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In Reply to: RE: gm70 power playing in the lowest freq's posted by used-hifi on January 19, 2017 at 14:23:28
I would look at the inductance value of the output transformer.
In the presence of low frequencies, a lack of sufficient inductance in the primary of the output transformer causes the load line to become very elliptical causing a loss of power and an increase in distortion.
The article linked below explains this.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Follow Ups:
Thanks I will look into the article
I measured the primary with a cheap lcr meter of 20H but i am not sure its measuring this correctly
the output transformer came from a 30watt PP amplifier FULL POWER @ 20 cycles
Now is there any temporary trick i can do to test this theory?
for instance put the other output transformers primary in series with the other transformer to ADD inductance?
Lawrence
Read the link that Tre posted, it will rain on your parade:*). JH
I see your amp is parafeed.I would look at the inductance of the plate choke. The same principles found in the article about output transformer inductance would apply.
BTW PP output transformers don't have a gap in the core so the inductance should be very high.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 01/19/17 01/19/17
Thanks Tre, I did for a test put the gm70 plate choke in series with the other one 100H each to now 200H and no change!
so whats left?
I don't remember seeing a schematic.
What about coupling caps? Are they sized correctly?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
yes I am using experimentally 5uf coupling caps and am using grid chokes of 1.1kH 20kohms dcr
there is no schematic all done up in my head and experimented until i got what i want sound wise and its distortion is .7% @ 3watts 1kc signal
6hv5 is biased at around 30ma 1150v on the plate
gm70 1250v 80ma
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