Re: LF: W1VD amp help - more waveforms

["Alan Melia" <alan.melia@btinternet.com>]

Paul, Chris, Jay et al
Just a wild thought....Jays LPF is not inside the PA box. The filter is 
giving a frequency dependent load on the PA. Could it be possible that some 
reflected impedance is exagerating the ringing. As Andy said unwanted 
resonance somewhere. For accurate efficiency measurement you need to know 
what you are actually measuring but from the stability point of view the 
filter is not necessary. Is it possible (and worth trying) taking the filter 
out of circuit and putting the transformer straight into the load ??  Then 
see if the ringing is more controlled??
I honestly cant see why the driver would affect this. As far as I can see 
there is no sign of a ring on the gate waveform. As it goes off it drops 
straight to ground, starting before the other phase switches on. My naive 
though is that the filter may not be damping the ring but the wide band load 
might. Filters need treating with care theycan behave oddly when not 
terminated with resistive loads. Then there is the coupling that might be 
occuring inside the case.
Probably rubbish but I think its an angle we have not considered yet. :-))

Alan
G3NYK

----- Original Message ----- 
From: "Chris Wilson" <dead.fets@gmail.com>
To: "N1BUG" <rsgb_lf_group@blacksheep.org>
Sent: Thursday, April 12, 2018 7:19 PM
Subject: Re: LF: W1VD amp help - more waveforms


> Hello Paul,
>
> I  am looking at your photo of the LPF. The specs say L1 and L3 should
> have  52  turns,  and  L2, the centre one, should have 73 turns. i was
> unable to get 73 turns on the toroid without winding on top of a lower
> layer,  and  insulated  with  Kaptan tape. This made the overall depth
> quite  a  bit  deeper  than  L1 and L3. In the photo it looks like the
> centre  toroid  overall is no deeper than the end ones, and the amount
> of bolt thread protruding *LOOKS* the same as the end ones. Your build
> is so painstakingly neat though, it may be that you have aesthetically
> made all the toroids look identical.
>
> http://www.chriswilson.tv/paul-lpf.jpg
>
> Thursday, April 12, 2018, 5:42:13 PM, you wrote:
>
> > Jay,
> > When the package arrives I will swap out the caps and the IR2110. If
> > that doesn't do it I will order a new 74F74 and swap out the
> > resistors. If all of that fails I don't see anything else I can do.
> > Realistically at my level of expertise if it doesn't work at that
> > point I will have reached the end of the road. :-(
> > The caps I have are KEMET part # R82EC1100Z350J
> > Here is a link to the datasheet:
> > https://www.mouser.com/datasheet/2/212/KEM_F3101_R82-1103738.pdf
> > Paul
>
>
>
>
> --
> Best regards,
> Chris                            mailto:dead.fets@gmail.com