• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

My First Amp

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Hello Alejo, Hello Kavermei
Thanks for your interest, but don't worry, I am an undergraduate in Phisics and a TV Repair Man, every day I work with 25KV and I know the risk, I had been "footed" by 25KV a few times (From the TV tube changing FBT, AC source disconected, I am not so fool!!!) and believe me, is painfool!!! Errors like this is the proof that I am human, nevertheless I became more and more cautious. But what about the circuit???
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Hi again
Is my own design, I plan to make a PCB (Epoxi of course!) I had calculated clearence between tracks, very high at 900V 7.64mm, if not there will be fireworks.
I am working in an upgrade with an EL34 as Cathode Follower to kill Miller of 845 and class A1/A2 operation, I have some problems here with heat, I hate metal resistors but I hate more Transformers, I have all the Math, even I hate them and I want only one in the output.
Transformers may be big and heavy but they're sometimes the best way to get the job done. They were put out of style originally because of their expense- and somehow the idea of them causing an expensive amp became the idea that they are just bad components. They are difficult to design- often resulting in a custom transformer to fit a particular application- but I don't know of a better way to couple the output of a class A stage to the output impedance of a typical loudspeaker.

Your amp looks like a good design- mu-followers, well-bypassed cathodes, fixed-bias on the final. Should be a good one- good luck and have fun building!
Hello kruesi
Many thanks for your concepts, for best clarity, I hate transformers, calculations are the easy part, I live in the end of the world and is very dificult to obtain good materials such as GOSS, only E-I are available and the problem is the direction of the Magnetic Field don't follow all the way (In coincidence with the orientation of the grain) in E, and it is necesary a double C Core.
Impossible to obtain in Argentina!
I agree with You only in the case of an Output Transformer because Valves are High Impedance Devises and Loudspeakers Low Impedance, but interstage only add nonlinearity because the inherent hysteresis of ferromagnetic materials.
Best Regards
Hello All
This is my first Amp ind I need your help and opinion about it
What do You Think?

Best regards from Argentina:cheers:

Everyone always wants to build their last amp first. Build something small first. Maybe a single ended amp based on the 6V6 tube running at about 300V B+ It will be a lot less expensive. Find a design with a parts count of about 1/2 to 1/3 the schematic you posted.

900 volts is not easy to work with, first off where are you going to buy wire? Wire is typically rated at either 300v or 600V. You'd be looking a 1KV rated hookup wire. And then the transformes and choke(s) will need to be made of 1KV wire too, mst of them are not rated so high. Even little parts like standby switch that are rated for 1KV are not common parts. Resistors too. Many common resistors have lower voltage specs so you have to use two or three in series.

The power suply is not shown on the schematic. Watch out that the 900V can NOT get into the 600V part even when the amp first starts up and before the tubes conduct. You will blow up those 450V caps. Think about what happens if a tube fails, can it start a chain reaction?

Finally if you need that much power build a push-pull amp. But I bet you don't need it, just get better speakers
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Hello All
This is my first Amp ind I need your help and opinion about it
What do You Think?

Looks like a schematic straight out of Elector Electronics. Did the article offer any tips and tricks for builders?

Two SRPP stages followed by an 845. Not exactly earth shatteringly different than anything else. I'm sure you could turn it into a project by experimenting with different driver stages, but there's probably not anything wrong with the circuit as designed.

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I Love Elektor since '80 but the schematics was made for myself with Tango Pcb, DOS Program, the Bests for me, I can Do everything, Schematics with custom libraries, PCB´s, House Plans... the Amp is more like the Smart 845, but with other Valves, and fixed Bias.
I will do an upgrade with an EL34 as cathode follower between the ECC99 and the 845. I promise the power supply after it works.
Cheers from Argentina
I know the risk, I had been "footed" by 25KV a few times
If it has happened more than once, then I suggest you don't know the risk!

900V from an HT supply could be much more dangerous than 25kV on a CRT, because the stored energy is much greater. As a physics student you should know about 1/2 C V^2 - you do the maths! You might only get one opportunity to touch a 900V rail, so remember to say goodbye to your family before each time you work on the amplifier.
Joined 2009
Paid Member
Popilin, you've received some excellent advice here. I'll second (or perhaps third) the suggestion given previously: build something more along the lines of a "beginner's" amp. In fact, build several!

This has its advantages. First, you'll have the opportunity to develop good safety habits. Second, you'll gain even more insight into the inner workings of these "tubey beasts". And finally, when you do get to build your "super-colossal 4X4 car-crushing 845 behemoth", you'll have several other amps to compare it to.

DF96 speaks the absolute truth. Not to sound unkind here, but a 900 VDC rail doesn't give any more of a flying d**n about your Physics background than it gives about my Engineering degree. I've been pootling about with this stuff for about 10 years now, and the standard 450V or so in the average Williamson-style amp still gives me the "heebie-jeebies!" :eek:

UTMOST RESPECT for electricity is the order of the day.

One final note: No matter what path you choose, I suggest you at least read Tubelab's excellent writeup on electrical safety.
Many thanks for Your advice, I Know the risk, I agree with all, but think a litle, 450V with 1000uF give aprox 100Joule, is the same than 900V with 250uF, 25KV in a CRT at say 1nF give 0.3Joule and can´t kill you and I can write this just now!!!. Energy can kill us!!! You will Die with the AC Mains above a 30mA discharge (I have 220 V AC in my country) mere 6.6Watt, so fragile We are!
You tell me as a stupid, and I suppose I am not.
I am not a kid playing with electricity... well, I am a man playing with electrons, electrons in a 845 are "bigger" than in a 6V6, that´s the reason I prefer them ("Medium" Energy Phisics) LOL.
But, again, What About the Amp?????
If anybody help me I promise a wonderfull Power Supply, +B, Filaments, etc. Low noisse, low heat, easy to build.
Best Regards
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Hello kavermei
Yes, by the moment I am still alive.
For the Forum happiness I will isolate very carefuly all +B pins in the PCB and I will work with a hand in my pocket, but is a pain in the ... When I repair a TV I need 3 hands!!!
Again, What About the Amp???
In all this time I learn more in the Wiki than in the Forum
What for is this?
Are there any "Valve Expert" or You are all "Paramedics" ???
I have many doubts with my design, perhaps, Is the final SRPP capable to give 240V peak to peak?
I haven´t "Tube CAD" neither a scope, I have a pair of multimeters and calculators, so I need:
1)Money (forget it)
2)More Knowledge (the info is poor and confuse, Engineers thinks a Valve is a prehistoric and useless device, Physicists only have concern over electrons in terms of its Relativistic or Quantum Properties)
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