info on old telefunkin tube power amp

[donald stringer]

could you explain just a bit more about the b+ voltage. What are screen taps?

[sean k]

Like I said at the top it'd be worth your while reading the articles at Audioexprees by Norman H Crowhurst as well as the basics of Tube amps at AX84.com.

Umm, Its been a while but the screen is held to a positive potential just under that of the plate to help get those electrons to the plate but it is a screen so the electrons can pass through. On voltage amps, or preamps, (when a pentode is used)the screen usually has a cap to ground as well which helps to just keep it at a DC potential. So screen taps and suchlike are there, in various ways to aid the electrons getting to the plate while also offering a little feedback but thats where my understanding stops.
http://www.tubecad.com/january2000/page3.html

Why not do as Pete suggests and essetially keep the stages you have as they are, either in the same chassis or on a new one, and then just build a preamp with a single dual triode tube to get the signal up to line level to feed your two amps?

I think that theres a certain amount you're going to have to learn to do this properly so it work well and thats a mixture of electronic and mechanical because tubes are electronic devices but their nature demands certain mechanical ideals to implement properly. Simply put is that if you're going to do this it'll set you on a path thats quite consuming so you may as well do it right.

So read all the stuff until your head hurts then let it go for a while and then realsie what you have.

[donald stringer]

I think the transformer is bad, I only get 104 volts on pin 7 of the el84. On the four poinst at the bottom right of the schematic showing what I should be getting out of the trans. they connect to the bias point and the four outs I get around 124 volts. This isnt going to be as cut and dry as I thought. At one time The tubes were glowing. At the speaker connections I get wall voltage is that normal?

[Dan N]

I think the transformer is bad, I only get 104 volts on pin 7 of the el84. On the four poinst at the bottom right of the schematic showing what I should be getting out of the trans. they connect to the bias point and the four outs I get around 124 volts. This isnt going to be as cut and dry as I thought. At one time The tubes were glowing. At the speaker connections I get wall voltage is that normal?

You're kind of scaring me. House voltage on the speaker outs is bad. Are you 100% sure you have the power connected right?

Pull the tubes. I hate to say it, but if those are Telefunken EL84's, they are (were?) probably worth some dough. Some people like those Amperex ECC83's too.

It's kind of a pity that you were able to find that schematic so fast. It's a good learning experience to trace out stuff on paper before going nuts and plugging it in.

And, before trashing your PT, test the AC on the secondary. If O.K., test downstream from there.

[donald stringer]

This is  the original power cord, it was never disconnected. I never thought it sounded right. As a matter of fact nothing has been altered. What would do that.

[donald stringer]

 First I want to thank everyone for answering my questions. I was a little let down when this thing ended up going downstream, but upon further inspection into those old dry brittle wires there were some shorting out on some sharp metal corners. The bright side is I think the trans isnt bad, those tubes are original and I have a schem. I am taking the ots out cleaning up there wires, power trans.and doing the same,making an chassis and come back at this thing after having acquiered a tad bit more knowledge, and making a dynamite little power amp with some over the top art work.......First I want to do some kinda gain clone chip amp project for that I already have a chassis and trans waiting for an rect. Those things are fascinating, how much sound you can get out of one little piece of silicon.

[sean k]

Yup, you've just passed the first hump...letting the initial excitement die down and go to contemplation. Congratulations