Hi Marco,

73, Stefan

Am 03.06.2017 16:02, schrieb [email protected]:

Hi Alan, Andy, Chris,

I replaced the caps in the output LC with WIMA FKP1, the 2 caps wich
replaces the missing half of the bridge are still Cornell Dubillier
940C serie (rated at 9A @100kHz), so now all the caps are pulse rated
but...
I regret to admit it, nothing changed :-((
Power out increases from 10 to 30Vdc and at 40Vdc after a first pulse
the power slowly decreases till a couple of watts..

Just to check another thing: being the coil of the guard circuit
disconnected, I jointed the 2 coils together (they are wound on the
same support) increasing so the inductance of the L (25T more). Of
course I had to retune and now I need C in the range of 5000pF but this
narrowed the 3dB bandwidth of the LC from abt 15kHz to abt 8kHz so is
the Q increased!

... I should visit Decathlon and look for a fishing rod!

your sincerely depressed IK1HSS

----Messaggio originale----
Da: [email protected]
Data: 2-giu-2017 15.58
A:<[email protected]>
Ogg: Re: LF: Re: I: Fw: For today the FETs survived...

Hi Marco, I may well be wrong I was experimenting with 150W at 35V I
measured 12 to 15A through the capacitors (from memory) .......the
confirmation is that the change is permanent. I dont remember seeing
any
heating effects. Single ended Class E may be considerably different to
H-bridge. The currents a lower power will be less,  about 1.5A or so
(??) I
am not sure it that would produce damage, but you would certainly see
it as
the power increased.

Good Luck with it
Alan
G3NYK

----- Original Message -----
From:<[email protected]>
To:<[email protected]>
Sent: Friday, June 02, 2017 2:00 PM
Subject: R: LF: Re: I: Fw: For today the FETs survived...


Hi Alan,

and thanks for joining :-)
it's hard to believe at this stage that is correct to speak of "high
currents"..
The PA is an half bridge like
Andy's 700W but now I'm testing at low voltage: I see these problem
trepassing the 30Vdc supply level (and power is about 15W)..
Anyway will try with the "pulse rated caps" you suggested just in case
my "low current" "low tension" ideas are wrong.
73 Marco
----Messaggio originale----
Da: [email protected]
Data: 2-giu-2017 14.36
A:<[email protected]>
Ogg: LF: Re: I: Fw: For today the FETs survived...

Hi Marco I dont know where you are putting the caps but I am assuming
they
are passing a high RF corrent. I found that the old style (valve) high
voltage caps in my Class E test rig changed capacitance permanently
during
and after a run (capacitance reduced). I assumed that the current was
fusing
the foil connection to the lead-out wires. When using "pulse rated"
capacitors as used in SMPSUs I had no further capacitance change
problems.
The ones I have are RIFA PHE 428 2000v from RS Components. I think
Farnell
do a WIMA equivalent.

Best Wishes
Alan
G3NYK

----- Original Message -----
From:<[email protected]>
To:<[email protected]>
Sent: Friday, June 02, 2017 1:06 PM
Subject: R: Re: Re: Re: LF: Re: I: Fw: For today the FETs survived...


now my thoughts are even more confused....
Hi Andy, me again....
after a long night of meditation, I remembered I had a bounch of old
style mica capacitators 1000pF 1000V..
I put
9 of them in parallel to get the closer value to the 8800pF I had
before.
Of course the resonance moved a bit and now is on 134.5 kHz with 3dB
bandwidth of 9 kHz (Q=15 I know is a bit to high..) so carried out some
tests on 134 kHz (of course on the dummyload) all without guard circuit
1st test xfmr 7T/19T (Ae197mm² R50 mat T38): 2Wout @10Vdc; 6,5
Wout@20Vdc; 13,7Wout@30Vdc stable.. @40Vdc after a quick peak the power
slowly goes down till below 1W!
2nd test I had still on hands the previous xfmr 5T/12T (Ae197mm² same
core as 1st test) so was worth to make a trial... same trend :-( for
Vdc>  30V after a first peak... it goes down.
I had another core available with different material (N30, Ae 154mm²
R58) so I prepared a new xfmr with this core 7T/14T:
1,4Wout@10Vdc; 4,6Wout@20Vdc; 9,2Wout@30Vdc .... at 40Vdc a short burst
with almost 15Wout and then down down down... :-((((((

I noticed a difference in comparison to your project: you connected the
+ and - rails to ground via 10nF and here I used 100nF caps could it
explain this behaviour?

73 Marco

----Messaggio originale----
Da: [email protected]
Data: 1-giu-2017 22.20
A:<[email protected]>
Ogg: R: Re: Re: Re: LF: Re: I: Fw: For today the FETs survived...

that was also my thought.. but they run at room temperature: the
resonance is obtained with 4 polyesther 2200 pF 2000 Vdc caps. the
classic boxes 25x15x5mm

Marco

----
Messaggio originale----
Da: [email protected]
Data: 1-giu-2017 22.03
A:<[email protected]>
Ogg: Re: Re: Re: LF: Re: I: Fw: For today the FETs survived...

If the conditions change as the PA is operating, it looks like
capacitors
heating up and changing its value.   I can't think of any other
component
that will change with dissipation / heating.  What type of capacitor
are
you using in the tank?

Andy


On 1 June 2017 at 19:59, [email protected]<[email protected]>
wrote:

anybody has good ideas for a replacement hobby?? fishing? growing
flowers?

Andy: the suggestion of try without the guard circuit revealed that
some effects in this area are present.

I left the guard coil in place (I'm a bit lazy...) and disconnected
simply the 2 wires from the rectifier bridge.
The output improve of about 4dB with Vdd from 10 to 30V, the output

is

stable up to 20Vdd, on 30V it show a peak of 16W, then the output
starts to decrease till a couple of watts :-( this happens also at 40
and 50V.
The resonance of the output LC (with the guard coil open) shifts from
137 to 140 kHz and the bandwidth decreases from 20kHz to 10 kHz.

I need a long weekend of meditation...
73 Marco IK1HSS


----Messaggio originale----
Da: [email protected]
Data: 31-mag-2017 21.05
A:<[email protected]>
Ogg: R: Re: Re: LF: Re: I: Fw: For today the FETs survived...

Andy.. you are almost better than online help desks :-D

yes the guard circuit is on place but no current is flowing toward

the

PA, testing disconnetting it needs just to warm up the iron ;-)

the PS should
provide enough juice for 1200W input and the IRF460A are rated for

20A

@ 25°C (13A @ 100°C) so.. I admit it would like to give a try ;-)

I don't guess the core is saturating specially at this power level
where rms is only 22V, the core is 50mm OD and has 195,7 mm²Ae: if I
am
not totally wrong B should be<  0,03T @50V with 7 turns on the

primary

Will tru to disconnect the guard circuit just in case the squirrel is
running in its cage ;-)

Thanks again for assistence

Marco IK1HSS



----Messaggio originale----
Da: [email protected]
Data: 31-mag-2017 20.39
A:<[email protected]>
Cc:<[email protected]>
Ogg: Re: Re: LF: Re: I: Fw: For today the FETs survived...

7:19 turns (assuming 50R output)  means you have a load resistance of
6.8
ohms which for 180V DC (81 V RSM fund sine) is nearly 1kW  I don't
think
you really mean to go that extreme do you?    13 ohms is more
realistic.

As for the tank resonance changing as power increases, that is very
wrong.
I wonder if the transformer is saturating.   Not sure of your core

Ae,

but
lets assume 200mm square, a core of about 16mm diameter.

V = 4.44.F.N.A.B    Plugging in 137kHz 7 turns, 200 mm^2 and a Bmax

of

0.1
that suggests 85V RMS.
Which is exactlyly what you have.  I suggest more primary turns .
Before
a transformer ratio of 1:2 was suggested, for Rload = 13 ohms

Is the guard circuit in place ?   Don't forget, it has to be
customised
to
you exact currents and coil Q.  Get teh PA operating to its proper
settings
foirst - that you can do at low voltage power, it scales perfectly.
Only
when it it working properly can you add and set up the guard circuit.

When I did teh 700W PA, I had a complete workign (albeit unreliable)
unit
before even thinking of teh guard circuitry.

Andy





On 31 May 2017 at 18:50, [email protected]<[email protected]>
wrote:

Hi Andy... me again...

I was so curious to see what could happen thatI had a very quick
dinner and connected all, but...

now the output xfmr has 7T/19T here my
readings/calculations:
(see attached picture)
again the power increase from 10 to 30Vcc then from 30 to 50Vcc

after

an initial burst it start to fall down..
I checked also the resonance of the LC: till 30Vcc is tuned on 137

kHz

with a 3dB bandwidth of 20 kHz, when I move to 40 and 50Vcc the
"maximum" output shifts to 165 kHz...

mumble mumble

I tempted to have roasted FETs for dessert and see what happens at
180V!

Marco, IK1HSS


----Messaggio originale----
Da: [email protected]
Data: 30-mag-2017 23.50
A:<[email protected]>
Cc:<[email protected]>
Ogg: Re: LF: Re: I: Fw: For today the FETs survived...

I've just looked again at the circuit diagram you sent - on there

the

values are different from your statement in the email.  It shows
primary 5
turns, secondary 12 turns so a load resistance in the order of 9

ohms

which
is rather low if you are intending a Vdd of 180V - but closer to

the

ideal
Rl

The tank components have a reactance of 130 ohms which is too high

a

Q

is
used with that 9 ohms Rload, You should be aiming for a Q in the

region

of
6.

Even with the optimum load R of 13 ohms described last time for 500
Watts
from 180V rail the resulting Q of 10 is a bit too high - you will

end

up
with high voltage and critical tuning

Andy  G4JNT

On 29 May 2017 at 19:07, Andy Talbot<[email protected]>  wrote:

Yes.
As you'll see in my original write up, I originally forgot that

the

peak

of the fundamental sine component of a square wave is GREATER

than

the peak

by a factor of 4 / pi and initially my PA delivered a lot more

power

(1.6

times) than it was supposed to.

So if the square wave has a peak value of 1, its fundamental sine
component has a peak value of 4/pi or around 1.27.  The RMS of

the

resulting sine  is SQRT(2) less than this giving a Peak square to

RMS-

sine

ratio of  0.9..   If you specifye peak-peak of the square wave, a

further

factor of 2 applies, leading to the 0.45 ratio described before.

Incidentally, this same ratio appears in that equation for  flux

in
a

magnetic code,   V = 4.44.F.N.A.B
The magic number 4.44  is actually SQRT(2) * pi     and comes

about

from

the same sort of sine to square transform.

Andy

On 29 May 2017 at 18:48, [email protected]<marcocadeddu@tin.

it>

wrote:

uhuh... a slightly silly misleading assumption... Vdc are the

same

of

Vrms before FETs make their work!

Thank you Andy for pointing out it!!
With this approach calculation changes a bit and probably with

the

right Xfmr  the PA can give higher satisfaction :-)

Hopefully the FETs will survive and this time I'm ready to

burnout

the

antenna hi

Will keep you both updated, thank you once more Andy

73 Marco, IK1HSS
----Messaggio originale----
Da: [email protected]
Data: 28-mag-2017 21.18
A: "[email protected]"<[email protected]>,
<[email protected]>
Cc:<[email protected]>
Ogg: LF: Re: I: Fw: For today the FETs survived...

First thing I noticed is that your turns ratio on the output
transformer
doesn't look right.
You quote "* ... with primary winding of 15 turns and secondary

of

12

turns...*"

180V DC in a half bridge is 180V peak-peak square wave.
The fundamental sine part of that is  4/pi * 180 = 229V pk-pk
so is 229V /[2.SQRT(2)] = 81V RMS

To a good approximation RMS(fund) from a half bridge is Vrms

(fund)
=

0.45VDC

For 500 Watts out, Rload =  81 ^ 2 / 500 =  13 ohms

So to match to 50 ohms you need a turns ratio of SQRT(50/13) =

1.9:

1     so
call it 2:1  Keeping 12 turns on the  secondary means you need 6

turns

on
the primary

When operating at reduced voltage, the power out will vary

exactly

as

the
square of the voltage.
Recalculating from first principles for a 12V supply:

12V  DC = 12V pk-pk = 12 / [2.SQRT(2)] * 4/pi = 5.4V RMS

(fundamental)

in 13 ohms should give 5.4^2/13 = 2.2 Watts

check using ratio of voltages, squared :

(12V/180V) ^ 2 * 500W = 2.2 Watts which is the same as above.
QED

Your 15:12 ratio result sin a load impedance of (15/12)^2 * 50 =

78

ohms

At 40V DC == 18V RMS(fund) that will give 18^2/78 = 4.1 watts

which

is

actually LESS that you are seeing - the 2* discrepancy is odd,

but

the

low
power is in the area of what you measured..

Andy  G4JNT



On 28 May 2017 at 19:34, [email protected]<marcocadeddu@tin.

it>

wrote:

Hi Chris,

I tried to post this message on the reflector but apparently I

had

no

success..
As promised I keep you updated but as you can read in the
attachment the first trials were not enocouraging...
Andy, may I ask you to read my report? your interpretation and
suggestion are welcome!

73, Marco IK1HSS


-----Original message-----

From: "[email protected]" [email protected]
Date: Sun, 28 May 2017 17:01:33 +0200
To: [email protected]
Subject: For today the FETs survived...

Hi LF,

hope that also the toroids of Chris survived!
My FETs survived, but they are not working as expected :-(
Attached the report on my attempt to duplicate the half bridge

of

Andy..
Has anyone suggestions before I try to cook all connecting to

the

180Vdc supply?

Thank you
73 Marco IK1HSS


--
This message has been scanned by E.F.A. Project and is

believed

to

be

clean.







---------- Forwarded message ----------
From: "[email protected]"<[email protected]>
To:<[email protected]>
Cc:
Bcc:
Date: Sun, 28 May 2017 17:01:33 +0200 (CEST)
Subject: For today the FETs survived...
Hi LF,

hope that also the toroids of Chris survived!
My FETs survived, but they are not working as expected :-(
Attached the report on my attempt to duplicate the half bridge

of

Andy..
Has anyone suggestions before I try to cook all connecting to

the

180Vdc supply?

Thank you
73 Marco IK1HSS


--
This message has been scanned by E.F.A. Project and is

believed

to

be

clean.