On Tue, 23 Nov 2010 18:21:50 +0000, Steve Sousa wrote:

Hello:

I have a tube radio to repair. It's output valve is an ELL80 (two EL95
in one tube) and was broken at the base and the socket showed signs of
overheat and cold solder joints. I have the valve on order but when
checking the output transformers (it has 2) onde of them has a primary
resistance of ~900ohm and the other ~4000 ohm. I measured the turns
ratio using a signal generator at 1khz and got 45,6 and 46,0 which
squared and multiplied by the speakers output impedance (5ohm) gives
~10kohms which is the expected impedance for the ELL80. Given all this
info how can i check which transformer is bad? they both drive an
speaker just fine using the Sig. Gen. but i can't believe they can have
such different dc resistance.

Thank you in advance

Best Regards

Steve Sousa

That's a heck of a difference in DC resistance. If you drive both with a
sig generator and look at the secondaries on a scope is there a big
difference in the signal amplitude between the two? If not I would be
inclined to replace the tube and take some voltages while the circuit is
live while monitoring the plate currents. You can look here for
operational voltages and currents in different classes of operation:

http://www.nj7p.org/Tube4.php?tube=6gu8



--
Live Fast, Die Young and Leave a Pretty Corpse