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Old 17th November 2008, 09:09 PM   #1
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Default Small beginner amplifier and hello :)

Hi all

This will be my first step into homebuild amplifiers of the kind for sound, my most beloved hobby is high voltage and tesla coils etc

I have just finished building a VTTC, which is a vacuum tube tesla coil and its basicly a RF transmitter that just sparks instead.

So I dug out some old stuff I got from a 1950s TV set or so, there are some common tubes that I have seen threads onhere with and I will try to recap what I have got.


Power transformer 230V mains, 50V/6.3V filament outputs.

Output transformer 400R/6R5 ohm values, its about 7x6cm iron core.

4x EF80 tubes

2x PCL 82 or 82 tubes, text is missing so hard to tell (can I have two pcl83 but they have different interior? shields is different etc)
But looking at datasheets they dont seem to be different but for 5mA cathode current values.

1x UCL 82 tube

So what have I learned tonight

EF80 can be used in a preamp, 2xPLC83 in a PP or 1x UCL82 in a SE PA.

I looked at this circuit : http://www.audiofanatic.it/Schemi/Ti...ECL82_SE_3.jpg

my UCL82 tube is just voltage heated instead of current for the ECL82, or did I miss something else than that.

Can I recalculate for my OPT values, or is it too low values for this use?

Should I leave out tone control? I was told that it only adds trouble.

Would I need a preamp for this circuit, and if so, any sugestions for one using ef80 tubes.

Kind regards
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Old 17th November 2008, 10:08 PM   #2
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So mads, u have found yer way here also
Welcome to diyaudio! Enjoy your stay.
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Old 17th November 2008, 11:47 PM   #3
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Mads,

The EF80 is a good audio pentode. Put the 4 pieces away for a future project. For instance, the EF80 will make a fine 2nd gain block in a phono preamp. Looks like you have 2 sets to go into that build.

Except for heater voltage/current draw, the 6BM8/ECL82, the 16BM8/PCL82, and the UCL82 are identical. The schematic you linked shows a wretched 1/2 wave rectified PSU and tone controls. IMO you should look for something better. It just so happens that I'm involved in a 6BM8 project. Look here.

BTW, did you get the power trafo winding voltages right? I'd expect to find something in the range of 300 V. for the B+ rail.
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Old 17th November 2008, 11:51 PM   #4
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Default leave out the tone!

and no - it shouldn't need a pre if you are using a CD or similar as a source. THe power transformer will be fine, the output transformers will need to be around 8k on the primary - get some real cheap ones or recover from another old TV or stereo
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Old 18th November 2008, 11:58 AM   #5
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Hey - Hi!

Odd, you've just been answering a question of mine on 4hv!

Welcome to the world of diyaudio!

Cheers
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Old 18th November 2008, 03:33 PM   #6
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Quote:
Originally posted by Eli Duttman
Mads,

The EF80 is a good audio pentode. Put the 4 pieces away for a future project. For instance, the EF80 will make a fine 2nd gain block in a phono preamp. Looks like you have 2 sets to go into that build.

Except for heater voltage/current draw, the 6BM8/ECL82, the 16BM8/PCL82, and the UCL82 are identical. The schematic you linked shows a wretched 1/2 wave rectified PSU and tone controls. IMO you should look for something better. It just so happens that I'm involved in a 6BM8 project. Look here.

BTW, did you get the power trafo winding voltages right? I'd expect to find something in the range of 300 V. for the B+ rail.
I chose the schematics I posted over the mullard one as I didnt have a rectifier tube fit for it, I guess it can just be replaced with normal diodes but im not sure what effects that would have.

You wrote that you used another schematic based on the mullard one, do you have this online?

I did mix up some wires on the power transformer, I put mains on the HV out, thats why it didnt look strange at first till there was a supply missing

Got my 6.3V+, 50V and 285V now.

Is the schematic I posted really that bad? also, is there anyway to use the original OPT, it was used once so even if its bad, it should be able to be used again.

I already got 3 major high voltage projects that drain enough money as it is, this was just something I wanted to do because I never tried it and had the stuff lying around
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Old 18th November 2008, 03:33 PM   #7
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I just did a simple calculations on my OPT according to this site: http://www.radioremembered.org/outimp.htm



At 200VAC on the primary I get 5VAC on the secondary,

So I got a 40:1 ratio, impedance ratio is roughly the ratio squared, so its 1600:1.

So with a 2 Ohm speaker load its around 3200 Ohm

The load impedance of the UCL82 tube is 3100 Ohm, so its seems that roughly a 2 Ohm speaker would work with my original OPT.
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Old 18th November 2008, 06:09 PM   #8
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Im starting to dislike the missing edit button

I only got a 8ohm speaker, would it work to parallel it with a 2R7 resistor for a total of 2ohm, or is this just nogo in audio business?

Forgive me for not knowing much, but in high voltage hobby we just push things till they burn
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Old 19th November 2008, 12:36 AM   #9
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Yeah the Power Supply really is that bad ,how about tweaking it with an isolation transformer (Easily available), a full wave bridge, A choke and a separate filiment TX?
The configuration for your mains directly rectify wall current.....The triple 'D'...Down, Dirty, Dangerous. Here in this forum we vehemently discourage Power Supplies of this configuration as it is very dangerous & lethal in this set-up.........
How about this??
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Old 19th November 2008, 12:42 AM   #10
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These are simple designs and probably sound a lot better.

-David

http://www.diyaudio.com/forums/showt...15#post1632415
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