I am new to the audio hobby. Anyone have experience with type 813 tubes in audio application?
I constructed the following breadboard and it sounds good so far.
813 output tubes in push pull
ultralinear taps at 40%
custom output transformer, 3" stack EI-1 3/4, interleaved windings 4section primary, 5 section secondary (one week to design and wind.) .010 Nomex between sections. .005 Nomex between layers. Soleniod wound using an engine lathe with wire tensioning control.
815 phase inverter and driver tubes
Goal: 100 watts rms class A, 200w class AB
So far, I am running 600v on the plate, (final design is for 1200 or more. ) I use a SMPS for the filaments and it works very well in addition to being light weight. I am designing a SMPS for the plate supply also, so that the finished mono block will be movable without a fork lift.
I use no cathode bypass caps. I have tried a little negative feedback, but no improvement over already good sound.
Providing I don't electrocute myself, I will report future developments. Anyone here ever work with this tube?
I constructed the following breadboard and it sounds good so far.
813 output tubes in push pull
ultralinear taps at 40%
custom output transformer, 3" stack EI-1 3/4, interleaved windings 4section primary, 5 section secondary (one week to design and wind.) .010 Nomex between sections. .005 Nomex between layers. Soleniod wound using an engine lathe with wire tensioning control.
815 phase inverter and driver tubes
Goal: 100 watts rms class A, 200w class AB
So far, I am running 600v on the plate, (final design is for 1200 or more. ) I use a SMPS for the filaments and it works very well in addition to being light weight. I am designing a SMPS for the plate supply also, so that the finished mono block will be movable without a fork lift.
I use no cathode bypass caps. I have tried a little negative feedback, but no improvement over already good sound.
Providing I don't electrocute myself, I will report future developments. Anyone here ever work with this tube?
When I was building, I spent a lot of time with 813.
Since I do not understand feedback (and now, never will!) I opted to strap the 813 as a triode. I have posted curves here I think some years ago. It makes a lovely triode. Ra 1.8K, 100W Pa, better than a 845 at a fraction of the price for a genuine one - and much easier to drive.
My last 813 amp was of course, push-pull. I ran the 813s at about 850V and 90mA, from memory bias was about -90V. Output tranformer was 7k a-a and I ran feedback from the secondaries to the 813 "cathodes" i.e. to the wiper on the hum balance pots.
The driver stage was balanced. I used 6SN7 DC coupled to 6BX7 with a EL822 as a current sink for the 6BX7.
I worked well, was reliable and sounded fine. I miss it.
7N7
Since I do not understand feedback (and now, never will!) I opted to strap the 813 as a triode. I have posted curves here I think some years ago. It makes a lovely triode. Ra 1.8K, 100W Pa, better than a 845 at a fraction of the price for a genuine one - and much easier to drive.
My last 813 amp was of course, push-pull. I ran the 813s at about 850V and 90mA, from memory bias was about -90V. Output tranformer was 7k a-a and I ran feedback from the secondaries to the 813 "cathodes" i.e. to the wiper on the hum balance pots.
The driver stage was balanced. I used 6SN7 DC coupled to 6BX7 with a EL822 as a current sink for the 6BX7.
I worked well, was reliable and sounded fine. I miss it.
7N7
Thanks for your replies. Gluca, I am not sure about the 100th. It would be overkill, but it lights up nice. Thanks HollowState for the link to the SE amp. I am amazed by the resources on this DIY board and thankful for them. 7N7, what happened to your 813 amp, anyway?
The 813 is very inexpensive, easy to drive. I purchased tube sockets and plate caps from an eBay dealer at a very low cost, also. I have a supply of 813's from surplus ham radio gear, which is one reason I chose this tube to start experimenting with audio.
My OPT is 10kohm P-P and I will increase the plate voltage to 1200v as soon as I have vacuum varnish dipped the xfmr and dielectric tested it to 4000vac. I have never built a SMPS for plate voltage at this power level (200w +) so I am not sure if it will be a flyback or a feed forward design. In either case, the capacitor energy storage will be small compared with a conventional supply. I plan several levels of safety interlocks.
Sparky
The 813 is very inexpensive, easy to drive. I purchased tube sockets and plate caps from an eBay dealer at a very low cost, also. I have a supply of 813's from surplus ham radio gear, which is one reason I chose this tube to start experimenting with audio.
My OPT is 10kohm P-P and I will increase the plate voltage to 1200v as soon as I have vacuum varnish dipped the xfmr and dielectric tested it to 4000vac. I have never built a SMPS for plate voltage at this power level (200w +) so I am not sure if it will be a flyback or a feed forward design. In either case, the capacitor energy storage will be small compared with a conventional supply. I plan several levels of safety interlocks.
Sparky
Hello Sparky.
I am the Paul Leclercq referred to in the Millett article.
I started building only in 1997 after a long absence from the hobby and the 813 amplifier was the first of a number that I built, usuually using obscure or strange valves. I actually wrote a small paper about triode strapping since it is/was a favourite topic.
There was a small amp using 6528 in p-p driven by a couple of 6SN7s one a cathode follower DC coupled. Then there was the 13E1 amplifier with +ve and -ve supplies (thanks to EC8010 for this idea), then finally the "Instock" and "Dashboard" amplifiers; these last were written up on this forum I think. There was also a pre-amp using 955 "acorns" with 6GK8 triode pentodes as cathode followers with built in pentode sinks; balanced output . This was very good although I never ran the finished pre-amp. The prototype was -3dB at 180kHz with very low distortion.
The last and maddest project, which was never finished sadly although all the elements had been tested in prototype form, was a stereo mid-range amplifier. This used triode strapped YL1071 (there is a US number but I have forgotten it) driven by 7788 pentode cathode followers with active G2 supply, with 7N7s at the front, all balanced of course. It was especially a pity as the driver stage had incredibly low distortion.
At the beginning of last year my employer went bust; after a couple of months of looking for a job,I ran away to France. All my equipment and amps I sold to fellow enthusiasts in London as I am living a somewhat basic life here...
7N7
I am the Paul Leclercq referred to in the Millett article.
I started building only in 1997 after a long absence from the hobby and the 813 amplifier was the first of a number that I built, usuually using obscure or strange valves. I actually wrote a small paper about triode strapping since it is/was a favourite topic.
There was a small amp using 6528 in p-p driven by a couple of 6SN7s one a cathode follower DC coupled. Then there was the 13E1 amplifier with +ve and -ve supplies (thanks to EC8010 for this idea), then finally the "Instock" and "Dashboard" amplifiers; these last were written up on this forum I think. There was also a pre-amp using 955 "acorns" with 6GK8 triode pentodes as cathode followers with built in pentode sinks; balanced output . This was very good although I never ran the finished pre-amp. The prototype was -3dB at 180kHz with very low distortion.
The last and maddest project, which was never finished sadly although all the elements had been tested in prototype form, was a stereo mid-range amplifier. This used triode strapped YL1071 (there is a US number but I have forgotten it) driven by 7788 pentode cathode followers with active G2 supply, with 7N7s at the front, all balanced of course. It was especially a pity as the driver stage had incredibly low distortion.
At the beginning of last year my employer went bust; after a couple of months of looking for a job,I ran away to France. All my equipment and amps I sold to fellow enthusiasts in London as I am living a somewhat basic life here...
7N7
Hello Sparky813,
I too have thought of fooling with high-powered 813s for audio since I don't use them for radio anymore (moved on to 4-400s and various ceramics like the 4CX1000A etc) and I have nearly a dozen laying around here. I'm curious about your output iron though. Did you wind it yourself or have it done? I was a bit reluctant to go that route for high voltage ( I'm talking in the 2KV range) as I was a bit concerned that the sheer amount of wire required to create the right load would result in so much C that it would hurt the high frequency response. Please let me know how this goes for you. It would surely be simpler than this 8x807 project I'm considering.
Thanks!
I too have thought of fooling with high-powered 813s for audio since I don't use them for radio anymore (moved on to 4-400s and various ceramics like the 4CX1000A etc) and I have nearly a dozen laying around here. I'm curious about your output iron though. Did you wind it yourself or have it done? I was a bit reluctant to go that route for high voltage ( I'm talking in the 2KV range) as I was a bit concerned that the sheer amount of wire required to create the right load would result in so much C that it would hurt the high frequency response. Please let me know how this goes for you. It would surely be simpler than this 8x807 project I'm considering.
Thanks!
AD5GB said:
I have never understood how a true "hi-fi" amplifier can be made with very high-voltage devices for this reason exactly.
I always took the view that above say 9k one would start to run into trouble; I know that there are some very clever transformer designers around, but for me 8k a-a (only push-pull at "Differential Towers"!) was the limit. This is OK as far as I recall with 813s at about 900V or so, although I did play a bit at 1.2kV.
Of course I am talking about triode mode here. With beam tetrode operation of course everything is different and feedback is necessary. I should think that a very mighty amplifier indeed could be built with a pair of 813s in BT mode running at about 1kV.
Paul
For the record, I am a beginner, and this is the first audio transformer I have ever wound. In order to get high frequency response, I am using interleaved primary and secondary. There are four primary sections, and five secondary sections. The secondaries are for 4, 8, and 16 ohms, so there are a total of 19 windings. Since this is a high voltage application, the insulation type and thickness is important. Between sections, I am using .010 Nomex. Between wincing layers, I am using .050 Nomex. VPI varnish is a must. Iron is 14 mil grain oriented silicon steel which is stacked with one on one interleave for minimum theoretical air gap. Windings are carefully soleniod wound, not dump wound, to get closest coupling possible. I have run the amp at listening levels all day long for several weeks and the transformer does not get even warm.
The high frequency response by calculation is 100khz, but this remains to be carefully tested. Right now, I have more roll off in my cap coupled driver stage than I see at the OPT, so I am far from done. I hope I don't have to wind this one twice. It was dog gone hard to do the first time. I am using a hands-on audio transformer design manual that I obtained from Ram Sales (Los Angeles) years ago. I will post the authors name and Ram's phone number for anyone interested. I will also post more details of the OPT if it is successful. Sparky
The high frequency response by calculation is 100khz, but this remains to be carefully tested. Right now, I have more roll off in my cap coupled driver stage than I see at the OPT, so I am far from done. I hope I don't have to wind this one twice. It was dog gone hard to do the first time. I am using a hands-on audio transformer design manual that I obtained from Ram Sales (Los Angeles) years ago. I will post the authors name and Ram's phone number for anyone interested. I will also post more details of the OPT if it is successful. Sparky
Manual is by Robert C. Wolpert, "Audio Transformer Design Manual" It is very detailed on the exact and practical methods of designing and building audio transformers with many examples and lots of supporting data and tables in the appendix. He also wrote an equally good manual on power transformers. Unfortunately, these manuals seem to be out of print. I bought mine from Ram Sales in the early 1990's. Ram Sales is a wonderful source for bobbins, transformer hardware, surplus lams from time to time, and also coil winding equipment. I have done business with them for 30 years or so and they are at the top of my list. They fill smaller orders for me. Their phone number is 800-423-2985
Paul (7N7) The idea of using acorn tubes, I assume for show, is unique. I would have never thought of it. If you get back into amp construction and need any tubes that I have in my junk collection and am not using, I will send them to you.
I have several tube types that I want to try and probably won't part with. I have a several 212 tubes which are old theater amp tubes from the 1930's. I even have sockets. I believe they have a plate dissipation of about 250 watts. How I came by them is a good story. Several years ago, I went to an estate sale near Microsoft in Redmond, Washington. There was a pile of stuff outside about 50 feet long and 3 feet high, covered with blue tarps and plywood, all in bad condition. I could see a few antique electronic items, so I offered $100 for anything I could salvage from the pile, and my offer was accepted. Most everything was rain soaked for years but there was a box containing 17 each WE-205d's as well as 8 each Duovac NIB 205d's with factory test sheets and warranty cards, all at the bottom of the pile. This is also where I found the 212 tubes. I gave the 205d's to my friend who told me about the sale. About half of the tubes turned out to be fine. This is the type of good luck that seldom happens to me.
I have thought about trying something with 304tl's and 450tl's. I have a few of them. If it doesn't work out, they make nice lamp stands.
Sparky
I have several tube types that I want to try and probably won't part with. I have a several 212 tubes which are old theater amp tubes from the 1930's. I even have sockets. I believe they have a plate dissipation of about 250 watts. How I came by them is a good story. Several years ago, I went to an estate sale near Microsoft in Redmond, Washington. There was a pile of stuff outside about 50 feet long and 3 feet high, covered with blue tarps and plywood, all in bad condition. I could see a few antique electronic items, so I offered $100 for anything I could salvage from the pile, and my offer was accepted. Most everything was rain soaked for years but there was a box containing 17 each WE-205d's as well as 8 each Duovac NIB 205d's with factory test sheets and warranty cards, all at the bottom of the pile. This is also where I found the 212 tubes. I gave the 205d's to my friend who told me about the sale. About half of the tubes turned out to be fine. This is the type of good luck that seldom happens to me.
I have thought about trying something with 304tl's and 450tl's. I have a few of them. If it doesn't work out, they make nice lamp stands.
Sparky
Response to email by "Bear" I am not familiar with the 417a, what do they look like? I have boxes and boxes of tubes than I have not gone thru yet. A lot of my friends who came over to see the estate stuff started drooling. In fact, their personalities changed temporarily when they saw the Western Electric tubes. I kept some of them for myself. We also pulled rack mount complete WE amplifiers out of the junk. They were rough on the outside, but pristine inside. I hauled home 4 navy shipboard 6 ft full rack size transmiters. One was a "TBM-8" I believe. There was a Breting 12 communications receiver and a good story behind it. Inside one of the sheds I found the receiver chassis which was installed in a high boy 1920's Sonora console radio cabinet with spindly legs, doors, etc. In spite of lack of the original cabinet, I negotiated for the receiver and finally bought it for $15. Later in the day when I was going through the outdoor mound of stuff, I found the original Breting cabinet along with a little cloth tobacco sack tied to the cabinet with the harware in it. You have to understand that this equipment was found mostly ouside in western Washington where it is damp or rains frequently and consequently the physical condition was poor. There were literally truck loads of neat stuff. I don't expect to ever find anything like this again.
Sparky
Sparky
I have found this http://www.tube-fullmusic.com/products/en-product0-805.htm
It seems the curve of a pentode
do these tubes normally work in class A2 or AB2 (with grid current) ?
It seems the curve of a pentode
do these tubes normally work in class A2 or AB2 (with grid current) ?
sparky813 said:
Helo Sparky, and thanks for the offer.
I doubt if I will be building yet though. Yes the acorns did fascinate me for appearance reasons, and I alsways loved anything that was old and "modern" at the same time: cutting-edge 30s technology. But it's worth looking at the example circuits that RCA devised. For example they knew about bypassing heater supplies at the valve, with small capacitors o get rid of RF noise.
However, when I tested the 955s aspecially as diff pairs I found that the distortion was very low, and as I wrote earlier the prototype pre-amp was very good. With 6SN7s I got -3dB at about 100kHz (I think) adn 180kHz with the 955s.
212s I have forgotten about; more info please!
Paul
7N7 said:
In SE the 955 is an excellent performer, as a differential pair it has the potential to be amazing:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=80128&highlight=
Love the 9002 equiv in the front end of my little 6CW5 SE. Also agree on the general recommendations here of 900-950 volts and ~-90 bias on the 813 trioded. At least with a modern Chinese sample voltages above around 975 greatly raised the level of higher harmonics regardless of standing current. This was driving a Hammond 1628Se, 5K:8 with an 8 ohm load on the 4 ohm tap for ~10K plate load.
And thanks for the triode curves!
Cutting-edge 30s technology: Westinghouse high power audio amplifier, the large tubes are 849s, smaller 211s. I just love the look of this sort of gear. 3 phase 6 pulse "low power rectifier" at left, note the 6 diode tubes.
Amperex 849A datasheet.
1936 Western Electric 212E datasheet.
1945 Amperex 212-E datasheet.
Amperex 849A datasheet.
1936 Western Electric 212E datasheet.
1945 Amperex 212-E datasheet.
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