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Failed to connect to MySQL: (1203) User howardkn already has more than 'max_user_connections' active connectionsPath: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail From: john larkin Newsgroups: sci.electronics.design Subject: Re: Valve frequency multipliers Date: Fri, 31 Jan 2025 16:28:38 -0800 Organization: A noiseless patient Spider Lines: 144 Message-ID: References: <1r71194.rtliy6v9cf4N%liz@poppyrecords.invalid.invalid> <4doqpjd9e3h5u9lt9tklkjs0k9unutbkct@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Injection-Date: Sat, 01 Feb 2025 01:24:44 +0100 (CET) Injection-Info: dont-email.me; posting-host="e9d28b5c702138d4ce28d5e4825b254d"; logging-data="3950682"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX19+orhbU55MqDW8TRn7/li6" User-Agent: ForteAgent/8.00.32.1272 Cancel-Lock: sha1:IrjqaoFNGHsGcwZDzSFSUZjwVUo= Bytes: 7671 On Sat, 01 Feb 2025 00:21:10 +0000, Cursitor Doom wrote: >On Fri, 31 Jan 2025 16:12:35 -0800, john larkin >wrote: > >>On Fri, 31 Jan 2025 23:50:56 +0000, Cursitor Doom >>wrote: >> >>>On Fri, 31 Jan 2025 13:51:25 +0000, liz@poppyrecords.invalid.invalid >>>(Liz Tuddenham) wrote: >>> >>>>I am trying to use a 15 Mc/s crystal oscillator to generate a 150 Mc/s >>>>signal, the obvious multiplication ratios are x5 and x2. The 150 Mc/s >>>>has to be distributed to two other units by a 120-ohm screened cable. >>>> >>>>The whole thing must be done with the minimum number of valves and no >>>>semiconductors. The Colpitts-derived xtal oscillator is an EF91 and the >>>>multiplier stage(s) can be either another EF91 or an ECC91. >>>> >>>>I have tried picking the x5 signal (75 Mc/s) off the anode of the >>>>oscillator with a tuned circuit but can only get a couple of volts >>>>pk/pk. This isn't enough to drive the ECC91, which I had hoped could >>>>be used as a 'push-push' doubler, it also won't drive an EF91 over >>>>enough of the curved portion of its characteristic to give sufficient >>>>frequency-doubled signal. >>>> >>>>Alternatively, I have tried using a parallel-tuned circuit at 15 Mc/s in >>>>the anode of the xtal oscillator to drive one of the triodes of the >>>>ECC91 which can then act as the multiplier. There is a whopping great >>>>15 Mc/s signal going into the grid of the triode (about 25v pk/pk) and, >>>>with the cathode earthed, this develops enough grid-leak bias that the >>>>valve is conducting anode pulses of over 20 mA about 10% of the time. >>>> >>>>I would have thought that under those conditions the triode would have >>>>given a large signal at 75 Mc/s in an anode circuit tuned to that >>>>frequency - but it doesn't appear to. I can't use the triodes as >>>>straight earthed-cathode amplifiers at those frequencies because of the >>>>Miller capacitance effect, but they should be perfectly satisfactory as >>>>multipliers where the grid and anode circuits are tuned to different >>>>frequencies. >>>> >>>>Does anyone know how to determine the optimum conditions for generating >>>>the 5th and 2nd harmionics in valves? >>> >>>Nowadays, just ask AI! >>> >>>Generating 2nd and 5th harmonics from a thermionic (vacuum) tube >>>involves specific operational conditions and circuit configurations. >>>Here's how you can achieve this: >>> >>>Conditions for 2nd Harmonic Generation: >>> >>> Non-linear Operation: >>> Grid Bias: The tube should be biased to operate in a >>>non-linear part of its characteristic curve. This typically means >>>biasing the grid slightly negative so that the tube's operation swings >>>into the non-linear regions of the plate current-grid voltage >>>characteristic. >>> Signal Amplitude: The input signal should be of sufficient >>>amplitude to drive the tube beyond its linear operating region, >>>causing even harmonics (like the 2nd) to be generated due to the >>>non-linear response of the tube. >>> Circuit Configuration: >>> Single-ended Amplifier: A simple single-ended triode or >>>pentode amplifier can naturally produce even harmonics if driven into >>>non-linearity. >>> Cathode Bias: Using cathode bias can help in achieving the >>>desired non-linear operation by introducing a dynamic bias that >>>changes with signal level. >> >> >>Crazy. >> >> >>> >>> >>>Conditions for 5th Harmonic Generation: >>> >>> Non-linearity and Symmetry: >>> Higher Order Distortion: The 5th harmonic is an odd harmonic, >>>which means the tube's operation needs to be asymmetrical around zero >>>to produce it effectively. However, tubes naturally produce less odd >>>harmonics than even ones unless manipulated. >>> Signal Drive: A very strong input signal might push the tube >>>into regions where higher-order harmonics become significant, but this >>>approach might also introduce unwanted distortion. >> >>Dumb AI. We WANT distortion. Specifically about a 10% plate conduction >>duty cycle. >> >> >>> Circuit Techniques: >>> Feedback: Using feedback in the right way can amplify certain >>>harmonics. Negative feedback can reduce even harmonics while >>>potentially emphasizing odd ones if designed for such. >>> Multiple Stages: Cascading multiple tube stages can increase >>>the harmonic content by compounding the distortion at each stage. Each >>>stage could be designed to push further into non-linearity. >>> Harmonic Enhancement Circuits: Specific circuits like those >>>with transformer coupling where the primary and secondary windings' >>>interaction can be tuned for harmonic enhancement. Also, using >>>resonant circuits or filters tuned to the 5th harmonic can help. >>> Tube Selection: >>> Tube Characteristics: Some tubes are naturally more harmonic >>>rich than others. Tubes like the 12AX7 might be used for their gain >>>and non-linearity characteristics, but for more harmonic richness, >>>sometimes pentodes or specific triodes known for distortion >>>characteristics are employed. >>> Operating Point: >>> Grid Voltage: Adjusting the grid voltage to operate closer to >>>cutoff can increase harmonic distortion since the tube's response >>>becomes more non-linear near cutoff. >> >>Operate it deep in cutoff, off most of the time. A high amplitude >>drive and grid-leak bias would be good. >> >> >>> Power Supply Design: >>> Power Supply Stiffness: A less stiff (or intentionally loose) >>>power supply can allow tube operation to vary more with the signal, >>>potentially increasing harmonic distortion. >>> >>> >>>In practice, generating a specific harmonic like the 5th is >>>challenging because tubes are inherently more suited to producing even >>>harmonics when driven hard. >> >>Why is that? >> >>>To get a pronounced 5th harmonic, you'd >>>often need to tailor the circuit design, including feedback, load >>>characteristics, and perhaps even use of additional harmonic >>>generators or filters post-amplification. >> >>AI platitudes, harvesting conventional wisdom. > >Well, there's AI and there's AI. The above was Grok. I did try to get >the 'new kid on the block' (DeepSeek) to regale us with its wisdom on >the subject, but it didn't seem to have any. Chat GPT might be worth >asking.... Won't it "learn" from amateur posts to chat sites? Collect opinions?