Great lashup here Andy. Works pretty good. Those 805's are a good tube. WARNING: IF YOU HAVE PETS- DO NOT USE ANDY"S OPEN CONSTRUCTION METHOD SHOWN HERE . Pets love to shove their noses into things and you may injure or kill your pet!! When I did TV servicing house calls, I had both dogs and cats shove their noses into the open backs of TV sets and bump into live B+ connections, where the voltages were substantially less than 1KV and up to 40KV in the HV section. I finally required pets to be shut in a separate room, and also small children to be out of the area. (The pets were less of a problem than the children! Not joking either.) Be sure your test leads insulation are rated for the voltage you are using too! many of the new ones seem to be very low voltage rated. Nothing like having test lead wires arc over on HV in tube projects. Andy- What info do you need on the 805 tube? I have a data book from RCA " Transmitting Tubes" early ARRL handbooks, and Tube Lore II by Lud Sibley where I can likely let you know what you need. In Ham service, we often ran the graphite plates at a dull orange or a red glow, in CW transmitters. Let the filament warm up for 30 seconds to a minute before applying B+. It will increase the life of your tube a lot. Think time delay relay on your finished amp. Adding a meter to monitor plate or cathode current will tell you if the tube starts to "run away". On using tubes that have been stored for decades, like the 805's, letting them sit with just filament voltage for 30 minutes or so will help the filament emission to stabilize. With thoriated tungsten filaments, low emission can -sometimes- be restored by running a filament voltage 50% higher for 30-60 seconds and then reduce it to 2-3 volts higher for 10 minutes or so. Then run at normal filament voltage for an hour or so to stabilize. This is an old trick to "boil" the surface of the filament and allow more electrons to the surface for emission, per an article from the 30-40's on rejuvenating transmitting tubes.
Thats a genius power supply. Thank you for sharing. If you use BIG industrial bridge rectifiers, that work at like 1600v and 100a each, they are 98 percent efficient at 120watts, the heat dissipation is 2.5 watts as per the datasheet. They are fuji 3 phase to dc. They can be used as full bridge single phase too. And they work better because theres more chunky bits of conduction. and you could probably never pop them.
These larger tubes are interesting. I once built a experimental amplifier using a pair of 811 triodes. I found it very neat that I didn't need any bias arrangement whatsoever. The tubes were essentially self biased into class B. I drove them with a interstage transformer to create push pull grid drive, driven by the output from another already existing audio amp. Worked flawlessly, and as you cranked up the volume, the anode current increased automatically. No noticeable distortion, sounded great and was extremely powerful. But couldn't make it work well with actual speakers because the output transformer was just an old AC transformer, and while it worked, the ratio was way off so it only delivered good power into 0.5 ohm loads which is not very practical for speakers, it could only deliver about 20 watts into 4 ohm subwoofers which is really dissapointing when such an arrangement could theoretically output several hundred. But one day I'm gonna revisit that project, and try to find proper transformers and try to build a complete amplifier with pre amp, mid stage amp, and the final output in one unit. It's always been a dream of mine to have an amplifier entirely based on vacuum tubes that can drive subwoofers with serious performance:) Would be so much fun to replace all my solid state amplifiers with tube, way more interesting:) Keep up the great work, really enjoyed this test :) that valve looks like it's in healthy condition, and I bet you could make one hell of a single ended amp with that if you wanted ;) of course, getting a pair would be best since in single ended mode you'd have to have it running at about 70 watts dissipation all the time, but... That's usually not a concern in our hobby :) it can pull as much power as it wants, hehe You could probably get a solid 50 watts maybe more of output from that one valve! :D
Thanks, interesting stuff. The datasheet shows a similar setup, two 2A3's driving an interstage tfmr driving two 805's. I have two 805's, I'd love to build a monster amp but would need another two 805's & they ain't cheap. TFW.
@@diabolicalartificer Heck yeah, that would be awesome. I'd like to build something capable of replacing a 3200W continious average power solid state amplifier to drive my 8 boxes of subwoofers, hehe. Insanity, but fun! I had a bit of a obsession with building speakers a few years back, but I don't regret it. It's a lot of fun to crank up music and just make the whole area absolutely shake itself to pieces :) I'd love seeing you build a monster of an amp, but be careful. At this voltage level one touch and one can take the last breath, so gotta be really careful! That's one thing that worries me if I'm going to build a monster tube amp, I need to absolutely make sure that my cats can't touch high voltage, I'd probably have to build some sort of cage type chassis for it :)
@@tigerelectronics5966 EHT or any power supply capable of over 500v ish is problematic, obviously, from a safety point. A few years ago I thought about building a 500w valve amp using 813's but ditched the idea for a few reasons. 1) The EHT & 2) The OPT needed for such an amp. I think it's better to use paralleled valves instead at a lower HT and that simplifies the OPT construction too. For sub use a SS amp is the only practical solution. At those low frequencies a powerful valve amp's OPT would be prohibitively expensive & you'd need a fork lift to shift the amp. Still, it's nice to dream.
Great lashup here Andy. Works pretty good. Those 805's are a good tube.
WARNING: IF YOU HAVE PETS- DO NOT USE ANDY"S OPEN CONSTRUCTION METHOD SHOWN HERE . Pets love to shove their noses into things and you may injure or kill your pet!!
When I did TV servicing house calls, I had both dogs and cats shove their noses into the open backs of TV sets and bump into live B+ connections, where the voltages were substantially less than 1KV and up to 40KV in the HV section. I finally required pets to be shut in a separate room, and also small children to be out of the area. (The pets were less of a problem than the children! Not joking either.)
Be sure your test leads insulation are rated for the voltage you are using too! many of the new ones seem to be very low voltage rated. Nothing like having test lead wires arc over on HV in tube projects.
Andy- What info do you need on the 805 tube? I have a data book from RCA " Transmitting Tubes" early ARRL handbooks, and Tube Lore II by Lud Sibley where I can likely let you know what you need. In Ham service, we often ran the graphite plates at a dull orange or a red glow, in CW transmitters.
Let the filament warm up for 30 seconds to a minute before applying B+. It will increase the life of your tube a lot. Think time delay relay on your finished amp.
Adding a meter to monitor plate or cathode current will tell you if the tube starts to "run away".
On using tubes that have been stored for decades, like the 805's, letting them sit with just filament voltage for 30 minutes or so will help the filament emission to stabilize.
With thoriated tungsten filaments, low emission can -sometimes- be restored by running a filament voltage 50% higher for 30-60 seconds and then reduce it to 2-3 volts higher for 10 minutes or so. Then run at normal filament voltage for an hour or so to stabilize. This is an old trick to "boil" the surface of the filament and allow more electrons to the surface for emission, per an article from the 30-40's on rejuvenating transmitting tubes.
Wise words Frank, thanks for the info, I'll drop you an email.
UA-cam just recommended your channel to me what a treasure trove.
Thank you for your video I just subscribed.
Wow, as my video's aren't monetised I didn't think YT did that. I'm crap at making video's but hope you find something interesting, TFW & for subbing.
Thats a genius power supply. Thank you for sharing.
If you use BIG industrial bridge rectifiers, that work at like 1600v and 100a each, they are 98 percent efficient at 120watts, the heat dissipation is 2.5 watts as per the datasheet. They are fuji 3 phase to dc.
They can be used as full bridge single phase too.
And they work better because theres more chunky bits of conduction. and you could probably never pop them.
Thanks, too kind, & ta for the info on those BR's.
These larger tubes are interesting. I once built a experimental amplifier using a pair of 811 triodes. I found it very neat that I didn't need any bias arrangement whatsoever. The tubes were essentially self biased into class B. I drove them with a interstage transformer to create push pull grid drive, driven by the output from another already existing audio amp. Worked flawlessly, and as you cranked up the volume, the anode current increased automatically. No noticeable distortion, sounded great and was extremely powerful. But couldn't make it work well with actual speakers because the output transformer was just an old AC transformer, and while it worked, the ratio was way off so it only delivered good power into 0.5 ohm loads which is not very practical for speakers, it could only deliver about 20 watts into 4 ohm subwoofers which is really dissapointing when such an arrangement could theoretically output several hundred. But one day I'm gonna revisit that project, and try to find proper transformers and try to build a complete amplifier with pre amp, mid stage amp, and the final output in one unit. It's always been a dream of mine to have an amplifier entirely based on vacuum tubes that can drive subwoofers with serious performance:)
Would be so much fun to replace all my solid state amplifiers with tube, way more interesting:)
Keep up the great work, really enjoyed this test :) that valve looks like it's in healthy condition, and I bet you could make one hell of a single ended amp with that if you wanted ;) of course, getting a pair would be best since in single ended mode you'd have to have it running at about 70 watts dissipation all the time, but... That's usually not a concern in our hobby :) it can pull as much power as it wants, hehe
You could probably get a solid 50 watts maybe more of output from that one valve! :D
Gosh I wrote 807... That's of course not what I meant, hehe. I meant 811 triodes.
Thanks, interesting stuff. The datasheet shows a similar setup, two 2A3's driving an interstage tfmr driving two 805's. I have two 805's, I'd love to build a monster amp but would need another two 805's & they ain't cheap. TFW.
@@tigerelectronics5966 Easily done : )
@@diabolicalartificer Heck yeah, that would be awesome. I'd like to build something capable of replacing a 3200W continious average power solid state amplifier to drive my 8 boxes of subwoofers, hehe. Insanity, but fun! I had a bit of a obsession with building speakers a few years back, but I don't regret it. It's a lot of fun to crank up music and just make the whole area absolutely shake itself to pieces :)
I'd love seeing you build a monster of an amp, but be careful. At this voltage level one touch and one can take the last breath, so gotta be really careful! That's one thing that worries me if I'm going to build a monster tube amp, I need to absolutely make sure that my cats can't touch high voltage, I'd probably have to build some sort of cage type chassis for it :)
@@tigerelectronics5966 EHT or any power supply capable of over 500v ish is problematic, obviously, from a safety point. A few years ago I thought about building a 500w valve amp using 813's but ditched the idea for a few reasons. 1) The EHT & 2) The OPT needed for such an amp.
I think it's better to use paralleled valves instead at a lower HT and that simplifies the OPT construction too.
For sub use a SS amp is the only practical solution. At those low frequencies a powerful valve amp's OPT would be prohibitively expensive & you'd need a fork lift to shift the amp.
Still, it's nice to dream.
I think they are pressed and sintered graphite. Still, carbon vs blackened steel, probably carbon is somewhat nicer.
Your probably right, I do get stuff wrong, TFW.