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Edcor transformers have arrived, but really puzzled!

rsumperl

Member
Paid Member
2009-10-16 9:31 pm
Cascade, Idaho
My long awaited (10wks) Edcor 3.3K 100w transformers have arrived however they don't "sound" as good as the 3.3k 50w organ transformers that I tested with. I have 26HU5's in P-P, voltages stayed the same, speakers stayed the same, just swapped transformers. It seems the bass has disappeared. Put the "old" transformer's back and bass has re-appeared. Any clues?????

Thanks
 
I bet its the LF response and the HF roll off of the Organ opts that is throwing you off. The Edcors are likely more balanced than the organ opts, so your ears are hearing greater HF response and less bass response, making them sound bright. Try and live with them for a week and the try the swap again and see if the organ opts sound dark.

Athos
 
How much do the 50W organ OPTs weigh? That's perhaps as good an indicator as any of bass power capability;) The Edcor CXPP don't have a bass response problem per se.

Treble roll-off sound like bass boost. Can you simply measure the frequency response?

michael

Another idea... Maybe the organ OPTs have much higher primary inductance than the Edcors and your output stage has a relatively high plate impedance. What's your NFB scheme and effective plate resistance?
 
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rsumperl

Member
Paid Member
2009-10-16 9:31 pm
Cascade, Idaho
Actually, everything is breadboarded while I do final tweaks. The 26HU5's are fed with 1:3 xfmr. The Eb is 500v, Eg2 is 200v, Ib is 50ma/tube (no signal). The input xfmr is being fed from a PC. If I crank the volume, Ib can peak to 500ma. It is really loud.
I want everything stable before I start cutting holes in a chassis.
The new Edcors probably weigh 2-2.5 times that of the organ xfmr.
 
I have a pair of Edcor CXPP 100W 5K OPTs and I just did a small signal test on one of them. Down to 10Hz I couldn't get a substantial finite primary inductance effect, even with 10K ohms generator impedance. I tested by driving 1/2 the primary coil (1/2 the inductance) to approximate class AB operation.

Based on this, I'd say the 100W Edcor transformer is not likely to be causing bass roll off unless you have a very high driving impedance.