Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on lipkowski.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=5.0 tests=FREEMAIL_FORGED_FROMDOMAIN, FREEMAIL_FROM,HEADER_FROM_DIFFERENT_DOMAINS,HTML_MESSAGE,RCVD_IN_DNSWL_MED, SPF_PASS,T_DKIM_INVALID autolearn=ham autolearn_force=no version=3.4.0 X-Spam-DCC: EATSERVER: mailn 1166; Body=2 Fuz1=2 Fuz2=2 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by lipkowski.org (8.14.4/8.14.4/Debian-8+deb8u1) with ESMTP id v35BOolU008474 for ; Wed, 5 Apr 2017 13:24:51 +0200 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1cvizt-0006tW-O3 for rs_out_1@blacksheep.org; Wed, 05 Apr 2017 12:21:09 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1cvizs-0006tG-Lb for rsgb_lf_group@blacksheep.org; Wed, 05 Apr 2017 12:21:08 +0100 Received: from mail-yw0-x22f.google.com ([2607:f8b0:4002:c05::22f]) by relay1.thorcom.net with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.89) (envelope-from ) id 1cvizl-0002h7-7H for rsgb_lf_group@blacksheep.org; Wed, 05 Apr 2017 12:21:07 +0100 Received: by mail-yw0-x22f.google.com with SMTP id p77so4346400ywg.1 for ; Wed, 05 Apr 2017 04:21:00 -0700 (PDT) X-DKIM-Result: Domain=gmail.com Result=Good and Known Domain DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:in-reply-to:references:from:date:message-id:subject:to; bh=0gWE65E2Zp2G3f3lCEtIlJKbZsAVi5QxiAo0vsc1xaM=; b=sWX6XqnbmtJ4nx2HvOLv7/rwONtRbQ6++qCHPUiChgbnKGybpan5CDgxYIFzG470G0 vsfWn9DTAU3kZsmx5EuRv6GDtswXd7C+pPXtmY7Yi60qZbOeNICBLuKDdyqMtm2QoKwy MLbHo13QAt9uLiIYIiV21HPamQwjn+KtQaw7yrG6IY9ZhmMTlfE+SyiQnl1FlQVhmMdY JsSm28Gb45FehMJlsAo7bNo+prDHneJePv0z/oQD5xJcQdBZbP+GdKwAm5ua3HNSVmhu Y0dlUbKAEn+gtXFoNO+cuWHpvQx1UqqmtTznkvnUqto4rPZzXn3OywZA2x5R5sxtV6Ae 3YcA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to; bh=0gWE65E2Zp2G3f3lCEtIlJKbZsAVi5QxiAo0vsc1xaM=; b=OQgoVYI8LZ8oQWAT5GzBXs3rnNMiAQIOfrR2Xf4AE8nK/1wrGzQ5tQ0XWLTPSUk1Ok tYZiWyWFK0dsmMpPtJBy50bNfWE0UXYfCwRB+nnfavcmXQ+XVpdAIC2CV0fPJuMK7Qpq tHH7drFDpztpjnb2sJwbSFEjjlwvlPYaOonTbaPzBw51kHFEda6kByzwCKQACvebwOdL 9RJosnKHjj1gWuu6/wU8Q0PGhPNU3puvBZhfXtvRdmNi2mUn9I86z1tJF6z+15vLJhmK spPF4uWhxeacWV2vXrDKcUDcxiirEvNvKVZZ9ziSErMZppdXoLaQDMYJd6S3d89ZW0oA +o1A== X-Gm-Message-State: AFeK/H0GFXv1DWg6hFATfVxDRvU0PpjtMxp7oTP6F/6rktt/uWCDHExS8jmOJwhYx2DwHoVeJEUOQQqjc5aUUg== X-Received: by 10.129.46.6 with SMTP id u6mr18062894ywu.240.1491391259148; Wed, 05 Apr 2017 04:20:59 -0700 (PDT) MIME-Version: 1.0 Received: by 10.129.155.88 with HTTP; Wed, 5 Apr 2017 04:20:58 -0700 (PDT) In-Reply-To: References: <15b2eda0ec6.marcocadeddu@tin.it> From: Andy Talbot Date: Wed, 5 Apr 2017 12:20:58 +0100 Message-ID: To: rsgb_lf_group@blacksheep.org X-Scan-Signature: be3259e96db1c5491a2991bd4b2cea6e Subject: Re: FW: LF: FETs getting sick - why not use tubes? Content-Type: multipart/alternative; boundary=001a11407da239069f054c6996cc X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false X-Scanned-By: MIMEDefang 2.75 Status: O X-Status: X-Keywords: X-UID: 11111 --001a11407da239069f054c6996cc Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable And I used that Decca guard circuit in my 137kHz transmitter http://www.g4jnt.com/137tx.pdf - absolutely foolproof. Immune to shorts, open, mistuning, seriously wrong frequency drive; anything you can throw at the transmitter or stick on the end of it Andy G4JNT On 5 April 2017 at 11:58, M0FMT wrote: > Hi all > > The Decca PA seems to be scattered with spike limiting diode from memory > Transils / Transorb TVS diodes. (don't know the values) I usually put one > in the drain set above the peak drain wave voltage seen on the scope and > below the peak operating value of the FET So far so good in single ended > amps. > > Jim M0MBU did a short treatise see http://www.wireless.org.uk/guard.htm. > > The Decca TX "guard circuit" by Jim Moritz, M0BMU. > > 73 petefmt > > On Mon, Apr 3, 2017 at 5:39 PM, wrote: > >> >> >> >> >> Sent from Mail for >> Windows 10 >> >> >> >> *From: *g3kevmal@talktalk.net >> *Sent: *02 April 2017 15:28 >> *To: *marcocadeddu@tin.it >> *Subject: *RE: LF: FETs getting sick - why not use tubes? >> >> >> >> HI PA AMP folks >> >> >> >> Surprised more LF/MF ops do not use the DECCCA 5501 design, class D >> mosfets in bridge configuration with series resonant output then matchin= g >> ferrite transformer to match either 50 or 75 ohms. >> >> I have been using this method now for several years and todate not had a >> failure. >> >> This design is narrow band but only needs the series resonant cct >> switched for band change >> >> Ie SMOKE FREE DESIGN >> >> >> >> Good luck all with your PA projects and also agree Tube PA,S are hard to >> beat. I use Dentron PA amps on the HF bands, These amps have a pair of 8= 875 >> tubes and live a long time. >> >> 73 gl de MAL/G3KEV >> >> >> >> >> >> Sent from Mail for >> Windows 10 >> >> >> >> *From: *marcocadeddu@tin.it >> *Sent: *02 April 2017 14:34 >> *To: *rsgb_lf_group@blacksheep.org >> *Subject: *R: LF: FETs getting sick - why not use tubes? >> >> >> >> Hi Tom, Wolf and the group, >> >> >> >> thanks for feedback, suggestions and nice pictures of the tube TX! :-) >> >> very nice to see! >> >> If I had not room restrictions probably >> >> will ... [I should have hidden in some place some 6146B and PL519s as >> >> spare parts of older rigs ;-) ]. >> >> >> >> The pushpull FET PA served without problems for at least 5-6 years.. >> >> withstanding several kind of insults (mismatchings.. missing antenna.. >> >> wspr15 etc..) this time the first FET shorted out after a ceramic >> >> trimmer in the directional coupler arched and it was the first of a >> >> long list: replace/short/replace/.. >> >> There is no bias (simply a couple resistances in serie to gate and from >> >> gate to ground) driving the pushpull with a IXD609 via a transformer. >> >> The PA is broadband and is followed from an external LPF for LF or MF. >> >> >> >> Hope next FET will survive enough time to check what is going wrong... >> >> >> >> 73 Marco IK1HSS >> >> >> >> ----Messaggio originale---- >> >> Da: DK1IS@kabelmail.de >> >> Data: 2-apr-2017 14.29 >> >> A: >> >> Ogg: LF: FETs getting sick - why not use tubes? >> >> >> >> Am 02.04.2017 um 13:09 schrieb Dr. Wolf Ostwald: >> >> > hi Marco ! >> >> > FETs die in many peculiar ways. Often they just become half >> >> conducting >> >> > on the Source-Gate path. If they are on a common bias source, the >> >> > Source voltage will open up all FETs connected. Leads to immediate >> >> > death of all of them. Use individual bias on each of them. I had >> >> that >> >> > happen a few times b4 i learned my lesson. Of course capacitive >> >> > blocking of DC from the input transformer is essential too. But i >> >> > think these thoughts have been published here b4. >> >> > I am in the process of putting a single tube to use on 472. But its >> >> a >> >> > time consuming enterprise. >> >> > >> >> > 73 de wolf df2py >> >> Hi Wolf and group, >> >> >> >> nice to hear that someone else is thinking about this approach! I=C2=B4m >> >> content with my homemade tube PA for LF and MF which has provided >> >> reliable service since nearly 4 years now. Only some thoughts about >> >> this >> >> concept - I hope not to bore all those hams who are happy with their >> >> semiconductor PAs: >> >> >> >> Years ago I had a MOSFET PA for LF, Class B push-pull with 250 W RF. >> >> It >> >> worked well at constant conditions, but when I had to retune the >> >> antenna >> >> due to larger QSY or made antenna experiments there always was the >> >> danger of blowing up these nervous semiconductors. After 4 or 5 times >> >> changing the MOSFETS I decided to build a new PA - with tubes! Looking >> >> a >> >> little bit anachronistic this PA is absolutey good-natured. Designed >> >> for >> >> broadband service on LF and MF it makes no problems when changing the >> >> antenna coars tuning from one band to the other even when the fine >> >> tuning is=C2=B4nt done yet. With my former MOSFET-PA this would have bee= n >> >> impossible. >> >> >> >> I wanted to have a linear PA - this usually means class B. You have to >> >> decide between narrow band and broad band (like an audio-amp) design. >> >> For narrow band you can use a single-ended PA but you have to add a >> >> resonance circuit. For broad band you should use a push-pull PA and >> >> have >> >> to build a suitable output transformer. I opted for broad band design >> >> because it is usable for LF and MF without changes at the PA. With >> >> this >> >> design and sin-driving I reach a total harmonic distortion of about 5 >> >> % >> >> at 700 W RF on a pure resistive dummy load. With the usual narrow, >> >> narrow band antennas on LF and MF you don=C2=B4t need additional filters= ! >> >> >> >> Concerning the tubes: If you take the common TX tubes with plate >> >> voltages of several kV all output circuits have rather high >> >> impedances, >> >> that means large coils for the resonance circuits resp. large >> >> transformer windings and very high voltages - potentially a >> >> construction >> >> problem. This led me to the choice of 2x 4x PL519 in push-pull, a >> >> rugged >> >> colour TV line output tube with low plate voltage and high plate >> >> current. In this way I came down to a plate-to-plate resistance of >> >> about >> >> 1 kOhm at 600 V DC plate voltage, where you easily can build a ferrite >> >> broad band output transformer down to 50 Ohms. A disadvantage of this >> >> concept is that you have to give individual bias to each tube, that >> >> means for the first start-up you have to align 8 potentiometers >> >> carefully to nearly equal cathode currents for all the tubes. But >> >> according to my experience this alignment remains stable over a long >> >> time. I have inserted 1-Ohm-resistors in each cathode line and have >> >> brought the voltage drops to 8 cinch connectors, where I can monitor >> >> the >> >> DC component (with external filtering) as well as the real time >> >> current. >> >> With 4 tubes in parallel per branch of course you have to take care >> >> for >> >> self oscillations. The extensive use of bypass capacitors, ferrite >> >> beads >> >> and parasitic chokes in the plate lines is mandatory as well as good >> >> grounding concepts are. The tubes don=C2=B4t pull control grid current >> >> (this >> >> would even be true in class C!) but you need 3 or 4 W RF input power >> >> due >> >> to all the ohmic loads at the tube=C2=B4s control grids caused by the >> >> individual bias paths. On the other hand this certainly helps to avoid >> >> oscillations. You can see some pictures of this PA at >> www.QRZ.com/db/dk1is. >> >> >> >> By the way: why not to try these tubes at class D? With DC plate >> >> voltages of perhaps 1200 V you should get a nice QRO-PA ... >> >> >> >> Wolf, you are right: building such a PA from scratch is a time >> >> consuming >> >> enterprise. I didn=C2=B4t count the working hours but according to my la= b >> >> log >> >> the whole project took about 9 months - an adequate time for a new >> >> baby! >> >> It was a great experience anyway. >> >> >> >> Good luck and 73, >> >> Tom, DK1IS >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> > > --001a11407da239069f054c6996cc Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
And I used that Decca guard circuit in my 137kHz transmitt= er =C2=A0http://www.g4jnt.com/13= 7tx.pdf=C2=A0- absolutely foolproof. =C2=A0=C2=A0
Immune to shorts,= open, mistuning, seriously wrong frequency drive; anything you can throw a= t the transmitter or stick on the end of it

Andy =C2=A0G= 4JNT


On 5 April 2017 at 11:58, M0FMT &= lt;peteg8fmt@gmail= .com> wrote:
Hi all

The Decca PA seems to be scattered with spike limiting diode from memo= ry Transils / Transorb TVS diodes. (don't know the values) I usually pu= t one in the drain set above the peak drain wave voltage seen on the scope = and below the peak operating value of the FET=C2=A0 So far so good in singl= e ended amps.

Jim M0MB= U did a short treatise see http://www.wireless.org.uk/guard.htm.

The Decca TX "guard circuit" by Jim Moritz, M0BMU.

73 petefmt

On Mon, Apr 3, 2017 at 5:39= PM, <g3kevmal@talktalk.net> wrote:

=C2=A0

=C2=A0<= /u>

Sent from Mail for Windows 10

=C2=A0

From: g3kevmal@talktalk.net
Sent: 02= April 2017 15:28
To: marcocadeddu@tin.it
Subject: RE: LF: FETs getti= ng sick - why not use tubes?

=C2=A0<= u>

HI PA AMP folks

=C2=A0

Surprised mor= e LF/MF ops do not use the DECCCA 5501 design, class D mosfets in bridge co= nfiguration with series resonant output then matching ferrite transformer t= o match either 50 or 75 ohms.

I hav= e been using this method now for several years and todate not had a failure= .

This design is narrow band but on= ly needs the series resonant cct switched for band change

=

Ie SMOKE FREE DESIGN

=C2=A0

Good luck all with= your PA projects and also agree Tube PA,S are hard to beat. I use Dentron = PA amps on the HF bands, These amps have a pair of 8875 tubes and live a lo= ng time.

73 gl de MAL/G3KEV<= u>

=C2=A0

=C2=A0

Sent from Mail = for Windows 10

=C2=A0=

From: marcocadeddu@tin.it
Sent: 02 April 201= 7 14:34
To: rsgb_lf_group@blacksheep.org
Subject: R: LF: FET= s getting sick - why not use tubes?

=C2=A0

Hi Tom, Wolf and the group,

=C2=A0

thanks for= feedback, suggestions and nice pictures of the tube TX! :-) =

very nice to see!

If I had not room restrictions probably

will ... [I should have hidden in some place some 6146B and= PL519s as

spare parts of older ri= gs ;-) ].

=C2=A0

<= p class=3D"MsoNormal">The pushpull FET PA served without problems for at le= ast 5-6 years..

withstanding sever= al kind of insults (mismatchings.. missing antenna..

wspr15 etc..) this time the first FET shorted out after = a ceramic

trimmer in the direction= al coupler arched and it was the first of a

long list: replace/short/replace/..

There is no bias (simply a couple resistances in serie to gate a= nd from

gate to ground) driving th= e pushpull with a IXD609 via a transformer.

The PA is broadband and is followed from an external LPF for LF o= r MF.

=C2=A0

Hope next FET will survive enough time to check what is g= oing wrong...

=C2=A0<= /p>

73 Marco IK1HSS

=C2=A0

----Messaggio origina= le----

Da: DK1IS@kabelmail.de

Data: 2-apr-2017 14.29

A: <rsgb_lf_group@blacksheep.org>

Ogg: LF: FETs getting sick - why not use tubes?

=C2=A0

Am 02.0= 4.2017 um 13:09 schrieb Dr. Wolf Ostwald:

> hi Marco !

> FETs di= e in many peculiar ways. Often they just become half

conducting

>= on the Source-Gate path. If they are on a common bias source, the <= u>

> Source voltage will open up all FETs = connected. Leads to immediate

>= death of all of them. Use individual bias on each of them. I had

that

> happen a few times b4 i learned my lesson. Of course capacitive =

> blocking of DC from the input tr= ansformer is essential too. But i

= > think these thoughts have been published here b4.

> I am in the process of putting a single tube to us= e on 472. But its

a =

> time consuming enterprise.

>=C2=A0

= > 73 de wolf df2py

Hi Wolf and g= roup,

=C2=A0

nice to hear that someone else is thinking about this app= roach! I=C2=B4m

content with my ho= memade tube PA for LF and MF which has provided

reliable service since nearly 4 years now. Only some thought= s about

this

concept - I hope not to bore all those hams who are hap= py with their

semiconductor PAs:

=C2=A0

Years ago I had a MOSFET PA for LF, Class B push-pull with 250 W= RF.

It

worked well at constant conditions, but when I had to retune= the

antenna

due to larger QSY or made antenna experiments there alw= ays was the

danger of blowing up t= hese nervous semiconductors. After 4 or 5 times

changing the MOSFETS I decided to build a new PA - with tube= s! Looking

a

little bit anachronistic this PA is absolutey good-natu= red. Designed

for

broadband service on LF and MF it makes no problem= s when changing the

antenna coars = tuning=C2=A0 from one band to the other even when the fine

tuning is=C2=B4nt done yet. With my former MOSFET-= PA this would have been

impossible= .

=C2=A0

I wanted to have a linear PA - this usually means class B. Y= ou have to

decide between narrow b= and and broad band (like an audio-amp) design.

For narrow band you can use a single-ended PA but you have t= o add a

resonance circuit. For bro= ad band you should use a push-pull PA and

have

to build a suitable o= utput transformer. I opted for broad band design

because it is usable for LF and MF without changes at the PA= . With

this

design and sin-driving I reach a total harmonic distorti= on of about 5

%

=

at 700 W RF on a pure resistive dummy load. With the= usual narrow,

narrow band antenna= s on LF and MF you don=C2=B4t need additional filters!

=C2=A0

Concerni= ng the tubes: If you take the common TX tubes with plate

=

voltages of several kV all output circuits have rath= er high

impedances, =

that means large coils for the resonance circuit= s resp. large

transformer windings= and very high voltages - potentially a

construction

problem. This l= ed me to the choice of 2x 4x PL519 in push-pull, a

rugged

colour TV = line output tube with low plate voltage and high plate

current. In this way I came down to a plate-to-plate r= esistance of

about <= /p>

1 kOhm at 600 V DC plate voltage, where you easil= y can build a ferrite

broad band o= utput transformer down to 50 Ohms. A disadvantage of this

concept is that you have to give individual bias to= each tube, that

means for the fir= st start-up you have to align 8 potentiometers

carefully to nearly equal cathode currents for all the tubes= . But

according to my experience t= his alignment remains stable over a long

time. I have inserted 1-Ohm-resistors in each cathode line and have =

brought the voltage drops to 8 cin= ch connectors, where I can monitor

the

DC component (with external f= iltering) as well as the real time

current.

With 4 tubes in parallel= per branch of course you have to take care

for

self oscillations. T= he extensive use of bypass capacitors, ferrite

beads

and parasitic= chokes in the plate lines is mandatory as well as good

<= p class=3D"MsoNormal">grounding concepts are. The tubes don=C2=B4t pull con= trol grid current

(this =

would even be true in class C!) but you need= 3 or 4 W RF input power

due

to all the ohmic loads at the tube=C2= =B4s control grids caused by the

i= ndividual bias paths. On the other hand this certainly helps to avoid

oscillations. You can see some pictures= of this PA at ww= w.QRZ.com/db/dk1is.

=C2= =A0

By the way: why not to try these tubes= at class D? With DC plate

voltage= s of perhaps 1200 V you should get a nice QRO-PA ...

=C2=A0

Wolf, you = are right: building such a PA from scratch is a time

consuming

enter= prise. I didn=C2=B4t count the working hours but according to my lab

log

the whole project took about 9 months - an adequate time for a new =

baby!

It was a great experience anyway.

=C2=A0

Good luck and 73,

Tom, DK1IS

=C2=A0

=C2=A0=

=C2=A0

=C2=A0

=C2=A0

=C2=A0

= =C2=A0

=C2=A0

=C2=A0

=C2= =A0



--001a11407da239069f054c6996cc--