ZS6DX's home page

As much as I love QRP I also love amplifiers, specifically tube amplifiers, I love modifying them, building them and just playing with them! There is something magical about glowing bottles and high voltages producing lots of RF....

I have also started using my station a bit more for "rag-chewing" with some local technical groups. Since I am no longer (from 2019) resident in a large city with a radio club I have been missing the technical discussions at the club. For these QSO's, mostly on 40m, I now often run higher power when conditions are not good or other stations have small antennas or bad QRM/QRN, it is far ore fun to chat when all signals are strong plus it gives me the perfect excuse to run my amplifiers!

Below are the amplifiers in no particular order I have at the moment with a few comments on them. This page is still "work in progress" as I will add more detail and photos when I get a chance.

Heathkit SB-200 Amplifier

Update 20/01/2015: After waiting since August 2014 for parts that I ordered from Harbach electronics for my Heathkit SB-200 amplifier they finally arrived! The delay was caused by our local, useless, postal service going on strike for months! Minutes after the parts were delivered I was busy assembling the kits. I ordered a power supply module, soft start and soft key for the SB-200. I also ordered 2 soft key kits for my TL-922's but I will install them later when I have nothing to do....

Below you can see the 3 kits for the SB-200 assembled.

Top view of old power supply

Bottom view of new power supply. The extra transformer at the bottom supplies 12V to an extra cooling fan on top that I installed a while ago.

Metron MA1000 Solid state HF amplifier.

The Metron MA1000 is very similar to the T1000 but it runs from 12V with a max output of 600w (The T1000 is a 1kw with 100% duty cycle amplifier.)

The Metron is extremely well made and robust, they don't build them like this anymore! This sample is brand new, I took it brand new out of the box. With it's switchable (manual or automatic) band pass filters, it produces a nice clean signal.

It does need a decent power supply that can produce at least 80A without a voltage drop. I have been testing it with an old Kenwood linear power supply than can do 40A all day, the power supply is in parallel with a 100Ah seep cycle 12V battery. When you are transmitting power is supplied by the power supply and the battery and when you are not drawing high current the power supply, set to 13.8V, is charging the battery till it is full and then it will float charge the battery. I have used a similar setup in the past for high current demand systems and it works well.

Metron MA1000 Solid state amplifier

Inside of the Metron MA1000, it uses 8 x MRF 454 transistors, you can also see the relay switched band pass filters.

In the above photo you can see that 2 of the relays are open. As standard maintenance I always clean T/R switching relays on all of my amplifiers on a regular basis.

Yaesu FL-7000 solid state amplifier.

What I like most about this amplifier is the no tune, no touch operation you can have when matched to a Yaesu radio with the internal tuner and auto band switching.

I finally have my FL-7000 running again. A while ago it had a brush with lightning, it was unplugged from both the antenna and the power but a direct hit on one of my antennas caused some sparks, and I assume induction, into the shack.

The next time I wanted to use it it was stone dead, a quick check showed that the fuse was fine so the amplifier was moved to the workbench for later attention, well, that attention only happened 4 years later!

It turned out that the fix was simple, the 48V supply seemed to be fine but there was no 8V or 12V to be found anywhere. So I replaced the 8 and 12V regulators and checked everything else on the power supply PCB.

After putting it all together again I switched her on and there was life! A few checks showed that all was well, she is producing power as expected, the auto-band changing and tuner is working and the fans switch on when they should.

I am happy to have the old workhorse back, the amp is so quiet and you do not have to even touch it when you change bands it is a real pleasure to operate.

Up and running again!

Inside top view

Power regulator section, this was where the problem was.

Automatic tuner

Finals heat sink and cooling fan.

Transformer and power supply.

Trans World T1000 solid state amplifier

I seldom use amplifiers these days but again I decided to keep it, the robust "no-tune" operation is just too good to give up, maybe one day I will need a bit more power?

Fischer F70 New

I finally found time to go and fetch my new 70cm amplifier. It is a Fischer F70. It runs a single 4CX250 for a maximum output of 500W, more realistically would be 300-400W. It seems to be well made (German) and in a great condition. Here she is.

Front panel, no tuning needed on this mono band amplifier.

Top view showing the RF compartment with the 4CX250R

Bottom view showing the power supply and blower inlet.

Connectors on the back

Closer look at the RF compartment open.

Update 18/09/2014 And then were two! I added a second TL-922 to the shack. The idea is to have 2 identical radios and amplifiers for the main contesting station.

Two Kenwood TL-922's in the main operating position.

Classic amplifier using 2 x 3-500Z tubes.

This is a new addition to my shack, I have cleaned it up, it was rather dusty, after a 2 hour warm-up to reform the capacitors and heat the tubes I applied RF and it is working well!

Below are a few photos of the inside of the amplifier.

Tubes removed and tuning capacitors ready to be cleaned.

Ready to close up and give it a try!

Update 15/06/2014: I have now been using this amplifier for a while and what a great amplifier it is! It just sits there with it's quiet fan producing lots of power without any fuss, I am glad I added this amplifier to the shack.

Yaesu FL-2100Z

This amplifier uses 2 x 572B tubes and is a classic from Yaesu.
This amplifier had been the work-horse in my shack for a long time, since we have a 400w power limit (Update - now 1KW) it copes well and has been reliable.

Heathkit SB-200

Amplifier using 2 x 572B tubes.
This amplifier had been modified, by someone else, for 6m use. I am not really happy with the mod so when I have time I will either return it to original configuration or maybe do a better 6m mod.

I need to replace the smoothing capacitors in the power supply before using the amplifier again, they are still original and not well!

Heathkit HL 2200

Classic amplifier using 2 x 3-500Z tubes
Currently (June 2014) this amplifier is down for maintenance with a faulty stand-by switch.

Update 15/06/2014: I thought I sorted out the standby switch after cleaning it but the problem returned after a while. Since only one side of the switch was used I simply turned it around and now she keys perfectly again. I operated her for a few hours, and then suddenly the output dropped. A quick looked showed that only one tube was lit up. This happened a while ago with the other tube and turned out to be heater pins that unsoldered themselves due to heat. I should have re-soldered both tubes last time! So I have to pull the amplifier from the bottom of the stack again to fix her.....

While she is open I will take a few photos to post here.

Update 16/06/2014: I spent some time today opening up the HL-2200 to find out why the output had dropped again. It turned out that I was correct, the one tube was dark, the one I did not re-solder last time. A quick check with a multi meter showed an open circuit filament. I carefully re-soldered both pins and the open circuit went away! After putting the tube back all was well again with the power output restored to previous levels!

Henry Tempo 6N2 New

The 6N2 is an interesting amplifier. It uses 2 x 3CX400A7 (8874) tubes, operating in push-pull mode for 2m and parallel for 6m. The amplifier is capable of 1kw output so it should add some punch to my signal on 2 and 6m. It has independent controls for the 2 bands and you can have 2 radios and 2 antennas connected at the same time.

Below are a few photos of the inside of the amplifier before I started cleaning it.

Interesting matching and tuning setup.

Time delay relay, I have never seen one of these before!

6m vacuum tuning capacitor.

Rather dirty 3CX400A7 (8874) valve

Update 10/06/2014: I did get a bit of time today to clean the Henry Tempo 6N2 amplifier, it is now looking new again! I was hoping to connect it up but after studying the manual it seems to be not that simple!

The amplifier does not have an internal antenna switch over relay so you have to add an external relay to switch the antenna over AND switch the tube bias, wonder why they did not add an internal relay? Anyway, I have a few relays but need to make sure I have one that can handle 1kw of VHF RF! So it will take a while to get it going.....

Homebrew HF amplifier with 4-400

My first (and only!) attempt at a completely home-brew amplifier, the 1 x 4-400 tube give me an easy "legal limit" (South Africa before we were allowed 1KW) output on all HF bands. I learned a lot while designing and building this amplifier. It is loosely based on a few different circuits I found in ARRL manuals and on the internet, had to make it work with the components I could find.

The case I made from sheet aluminum and a few bars, it is not pretty but it is sturdy and functional. The cooling fan is from an old mainframe computer and the high voltage transformer was salvaged from a microwave oven.

At the moment (June 2014) I am not using this amplifier but the plan is to give it a good check over and return it to service soon.

Update August 2023: After many years of gathering dust and being move twice to new QTH's I have decided to give this amplifier a good clean and maybe repaint the case. I then want to move it to my "rag chewing" station (space! I need more space!) to be used on mostly 40m for my daily chats, would be nice to report that I am running a "home-brew" amplifier!

Update 16/06/2014: I opened up the amplifier today and checked everything, no problems were found and when I applied power she worked perfectly like the day I finished building her.

Looks ok, lets apply power!

Running and producing power, the single 4-400 (have also used a 4-250) will give me 400w but not much more, since 400w is our legal limit that is perfect.

Yaesu FL-7700

A nice SS amplifier with internal auto tuner. Mine needs some work at the moment as the12V supply is dead after an encounter with lightning, and it was not even connected to the antenna.... I am hoping to sort it out sometime soon.

TW-1000 1KW SS

A SS HF amplifier build like a tank! I have not used this amplifier for years, I think the last time I did was when I used it in a contest, and I have not run a high power contest since 1998! This amplifier will run 1kw with 100% duty cycle in any mode for as long as you want, it was used by embassies for RTTY, CW and SSB in the days before satellite telephones.

Update 26/06/2014: I decided to check my TW-1000 amplifier and prepare it for use. I decided to connect PTT and ALC cables internally to the controller rather than the 12 pin external plug, I plug I could never find and I was not happy with my previous temporary arrangement. I must say I forgot how heavy the amplifier is, around 40kg, everything is super heavy duty including the internal 120A 28V power supply!

This amplifier is a thing of beauty, I normally prefer tube amplifiers but this one is special. It can run any mode full power with 100% duty cycle for as long as you want.

I cleaned the inside and made sure everything is ok, the insides look like new. A quick test showed that the new PTT and ALC connectors are working. Now I need to make space for her in the shack, not yet sure where to put her due to her weight and size.

I have not connected the auto band switching yet, might do it sometime but it is easy enough to push the correct button on the front panel.

TE Systems 1452G

400W SS amplifier for 2M.

I have used this amplifier for 2m weak signal work in the past, it will now largely be replaced by the Henry Tempo 6N2