[patrick-turner]

On Thursday, 21 November 2002 01:15:18 UTC+11, Denis wrote:
(Jon Yaeger) wrote in message ... Denis, That being said, do you have a recommended alternative? Spasebo, Jon Yes, I have. I'm sure this is a cathode-feedback (CFB), or by other words, distributed loading pentode stage. I've already posted much about this technique here in RAT. This equally works with PP and SE, but I prefer PP amplifiers and all my designs up to date are PP. I use CFB circuit much similar to that introduced by Peter Walker in QUAD tube amps. A small (from 10 to 20%) portion of the primary winding is connected to the cathode of the power tube thus providing a precisely tailored amount of local negative feedback in the output stage. The screen grid of a pentode is tied to a constant B+ supply, and the Eg2 in general case can differ from Ep. Moreover, when a pentode or ray tetrode operates at Eg2 Ep, the distortion spectrum remarkably simplifies, and it is possible to almost completely suppress 3rd and higher order harmonics over a considerable portion of dynamic range.The internal resistance of a pentode with such small percentage CFb is nevertheless very low, and the speaker damping is already sufficient without adding global NFB. At the same time, the g1 driving voltage is comparable, or even lower than that for DHTs like 300B.If we take for comparison a possible SE CFB stage with EL509 against some typical 300B amp (this is especially interesting as these two tubes have comparable plate dissipation limits), the EL509 CFB SE amp will have less than 1/10 of 300Bs distortion with same benigh spectrum and supposedly 1/3 of 300Bs Ri.. Moreover, EL509 will give more than 6 dB of plate current headroom in respect to the 300B - like 9W output, and will better handle reactive loads. So there is something to thinkof. EL509 has also other special features which place it well above other known tubes, both pentodes and triodes.Best regards,Denis N. Afanassyevwww.cortmi.com.ua/omak In article , (Denis) wrote: "Simon van de Laak" wrote in message ... Hello RATs, Has anybody build the Direct-Coupled SE Amplifier using the EL509/6KG6 designed by Bob Danielak? (http://www.geocities.com/bobdanielak...oteNo33..html). What are your remarks/tips on this design? Did you have any problems building this design? Thanks. Simon EL509 certainly asks for better amp design than this one. No need to lobotomy this magnificient tube! Denis.

Hi Denis, long time no see!
I'll never forget you succeeding to convince me there was NFB in all triodes.

I still believe strongly that pentodes and beam tetrodes can work so well and sound so well with FB windings in the OP stage from OPT they give a new "gold standard" for music. Of course the old standard was the 300B or other "real" triodes, but there are more pathways to good music other than using real triodes. I recently posted on using Partial Circlotron with a normal UL OPT. Dual floating PSUs are needed for anode supply but it can be worth it.
Regards, Patrick Turner.