K5LAD - 50 Years of Ham Radio Memories

Volume XXV


DX Building HF Amplifiers

 I recently received the following interesting email message from Andre – V51B in Namibia, (SW) Africa.  (Note that Namibia is marked on the map below with a red square border surrounding a yellow dot.)  This screen print is from Logger32’s Tracking window - DX View.  Logger32 software is available (free) at http://www.logger32.net.

 clip_image002.jpg (24472 bytes) 

Andre had seen the article on my website about the 4-1000A amplifier http://www.hayseed.net/~jpk5lad/4-1000A Amp/4-1000a Menu.htm that I’d built back in the 1970s.  Only within the past several years did I finally get around and get together all the random notes and scraps of paper where I had designed, drawn, borrowed ideas, and identified pieces actually used in my amplifier.  Good design principles would have dictated that I do all of this before ever starting the construction job.  Since I’ve already admitted to not preparing the documentation package until 25+ years after completing the amplifier, I guess that shows anyone reading this what type of designer/builder of electronics equipment that I am.  I throw myself on the mercy of the court (is there a statute of limitations on these things?) 

Andre had built his own 4-1000A amplifier but had “taken my bet and raised me two” by doubling the number of these tubes for his unit.  The picture he included shows his finished product and it looks like a really nice job, and by his description of his first efforts on the air with it, it must have been, what we call, “Smokin’ Hot!”

I thought, perhaps, it might be of some interest to readers of the TARC Transmitter Newsletter and later to anyone else who stumbled across the information on my ever-growing website www.hayseed.net\~jpk5lad\    Every ham should have the experience, at least once in their life, to build an HF amplifier.

The amplifiers mentioned in the article are capable of running higher power than is dictated for amateurs in these African nations.  The amateurs involved used these parts, including tubes, which were available to them and these particular devices run much more efficiently at the higher voltages.  Also, the countries involved are currently in discussions and negotiations to raise their power limits for amateur radio operators.  As it stands now, these operators are like the guy with a 500+ horsepower automobile engine having to drive on a highway that only allows drivers to go 25 MPH.  When the time comes, however, they’ll be ready.

From:                 "Andre & Ronelle Pretorius" <anro@iway.na>

To:                     <jpk5lad@cox.net>

Subject:              4-1000A amplifier

Date sent:          Sat, 24 Jul 2010 22:03:39 +0100

 Hi Jim, I thought it best to send you this mail.

I have seen your website a couple of months ago and decided this is the amp I need. Thus, I started in the beginning of May and completed the amp last week Friday. I ended up putting 2 of these tubes in parallel in the finals.

HExxS BELLS it almost puts my trees on fire. 

Just want to say thank you for such comprehensive schematics. It made life much easier. Included is a pic of my amp. It is a split unit. On the left is power supply and to the right is the RF deck.


clip_image004.jpg (12866 bytes)

This amp has certainly put me on the map!!!


Andre V51B

From:                 jpk5lad@cox.net

To:                     "Andre & Ronelle Pretorius" <anro@iway.na>

Subject:              Re: 4-1000A amplifier

Date sent:          Mon, 26 Jul 2010 18:35:58 -0500

 Hi Andre --

Thanks for the nice note and the picture of your new amplifier.  It looks like it's a dandy and, hey, if it almost sets the trees on fire...... it must be doing its job.

 I built mine back in the 1970s and it was only within the last few years that I finally took all the scraps of paper with various bits and pieces of the whole thing and placing them all together.   Waiting more than 25 years to complete the documentation has caused me to lose a lot of the original information in the building but I guess I remembered enough to be a small bit of help.

I went back to my log and noticed that I'd worked you on 20m back on Nov. 12 of 2007 and I've got my logbook marked to send you a card the next time I send out a batch of cards.  (Gosh, am I THAT FAR behind in my QSL cards?........... I guess I am)  I've been looking to get some more printed so look for a QSL card from me................... but don't stand out by the mailbox waiting.  It will be there, however, .......................... eventually.

By the way --- I don't remember if I mentioned it in the info on my website but I remember, back in the 70s, talking to a guy or reading about a guy building a 4-1000A amp and he took a one gallon pickle jar and cut out the complete bottom and part of the

top and he used that as a forced-air chimney for his 4-1000A.  When I built my amp, I bought a regular commercial Pyrex chimney made for it (seems like it only cost about $12 back then but I'll bet they're plenty more than that now).  I always tucked that pickle jar hint into the back of my mind and figured I'd give it a try if something ever happened to my Pyrex chimney.  Maybe you can hang onto that info too and maybe some day it will come in handy.

Again, I appreciate your note and it makes it all worthwhile to have gotten all the info together and publish it if it helps others.

  I'll be looking for your signal on the bands and will, for sure, give you a call and I KNOW I'll be able to hear you!!!  I just hope when we make contact that you won't need to QRT immediately to go outside and put the fires out in your trees.

73,  Jim - K5LAD

 Hmmmmm --- I just had another thought............ I wonder how long it would take to eat a gallon jar full of pickles............. and you'd need to eat two gallons!  How well do you like pickles? 

From: "Andre & Ronelle Pretorius" <anro@iway.na>

To: <jpk5lad@cox.net>

Subject: FW: 4-1000A amplifier

Date sent:          Tue, 27 Jul 2010 06:44:28 +0100

Hi Jim, thanks for the reply. I have to admit; some of the credit must go to Danie ZS3D as he directed me to your website. Danie built your amplifier about 2 months ago and that made me decide to in turn build your amp (after having heard Danie on air).

 It's strange you mentioned the pickle jar thing..... I don't have the original Pyrex chimneys. So I contacted Danie and got the measurements of the chimneys, and thus made 2 of the "homebrew chimneys". Included is a picture of the chimney(s). That was while I was busy with the construction. 

Front deck


HV power supply

Filament transformer and caps

Rectifier and bleeder board

Rebuilt power supply

100%, as you said we have worked before. I did not even think to actually look into my log, and yes on the 12th November 2007. Not to worry to much as I've got a State side manager.

Thanks very much for putting your info on the web. That resulted in 2 hams from Africa building according to your design.

 73   Andre

From: jpk5lad@cox.net

To: "Andre & Ronelle Pretorius" <anro@iway.na>

Subject: Re: FW: 4-1000A amplifier

Date sent:          Tue, 27 Jul 2010 01:50:41 -0500

 Andre --

Hey, that's super.  That makes me even happier to hear that several others have built an amp from some of my information.   Just a couple of hours ago, after re-reading your original message, I went back and did some looking at my website info on the amp and I see that I left out some pieces of information...... for instance in the list of materials I was listing where a particular piece was used and I'd just left them blank.  I'm sure that didn't slow you down any but it might cause someone to hesitate a bit.

 Also, some of the original photographs that I took back 35 years ago and just tried to rescan them to digital files are really bad.  I think I'll spend some good time with my digital camera and try to duplicate the angles for those first pictures and improve the resolution.  Then I can swap out the new pix for old.

 I noticed also that you might do LoTW QSLing so we could also do that.  I try to upload a new batch of mine about every week or so and often do a download every day.   I didn't see any contacts with Danie in my logbook but I'll listen closely for him too.  Logger32 has a feature to add calls you're on the lookout to catch.  I've already added yours and I'll add him too.  It constantly looks at the DX clusters and checks against my list. 

 Andre, would you mind if I put all of our email communications and your pictures into an article to be used for our radio club newsletter?  I write an article just about every month and once it's been published to the members, I add it to my website, usually in the 50 Years in Ham Radio area.  I think others would find your experiences and your pictures to be helpful to them too.   If you had any other pictures that you think might add to the article, I wouldn't turn them down either.

 Well, it's coming up on 2 AM here in Oklahoma and even though I'm retired and don't have to get up for a job, I probably should hit the hay so I don't sleep until noon tomorrow.  I'm always afraid that if I sleep too late my wife will just call the undertaker (or the trash service people) to carry me out, feet first.

 Thanks for all the feedback on your building project.  It might encourage me to get back to a few "on hold" projects myself.


Jim - K5LAD

 From: "Andre & Ronelle Pretorius" <anro@iway.na>

To: <jpk5lad@cox.net>

Subject: My 2 x 4-1000A amplifier

Date sent:          Tue, 27 Jul 2010 13:52:24 +0100

Hi Jim, ok herewith my story.

At the end of April 2010 I heard Danie ZS3D on air with his newly constructed 2 x 4-1000A in the finals. That was a booming signal (not that Danie has never had a good signal…………. but wow). Being very good friends with Danie, I asked him what schematic he used and Danie directed me to your website.

With NO experience in building an amplifier let alone a tuner I set my mind into constructing this beast. I started at the beginning of May and managed to finish it by Friday 16 of July (just over 2 months). It took me some time to find all the parts. Between Danie and I we got all the critical components for my amp….. filament transformer, HV transformer, etc, and most importantly the tubes and bases.  I will save the best for last (what to do with the chimneys)?

The cabinet that holds the HV supply, rectifier board (full bridge), filament transformer, soft start circuit, etc. comes from a reclaimed/scrapped utility kiosk –the type you would find on the corner of the streets. The RF Deck I managed salvage from the original HV supply cabinet had. Thus, I had to convert the HV cabinet to house the tubes, etc.

After many text messages, emails, telephone calls between Danie and I we eventually got it working and it nearly sets my trees on fire!!!! Included are some of my construction pictures.

As a last word to your original diagram: we did not include a tuned input circuit, as we decided we both have tuners on our rigs (Icom 756) and that should tune the input side of the amplifier. We both used roller inductors for band selection.

So what about the chimneys you might ask? Well Danie was lucky enough to got hold of the original Pyrex chimneys, but I was not. I had to improvise and decided to use empty “coffee tins”. After getting the dimensions/measurements from Danie, I measured and cut the tins accordingly. Believe me they might not be pretty but yet they are very effective!!

Thank you for your website and diagrams. Ours was constructed to almost exactly to your specifications!!!


73 Andre V51B

PS: I am very active on 40m in the mornings (around 05:00Z) on (+/- QRM)7.140

 From: "Danie Mans" <zs3d@vodamail.co.za>

To: <jpk5lad@cox.net>

Subject: From Danie Mans

Date sent:          Tue, 27 Jul 2010 19:39:46 +0200

 Hi Jim

Andre, V51B, has told me to send you a email.  I have used your schematic on the 4-1000a Linear and have completed my linear about 2 months ago and is very please with its performance.

Thanks for all the info on your website.

I have about 5000v on the plate and with 100w drive the output is about 2, 8kw and with 200w drive it is ………… !!!!!!! ( Plate 5000v @ 1.5amp and with 250w drive plate is 5000v @ 1.75amp )

Here is a few pics and if you want to know more please let me know.


The hv power supply

The slow start.

The rf deck without tubes

The rf deck with tubes and vacuum cap fitted for plate tuning,

The top front panel

The big boy.


Thanks again.   

Looking forward to a contact with you. I am most of the time on 40 meters.


Danie Mans - ZS3D

 From: jpk5lad@cox.net

To: "Danie Mans" <zs3d@vodamail.co.za>

Subject: Re: From Danie Mans

Date sent:          Tue, 27 Jul 2010 13:08:47 -0500

 Hi Dani ---

WOW!!  That's a nice looking piece of equipment.  You do some excellent construction work.

 Actually I was just answering Andre via email.  I just put the message in the stream and came back to see what other email I had and there was your message.   Thanks.

 I don't know if Andre told you what I had said but I mentioned that years ago I talked to or read about a guy who used one gallon pickle jars as replacement chimneys.  The bottom and part of the top was cut out to "chimneyize" it.  Andre used cut out coffee tins and that's a neat trick too but he misses the joy we have of watching those plates glow cherry red.

I haven't actually been using my big amp in several years, mostly because it takes up too much space for convenient operation but after talking to you and Andre, I may dig back into it and see about setting it back up.  Right now I'm using a new Yaesu Quadra and it's pretty fine too.  Actually I've been drawing up some ideas to have a relay box to allow me to switch to different amplifiers.  Some people just don't understand the statement that "a ham can NEVER have too many amplifiers"......... or rigs or antennas either, for that matter.

 Thanks again for writing and I'm happy the information on the website was useful.  I've put your call into my Logger32 DX audio alert box so whenever you and/or Andre show up on a DX cluster, it will tip me off, even if I'm across the room working on something else.


Jim - K5LAD

 From: jpk5lad@cox.net

To: "Andre & Ronelle Pretorius" <anro@iway.na>

Subject: Re: My 2 x 4-1000A amplifier

Date sent:          Tue, 27 Jul 2010 12:42:58 -0500

 OK Andre --

Thanks for the additional pictures and information on your new amplifier.   Although you didn't say anything about my request to use some of your pictures and communications, I'm assuming that you have no objection to me using them in an upcoming article.  I'd rather have a person's definite permission before using their information.

 When you mentioned about using two of the 4-1000As, the first thought that came to me was, "how easy was it to find a filament transformer for your beast?"  With each tube requiring 7.5 volts at 21 amps just for the filament, that's a BUNCH of power to provide and a gut-busting piece of iron to lift.  You didn't tear apart your arc welder did you? 


Your chimneys are neat and evidently quite practical and serviceable.  The only thing you miss out on is to be able to watch those plates glowing cherry red as you dominate the pileup.  The picture I use on my website was taken with a digital camera using only the light of the tube's filament.  Obviously the HV was off, grounded, and I made absolutely sure before I stuck my camera (and my hands) into that box.  The picture turned out so well that I use it as the wall-paper picture on my computer's desktop.  Also, they asked and I gave permission for them to use this picture in the Wikepedia entry for their info on 4-1000As.




As far as the construction of the amplifiers for both you and Danie, you both were able to complete your projects in a lot less time than it took me.  When I built mine I was teaching school full time and running a ham store full time.  That didn't leave too much time for building an amplifier (or sleeping, for that matter).  Somehow I was able to get them all done, or at least most of them all done.

 I'll try to listen for you on 40 meters but I don't have much of a 40 meter antenna.  Still I've worked into Europe and South America on 40 but I don't think I've gotten anyone in Africa.  I'll be listening but you may not be able to hear me.

 BTW - Who is your stateside QSL manager?


Jim - K5LAD

 From: "Andre & Ronelle Pretorius" <anro@iway.na>

To: <jpk5lad@cox.net>

Subject: RE: My 2 x 4-1000A amplifier

Date sent:          Tue, 27 Jul 2010 19:48:19 +0100

  Hi Jim, thanks for the reply and sorry for not saying so many words you're more than welcome to use the pictures in your article. Yes, the Pyrex does look nicer than the tins as you can see the filaments glow...........

 For the filament transformer: Danie had one for me (as he had 2 in the junk box) so I was lucky not to cannibalize my welding machine - and yes one could probably weld with it.

 My Stateside manager is OM Jeff Ai4U

 73 & enjoy the day


 This article has been a bit different than others I’ve prepared and may not appeal to all readers, but I suspect several of my stories and articles have not been interesting to some folks.  I’m just like the old codger who sits in his rocking chair on the front porch and tells stories about what it was like “in the good ole days,”   My stories just happen to be about ham radio experiences and I write mine down instead of telling them.

 If you’re an operator on the HF bands and like to spend most of your time operating rather than calling for stations, an amplifier will add that additional “umph” to your signal.  A good antenna is very important and provides improved communication on both transmit and receive but once you’ve got as good an antenna as you can provide to your station, much can be said for higher output power. 

 Written July 30, 2010

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