Paul
Roger all.
Now that you mentioned the scope probes ... to get an accurate view of the waveform I remove the
long scope probe 'hook tip' and use just the remaining short pin as the probe. I also don't use the
wire / aligator clip for ground. I fashion a 2 turn 'spring' from #14 solid wire that slips tightly
over the probe ground 'tube' just back from the pin. One end of the spring has a 1/2 inch
'extension' to make the ground connection. In other words, both scope probe connections are kept as
short as possible. I found this necessary in high power, high current amplifiers ... more so at HF
but to some extent at MF and LF. Assume you're using a 10x probe.
We're running out of straws to grasp at ;~) .
Jay W1VD
----- Original Message -----
From: "N1BUG" <[email protected]>
To: <[email protected]>
Sent: Tuesday, April 10, 2018 3:12 PM
Subject: Re: LF: W1VD amp help - more waveforms
Jay,
The secondary is #14 solid THHN. It is tight to the core only at the
sharp bend areas, that is to say four places per turn at the
"corners" of the core. This was the best of *many* attempts.
Initially I could not move any of the turns. After several cycles of
mounting and dismounting and rewinding the primary, I guess the
insulation has deformed just enough that some turns can now be
nudged around slightly. I should add that when I do nudge them
about, the lower peaks in the ringing change a bit. The first and
highest of them is not affected at all.
Today I wound and tested two more primaries: one with #16 zip cord,
then with #18. It now looks tighter than any pictures of successful
amplifiers I have seen. Peak ringing voltage is perhaps 2 volts
lower than my original transformer. In other words negligible
improvement.
I don't think I can do any better on the transformer unless perhaps
I use something extremely pliable for the secondary, such as very
high strand count wire with silicone insulation.
As a reality check I tried a different (dissimilar) scope probe...
absolutely no difference.
The only things left on the list to try are moving the driver board
to get shorter gate leads and replacing those snubber caps. I will
try both when I can.
Paul
On 04/10/2018 09:17 AM, [email protected] wrote:
Paul
Sangamo is a good brand ... so if they're NOS, and the correct
value, the problem probably lies elsewhere. Is your secondary
winding solid or stranded wire? I find solid #14 THHN better
conforms to the shape of the core. My windings are tight enough that
it's not easy to move them on the core.
Jay W1VD
*----- Original Message -----*
*From:* N1BUG <[email protected] <mailto:[email protected]>>
*Reply-To:* <[email protected]
<mailto:[email protected]>>
*To:* <[email protected]
<mailto:[email protected]>>
*Sent:* 4/10/2018 8:22:15 AM
*Subject:* Re: LF: W1VD amp help - more waveforms
--------------------------------------------------------------------
Jay,
I have no reliable way to measure capacitance. The ones I used
originally were NOS Sangamo caps. The physical dimensions are the
same as I find listed for DM19 caps. Last night I swapped one out
for a CDE of same length and height but thicker. Zero measurable
change in ringing. I put squares of thin shim stock under the
grounded lead of each snubber resistor so that now lead length is
basically zero. Absolutely no measurable change in ringing.
I was just curious whether the fact that changing cap values has an
affect might point us toward something we're somehow missing.
I will find some of the Russian mica caps for a try at some point.
Meanwhile I'll find some smaller lamp cord and try once more. To be
honest I'm not at all convinced my secondary winding is tight enough
either. In places it can be manipulated a bit while the amp is
operating at low power. Doing so makes an easily observable change
in the ringing. If there is a technique for getting that first
winding any tighter, it's one I haven't yet learned!
Paul
On 04/10/2018 06:25 AM, [email protected]
<mailto:[email protected]> wrote:
> Paul
>
> Okay on 78 material.
>
> Wonder if you measured your snubber caps? Notice they're maroon
> color which would indicate they're old ... possibly used or an off
> brand? All new CDE mica caps have been yellow in color for some
> time. Can't tell from the pix ... are they really DM19 size? The
> russian blue glass mica's that Chris mentioned (same as I
used) are
> excellent. I've used these in applications where other 'lesser'
> mica's were pushed beyond their limits. Will check to see if I
have
> a couple extra. Don't be in a hurry to start changing values
since a
> number of these amps have been built 'to spec' with the no ringing
> problem. There's something in your amplifier / system thats
causing
> the anomoly.
>
> Did you try using a wider connection to ground on the snubber
> resistor? Grab some zip cord off a little used lamp ... it will be
> fine for 'low power' testing. It will wind tight aagainst the
core.
>
> Jay W1VD
>
>
>
>
>
> *----- Original Message -----*
> *From:* N1BUG <[email protected] <mailto:[email protected]>
<mailto:[email protected] <mailto:[email protected]>>>
> *Reply-To:* <[email protected]
<mailto:[email protected]>
> <mailto:[email protected]
<mailto:[email protected]>>>
> *To:* <[email protected]
<mailto:[email protected]>
> <mailto:[email protected]
<mailto:[email protected]>>>
> *Sent:* 4/9/2018 9:37:37 PM
> *Subject:* Re: LF: W1VD amp help - more waveforms
>
--------------------------------------------------------------------
> The core is 78 material.
>
> I tried again with different wire. The winding is somewhat tighter
> on the core but definitely not what I was hoping for. Clearly I am
> not bringing required skills to the table on constructing this.
>
> Drain waveforms became somewhat asymmetrical with one phase
having a
> somewhat different shape from the other but peak voltage was
> similar... 65V on one side, 63V on the other with 13VDC supply.
>
> I'm sure this was a bad idea but out of curiosity I tried adding
> another 500 pf in parallel with the 1500 pf snubber cap on one
side
> only. Power output and efficiency did not change but peak
voltage on
> that side dropped a couple of volts. I then increased that
side to a
> total of 3000 pf. Power output and efficiency has still not
changed
> at all but peak voltage on that side is down to 50V and it stops
> ringing significantly sooner than the other side. Does this
suggest
> anything other than insanity of the builder?
>
> Paul
>
>
>
> On 04/09/2018 05:29 PM, [email protected]
<mailto:[email protected]>
> <mailto:[email protected] <mailto:[email protected]>>
wrote:
> > Paul
> >
> > Maybe try some 14 or 16 gauge lamp cord ... it's pretty
> pliable and can be wound tight against the
> > core. That's what I used in the 500 watt deck. Put a piece of
> wet paper towel around the insulation
> > when soldering to prevent 'melt back'.
> >
> > Is your core 77 or 78 material?
> >
> > On your driver board ... are there reasonably wide traces ...
> especially from the 12 volt power
> > supply to the IR2110? Peak currents can be high driving the
> gate C. Is the 12 volt supply reasonably
> > stout?
> >
> > Jay W1VD
>
--
Paul
N1BUG 160m-2m DXCC Honor Roll
WI2XTC 2200m-630m Experimental license
FN55mf ME Piscataquis County
http://www.n1bug.com
http://www.aurorasentry.com
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