I designed a nice amp that used $4 worth of tubes and made 100 WPC. I might have mentioned the 13GB5 once or twice, and POOF both of the suppliers that I use were cleaned out.....except for the junk Korean versions.
We both badmouthed the Korean tubes, and Stan still has them all. The buyer specifically asked for all the Mullards. I never mentioned the input tubes, and they are still on the list. Do you think someone is reading our words and buying up the tubes? Well if they are, they are going to need to learn how to design amps, because all 4 of my breadboards have gone into the trash and I will never give up the schematic.
The project is not a Dual-SE anymore, after lots of auditioning the PP topology won.
It is slowly coming out, the HV part is now completed. This is the preliminary assembly, after becoming a working piece it will be taken apart and painted. Hence, I put some connectors in use. The OPTs are the cheapo Edcors SEs, which after the audio tests been converted into the PPs.
It is slowly coming out, the HV part is now completed. This is the preliminary assembly, after becoming a working piece it will be taken apart and painted. Hence, I put some connectors in use. The OPTs are the cheapo Edcors SEs, which after the audio tests been converted into the PPs.
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I abandoned this project for a couple months as I was not happy with sound. It sounded ok, but... smth just felt wrong. Particularly, on the very small levels the sound had that slight "ripping" thing.
After quite of reading, thinking, and getting busy with something else I put it on breadboard again considering that all the plate characteristics in specs are actually... pentode. So I built it new in all-pentode, and bingo! It plays really well, with no pentode "harshness", clear and airy, plenty of power. The P-to-P impedance is 20K at 8E load.
I will put the updated schermatics on once hear-tested some minor things.
smoking-amp, thanks for the suggestion on pentode mode for the input/driver stage.
Mona, your proposed auto-biasing CCS turned out to be the best suitable on simplicity/efficiency for pentode way.
The originally UL-strapped beam output sections tested in triode with worse result, but the pentode with a 12V zener also worked out the best (to my ear).
Also, the R + C + Zener cathode bias after all turned out sounding better than LM317, well, someone mentioned it a quite mediocre one.
6AD10 is difficult to source the good ones, tested the amp with 6T10 - they scored as good (or even better as there is plenty of them to choose from). Tried RCA, Admiral, Lindal, Sylvania, GE, some no-name Japan made, all sound well. The amp shows be tolerant to non-matching tubes and there is no pots to tune it up; if a pair is waay out - still ok, gives just a little less non-distorted power, but with well matching tubes it is up to 7 Wa.
Moderator, please change the thread's title to "SHIII project, All-Pentode PP"
(Though, it could run as Dual-SE, I just do not have those trafos anymore - they were combined into the PP shown on the above photo)
After quite of reading, thinking, and getting busy with something else I put it on breadboard again considering that all the plate characteristics in specs are actually... pentode. So I built it new in all-pentode, and bingo! It plays really well, with no pentode "harshness", clear and airy, plenty of power. The P-to-P impedance is 20K at 8E load.
I will put the updated schermatics on once hear-tested some minor things.
smoking-amp, thanks for the suggestion on pentode mode for the input/driver stage.
Mona, your proposed auto-biasing CCS turned out to be the best suitable on simplicity/efficiency for pentode way.
The originally UL-strapped beam output sections tested in triode with worse result, but the pentode with a 12V zener also worked out the best (to my ear).
Also, the R + C + Zener cathode bias after all turned out sounding better than LM317, well, someone mentioned it a quite mediocre one.
6AD10 is difficult to source the good ones, tested the amp with 6T10 - they scored as good (or even better as there is plenty of them to choose from). Tried RCA, Admiral, Lindal, Sylvania, GE, some no-name Japan made, all sound well. The amp shows be tolerant to non-matching tubes and there is no pots to tune it up; if a pair is waay out - still ok, gives just a little less non-distorted power, but with well matching tubes it is up to 7 Wa.
Moderator, please change the thread's title to "SHIII project, All-Pentode PP"
(Though, it could run as Dual-SE, I just do not have those trafos anymore - they were combined into the PP shown on the above photo)
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