Manfred
If you need any other measurements for comparison let me know.
With that in mind, I reviewed all the usual suspects for manuals Bama,
Ebaman, Elektrotanya and W140, which look to me to be all the same version
with the schematic for the transformer circuit labeled "CRT CIRCUIT" "700
thru 760". I could not get the Manoman copy of the manual.
The voltages on the tubes are fairly well noted.
To help test the transformers out of circuit, the oscillator and feed back
loop, I fixed a 100 Watt PA amp and was driving the transformer primaries
with a resistor for current measurement and short protection. I did not have
a AC probe for 2000V, 30 Khz so I connected a HV diode and capacitor to the
secondary to get a DC voltage.
The PA amp is not rated at the high frequency but has enough power to drive
the transformer in that range. The PA amp has a transformer output so you
can get a floating voltage which makes the primary voltage and current
measurements easier to connect to a scope with a common ground and it has
some options on drive voltage vs current. I think I was on 8 ohms output. I
also looped 10 turns of wire on the core to monitor the V/turn ratios
The 647 has a 4 turn primary with a 2.6V/Turn.
There clearly are some resonate issues with the transformers.
I was able to take the black epoxy transformer up to the arcing voltage with
out worrying about harming something and with a fair amount of control.
Having turned towards computers early in my electronic path during the
period of linear supplies I missed the use of inductors in my work.
So I got somewhat side tracked from my transformer project by looking at
inductors nature using a scope and signal generator/PA amp.
I think I was able to measure inductance and series resistance fairly well
on various inductors
But I did not get to the point to be able to measure loss in the transformer
due to the distributed capacitance or the limits of the core.
It was not clear to me what the measurements could be made on an arcing
transformer that would be valid, or a brown epoxy lossy transformer.
Then more distractions happened.
Having said all that and not having the note on the issue in front of me, I
think the transformer I wound was running a low frequency of about 80% of
the normal frequency before it died in the 647. I attributed that to the
extra capacitance in the winding (with no measurements to back that up) but
I would not say it was getting hot like the brown epoxy transformers but I
was not running a temp test when it died. I think my failure was an arc.
As chuck has mentioned we have a lot of cheep "diamonds" and I just picked
up a few cut off blades with the idea to cut into some 2000's TV
transformers to see if I could see how they were made. When I get dirty
enough that the mess of cutting a transformer open won't mater I will give
that a try.
Three thoughts, keep focused, do you have room for more insulation between
layers that might reduce capacitance? And third you might try cutting C705
to 75% or 50% of it's value to see what the difference in frequency will do?
You could also increase it to see if your losses drop to try to get an idea
of the loss vs freq.
Good luck
John
