Pano, if you don't already have Rod Coleman's filament supply have a look at this little circuit which is based on the same idea, a CCS after the filament, and a bjt filter before it. I have used both Rod's circuit and mine in my 26 preamp and could not tell the difference (sound or measurement wise). All kind of different power bjts can be used, of course. I developed this after ordering a pair of Rod's supply because I ran out of patience. 
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Thanks Iko! I'll look into it. At the moment I'm running the filaments in CV mode from a lab power supply. Overkill, but convenient for prototyping. I could run in CC mode, too.
Below is the output circuit that I'm running now. The DC voltages are from the sim'd model and agree with measurements. The 330R is the DCR of the primary.
Even in the messy wiring stage noise is OK, about 27mV into an 8 ohm load. With the vintage Tamura iron I'm running the -3dB points are 12Hz-38Khz. Not bad, really.
Below is the output circuit that I'm running now. The DC voltages are from the sim'd model and agree with measurements. The 330R is the DCR of the primary.
Even in the messy wiring stage noise is OK, about 27mV into an 8 ohm load. With the vintage Tamura iron I'm running the -3dB points are 12Hz-38Khz. Not bad, really.
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Yes, there will be transformers for parafeed drive. Let me test them first. I started a headphone 6W amp project about an year ago, then when potential partner became inpatient the project had been canceled, then the plant I contacted before come with some solution, so may be I will re-open the project if transformers are really as nice as they claim.
You don't need 300 Ohm transformer. If you will try to drive 300 Ohm headphones from 300 Ohm secondary of 2W amp you will be deaf, and your headphones fried.
Speaking of 32 and 50 Ohm 2 and 6W headphones, we mean special planar drivers that have very low sensitivity. For conventional dynamic headphones 2W will be too much.
Yes, it is exactly what I meant. I never saw 300 Ohm headphones that require 2-6W of power. Nor never heard.
Maybe I should try the Speaker Voltage Test on my headphones. (HD 580). Would be interesting to see what the voltages are.
The 600 ohm tap on my OPT puts out wayyyyyy too much voltage for the headphones. A 300 ohm tap would, too. I suppose the "Ear Speaker" types really need an amp suited to low efficiency speakers.
The 600 ohm tap on my OPT puts out wayyyyyy too much voltage for the headphones. A 300 ohm tap would, too. I suppose the "Ear Speaker" types really need an amp suited to low efficiency speakers.
Pano, if you don't already have Rod Coleman's filament supply have a look at this little circuit which is based on the same idea, a CCS after the filament, and a bjt filter before it. I have used both Rod's circuit and mine in my 26 preamp and could not tell the difference (sound or measurement wise). All kind of different power bjts can be used, of course. I developed this after ordering a pair of Rod's supply because I ran out of patience.
What would be a real (as in something that is available off the shelf) qd44h11transistor ?
The venerable D44H11 like here: D44H11 STMicroelectronics | Mouser
However, I've used D1912 successfully as well.
However, I've used D1912 successfully as well.
Looks like not well presented OPT for SIM program.
Check 5 Kohm in the primary. Like this:
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So what !
I saw in a simulation that the primary impedance of your OPT in real is very bad.
No surprise Andy. I have always stated that the 300B looks good on paper but when you look carefully it requires so much effort and money to be not convenient anymore, from any point of view. Self bias is not good for this valve, IMHO.
Looking for a SET you might be better off with a good Chinese 211!
Yes, you need 1KV plate voltage and 32.5 VA for the filament but such effort will be well paid back with sumptuous musical performance and more power, at least! 4P1L would be a nice driver.....
Cheers,
45
You'll never get me playing around with anything over 400v and usually much less! I don't listen loud and have just a medium size room. On paper I could have used the 813, for instance, and I had a drawer full once which I never used. Same with 845s - sold them too. The comment about the PP 2a3 amp is out of date - it's a very good amp but I'm now using PSE 4P1L outputs in filament bias. I've got rid of the cathode bypass at last, and that was a big step up in clarity. I would use the 2a3 in filament bias, but it's too hungry to be practical. PSE 10Y is a possibility in filament bias - one day.
But the truth is that I'm so happy with my all-4P1L setup in 3 stages that I have no special desire to build anything else right now. It just works. Masses of tone and detail, just the sound I like. And the tubes are so cheap I just leave it all on 24hrs a day. I have a big box full of spare tubes, so I'm a happy camper.
But the truth is that I'm so happy with my all-4P1L setup in 3 stages that I have no special desire to build anything else right now. It just works. Masses of tone and detail, just the sound I like. And the tubes are so cheap I just leave it all on 24hrs a day. I have a big box full of spare tubes, so I'm a happy camper.