New guy intro, looking for scavenged parts for guitar amp

a fine line between stupid and clever

Postby ddr » Thu Dec 31, 2009 9:26 am

I have not been able to find specs on the Sovtek 5Y3GT, but I find lots of posts saying that the voltage drop is only 10V, where the 5Y3GT spec here http://www.kbapps.com/audio/tubespecs/5y3gtp49.html lists 60V at 125 mA.

Have a good one,
Dan
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Postby TomMcNally » Thu Dec 31, 2009 10:20 am

The 60 volt drop at 125 ma is maximum ... that little tube would
so hot the glass would be melted before you have to worry about
that !
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Postby ddr » Thu Dec 31, 2009 10:56 am

Thanks, I did not realize that the drop is gradual. Here is my dilemma, the 5E1 layout has voltage readings that show 320VDC coming off of pin 8 of the 5Y3GT. From what I have read the way to get here is:

((Output of PT) X 1.4) - (Voltage drop of rectifier)

My Weber PT ( https://taweber.powweb.com/store/022772sch.jpg ) has a 600V secondary with a 300V center tap, so:

300 * 1.4 = 420Isn't this too high for a 6V6?

So, this makes the question, should I have gotten a PT with a 500V secondary?
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Postby EWBrown » Thu Dec 31, 2009 2:13 pm

That trannie sounds about right, the original 5E1 and similar circuits used 325-0-325 @ 70 mA, 5V @ 2A and 6.3V @ 2 or 3A. The Triode Electronics replacement trannie has the same ratings

The ideal SE 6V6 package si one of these power trannies, a 4H, 90 mA choke and teh TF-103-48 5K UL SE OPT with 4 and 8 ohm secondary. Any 5K to 4 or 8 ohms will work just as well.

The 300VACX 1.4 = 420VDC would be for an unloaded PSU, once the tubes start drawing current, the voltage will go lower. Between the 6V6 and the 12AX7, it is going to draw around 50 mA and betwen the choke and a series resistor, the B+ can be brought down to desired voltage levels.

If your power trannie has 3A available on the 5VAC winding, then a 5U4GB or 5R4 could be used, these have more forward voltage drop. They're raller and "fatter" so they'll need more space. They haev the same generic "2, 4, 6, 8" pinout as the 5Y3GT, so they are readily interchangeable.

In any case these vintage amps never really ran at 325V, I've seen them between 350 and 380V. 6V6s are pretty tough tubes, and from what I've read the J/J ones are especially hardy, almost a slimmed down 6L6.

HTH

Happy New Year

/ed B
Real Radios Glow in the Dark
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