When you say it I just remembered that I creamed up the 6V6 bootstrapped CF to some 10-20 Vpp input without seeing any deviations on the scope output back in those days.
Good afternoon.
Sorry, if i am offtopic, but, I suppose, it should be interested.
I've built stereo preamplifier using 6AS6 (unfortunately, not 6V6, but it is really likely) or 6Ж1П / 6Ж2П - Russian analogue. Circuit is really similar.
And - specially pleasureful - works with low voltage (+15V DC)
Sounds very well.
This is circuit. May be converted to be used with anothe tubes.
Article about building in my blog, and a few more pictures of variation inside mount
Sorry, if i am offtopic, but, I suppose, it should be interested.
I've built stereo preamplifier using 6AS6 (unfortunately, not 6V6, but it is really likely) or 6Ж1П / 6Ж2П - Russian analogue. Circuit is really similar.
And - specially pleasureful - works with low voltage (+15V DC)
Sounds very well.
This is circuit. May be converted to be used with anothe tubes.
Article about building in my blog, and a few more pictures of variation inside mount
Is he possibly starving them into positive grid territory with very low gain when on just 15V rail and no cathode resistor Anatoly?
Yes.
By the way, Collins used them an a high-end portable shortwave receiver R392/URR with +27V B+
How so? Besides the obvious difference in the supply voltage, the bias scheme is also completely different, but I guess if you net everything out - all common cathode stages are very similar...
How so? Besides the obvious difference in the supply voltage, the bias scheme is also completely different, but I guess if you net everything out - all common cathode stages are very similar...
...and tubes made of glass, and glow inside. 😀
Dropping the 6V6 in the same NovaPA's circuit it would take 10K anode load to centre and it would be good for up to 1V RMS input signal with 5x gain and rather gross THD as in the attached picture. With the 6AK5 and 1K anode load it should be making much lower gain I guess. Also better THD I hope.
Attachments
I honestly don't see the point in starving tubes when there is no limit in available voltage. I would rather use JFETs and BJTs if a voltage is limited, or used some cheap SMPS converter for tubes. 🙂
I can see two purposeful occasions. One of a marketing trick like they do with some $50 Chinese headphone amps on eBay so to stick some glowing bottles on them for "wow factor" while relying on op-amp output and buffering the line input with the tube. The other rather more serious way is to starve some specific tubes that show low noise in that way so to parallel some, feed them with a depletion mode anode CCS and use them as MC input stage.
Merlin has a paper on his site, "Triodes at Low Voltages", the starved triodes do work, albeit calling these circuits "hi-fi" would be a stretch.
With very low input signal like in instrumentation occasions and turntable cartridges maybe there is a meaningful niche of application. When used in so low power i.e. cold anode, some noises get better but it takes the less grid leaky high gm types to use. Mainly picked out novals. Must be stable without grid stoppers also else it defies the low noise purpose.
