Ever tried mercury vapor rectifier tubes (i.e. 83, 816, 866A, etc.) ? Drawback is the pre-heat time and don't break one, but the voltage drop across the tube is 15 volts regardless of current drawn. Also neat to see the blue glow with types like the 816 or 866A brighten with the audio. Unless you have 4 tubes and 3 filament transformers, a bridge rectifier with 816's or 866's can run the budget... but 816's and 866's are around on ebay and other sites...
I located the 6D22S = 6Д22С half wave rect tube, very cheap and long heating time doing a very nice soft start. I would like ask if 2 these tubes are recommeded for a Triode EL34/KT88 SE 6W conservative amp?
https://www.newsensor.com/pdf/svetlana/6d22-svetlana.pdf
https://www.newsensor.com/pdf/svetlana/6d22-svetlana.pdf
Looks possible as long as you have separate 6.3V @ 4.2A available. I don't see the benefit over a more common option such as the 5AR4 or 5U4.
I am always willing to learn - would you care to shed more light on the subject of 'sag' in relation to class A valve amps for me?
Apart the raising debate here, I'm still thinking to use a tube rectifier for my next hifi project, but I have a doubt.
With a total current demand of 60-70 mA for the amp, is OK using an EZ80 (rated up to 90 mA)? Since there is a certain AC/DC efficiency depending from tube to tube and from approaching the current limit, I wish to use a suitable tube in the "optimal area". Transformer I can use has 2.5A(6.3 V) and 1.5A(5V) available for heaters.
With a total current demand of 60-70 mA for the amp, is OK using an EZ80 (rated up to 90 mA)? Since there is a certain AC/DC efficiency depending from tube to tube and from approaching the current limit, I wish to use a suitable tube in the "optimal area". Transformer I can use has 2.5A(6.3 V) and 1.5A(5V) available for heaters.
Lots of experts contributing to this thread, so I am almost afraid to ask:
Have you a reason for not considering an EZ81 (rated up to 160mA)?
The EZ80 and EZ81 are pin compatible. You really need to study the spec sheets for your application to be able to determine if EZ80 is adequate. The B+ you are aiming for plays a part. EZ81 will provide more head-room and appear stiffer. It will also be less stressed at start-up.
It is good practice to separate the rectifier heaters from the other tubes in the circuit. One way you can do that is by rectifying the 5V through a bridge + PI filter, then a dropping resistor for 6.3VDC. The max current you should draw from it is about 1A which should be right on target for the EZ81 (should you need it). For EZ80 there is plenty of room as it only draws 0.6A. For the HV, study the spec sheets and adhere to recommended max size for first capacitor in the PI filter after the rectifier, and work out Rt for the components you are using.
[url]EZ80[/URL]
EZ81
It is good practice to separate the rectifier heaters from the other tubes in the circuit. One way you can do that is by rectifying the 5V through a bridge + PI filter, then a dropping resistor for 6.3VDC. The max current you should draw from it is about 1A which should be right on target for the EZ81 (should you need it). For EZ80 there is plenty of room as it only draws 0.6A. For the HV, study the spec sheets and adhere to recommended max size for first capacitor in the PI filter after the rectifier, and work out Rt for the components you are using.
[url]EZ80[/URL]
EZ81
pblix,
Can you explain to me why an indirectly heated rectifier needs DC for the filaments? Do not do that just because the only unused winding for the rectifier is a 5Volt one.
5V x (Root of 2) = 7.07V. 7.07V - 6.3V = 0.77V. That means the Total voltage drop of 2 schottky diodes, and resistor or DCR of the choke in the pi filter can only drop 0.77V. You will either not get 6.3VDC, or you will not have an effective filter.
Just use a separate 6.3VAC winding and connect it to the rectifier filament. 6.3V 2A filament transformers are small, light, and inexpensive. Fixing a Buzz or other noises is more expensive than the cost and real-estate of that extra transformer.
The EZ80 and EZ81 have a 500V rating from filament to cathode. But even so, you are correct, reduce the risk of noise, and reduce the chance of a catastrophic failure throughout the multi filament circuits. That is why I also prefer using separate filament windings for the rectifier and signal tubes. You have much less risk of rectifier noise getting into the signal tubes. A bad rectifier tube (filament cathode short) will not take out the other tubes if they are on a Separate filament winding (the B+ can not appear on the lower voltage filament to cathode voltage ratings of the signal tubes).
Can you explain to me why an indirectly heated rectifier needs DC for the filaments? Do not do that just because the only unused winding for the rectifier is a 5Volt one.
5V x (Root of 2) = 7.07V. 7.07V - 6.3V = 0.77V. That means the Total voltage drop of 2 schottky diodes, and resistor or DCR of the choke in the pi filter can only drop 0.77V. You will either not get 6.3VDC, or you will not have an effective filter.
Just use a separate 6.3VAC winding and connect it to the rectifier filament. 6.3V 2A filament transformers are small, light, and inexpensive. Fixing a Buzz or other noises is more expensive than the cost and real-estate of that extra transformer.
The EZ80 and EZ81 have a 500V rating from filament to cathode. But even so, you are correct, reduce the risk of noise, and reduce the chance of a catastrophic failure throughout the multi filament circuits. That is why I also prefer using separate filament windings for the rectifier and signal tubes. You have much less risk of rectifier noise getting into the signal tubes. A bad rectifier tube (filament cathode short) will not take out the other tubes if they are on a Separate filament winding (the B+ can not appear on the lower voltage filament to cathode voltage ratings of the signal tubes).
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If it is of any help, UK based Watford Valves will ship to Italy.
The EZ81 is available from around £10.
www.watfordvalves.com
Hi Indaco!
Your original question in post #1 has been answered, and you have decided to opt for valve rectification in your hi-fi amplifier.
The only information you have given about your project is that the power transformer has secondaries of 6.3V @ 2.5A ; 5.0V @ 1.5A ; 350V - 0 - 350V @ ??? mA
If you require further help with your power supply design, please supply as much information as you can and I'm sure the forum members will chip in.
Good luck with your project!
Your original question in post #1 has been answered, and you have decided to opt for valve rectification in your hi-fi amplifier.
The only information you have given about your project is that the power transformer has secondaries of 6.3V @ 2.5A ; 5.0V @ 1.5A ; 350V - 0 - 350V @ ??? mA
If you require further help with your power supply design, please supply as much information as you can and I'm sure the forum members will chip in.
Good luck with your project!
Thanks! In reality, I'm not so sure at 100%....that was an option.
I noticed I could have not enough room in my case for the tube and maybe the bulky inductance (it's raccomended with this kind of circuits). So I could turn back to S.S. rectification, that in my previous works wasn't so bad. I'm going to see...
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