but this is still 500 V. So it looks like i have only 2 variants- 2a3 (which is quite expensive) and 6v6 (for this one i did not see any interesting project yet)
That's a great classic SET design.
Due to the issues getting hold of a decent power triode you could consider using a SuperTriode - i.e. synthesise an ideal triode with a couple of pentodes or a triode/pentode pair with some tight feedback around the pair.
For instance a 6N2P-ev + GU50. In fact any pairing with a GU50 in pentode mode would do the job well - good for 200mA or 800V so it'll fit in pretty much anything.
Here in Europe, Polish Toroidy manufactures 8 different types of SE output transformer. From 600 ohms to 7k.
There should be suitable for most designs.
Single Ended - Shop Toroidy.pl
Parallel Single Ended - Shop Toroidy.pl
I have used Toroidy PP transformers only. My experience is good. Bass end works cleanly up to specified power level and frequency response is very wide.
The types of OPT / amplifiers I have built are:
1. 1k2 PP with JJ EL509 Circlotron
2. 5k with 6AS7G PP
3. 6k6 with EL34 UL
4. 10k with QQE03/12 PP (pentode) and 6N6P AB2 PP
I have no experience with their SE transformers, but I have no doubt about their performance.
The types of OPT / amplifiers I have built are:
1. 1k2 PP with JJ EL509 Circlotron
2. 5k with 6AS7G PP
3. 6k6 with EL34 UL
4. 10k with QQE03/12 PP (pentode) and 6N6P AB2 PP
I have no experience with their SE transformers, but I have no doubt about their performance.
Exactly! It's like picking 1 from column A and 2 from column B in a neighborhood Chinese restaurant. There is very little new under the sun, when it comes to tubed electronics. The creativity in a new design lies in careful selection and blending of proven building blocks.
In a previous post, I mentioned MOSFET buffering of a 12AX7 section voltage amplifier so that it can drive a "fixed" bias UL or triode mode "final" well. The tweaked RCA phono preamp shows how it's done. Your voltages and parts values will be different, but the principles involved don't change. Pay close attention to the data sheets for all of your parts. Make certain to stay well within the documented safe area of operation. A belt and suspenders ensure your trousers don't fall.
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...unless it is something better than what was known before. Otherwise, buy some cheap Chinese amp and start improving it!
My thoughts as well. I recently finished a Chinese FU-50 kit. I did upgrade a few components but not many. The iron looks and works fine. Any thoughts on how to improve the circuit. I did leave off the feedback network. Any way I tried hooking it up it oscillated. Sorry for the sideways view.
Let me try schematic again a different way. Anyone with suggestions?
Let me try schematic again a different way. Anyone with suggestions?
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Will do, thanks.
While installing the 10K resistors I noticed I omitted grounding the secondaries of the OPT. What can I say, did the same thing a few years back on a PP EL84 amp with the same problem. Not remembering probably has something to do with being 69 years old in a few months. At least it is an excuse. Installed the 10K resistors with proper grounding no oscillation so I then installed the called for 5.1K resistors without any oscillation either. If not for your suggestion I may not have ever tried to correct feedback again moving on to another project. Thanks
While installing the 10K resistors I noticed I omitted grounding the secondaries of the OPT. What can I say, did the same thing a few years back on a PP EL84 amp with the same problem. Not remembering probably has something to do with being 69 years old in a few months. At least it is an excuse. Installed the 10K resistors with proper grounding no oscillation so I then installed the called for 5.1K resistors without any oscillation either. If not for your suggestion I may not have ever tried to correct feedback again moving on to another project. Thanks
...unless it is something better than what was known before. Otherwise, buy some cheap Chinese amp and start improving it!
I agree with Wavebourn for a first time builder. Buy one of the Chinese kits. They are a tremendous value. I built 2 of the kits the last few months just to see how good they are. One being the pentode 6P3P + 6N8P kit and the FU-50 + 6N8P and both sound very good after swapping the Chinese tubes for Russian NOS equivalents which are dirt cheap. Parts, chassis already drilled, tubes, iron and miss. parts to build an amplifier for around $250 or less. Of course one could purchase the same amplifiers already built for just a little more but what fun is that.
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