100V output

[Leevi]

In the specification of the Philips EL6431 mixer amplifier has been stated
(page 2 in the pdf below) that the load impedance is 84 Ohm at 100V output. How are the different output voltages related
to load impedance? The lower output voltage the lower load impedance? I have not seen this kind of output specification before. The amp is probably from 50's.

http://frank.pocnet.net/instruments/Philips/EL6431/EL6431.pdf

/Leevi

[Shrapnel]

You are talking a PA amp here, so I would presume that it is referring to the the load seen on the 100v PA tap. (the one where all the 100v PA speakers would tie onto with their own transformers.)

I reserve the right to be in error.

[Tiny_Daddy]

I would assume that means the max power output is E squared / 100VRMS = 119 watts. It should say something about this in the owners manual, if you have it.

[PRR]

> max power output is E squared / 100VRMS = 119 watts

E squared / 84 ohms.

Which is indeed 119W. (They mean 83.3333 ohms.)

What you really want to know, today, is: what Ohms to put on what Volts-tap to get near 120 Watts?

V^2/120W = R

So the 10V tap can take 10^2/120 = 100/120 = 0.8333 ohms for 120 Watts.
25V tap supports 5.2 ohms.
35V tap supports 10.2 ohms.

I hope you don't really have one of these. It will be very hard to find EL34 which take 860V reliably. (One of the footnotes suggests drilling the tube base!)

[flocentblack]

....It will be very hard to find EL34 which take 860V reliably. (One of the footnotes suggests drilling the tube base!)

I'm guessing this is to discourage a carbon track from forming on the base between pins 2 and 3 ??

[Tiny_Daddy]

860v, I would use a tube with a top cap such as 6BG6. Such as the ones this guy is selling:
http://www.vacuumtubes.com/6BG6.html

[RicharD]

I did a bunch of experiments with the 6BG6 a couple of years ago.  I concluded that it's an awful tube for hi power audio applications.  They suffer greatly from acoustic coupling + they ring.  With a 100W 8 ohm resistor in lieu if a speaker, I could actually hear my guitar coming from the tubes. 

[Leevi]

25V tap supports 5.2 ohms.
35V tap supports 10.2 ohms.

I hope you don't really have one of these. It will be very hard to find EL34 which take 860V reliably. (One of the footnotes suggests drilling the tube base!)

PRR,

I don't really get what you mean by 860V? Is that I have to have 860V B+ in order to
reach the 120W power with lower taps?

/Leevi

[HotBluePlates]

I don't really get what you mean by 860V? Is that I have to have 860V B+ in order to
reach the 120W power with lower taps?

Page 5 of the file you linked. The Voltage chart specifies 805-860v on the plates of the EL34's at no load. That sags to 660-720v at full-load. Which is still mighty high for some of today's EL34's of questionable pedigree.

[Leevi]

OK, thanks.
The output was set to 10V. I switched it to 25 which increased the power.
I suppose the 35 is then suitable for 8 Ohm speaker.

Some pictures. I have never met so old amp in so good shape-

http://i218.photobucket.com/albums/cc183/kz14100/PhilipsTop.jpg
http://i218.photobucket.com/albums/cc183/kz14100/PhilipsInside.jpg

See the SS-diodes between the cooling plates!
http://i218.photobucket.com/albums/cc183/kz14100/PhilipsRectifier.jpg

/Leevi

[Tiny_Daddy]

Cooling plates huh? Are those selenium? I am thinking: Ground the center tap and replace the bridge with a pair of diodes and forget about the 800+ volts.