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triode_al triode_al is offline

diyAudio Member

About Me

  • About triode_al
    Biography
    professor of fluxus
    Location
    Westland
    Interests
    triodemania
    Country
    Netherlands
  • Signature
    DAC TDA1541 S1; Kondo post-I/V filter; MC30-Super --> two stage RIAA; Pre: SP-6 clone ; F5 ; 300B PP ; ESL 57

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General Information
  • Last Activity: Today 08:28 AM
  • Join Date: 30th May 2004

Blog

View triode_al's BlogRecent Entries
Latest Blog Entry

Posted 18th May 2012 at 03:03 PM by triode_al Comments 0
Posted in Uncategorized
I have been reworking my RIAA preamp the past weeks - main effort to install a SALAS shunt in the HV.
I had some problems looking like instability of the DC. I also noted that every on/off cycle, the problem got worse. And while developing, I would switch the preamp on an off often, to see the effect of the tweaks, such as setting the shunt cuirrent.

Later I found that one 6N9S tube was 'dying', really, it went black, but intermittent.
The heater wires probably had been stretched a bit and in cold state they made some contact (measured 3-4 ohm) but when heated up it lost contact. The effect cascaded into the Vb, and was seen on both outputs similarly.

I conclude The [Russian, Reflektor brand, big logo] tube is very sensitive to the heater.

I had the two tubes running in series from a medium impedance 12 V source (IRF250, gate connected to drain via 100k resistor and a 300 uF cap: relatively slow start of 2 secs. But too fast probably...
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