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=HEADER_FROM_DIFFERENT_DOMAINS, HTML_MESSAGE,RCVD_IN_DNSWL_MED,SPF_PASS,T_DKIM_INVALID autolearn=unavailable autolearn_force=no version=3.4.0 X-Spam-DCC: : mailn 1480; Body=2 Fuz1=4 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 v33Gl4M2017133 for ; Mon, 3 Apr 2017 18:47:05 +0200 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1cv512-0006Zo-4l for rs_out_1@blacksheep.org; Mon, 03 Apr 2017 17:39:40 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1cv50x-0006Zf-91 for rsgb_lf_group@blacksheep.org; Mon, 03 Apr 2017 17:39:35 +0100 Received: from smtp-out-6.talktalk.net ([62.24.135.70]) by relay1.thorcom.net with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.89) (envelope-from ) id 1cv50t-0004cJ-Dx for rsgb_lf_group@blacksheep.org; Mon, 03 Apr 2017 17:39:33 +0100 Received: from [IPv6:::ffff:192.168.1.2] ([79.69.134.92]) by smtp.talktalk.net with SMTP id v50UcefydgKstv50gcLp3Z; Mon, 03 Apr 2017 17:39:30 +0100 X-DKIM-Result: Domain=talktalk.net Result=Signature OK DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=talktalk.net; s=1605; t=1491237570; bh=ro2Z0KapDVqtjK74U6Axu0FBHxyiq8NN+RIj4z/xe5I=; h=To:From:Subject:Date:References; b=amY8pZhG5iJzJ1wIRO3xsDMRn1N4tdRAcmrooOjwAOs3q/DXvgOBxOuym6W1gv4iw qXPTyAoHjogUr2pWMnUX1aJpwnOaoDAir690BAdx/SZ/X8TmtC6jmi8oB9IwQ+UZOu Zta4X5tbQX7jRzXZOeRZie4qsb+Ss4bMtKQ5Xpv0= X-Originating-IP: [79.69.134.92] X-Spam: 0 X-OAuthority: v=2.2 cv=GdBVpkfL c=1 sm=1 tr=0 a=14bG1rlh7g6vKImaYKDuRw==:117 a=14bG1rlh7g6vKImaYKDuRw==:17 a=xqWC_Br6kY4A:10 a=nN7BH9HXAAAA:8 a=F3M5lZpKAAAA:8 a=giydrZjGAAAA:8 a=HTea2CqFMyEj9nV7o7QA:9 a=RJ3RbnZXx-CiKtlU:21 a=mZhJcPAU--pkubRE:21 a=QEXdDO2ut3YA:10 a=oECC79clBFYA:10 a=G2-_YpdUlmoA:10 a=yMhMjlubAAAA:8 a=SSmOFEACAAAA:8 a=DIYLZqMOtC_bU5WtZ1IA:9 a=BSDbIXGVRBtOX448:21 a=s86qoXiN5nXZCXwY:21 a=Wg0sI8QYfsWS6UuB:21 a=gKO2Hq4RSVkA:10 a=UiCQ7L4-1S4A:10 a=hTZeC7Yk6K0A:10 a=frz4AuCg-hUA:10 a=slCku8JSH3TyizEDQ3pD:22 a=JyT0kAtC2-hSCwV5kcG3:22 MIME-Version: 1.0 To: "rsgb_lf_group@yahoogroups.co.uk" , "rsgb_lf_group@blacksheep.org" From: Date: Mon, 3 Apr 2017 17:39:24 +0100 Importance: normal X-Priority: 3 References: <15b2eda0ec6.marcocadeddu@tin.it> X-CMAE-Envelope: MS4wfIbxVIdfqiIfGH4+dKUE7Z8KnVE5wo0nrUidK87c8c88i7D9DUhPY7+WV0ZsglFnBUlLvOmKfQHuI7vJI6BinNUQTEv24csqGxyObvb+ACJIj1htZ/YQ JI9STOEoepgRlGjxrjjbrgNz41cuE0rHniqYMnUm+boet4dEhfHVnX8N/D5W3m0xImVGTrHWezFI/xxDad/R379stBkh9eOpZWeuyxnyBULubbcOwJSUjrD3 sRHJlqyvWdIgMQgqaudbCA== X-Scan-Signature: 0bac830672365eda92e91f63ed58b412 Message-Id: Subject: FW: LF: FETs getting sick - why not use tubes? Content-Type: multipart/alternative; boundary="_853A0BB3-2753-48F1-B94E-3AA9DDB0CA3C_" 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: RO X-Status: X-Keywords: X-UID: 11103 --_853A0BB3-2753-48F1-B94E-3AA9DDB0CA3C_ Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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 fa= ilure. This design is narrow band but only needs the series resonant cct switched = for band change Ie SMOKE FREE DESIGN=20 Good luck all with your PA projects and also agree Tube PA,S are hard to be= at. I use Dentron PA amps on the HF bands, These amps have a pair of 8875 t= ubes 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! :-)=20 very nice to see! If I had not room restrictions probably=20 will ... [I should have hidden in some place some 6146B and PL519s as=20 spare parts of older rigs ;-) ]. The pushpull FET PA served without problems for at least 5-6 years..=20 withstanding several kind of insults (mismatchings.. missing antenna..=20 wspr15 etc..) this time the first FET shorted out after a ceramic=20 trimmer in the directional coupler arched and it was the first of a=20 long list: replace/short/replace/.. There is no bias (simply a couple resistances in serie to gate and from=20 gate to ground) driving the pushpull with a IXD609 via a transformer.=20 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=20 conducting=20 > on the Source-Gate path. If they are on a common bias source, the=20 > Source voltage will open up all FETs connected. Leads to immediate=20 > death of all of them. Use individual bias on each of them. I had=20 that=20 > happen a few times b4 i learned my lesson. Of course capacitive=20 > blocking of DC from the input transformer is essential too. But i=20 > think these thoughts have been published here b4. > I am in the process of putting a single tube to use on 472. But its=20 a=20 > 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=20 content with my homemade tube PA for LF and MF which has provided=20 reliable service since nearly 4 years now. Only some thoughts about=20 this=20 concept - I hope not to bore all those hams who are happy with their=20 semiconductor PAs: Years ago I had a MOSFET PA for LF, Class B push-pull with 250 W RF.=20 It=20 worked well at constant conditions, but when I had to retune the=20 antenna=20 due to larger QSY or made antenna experiments there always was the=20 danger of blowing up these nervous semiconductors. After 4 or 5 times=20 changing the MOSFETS I decided to build a new PA - with tubes! Looking=20 a=20 little bit anachronistic this PA is absolutey good-natured. Designed=20 for=20 broadband service on LF and MF it makes no problems when changing the=20 antenna coars tuning=C2=A0 from one band to the other even when the fine=20 tuning is=C2=B4nt done yet. With my former MOSFET-PA this would have been=20 impossible. I wanted to have a linear PA - this usually means class B. You have to=20 decide between narrow band and broad band (like an audio-amp) design.=20 For narrow band you can use a single-ended PA but you have to add a=20 resonance circuit. For broad band you should use a push-pull PA and=20 have=20 to build a suitable output transformer. I opted for broad band design=20 because it is usable for LF and MF without changes at the PA. With=20 this=20 design and sin-driving I reach a total harmonic distortion of about 5=20 %=20 at 700 W RF on a pure resistive dummy load. With the usual narrow,=20 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=20 voltages of several kV all output circuits have rather high=20 impedances,=20 that means large coils for the resonance circuits resp. large=20 transformer windings and very high voltages - potentially a=20 construction=20 problem. This led me to the choice of 2x 4x PL519 in push-pull, a=20 rugged=20 colour TV line output tube with low plate voltage and high plate=20 current. In this way I came down to a plate-to-plate resistance of=20 about=20 1 kOhm at 600 V DC plate voltage, where you easily can build a ferrite=20 broad band output transformer down to 50 Ohms. A disadvantage of this=20 concept is that you have to give individual bias to each tube, that=20 means for the first start-up you have to align 8 potentiometers=20 carefully to nearly equal cathode currents for all the tubes. But=20 according to my experience this alignment remains stable over a long=20 time. I have inserted 1-Ohm-resistors in each cathode line and have=20 brought the voltage drops to 8 cinch connectors, where I can monitor=20 the=20 DC component (with external filtering) as well as the real time=20 current.=20 With 4 tubes in parallel per branch of course you have to take care=20 for=20 self oscillations. The extensive use of bypass capacitors, ferrite=20 beads=20 and parasitic chokes in the plate lines is mandatory as well as good=20 grounding concepts are. The tubes don=C2=B4t pull control grid current=20 (this=20 would even be true in class C!) but you need 3 or 4 W RF input power=20 due=20 to all the ohmic loads at the tube=C2=B4s control grids caused by the=20 individual bias paths. On the other hand this certainly helps to avoid=20 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=20 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=20 consuming=20 enterprise. I didn=C2=B4t count the working hours but according to my lab=20 log=20 the whole project took about 9 months - an adequate time for a new=20 baby!=20 It was a great experience anyway. Good luck and 73, Tom, DK1IS --_853A0BB3-2753-48F1-B94E-3AA9DDB0CA3C_ Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset="utf-8"

 

 

Sent from Mail for Windows 10

 

=

From: g3kevmal@talktalk.net
Sent: 02 April 2017 15:28
To: m= arcocadeddu@tin.it
Subject: RE: LF: FETs getting sick - why n= ot use tubes?

 

HI PA AMP folks

 =

Surprised more LF/MF ops do not use the DECC= CA 5501 design, class D mosfets in bridge configuration with series resonan= t output then matching ferrite transformer to match either 50 or 75 ohms.

I have been using this method now for sev= eral 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 b= eat. 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

 

 

Sent from Mail for Windows 10=

 

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

<= p class=3DMsoNormal> 

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 so= me 6146B and PL519s as

spare parts of o= lder 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: re= place/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 tr= ansformer.

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

 

Hope next FET will survive eno= ugh time to check what is going wrong...

 

73 Marco IK1HSS

 

----Messaggio = originale----

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?

 

Am 02.04.2= 017 um 13:09 schrieb Dr. Wolf Ostwald:

&= gt; hi Marco !

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

conducting

> on the Source-Gate pat= h. If they are on a common bias source, the

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

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

that <= o:p>

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

> block= ing 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 a= nd MF which has provided

reliable servi= ce since nearly 4 years now. Only some thoughts about

this

concept - I hope no= t to bore all those hams who are happy with their

semiconductor PAs:

&nb= sp;

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 the= se nervous semiconductors. After 4 or 5 times

changing the MOSFETS I decided to build a new PA - with tubes! Looki= ng

a

little bit anachronistic this PA is absolutey good-natured. Designed

for

bro= adband 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 us= ually 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. Fo= r 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

d= esign and sin-driving I reach a total harmonic distortion of about 5 <= /o:p>

%

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

impeda= nces,

that means large coils for the re= sonance circuits resp. large

transforme= r 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 out= put 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 <= o:p>

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

<= p class=3DMsoNormal>means for the first start-up you have to align 8 potent= iometers

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

acc= ording to my experience this alignment remains stable over a long

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

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

the

DC component (with ext= ernal filtering) as well as the real time

current.

With 4 tubes in parallel pe= r 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 line= s is mandatory as well as good

groundin= g concepts are. The tubes don=C2=B4t pull control grid current <= /p>

(this

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

=

due

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

individual bias paths. On the other hand this certainly he= lps 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 d= idn=C2=B4t count the working hours but according to my lab

<= p class=3DMsoNormal>log

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

baby!

It was a great exper= ience anyway.

 

Good luck and 73,

Tom, D= K1IS

 

 

 

 

 =

 

&nb= sp;

 

 

 

= --_853A0BB3-2753-48F1-B94E-3AA9DDB0CA3C_--