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O'kay I got a nice old trans from an EL 84 amp. It reads 130v 160ma on the sec.. 117/100/0 on the primary. I measure 7.5ohm across the primary and 3 ohm across the secondary. It has a 6v leg on the sec and a 6.3v leg. It also has a 6v leg on the pri tied to the 6v leg on the sec with a wire to both ends. On the pri. there is a tab E also. So source impedance. SI = pri dcr x turns ratio^2 + sec DCR from Damir's formula. 7.5 ohm * ( Ns/Np) + 3 ohm 7.5 ohm * (130/117) +3= 12.26 Is that the figure we use on the trans in PSUD? Thanks Guys.
You forgot to write ^2, but you compute it well Rtr = 7,5*(130/117)^2 + 3 = 12,26 Ohms It isn`t "mine", but it is well known formula...you have it elsewere, in some tube rectifiers data, for example. The problem is - only 130V of sec. voltage means max. 130*1,4=182V (probably less in practice) - too low...except by using voltage doubler?! Is it 130-0-130V or just 0-130V secondary? And another thing I didn`t quite understand from your description: "It also has a 6v leg on the pri tied to the 6v leg on the sec with a wire to both ends. On the pri. there is a tab E also." Is it some form of "boost/buck" voltage, or...? Any chance that you can post a picture/diagram or a better description?
I had a problem with that voltage also; and the trans weighs about 5 lbs. But this comes out of a Lafayette reciever so it may have used a voltage doubler. Here's a better description. The primary side has 7 tabs. Looking from left to right they are marked E 6V 2.3A( This one is connected across the trans to the other secondary) 6v.6a tab. 117v/100v/0v Tabs 4&5&6 The last tab is blank; no writing. On the sec side; 6 tabs; starting from left to right; 6.3v 2.7a Tab 1&2 6v .6A tab 3 and 4 130V DC .16A tabs 5&6
I don`t know - besides paper holder, this PT probably can have other useful functions...like auxiliary PT in big amp, filaments + negative DC voltage (bias and/or neg. supply for CC sink)...
It came out of a Lafayette LR 300. I know nothing of this unit except rumor and rumor says the PT was sourced from Thorardsen. The three reviews I could find of this amp were very complimentary; not that that means much. I may send for the service manual; Tannenbuam has it. I know it used 12ax7's in the pre-amp and 6bq5's in the power stage and 6au7 as phase splitter.
Manualblock, Lafayette LA-215 schematic shows PT with a very similar winding to what you mention: 6.3V 2.7A 6.3V 2.3A 6.3V 0.3A 130V DC 0.16A 130V winding did use doubler and fed 255V DC to EL84 single ended output stage amongst many other things (seems fairly common to Lafayette design). Perhaps LR300 was single ended EL84 also?
Much Thanks AKI; that may be the case. There is some mention on the net about that EL 84 SE Lafayette circuits. Let me examine the chassis a little more; thanks.