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    Building, troubleshooting and testing of these amplifiers should only be
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    the safety precautions around high voltages.

GU-81m tube amp schematics???

Hello,
Anyone have schematics for gU-81M?I have some tubes with sockets and i like to use them.I don't care if it will be hybrid or to drive it with a solid state amp to not use a lot of tubes.Just something simple to hear some watts of music from this tubes.I dont have experience with tube amps.But have the experiencfe with the high killing voltages from other projects.
Any help please?

Thank you
George
 
Haven't found anything but a description (in Dutch) of a bloke who built an amplifier and considered using this tube, but settled for the smaller TB2.5-300.
Fishbowl TB3 Amp - Experimenten
Apparently, he used a SE parafeed design, but it's unclear what he used for a plate load. I suppose that will be the biggest challenge in any case: finding a plate load that will handle that sort of power. Maybe a push-pull design with a ginormous center-tapped power transformer acting as OPT is more realistic. Frequency response will probably horrible, but you might get some sound without mortgaging the house for the proper parts. With any kind of luck, the low frequency response will be halfway decent and you might be able to use the amp to drive a subwoofer.

However, it's going to be a challenging project in any case. You'll need >130W of heating power, anode voltage somewhere north of 1kV @ > 100mA per tube for PP (say, 200mA for SE), and to drive the gU's you'll need something like a single ended EL84 at the very least (a beefy mosfet could be used as well). -Vg of 100 to 150V, Vg2 of 500 or 600V @ 50 or 100mA.

It's one of those projects for which a schematic can be drawn up in 15 mins, but that'll take 2 years to complete.
 
Just give me a schematic to start!!I'm horrible to this part!!
I prefer to drive the tube with a mosfet.I know that will not be a good amp in the ears.But will be a good to the eye and "i have done that!!!" amplifier.
Thats the reason i want a design with less tubes and more solid state.

Any help accepted please for the little monster!!
 
Just give me a schematic to start!!I'm horrible to this part!!
I prefer to drive the tube with a mosfet.I know that will not be a good amp in the ears.But will be a good to the eye and "i have done that!!!" amplifier.
Thats the reason i want a design with less tubes and more solid state.

Any help accepted please for the little monster!!

Just forget the GU81M tube for Audio aplication !

Generaly this big RF power tube live is relative short ,common failure is usual break of extreme tiny DC heated thoriated tungsten kathodes wire .They live for around 1000 Hrs,and thats tube live expectancy is signed in the factory specs to.

BTW this GU81M tube power capacity is aproximately like 2 x 813 tube in the parallel,but 813 tube(GU13) is the right one, for AF or RF aplication !

Best Regards
 
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giorgos - A dynamic coupled mosfet as you described would work but a Gainclone and grid-drive transformer would probably be simpler to design.

A simple TDA2030 amplifier connected to the secondary of a 230VAC:24VAC-36VAC toroidal should work. One end of the primary would be connected to the grid while the other goes to the bias supply.

If you are insistent about using a dynamic coupled mosfet, the tubelab powerdrive might be something to look into...

I don't mean to question your expertise but are you sure you're experienced enough to play with high B+ voltages? A large tube like the GU-81 will require +1kv to get any decent power/performance...
 
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hey-Hey!!!,
Since you want to do it...get a big 5k a-a, U-L output trans and build a B+ of ~700V. Idle at 250-275 mA for Class A. That is a nearly 2/3 of an amp per channel...:) We'll build the phase splitter out of resistive loaded 7355's( or perhaps 7591's ) in LTP riding a good sized CCS.

Maybe we can work together on an output trans design...and I can build this for myself.
cheers,
Douglas
 
There aren't too many SE OPTs that will handle 275mA... Cheapest one that comes to mind is the hammond 1642SE. IIRC it's sells for about $300-350 and it weighs 28lbs...

I think CCS or gyrator loaded parafeed would be more realistic...
 
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If you take a look at the OPT spec it says '5k a-a'. That's a PP topology. Now did I miss that he wants SE? I suppose it is possible...:yawn: Now he did mention willingness to use this beastie in order to achieve large power output. SE is *NOT* the way to that end; in this case we wish to be as efficient with OPT size as it possible( well actually about 3x past what is even theoretically possible I think )...again, not the case with SE.
cheers,
Douglas
 
Wow!!!A lot of answers a lot of different projects.I confused a little!!

db! i have the experience with the lethal B+ voltages from radio amateur transmitters. :)
I can make here good quality output trans with a friend that he have a shop that makes transformers.Thats not my problem or the size of the trans.
It's not my willingness for high power output.Just something simple to build with not too mucu tubes.It will not be cheap and will not be simple.especially with those B+ voltages.
 
giorgos - Do you have any preferences for a specific topology(PP, SE, parafeed, OTL)? Also, I'm a bit confused as to your main goal; are you going for power, performance, uniqueness, etc?

Another thing you need to realize is that OPTs for such an amplifier are not trivial; more than often, complex OPT geometries are required to obtain good performance. Fabrication of the OPT will be easy compared to the design process...

I strongly recommend you consider parafeed as an alternative to SE or PP.
 
A russian diy made GU80 SE triode mode, Alexander Rezvoi (nic- Rezvoy). With Ua = 1100 V, Ia = 380 mA, Ug1 =- 270 he got 80 watts of nominal power.
The quality of the sound he liked.


another diy, Sergey Z (nic- Сергей Z), making the SE triode mode, using half of the cathode.
Mode : Ua - 820 v, I - 190 mA, Ug - -166 v, 25W. Used cathode pin 1 and 5.
heating - 6.1 V.

ÃÓ81, ÃÓ80, ÃÓ81Ì. - Ôîðóìû ÀÓÄÈÎ ÏÎÐÒÀË
 
according to your answers,i think that SE will be better and easier(is this right?).My main goal is a working prototype.Output power is not a target.Just to listen music in a small room.I have the tubes and i want to use them with an amplifier.They are huge tubes and i will like to use them as an audio amp.I have a lot of some big caps from the transmitters and a friend with a store that can make me handcraft transformers and chokes.
Thanks for the answers and that you working on my needs!!!
 
I can make here good quality output trans with a friend that he have a shop that makes transformers.Thats not my problem or the size of the trans.
.

hey-Hey!!!,
I think you'll find that a suitable SE output TX for 80-100W will be so big it won't do well. Bigger ultimately means higher power but at that size the 1-10Watt output level will suffer a great deal.

As to SE easier than PP I must disagree with you there. Also, since the OPT can be smaller you can get more good power from what ever size you settle on. PP is actually quite easy. I assume that you'll stay Class A in all designs; there is no need to try for a 6-700W AB amp you'd be able to do with a single pair of tubes. Say something around 250W should be indistinguishable from 350W...and easier to support with a good OPT.
cheers,
Douglas
 
Then I would suggest you only run the heaters of the GU-81s for show, and hide a couple of EL84s under the chassis to take care of driving your speakers ;)

Kenneth

:eek::eek::eek::eek::eek:
I dont know if i can make you understand because of my poor english.
I want to make the project for me.I have the gu-81's sitting in the self some years complete with the sockets.I want to make something simple and as i can economical.I know that with this type of tubes it will not economic and will be BIG.But when i say BIG i dont say the output power but the size of the transformers the coils and the chokes.I will be happy with 15 watts.They will drive my scan-speak speakers well.
I know that this is crazy fro most of you and this tube is not good for performance amplifier.
 
In this case, ground g3 and the anode and run the tubes as triodes with g2 as the anode. You'll still have a 120W dissipation element to use as the plate in that implementation. Should make a nice PP Class A triode amp. In this case it should not take too expensive an OPT to deliver a very nice amp indeed. You'll get a plate resistance( and mu ) like a 2A3's so 5k a-a will do quite well...so will 6k6 kOhm plate-to-plate...:)
cheers,
Douglas