Hi Waveburn,
Wow, 4 GU50 that will give your amp the real grunt.For my taste, I would prefer it with the narrow side to front.
I made a test setup with 6 of the GU50. I drive them hard into grid current (B2) They drive 450W into the Load at 1000V plate and 250V g2 . What an amazing valve. My aim is to build a Bass Guitar amp with these.
Yes, nice tubes. They were designed by Telefunken for military applications. They easily survive red anodes dissipating 100+ Watts, after that work like nothing happened.
Good luck with your Bass Guitar amp Wolfgang!
Hi Wavebourn,
see this thread, there are Pics an a digram of my test setup.
http://www.diyaudio.com/forums/instruments-amps/199099-real-bass-amps-have-tubes-semiconductors-musical-director-trainees-3.html
I came across about 30 GU50, so enough for further testings. By the way, I never managed to blew up even a single valve , as you stated they rugged like a tank. (what they are made for)
Please keep us informed with your neat little beasts!
73
Wolfgang
see this thread, there are Pics an a digram of my test setup.
http://www.diyaudio.com/forums/instruments-amps/199099-real-bass-amps-have-tubes-semiconductors-musical-director-trainees-3.html
I came across about 30 GU50, so enough for further testings. By the way, I never managed to blew up even a single valve , as you stated they rugged like a tank. (what they are made for)
Please keep us informed with your neat little beasts!
73
Wolfgang
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I don't like sockets on sides. Better to use shielded cables.
I think I will probably design the chassis for 2 versions of orientation, with both versions of holes pre-cut. Extra hols will be closed by false-panels. Such a way I will have more freedom in the future. And 2 models of the amp on the same chassis.
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good job you don't design cars
I never saw cars with sockets on sides. Or what do you mean?
Actually, I worked for an automotive company. But I did not design cars. I designed information systems to steal money when manufacture and sell cars (just kidding - good information is valuable both to steal and to save money)
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I do not like them either, but to make something that is acceptable as a home appliance, you can't have them in the front either. Only if it is for temporary connection i.e. digital media player. That's why i vote for long side front
Here are my thoughts:
1. I would turn all the components 90° on the chassis so you can space out the output tubes. I think they are spaced too close together and need more ventilation.
2. I would locate the two transformers all the way to the back and at opposite sides with the heat sink between them.
3. I would orient the front of the chassis on the long side so that all the output tubes are facing you and are equidistant from your point of view.
1. I would turn all the components 90° on the chassis so you can space out the output tubes. I think they are spaced too close together and need more ventilation.
2. I would locate the two transformers all the way to the back and at opposite sides with the heat sink between them.
3. I would orient the front of the chassis on the long side so that all the output tubes are facing you and are equidistant from your point of view.
An externally hosted image should be here but it was not working when we last tested it.
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I never saw cars with sockets on sides. Or what do you mean?
Actually, I worked for an automotive company. But I did not design cars. I designed information systems to steal money when manufacture and sell cars (just kidding - good information is valuable both to steal and to save money)
I mean, imagine if you designed car with doors on front and sides, just use which one according to whether you park parallel or straight in !
Interesting suggestion; I've also found that more powerful the tube amp is, the better the sound quality, esp at lower levels. Obviously the perception to overload is far reduced, but other boundary conditions must appear to be better optimised. Distortion may already be very low and undetectable; but what creates the transparency when good quality commercial components are used ? No deoxidised rubbish, no silver, nor gold connections. Yes, all my amps use input transformers, balanced line.
The sound quality of my Vampire 500W is astounding when at low sound levels is put against the original Mullard 20W design, or the GEC 88-50, 3 stage amp which is an excellent sounder. In the mid 1950's-60's these were considered, well designed. The 500W is the final design, the most complicated I've ever built, the best and there we have it.
Over decades I accumulated quite a collection of homebrewed tubed HiFi stereo amps, many are sold and my own favourite chassis is the two chassis 500+500W; I chassis 2x25W;2x7W..etc ...It's taken a long time to reach nirvana, what I consider the best quality tube amp for a given set of loudspeakers.
Others may have their liebling amps too.
richy
The sound quality of my Vampire 500W is astounding when at low sound levels is put against the original Mullard 20W design, or the GEC 88-50, 3 stage amp which is an excellent sounder. In the mid 1950's-60's these were considered, well designed. The 500W is the final design, the most complicated I've ever built, the best and there we have it.
Over decades I accumulated quite a collection of homebrewed tubed HiFi stereo amps, many are sold and my own favourite chassis is the two chassis 500+500W; I chassis 2x25W;2x7W..etc ...It's taken a long time to reach nirvana, what I consider the best quality tube amp for a given set of loudspeakers.
Others may have their liebling amps too.
richy
Hi Rich, I realize this thread is ancient but is there any chance you could share the Vampire schematic?
Still waiting!Thanks gentlemen for the encouragement!
I will report results.
Hi Wavebourn,
I collected your suggestions on GU-50 in PP during the years and it seems the best way is to use them in pentode mode, with around 10% a-g1 feedback like UNSET, at around 850-900V B+ and 8-10 kOhm Raa per pair of tubes, setting Vg2 to have the best harmonic content and adding a LDR in series with a 100 Ohm resistor across the screen resistors to limit the signal and avoid that the amp goes into clipping. It should give around 110 Wrms per pair of tubes.
It is a great tube, its drawback is the need of custom transformers and it works with very high voltages.
I collected your suggestions on GU-50 in PP during the years and it seems the best way is to use them in pentode mode, with around 10% a-g1 feedback like UNSET, at around 850-900V B+ and 8-10 kOhm Raa per pair of tubes, setting Vg2 to have the best harmonic content and adding a LDR in series with a 100 Ohm resistor across the screen resistors to limit the signal and avoid that the amp goes into clipping. It should give around 110 Wrms per pair of tubes.
It is a great tube, its drawback is the need of custom transformers and it works with very high voltages.
Hi,
the GU50 ist a russian(improved) Version of the old Luftwaffen (german air force) tube LS50, developed by Telefunken. The opereration of 2 tubes in push-pull without driven in positive grid voltage is the best way of maximum power vs. tube life . As these tube is primarily made for HF/VHF power amps in aircrafts it perform perfect in audio circuits. In the datasheets you will find the term Modulator which was simply a powerful amp to drive the RF final with plate modulation .
So the Suggestion of "Zintolo" is the best way to operate these tube. The screens should held in the 250-300V range at best with stabilized voltage. The TFK datashet say plate load should 11k . max plate supply 1kV.
P wrote here a time ago abaout my 450W power amp with 6x of the GU50. Idrive the grid into posive range. Therefore it is necessary to have enough gain for NFB to reduce the distortion at higher output levels.
but for home hi.fi use the feasible output of 120W rms is more than enough so there is B2 operation really not necessary. The focus shoud be to the opt. It need a lot of good quality iron. I suggest a EI120b or the US equivalent size. C-cores are much better.
73
Wolfgang
the GU50 ist a russian(improved) Version of the old Luftwaffen (german air force) tube LS50, developed by Telefunken. The opereration of 2 tubes in push-pull without driven in positive grid voltage is the best way of maximum power vs. tube life . As these tube is primarily made for HF/VHF power amps in aircrafts it perform perfect in audio circuits. In the datasheets you will find the term Modulator which was simply a powerful amp to drive the RF final with plate modulation .
So the Suggestion of "Zintolo" is the best way to operate these tube. The screens should held in the 250-300V range at best with stabilized voltage. The TFK datashet say plate load should 11k . max plate supply 1kV.
P wrote here a time ago abaout my 450W power amp with 6x of the GU50. Idrive the grid into posive range. Therefore it is necessary to have enough gain for NFB to reduce the distortion at higher output levels.
but for home hi.fi use the feasible output of 120W rms is more than enough so there is B2 operation really not necessary. The focus shoud be to the opt. It need a lot of good quality iron. I suggest a EI120b or the US equivalent size. C-cores are much better.
73
Wolfgang
If you get custom wound transformers please share the job number/manufacturer as you have piqued my interest.
Hi Wolfgang,
my "adventure" in trying to design my own Hi-Fi started with your 450W bass amp with the sextet of GU-50, changing the design to have one single stage after the loop recovery stage, and local feedback on output tubes. It gave me the occasion to annoy alot of very gentle, knowledged and comprehensive users that helped me to find a way in the fog.
I've still not built that specific amp, not an Hi-Fi amp with GU-50 due to the scary B+.
But yes, it is in the list of things I want to try when I'll feel more confortable with 1 kV on the plates.
I forgot to write another trick to squeeze some more power from these tubes: set g3 at around 15V above the cathode.
This will square the knees of the pentode moving the curves up-left.