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 v35B3lXE008338 for ; Wed, 5 Apr 2017 13:03:48 +0200 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1cvieO-0006i2-3B for rs_out_1@blacksheep.org; Wed, 05 Apr 2017 11:58:56 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1cvieN-0006ht-2g for rsgb_lf_group@blacksheep.org; Wed, 05 Apr 2017 11:58:55 +0100 Received: from mail-it0-x230.google.com ([2607:f8b0:4001:c0b::230]) by relay1.thorcom.net with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.89) (envelope-from ) id 1cvieH-0002aW-RI for rsgb_lf_group@blacksheep.org; Wed, 05 Apr 2017 11:58:53 +0100 Received: by mail-it0-x230.google.com with SMTP id a140so6245159ita.0 for ; Wed, 05 Apr 2017 03:58:49 -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=x3XjKRjL202HAPH7w2Ozq0bNn/JeKj5PrL1EtmGZZF0=; b=KOAuZZO0NN4eD8f0tfyaaXjVWZmqy+CfzCWAEs1OJHEJsxsye2QuR5fSSMqsijwe3j pHYFw1S/TYMbtCrKolGzFpePwLbr6wGGAyOmRqLwHEKUuNQwzkrPHOhAOB6sCjPbFazR dMwGgkHAskbJTl+XpeN3dFiRHnF0l2sYbvv/wHjpY6OyiwwpXioN4s+2XflXFYln8zX3 +Xz0A/o6k7XG2IqPULNyVIcJTBPelFPMnIb+ppibE0vHkaISHVuUemNFvAGQ976OpfEg hKA244/AWAxYgahg9e7WqVTVRsE5jLvzutsS5So5JzpERp0+ajCkmwt4VBq44zIzywbc 4BDQ== 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=x3XjKRjL202HAPH7w2Ozq0bNn/JeKj5PrL1EtmGZZF0=; b=RO7ge8vmFxzBxKgkrL0yO2Y0MlVtDuzqB7n0Ri7i+u5l2hbdmvKQLvOf64hls2S1Rr XHVuuZnkdGrWsnUFfpbuHrH4OXCO68LO7uL1+37ii9q9/oxt9zSaRwBzMhJX/dGprhXk 5xIUvDqY3l1Z/PQ8ZdoW7ssFL+zA+MMaK8xG2HIpGWqAkAKKkWcIzz3ODgyiMnF88Adb npEDGUdfjOy6HTcLHzaOcQlei9w3OrFZbp3pxRdSb1xr/F78RfJkBJpbWjcueKyNo5ub vu3whtBXmwFwn68CnMkHzcnOGEAO3Bnb7JsWDW608645xIiLhaWFH8glGWLkr8b0W1KK /dJw== X-Gm-Message-State: AFeK/H2OTBV+z6GQgf72s7XHdKPlBY4uooTAhfy1rn4Nz3ndf8y+tEwa 0Hm26tg5dDrTuHONLLMW9TYqo9EvU73I X-Received: by 10.36.4.67 with SMTP id 64mr19522131itb.19.1491389927469; Wed, 05 Apr 2017 03:58:47 -0700 (PDT) MIME-Version: 1.0 Received: by 10.36.7.146 with HTTP; Wed, 5 Apr 2017 03:58:46 -0700 (PDT) In-Reply-To: References: <15b2eda0ec6.marcocadeddu@tin.it> From: M0FMT Date: Wed, 5 Apr 2017 11:58:46 +0100 Message-ID: To: rsgb_lf_group@blacksheep.org X-Scan-Signature: 197e3b57b6f6f3314687a7b82bb93a83 Subject: Re: FW: LF: FETs getting sick - why not use tubes? Content-Type: multipart/alternative; boundary=001a1140ad4ed93aff054c694669 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: 11110 --001a1140ad4ed93aff054c694669 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable 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 matching > 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 switche= d > 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 88= 75 > 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 been > > 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/dk1i= s > . > > > > 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 lab > > 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 > > > > > > > > > > > > > > > > > > > > > --001a1140ad4ed93aff054c694669 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Hi all

The Decca PA seems to be scattered with spike limiting d= iode 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=C2=A0 So far so= good in single ended amps.

Jim M0MBU did a short treatise see http://www.wirele= ss.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

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 getting sick - why = not use tubes?

=C2=A0

HI PA AMP folks

= =C2=A0

Surprised more LF/MF ops do = not use the DECCCA 5501 design, class D mosfets in bridge configuration wit= h series resonant output then matching ferrite transformer to match either = 50 or 75 ohms.

I have been using th= is method now for several years and todate not had a failure.=

This design is narrow band but only needs the se= ries resonant cct switched for band change

Ie SMOKE FREE DESIGN

=C2=A0

Good luck all with your PA projec= ts 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 long time.=

73 gl de MAL/G3KEV

=C2=A0

=C2= =A0

Sent from Mail for Windows 10<= u>

=C2=A0

From: marcocadeddu@tin.it
Sent: 02 April 2017 14:34
= To: rsgb_lf_group@blacksheep.org
Subject: R: LF: FETs getting s= ick - why not use tubes?

=C2=A0

Hi Tom, W= olf and the group,

=C2=A0=

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

very ni= ce to see!

If I had not room restri= ctions probably

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

spare parts of older rigs ;-) ].

=C2=A0

The pushpull= FET PA served without problems for at least 5-6 years..

=

withstanding several kind of insults (mismatchings..= missing antenna..

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

trimmer in the directional coupler arched and it was the f= irst of a

long list: replace/short= /replace/..

There is no bias (simpl= y a couple resistances in serie to gate and from

gate to ground) driving the pushpull with a IXD609 via a tra= nsformer.

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

=C2=A0

Hope next FET wi= ll survive enough time to check what is going wrong...

=C2=A0

73 Marco= IK1HSS

=C2=A0

----Messaggio originale----

Da: = DK1IS@kabelmail.de

Data: 2-apr-= 2017 14.29

A: <rsgb_lf_group@blacksheep.o= rg>

Ogg: LF: FETs getting si= ck - why not use tubes?

=C2= =A0

Am 02.04.2017 um 13:09 schrieb Dr. Wol= f Ostwald:

> hi Marco !

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

conducting <= u>

> on the Source-Gate path. If th= ey are on a common bias source, the

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

> death of all of them. Use indi= vidual 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 i= n the process of putting a single tube to use on 472. But its

a

>= time consuming enterprise.

>= =C2=A0

> 73 de wolf df2py=

Hi Wolf and group,

=C2=A0

nice to hear = that someone else is thinking about this approach! I=C2=B4m <= /p>

content with my homemade tube PA for LF and MF wh= ich 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:

=C2=A0

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

It

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

antenna

due to larg= er QSY or made antenna experiments there always was the

<= p class=3D"MsoNormal">danger of blowing up these nervous semiconductors. Af= ter 4 or 5 times

changing the MOSF= ETS I decided to build a new PA - with tubes! Looking

a

little bit a= nachronistic this PA is absolutey good-natured. Designed

=

for

broadba= nd service on LF and MF it makes no problems when changing the

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

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

impossible.

=C2=A0

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 bro= ad band design

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

this

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

<= p class=3D"MsoNormal">%

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

=

narrow band antennas on LF and MF you don=C2=B4t nee= d additional filters!

=C2=A0=

Concerning the tubes: If you take the com= mon TX tubes with plate

voltages o= f several kV all output circuits have rather high

impedances,

that m= eans large coils for the resonance circuits resp. large

<= p class=3D"MsoNormal">transformer windings and very high voltages - potenti= ally a

construction =

problem. This led me to the choice of 2x 4x PL51= 9 in push-pull, a

rugged

colour TV line output tube with low plate v= oltage 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 <= /u>

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

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

means for the first start-up you have to align 8 p= otentiometers

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 t= ake care

for

self oscillations. The extensive use of bypass capacito= rs, ferrite

beads

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

grounding conce= pts are. The tubes don=C2=B4t pull control grid current

<= p class=3D"MsoNormal">(this

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

due

t= o 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

osc= illations. You can see some pictures of this PA at www.QRZ.com/db/dk1is.

=C2=A0

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

voltages of perhaps 1200 V you should get a nic= e QRO-PA ...

=C2=A0

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

consuming <= /u>

enterprise. I didn=C2=B4t count the working h= ours but according to my lab

log <= u>

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

ba= by!

It was a great experience anyw= ay.

=C2=A0

Good luck and 73,

T= om, DK1IS

=C2=A0

<= p class=3D"MsoNormal">=C2=A0

=C2=A0

=C2=A0

=C2=A0

=C2=A0=

=C2=A0

=C2=A0

=C2=A0

=C2=A0


--001a1140ad4ed93aff054c694669--