• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

ECC88/6DJ8 at higher Va

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dgta

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Joined 2011
#1
Looking at the Philips datasheet, I see the max Va is 130, but then the curves are drawn up to 300V and they look perfectly fine and usable.
Has anyone used this tube at higher Va, say in the 200-250V range? Any downside when using it in the higher Va ranges?
 
#3
Heed the datasheet, when working with genuine 6DJ8/ECC88 stock. The "sibling" types: 6922/E88CC and 7308/E188CC are tougher; therefore, you can safely go somewhat higher than 130 VDC. The Russian 6n23p-ev is easily a 6922 equivalent that's "as tough as old rubber boots". Tubes marketed under the ElectroHarmonix (EH) label as 6922 are, in fact, 6n23p-ev.

Please remember that the 6DJ8, etc., were developed for use as cascode TV tuner front ends. It's fortunate happenstance that the bunch have HIFI uses.
 
#4
As you can see in datasheet 220V, -6.8V, at 20k load is valid operating point.... but distortion is high (up to 7%), anode current is low (6.5-9mA). The most linear part of curves about 100V Va.

I have ECC88 tubes, but only use more robust E88CC.
According to my experiences (I have a few dozens 88CC variants -Philips, Telefunken, Siemens, Tesla, Tungsram, JJ, russian) at higher Va and low Ia the sound would be thinner, metallic (I think this is due to the growing 3th harmonic distortion).
I'm in love Siemens CCa "sound", fortunately I have few tubes with good condition. 🙂
 
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