• 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.

EZ80 or 81

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gr_virgmann

Member
2007-11-10 10:41 am
Hello,

i've built a preamplifier with solid state power supply, but i want to replace it with a vacuum tube one. I have some Philips Miniwatt EZ80s and 81s which are capable of giving 90mA and 100mA respectively. It would be great if you have any tested schematic to upload.

Thanks anyway, Yannis
 
Is the whole preamp solid state, or only the power supply? What kind of transformer do you have on hand? The greatest cost is going to be the power transformer and the filter choke, not the rectifier tube. Identify what supply voltages you need, and how much current is required. If you already know these things, share them with us. Then we'll worry about how to fit an EZ80 into your circuit.
 

gr_virgmann

Member
2007-11-10 10:41 am
Sorry, i forgot to describe it!

each section of the line preamp is built arround an 12AU7 tube and the phono stage around an 12AX7. So we have 2*AU7 and 2*AX7.I'm planning to add an EM80 driven by an 12AX7.

My transformer has two secondaries, one for the filaments an the other which provides 300V @ 100mA.
 

kevinkr

Administrator
Paid Member
I think a separate filament transformer is going to be required as the current tube complement gobbles most of the available filament current, and the additional EM80 and 12AX7A I think takes care of the rest.

A small additional filament transformer evidently will be required - at the low currents involved here even the EZ81 will do the job nicely, although the 6BY5 would probably have an even lower drop.. UF4007 are a cheap and economical choice for the other two diodes and are relatively quiet compared to the garden variety 1N4007.
 
hey-Hey!!!,
100 uF is too much for the input cap( first one the rectifier sees ). Waaaaay to big in fact. On the other, from 300VAC fed to a bridge your maximum will be root2 times that, and add some losses I'd bet on something like 400V. Your 200 mA is also too much DC output for a single 6CA4, perhaps two, with plates in parallel?
cheers,
Douglas
 

bequerel

Member
2003-09-01 8:35 am
hey-Hey!!!,
100 uF is too much for the input cap( first one the rectifier sees ). Waaaaay to big in fact. On the other, from 300VAC fed to a bridge your maximum will be root2 times that, and add some losses I'd bet on something like 400V. Your 200 mA is also too much DC output for a single 6CA4, perhaps two, with plates in parallel?
cheers,
Douglas


The picture and values were only used to illustrate the concept, and not what I will use. I was fishing for a formulae or how to calculate the voltage. You gave me a ballpark way of calulating it. Thanks.:)
 
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