Hi Reinout,
Many thanks for the info. that helps tie things down. I think I will need to look at raising the static Va to 1000V. in an attempt to reduce the Ia requirement. The OPT primary impedance info is a useful guide too.
For a driver stage I have been looking at a couple of options - both push pull into step down interstages. The first is a pair of PL802s in triode mode through a 2.5:1 interstage that should give me up to +/- 70mA of drive current. The alternative is a pair of PCL82 in push pull partial feedback configuration through 4:1 step down. This should give +/- 120mA of drive. I'll probably build both and see which I prefer.
The power supply is a little bit daunting! I thought I would use a bipolar supply at +/- 500V to give me the 1000V but let me feel a little bit safer! Of course this means doubling up on the number of chokes in the psu...
I have to say I am very excited about finishing this amp and very interested in how it will compare with the 845 amps I have built before.
I should also mention that I am building a pair of 211 cathode follower push pull pair of amps of about the same output power. I have been asked to develop a pair of valve amplifiers to drive a pair of Apogee speakers - hence the need for a lot of power and good current delivery as the speakers are 3 ohm nominal impedance with a low of just under 2 ohms... should be interesting to see which amplifiers manage this the best.
ciao
James
Many thanks for the info. that helps tie things down. I think I will need to look at raising the static Va to 1000V. in an attempt to reduce the Ia requirement. The OPT primary impedance info is a useful guide too.
For a driver stage I have been looking at a couple of options - both push pull into step down interstages. The first is a pair of PL802s in triode mode through a 2.5:1 interstage that should give me up to +/- 70mA of drive current. The alternative is a pair of PCL82 in push pull partial feedback configuration through 4:1 step down. This should give +/- 120mA of drive. I'll probably build both and see which I prefer.
The power supply is a little bit daunting! I thought I would use a bipolar supply at +/- 500V to give me the 1000V but let me feel a little bit safer! Of course this means doubling up on the number of chokes in the psu...
I have to say I am very excited about finishing this amp and very interested in how it will compare with the 845 amps I have built before.
I should also mention that I am building a pair of 211 cathode follower push pull pair of amps of about the same output power. I have been asked to develop a pair of valve amplifiers to drive a pair of Apogee speakers - hence the need for a lot of power and good current delivery as the speakers are 3 ohm nominal impedance with a low of just under 2 ohms... should be interesting to see which amplifiers manage this the best.
ciao
James
Here is my latest amp.
It's a stereo 35W SE with Eimac 250TL tubes. The output, power transformer, and chokes are Tamura. The circuit is identical to the 833A amp, but the power supply use vacuum tube rectifier for both driver and output stage, double chokes and oil caps.
It's a stereo 35W SE with Eimac 250TL tubes. The output, power transformer, and chokes are Tamura. The circuit is identical to the 833A amp, but the power supply use vacuum tube rectifier for both driver and output stage, double chokes and oil caps.
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Thanks James,
I hesitated quite a few time when I started building this 35W SE amplifier using the Eimac 250TL tube which I have never seen anybody used them in audio amplifier. The parts I gathered for this amp was originall designed for an 845SE amplifier. The glow of the 250TL has started it all.
This amp sounded much better than my 833A amp and also a pair of 845SE that I build (using identical Tamura output). In the pass, it is just as strong as the 845, the 833A lacked the bass, but It might be due to the output transformer that I used and the higher bias current. On the mids the 250TL is warm, the 845 is darker and the 833 is lighter. The highs on the 250TL is more open than the 845, the 833 has a slight touch of brightness.
I would not say the 250TL tube is better than the 833 since both amp are constructed with different parts quality, they do share same circuit though. The 250TL used tube rectifier for driver/output stage while the 833 used solid state rectifier.
I hesitated quite a few time when I started building this 35W SE amplifier using the Eimac 250TL tube which I have never seen anybody used them in audio amplifier. The parts I gathered for this amp was originall designed for an 845SE amplifier. The glow of the 250TL has started it all.
This amp sounded much better than my 833A amp and also a pair of 845SE that I build (using identical Tamura output). In the pass, it is just as strong as the 845, the 833A lacked the bass, but It might be due to the output transformer that I used and the higher bias current. On the mids the 250TL is warm, the 845 is darker and the 833 is lighter. The highs on the 250TL is more open than the 845, the 833 has a slight touch of brightness.
I would not say the 250TL tube is better than the 833 since both amp are constructed with different parts quality, they do share same circuit though. The 250TL used tube rectifier for driver/output stage while the 833 used solid state rectifier.
More transmitting tubes !
Hi Unison845,
it's good to see that there are more transmitting tube users. There is so much out there. 75TL / 100TL / T-55 / HY-75 / 250TL / 800 / 838 / 833 or go for the 450TL if you're really a daredevil......
Personally i would not chose for the 152TL/304TL. Those tubes are simply more 75TL's stacked together in a single glass envelope. Parallelling tubes outside would be the same....go for parallel 833's ?
There are options ! Don't stick to the 211/845. not that these are bad.....but there is a whole new world out there (ever seen a UV-204 bases amp.....also known as a VT-8....check Ebay now under "uv-204-a")
The commercial tubebuilders are just stepping into the transmitting tubes. For example Electronluve with their stylish 75TL (if you like the style).
Why did i pick the 833 ?
- nice specs. 5 KOhm opt is a nice ratio so you don't have to overcome huge ratio-differences. The higher the impendance the more difficult to get more wire on to the bobbin... So your opt will be even more large or the wire will be to thin which is not advisable with these mA's rushing through....
- still in production. And NOS reasonable priced.
- there are commercial amps using the 833 available......which means it is possible. For instance the Wavac HE-833 received good comments.
Yes, i did consider the 250TL but the impendance of the opt would be around 10K-ish ?
Of course that is al theory. I never had the luxury to listen to both a 833 and a 250TL amp using the same components and schematics. To be honest: who has ??
The most important thing: you've build a great looking amp and i bet it sounds fantastic. With 2 nice features:
1. DIY....you should be proud of your acomplishment
2. not everyone has a 250TL amp
I think you're not the first 250TL builder. Ed Billeci (audio bizarro) made one a couple of years ago and of course those Japanese are sitting still and do nothing.
Included is a picture of the the Billeci amp. I'll try to find others and in any case the 450TL-amp. And that is seriously way out of my leage !
Again: congratulations with the 250TL-amp. Wish we could listen to each others projects........
Reinout
Hi Unison845,
it's good to see that there are more transmitting tube users. There is so much out there. 75TL / 100TL / T-55 / HY-75 / 250TL / 800 / 838 / 833 or go for the 450TL if you're really a daredevil......
Personally i would not chose for the 152TL/304TL. Those tubes are simply more 75TL's stacked together in a single glass envelope. Parallelling tubes outside would be the same....go for parallel 833's ?
There are options ! Don't stick to the 211/845. not that these are bad.....but there is a whole new world out there (ever seen a UV-204 bases amp.....also known as a VT-8....check Ebay now under "uv-204-a")
The commercial tubebuilders are just stepping into the transmitting tubes. For example Electronluve with their stylish 75TL (if you like the style).
Why did i pick the 833 ?
- nice specs. 5 KOhm opt is a nice ratio so you don't have to overcome huge ratio-differences. The higher the impendance the more difficult to get more wire on to the bobbin... So your opt will be even more large or the wire will be to thin which is not advisable with these mA's rushing through....
- still in production. And NOS reasonable priced.
- there are commercial amps using the 833 available......which means it is possible. For instance the Wavac HE-833 received good comments.
Yes, i did consider the 250TL but the impendance of the opt would be around 10K-ish ?
Of course that is al theory. I never had the luxury to listen to both a 833 and a 250TL amp using the same components and schematics. To be honest: who has ??
The most important thing: you've build a great looking amp and i bet it sounds fantastic. With 2 nice features:
1. DIY....you should be proud of your acomplishment
2. not everyone has a 250TL amp
I think you're not the first 250TL builder. Ed Billeci (audio bizarro) made one a couple of years ago and of course those Japanese are sitting still and do nothing.
Included is a picture of the the Billeci amp. I'll try to find others and in any case the 450TL-amp. And that is seriously way out of my leage !
Again: congratulations with the 250TL-amp. Wish we could listen to each others projects........
Reinout
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transmitting tubes 2
Hi Unison845,
nope......only found Japanese 808-based amplifiers.
And Ed Billeci has abandoned his WE437/WE437/250TL amp.
So that means that you have the only functional 250TL audio amp. Very nice ! Now that is something special.
I know already a handfull diy 833-amps and there even available commercial form Wavac, Lancroft, Lumley and Legend Audio. That makes the 833 "common" ??
Nevertheless my "statement" in the last post remains the same: go out there and reach for these funny tubes.
Included is a picture of a Japanese 808 amp. And i've got here some 808's and 826's lying around. They simply beg to be used....
Reinout
Hi Unison845,
nope......only found Japanese 808-based amplifiers.
And Ed Billeci has abandoned his WE437/WE437/250TL amp.
So that means that you have the only functional 250TL audio amp. Very nice ! Now that is something special.
I know already a handfull diy 833-amps and there even available commercial form Wavac, Lancroft, Lumley and Legend Audio. That makes the 833 "common" ??
Nevertheless my "statement" in the last post remains the same: go out there and reach for these funny tubes.
Included is a picture of a Japanese 808 amp. And i've got here some 808's and 826's lying around. They simply beg to be used....
Reinout
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This had turned into a very nice thread indeed. In more than one way...
Slowly but surely the BIG valve builders are crawling out of the woodwork
And I thought a 845 was a big project!! Was I ever wrong.
It is refreshing to see something different to the 45/2A3/300B/EL84/EL34 crowd!!!
Keep em coming...I can handle it!!!!
But please don't let it deteriorate into a mine is bigger than yours contest!!!
Cheers,
Bas
Slowly but surely the BIG valve builders are crawling out of the woodwork
And I thought a 845 was a big project!! Was I ever wrong.
It is refreshing to see something different to the 45/2A3/300B/EL84/EL34 crowd!!!
Keep em coming...I can handle it!!!!
But please don't let it deteriorate into a mine is bigger than yours contest!!!
Cheers,
Bas
transmitting tubes 4
And the last post for tonight: another 450TL-picture.
My 833 is simply dwarfed by this monster.
Remarks about the 833-sound. Although "light" in presence i would not call this tube bright or bass-lacking. It simply is less pronounced as for instance a 845.
Well designed amplifiers + good components inside a good audio-set. How do you compare tonalities through internet. Isn't taste ?
Of course there will be differences. Just like cars. what is "better": a Mercedes or a BMW ? There both German, good quality, very fast, fuel-hungry and expensive. But a Mercedes-fan will simply not chose the BMW. And vice versa.
Have a good night,
Reinout
And the last post for tonight: another 450TL-picture.
My 833 is simply dwarfed by this monster.
Remarks about the 833-sound. Although "light" in presence i would not call this tube bright or bass-lacking. It simply is less pronounced as for instance a 845.
Well designed amplifiers + good components inside a good audio-set. How do you compare tonalities through internet. Isn't taste ?
Of course there will be differences. Just like cars. what is "better": a Mercedes or a BMW ? There both German, good quality, very fast, fuel-hungry and expensive. But a Mercedes-fan will simply not chose the BMW. And vice versa.
Have a good night,
Reinout
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Hello ReinoutdV,
Thanks for the comments on my EImac 250TL amp.
After the 250TL , I have planned to build a 450TL amp, and order the 100W SE output transformer. Very unfortunately, the pair of 450TL that I bought on Ebay arrived with both filaments damaged broken !!! Not only the 450TL tube got damaged but other 250TL that was shipped also have same problem. I guess the filament of these tubes are very fragile. I just have to wait to buy the 450TL again.
I also build a 808 amp using Tamura F2007 transformer, but later changed to 300B. I preferred the sound of 808, some day I will modify it back.
I also thinking about building a 100TL amp for a pair of Tamura F7003, since I really like the sound of the 250TL, but I need to buy these tubes, getting pretty difficult to buy Eimac tube these days.
Regarding the 833A, when I said said that they are a little bright, I meant that when compare to my 845 and 250TL, the 833A highs was never fatiguing, I guess I should have said more extended high.
Here is my 808:
Thanks for the comments on my EImac 250TL amp.
After the 250TL , I have planned to build a 450TL amp, and order the 100W SE output transformer. Very unfortunately, the pair of 450TL that I bought on Ebay arrived with both filaments damaged broken !!! Not only the 450TL tube got damaged but other 250TL that was shipped also have same problem. I guess the filament of these tubes are very fragile. I just have to wait to buy the 450TL again.
I also build a 808 amp using Tamura F2007 transformer, but later changed to 300B. I preferred the sound of 808, some day I will modify it back.
I also thinking about building a 100TL amp for a pair of Tamura F7003, since I really like the sound of the 250TL, but I need to buy these tubes, getting pretty difficult to buy Eimac tube these days.
Regarding the 833A, when I said said that they are a little bright, I meant that when compare to my 845 and 250TL, the 833A highs was never fatiguing, I guess I should have said more extended high.
Here is my 808:
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Big is Back!
Wow! This thread is getting very inspiring! At last some real SE amps apart the anemic and expensive 300Bs etc! I got easy access to such monster tubes that I love, but never got the guts to involve in such a project yet. I am now rethinking this seriously! I would like to ask what are the options we got for the output transformers? Any nice source in Europe? Guys, keep up the good work!!
Wow! This thread is getting very inspiring! At last some real SE amps apart the anemic and expensive 300Bs etc! I got easy access to such monster tubes that I love, but never got the guts to involve in such a project yet. I am now rethinking this seriously! I would like to ask what are the options we got for the output transformers? Any nice source in Europe? Guys, keep up the good work!!
Very inspiring projects guys!
However I was thinking in practical terms for your not very advanced DIYer - that does not want to risk high voltages and other complexities (i.e. extra driverstages/interstage tx etc) in transmitting tubes - that the new enhanced 300b type available from quite a number of manufacturers and offering up to 30w in some cases would be the way to go if one was looking for a high powered SET amp.
There are now quite a number of options for tubes in this range from KR , EML and 2-3 others.
However I was thinking in practical terms for your not very advanced DIYer - that does not want to risk high voltages and other complexities (i.e. extra driverstages/interstage tx etc) in transmitting tubes - that the new enhanced 300b type available from quite a number of manufacturers and offering up to 30w in some cases would be the way to go if one was looking for a high powered SET amp.
There are now quite a number of options for tubes in this range from KR , EML and 2-3 others.
....for a huge price like 600USD/pair...
You can find the best GM70 copper plate tubes for 180USD/pair and sometimes for 100USD/pair.
833 usually is under 100USD/each.
To drive most of the MEGA 300Bs you need a driver similar to what you need to drive 845 /for EML 520-V3/V2 you have -124V on grid/. The only advantage I see is 2K or even less impedance OPT.
regards
Maciej
You can find the best GM70 copper plate tubes for 180USD/pair and sometimes for 100USD/pair.
833 usually is under 100USD/each.
To drive most of the MEGA 300Bs you need a driver similar to what you need to drive 845 /for EML 520-V3/V2 you have -124V on grid/. The only advantage I see is 2K or even less impedance OPT.
regards
Maciej
Completely agree.
Those tubes are way too expensive, for the price difference you can have a lot of interstage, special outputtransformer wound.
and the driver is as complicated as for a transmitting tube.
Even a simple graphite gm70 only costs 25€....
it heats the room, it gives a nice light, and sounds nice.
For the price difference, you can go all out and have some more/better metal.
Do something special instead of a 300b on steroids.
you'll feel better afterwards
Filip.
Not to forget the dependency on one, sometimes not so reliable, manufacter if you go the special 300b route.
Ofcourse there isn't that much choice also for gm70, but a lot of those were made.
Those tubes are way too expensive, for the price difference you can have a lot of interstage, special outputtransformer wound.
and the driver is as complicated as for a transmitting tube.
Even a simple graphite gm70 only costs 25€....
it heats the room, it gives a nice light, and sounds nice.
For the price difference, you can go all out and have some more/better metal.
Do something special instead of a 300b on steroids.
you'll feel better afterwards
Filip.
Not to forget the dependency on one, sometimes not so reliable, manufacter if you go the special 300b route.
Ofcourse there isn't that much choice also for gm70, but a lot of those were made.
FILIP,
You are right, money is better spend on good interstage and output transformer. You can build a good pair of amp with 845 or GM70 with top quality Tamura output transformer for a price of a pair of expensive 300B. For Diyer, it does not take much more work to build a 300B than these monsters and the result is very rewarding.
Anybody have other output tube suggestion? Russian tubes perhaps?
You are right, money is better spend on good interstage and output transformer. You can build a good pair of amp with 845 or GM70 with top quality Tamura output transformer for a price of a pair of expensive 300B. For Diyer, it does not take much more work to build a 300B than these monsters and the result is very rewarding.
Anybody have other output tube suggestion? Russian tubes perhaps?
