matched and in NOS condition. 

Valve  V42

Ia (plate current): Transconductance (Gm): Gas test, Shorts test:

107  mA 12,4  mA/V OK

>  NOS > NOS

Valve  V177

Ia (plate current): Transconductance (Gm): Gas test, Shorts test:

104  mA 12,1  mA/V OK

> NOS > NOS

Valve  V208

Ia (plate current): Transconductance (Gm): Gas test, Shorts test:

119  mA 12,9  mA/V OK

> NOS > NOS

Valve  V209

Ia (plate current): Transconductance (Gm): Gas test, Shorts test:

107  mA 12,4  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