EZ80 or 81

[gr_virgmann]

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

[Ty_Bower]

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]

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.

[gr_virgmann]

Each channel draws 20+2=22*2=44 mA and about 5 mA the magic eye with the 12AX7 driver, we have 50 milliampers total current.

[kevinkr]

300V single secondary sounds like a job for hybrid (Graetz) bridge.

How much current capability on the filament winding?

[Eli Duttman]

Originally posted by kevinkr
300V single secondary sounds like a job for hybrid (Graetz) bridge.

How much current capability on the filament winding?

Kevin,

Are you thinking of a 6BY5 combined with 2X quiet SS diodes? The forward drop in dampers tends to be small.

[gr_virgmann]

The filament winding is capable of 2 amperes at 6 volts...I use the parallel filament connection on the triodes.

[kevinkr]

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.

[Bandersnatch]

hey-Hey!!!,
At those currents the EZ81/6CA4 is a very low drop pair of diodes. Combined with a pair of 600V SiC Schottky types would be my first choice, followed closely by a whole bridge of the SiC diodes; they're very nice and a step above the PN junction types.
cheers,
Douglas

[bequerel]

Gentlemen,
Will the hybrid bridge in the picture give me 300-0-300V if I have a single secondary 300V/200mA transformer, or will it give 150-0-150V? And will I still have 200mA available before CLC filter drop?