Will do. Well spotted! Thanks.
For your reference, here are a couple of measurements I made on the follower version today. 2V RMS input ~1VRMS output (near 0dBV) for the volume pot to be at half division on its max output impedance and contribute all of its noise. Used an old music recording interface from E-MU on ASIO.
First chart is for 6Π6C Soviet NOS (Saratov factory Reflector logo also marked x 69 and OTK)
Second chart is for 6V6GT Tung-Sol currently made in the same factory for New Sensor corp.
Heater PSUs are DC. Dual mono current sources set at ~0.45A each. From the original gain mode schematic*
*It can be found linked in post#1 as "comprehensive schematic".
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Thanks for posting those measurements. I've actually got some parts to try out DC heaters so will post those in the next couple weeks.
From your experience what is the biggest contributor to H2? I've got consistently another 10db if it no matter which tubes I roll (-70db). I'm not overly concerned about it, mainly curious. Is it mostly about the output capacitor?
From your experience what is the biggest contributor to H2? I've got consistently another 10db if it no matter which tubes I roll (-70db). I'm not overly concerned about it, mainly curious. Is it mostly about the output capacitor?
It's because I have 10k//33k=7.7k instead of 5k main cathode load and 300V B+ in this example I would think. Bias current is 20mA. I did that at a point to can test lossier rectifier tubes and more rail drop on higher RC with the same power transformer. Although some may prefer the original H2 level.
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The 6p1p-ev is free from microphonics...at least the pair I had in my preamp. BUT here is the thing. I don't think this tube is on par with the 6v6 sound wise in a preamp. Last night I plugged it into my main system with and the sound was meh. It sounded fine in the my son's bedroom system though. (Not sure if the tubes were ok..I did not bother to try other 6p1p's I have in my stash)
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unregulated dc heaters
I decided to try a very basic unregulated DC heater just for giggles, cause I had some parts laying around. Seems to result in about 10db less noise in the 60/120/180 Hz points vs just AC. More details and some measurements later. But did I do this correctly? I blew the side door off one cap because I had the +/- reversed, but I'm hoping that was the only reason.
Specifically:
1) is it ok to use the center tap still tied to 80V? Resulted in less noise than when CT attached to 0V in this case.
2) Am I ok with 25V and 16V caps, even with it center tapped to 80V? I think so, since no current flowing there (I think).
I've got about 6.5VDC, but will try trimming it down just a bit more to 6.2 or thereabouts. The 6.3V winding is rated for 5A, so I should be ok even with the power factor loss.
Thanks!
I decided to try a very basic unregulated DC heater just for giggles, cause I had some parts laying around. Seems to result in about 10db less noise in the 60/120/180 Hz points vs just AC. More details and some measurements later. But did I do this correctly? I blew the side door off one cap because I had the +/- reversed, but I'm hoping that was the only reason.
Specifically:
1) is it ok to use the center tap still tied to 80V? Resulted in less noise than when CT attached to 0V in this case.
2) Am I ok with 25V and 16V caps, even with it center tapped to 80V? I think so, since no current flowing there (I think).
I've got about 6.5VDC, but will try trimming it down just a bit more to 6.2 or thereabouts. The 6.3V winding is rated for 5A, so I should be ok even with the power factor loss.
Thanks!
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Raw DC has to have 120Hz ripple and smallish filter caps allow it more amplitude. You can see it on the scope. Choose AC coupling and probe across each one of the filter caps. Its pointy saw-tooth, mostly before any precious voltage eating RC damping, and if enough to couple well it can give a harsher harmonic noise profile.
Anyway, I would alternatively DC lift at the output i.e. at the heaters one side, to compare results. No danger to bias with a lifting DC in any single central node if the whole thing is floating. What matters to the filter caps rating is voltage difference across them not where they sit at in reference to some non correlated ground.
Anyway, I would alternatively DC lift at the output i.e. at the heaters one side, to compare results. No danger to bias with a lifting DC in any single central node if the whole thing is floating. What matters to the filter caps rating is voltage difference across them not where they sit at in reference to some non correlated ground.