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Tubelab Discussion and support of Tubelab products, prototypes and experiments

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Old 21st October 2019, 03:41 PM   #11
mctavish is online now mctavish  Austria
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Location: Niederösterreich
Thanks for the reply. At the moment I have no cap in the feedback circuit and it sounds quite good with high frequency content.

I will start out with 68pf and go from there, unfortunately I will have to wait until next week, we are moving house this week....

The outputs are of very good quality, I have used them before and I can say with confidence that they were the BEST part of the Heathkit AA-100...

One other thing, I have only .86v at the cathode of the input triode of the 12AT7s. Is this normal or am I looking for more like 1-2 volts there?
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Old 8th November 2019, 05:37 PM   #12
mctavish is online now mctavish  Austria
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Got everything up and running with the gas reg tubes. sounds fantastic and all of the voltages check out now.

I am still curious about the low cathode voltage on the input triode - 12AT7.

Is this normal and a part of the design or should I be looking for more negative voltage on the cathode.

I am now thinking about playing with a bit more negative feedback as the gain seems still to be a bit too high in pure pentoad mode....
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