Eimac 3-400Z or 3-500Z Grounded Grid Linear Amplifier Build For Amateur Radio 

Thank you. I am glad you liked it. That approach has served me well for a very long time. I started this forst project in 1983 and have placed 4-400A, 4CX1000A and 3-1000Z amplifier chassis in the Collins 30K-1 cabinet for RF amplifiers. . As for this smaller cabinet in the video. I have placed 813 audio amplifier, 833A SE amplifier, 3-400Z RF amplifier, all I can remember at the moment, using the common power supply. Sure saves a lot of time and work building the power supplies over and over. Stay safe from the high voltage and enjoy.

Jim, Thank you. This amplifier gets used (daily) more than any other amplifier I have. I have moved it into the PS cabinet I used for the 833A amp as the PS components in that cabinet are a bit larger than the cabinet I installed this amplifier in originally. It delivers between 500 and 600 watts (depending on the line voltage at any one time during the day) and just keeps on working. The Eimac tubes are, by far, the best. I am told it sounds good and is definitely a "keeper" in my opinion. When I operate the 4CX1000A amp I do get reports of a little more S-meter increase but really nothing as far as strength or quality of sound level even though the bigger amp puts out twice the power. I have found that 500 watts is a good power level and anything over that is generally not going to help very much. 73

Hi Johan, Interesting that you found more output on the 3-400Z than the 3-500Z. That has been my experience also. I do not have any new Eimac 3-500Z's to test only the newly made ones in China. There was a seller that had a stash of about a dozen beautiful 3-400Z's not long ago on Ebay. I bought two of them and have, I think, six of 3-400Z's now. I agree that the 813 is a true workhorse. I have a number of good 813's and am considering an amplifier using two of them. The 4-1000A is a tube that during the days I had a number of them, did not choose to build a 5-6 KV power supply and found quickly that even at 4KV they don't perform that well. My biggest amp is the 3-1000Z and I am pleased with it but lately I seem to use the 833A amp and the iCom 736 rather than all the S-Line stuff and R-390 which I love. I assume you found the 833A videos I have posted. Here is one of them. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-ChHPL84f22Q.html Please send me the link to your 4-1000A video. Thanks for your comments.

Thank you.

They made 3.500z and a 4-400a..Nice work as usual.

I am building another as I write... a little different but it is going to be a 833A. Can't be a GG amp as the 833A is a medium mu triode but of the few I can find around on the Internet where others have built and posted, driving the grid with somewhere around -100 volts on the grid (depending on the plate voltage) seems to work well. I have a very nice B&W 852 which I would like to use but I have some homework before I decide if it can be used. I only operate on 20 M but rather not make it just a single band with 1/4 inch copper tubing for the tank coil. Thanks for the nice comments. I operate this amplifier along with my 3-1000Z and the performance of this smaller amp is impressive. What made a Huge difference is running 240 with #6 wire into the radio room. Wow... it makes a serious difference even in a "smaller" 1 KW PEP amp like this one. I tried using this amp plugged into the wall along with the exciter and it loaded the AC circuit so much that the power dropped out of the driver (32S-3) and just became strange to try to tune up. Now that it operate on its own 240 volt circuit. it works great. Lastly, all of my equipment is 120 volt but, the 240 V I run into the radio room is stepped-down with a 5KVA auto transformer. That is the way I get sufficient power to my amplifiers. Are you considering getting back into your 3-500Z project?

Hi Joe, I don't know if I can answer all your questions but I will try. I did not check the plate choke for resonate points. I know that can be a problem if I plan on using it on all bands but I only have antennas for 20 and 40. I have built many amps with the B&W 800 and the National R-175 and I have never had any issues. I used the B&W tank just because I have it. Most of the amps I have built starting in 1970 are single band amps and I wound those tank coils out of 1/4 inch copper tubing. Worked great. I don't have room for 160 meter antennas and basically I only operate 20 meters, so, there again. I have made the PS with the ability to use it as choke input or capacitor input just in case I need one of the voltages. With the switch to change the secondary taps and the ability to add or remove the input capacitor, I have basically six voltage selections on my HV supply. I use series electrolytic as they are cheap and small. I like the big oil filled caps and I do use them in my 3-1000Z amp built into a Collins 30K-1 cabinet (there is a video on that also) but they are large. My plate current may be a bit high as I run 3500 bolts on the 3-400Z instead of 3000. The amplifier slides into a cabinet with a cover over the back mostly for safety and I suppose it offers some RF shielding and yes, the only cooling I have is the little muffin fan. It puts a good bit of air across the tube at least as much as Heathkit did with their SB-220 and pair of 3-500Z's. I have built and run a 4CX1000A for over 30 years but I like the glass tubes where I can see the plate running orange hot. 73, WA4QGA Maybe we will meet on 20 meter SSB some time.

Thank you. Yes, some of the parts are not available on Ebay very often like the B&W 850A or either they are in bad shape. I agree that the tubes are still available and the Jennings vacuum capacitors are always out there for sale but sometimes they are a bit too expensive for me. With patience I seem to be able to find most anything, eventually, at a reasonable price. This is the first time I have used a commercially made filament choke, in this case the B&W FC-15. I have always wound my own with #10 formvar wire around a ferrite rod.

Absolutely unbelievable and professional build on that amp! Thank you for the video.

Michael Lloyd amp Li. Amplifitori rf hf con valvola russa ry81

I has several pole pigs years ago. They were all 10:1 so I could get 2400 volts. Into a doubler I would have had about 6500 volts DC but I couldn't afford capacitors to handle that voltage during those years. That would have surely made the 4-1000A scream. I have built 4-1000A amps but always at a plate voltage of 3500 volts (my capacitors in those days were limited to 4 KV) but they didn't perform very well. Same for the 833A. Nowadays I could afford it but don't have the room. I am really pleased with my latest 3-1000Z amp at 3500 volts on the plate although I think the pair of 4-400A may look the best in the old Collins cabinet. I do feed this amp with 240 and the regulation is very good. Too bad when we are young and have the energy, we don't have the money and you know the rest... :-) Thanks for your comments.

I know what a pole pig is...

The turns counters are from multi-turns pots. They can count to 14.99 and then it just wraps around to zero again and starts over. That can be dealt with, with close attention. Certainly that is not ideal but the better turns counters that I have are too large to fit the front of this amplifier. You can notice that I made a bracket to stack the vacuum capacitors vertically just to save a little room. The B&W 850A takes up a lot of room on the chassis. I will keep looking around for some simple, and smaller, turns counters on Ebay and may change them out with better ones in time. I personally love the vacuum capacitors because the tuning cap goes from 5-500 pF at 5KV in such a small package. Also, the loading cap is 2000 pF at 5 KV. An air variable capacitor of that raging wouldn't fit on the chassis. I haven't tuned it up on any other band but 20 meters so far. I am thinking of building an outboard 80-10 meter tuned circuit with switching that I can mount on the rear of the chassis so I can use it on all bands. Thanks for your comments.

Thank you. I use this amplifier a lot for 20M and 40M SSB. I have never gotten into building PI L networks. The old B&W tank coils are real jewels to build with and will take a full KW of high-level plate modulated AM so they are just loafing along with a few hundred watts of SSB. 73

Thank you. That's a good question and I have been asked it before. Since my first larger amplifier in 1970, I have turned the HV power supply on when transmitting and off during receive. I know that is not common but if I remember correctly, way back when... I only had oil type capacitors that were rated at 3KV and with a load on the PS the voltage would be proper at about 2500 for a pair of 813's but under no load (or with the tube biased off) the voltage would soar above the voltage rating of the capacitor so I build my amplifiers so there is no HV unless the amplifier is actually amplifying and transmitting so I don't need any bias to cut the tube off. A similar style of building is my placement of the meters, in particular the plate meter, in the HV line. Only recently have I started putting the plate meter in the return line of the HV power supply. In a similar manner, I do not DC ground the grids of triodes, like the 3-400Z, etc., at the socket. I bypass each grid connection to ground with capacitors and then DC ground the grid thru the grid current meter. In the case of GG tetrode amplifiers, I do ground the screen for DC at the socket but once again, bypass the grid connections to ground for RF and provide the DC path to ground thru the grid current meter. I know this is not all according to some old and approved methods but I have never had instability or parasitic issues with any of my GG amplifiers. Hope this helps.

The only time I seem to be happy is when I am working on my projects. Besides, being sane is boring. :-)

I guess that could be a little confusing. In this video it is running the foreign made 3-500Z but in real life I use an Eimac 3-400Z and get more power out of it.

I will take a look. theaudioshop@sbcglobal.net is my RU-vid email.

Many of my tubes were made in the 1970's and '80's, some even in the 1950's and they work fine. If a tube is "born" good and strong and it is not run hard and overloaded and over heated, it can last a long time. An exact number of years is impossible to say. Many of the high-power transmitting tubes available today were run for some allotted amount of time in commercial transmitters, then replaced on a schedule and they are very good today in amateur radio transmitters even thought they are likely well over 40 years old. Most are not even made anymore but we keep building with them. Tubes like, just for examples, 6L6, EL34, 6550/KT88 that you find on Ebay with great test numbers, do not often times turn out anywhere near they are advertised to be in performance. Just because a tube "tests strong" does not mean it will perform well in real equipment. Tube testers are not worthless but they only tell a little bit of the story of a tubes performance. Most of the power-tubes as mentioned above for sale on Ebay perform poorly. On the other hand, tubes like the 12AX7 family of tubes can perform very well even though they are 50 years, or more, of age. They don't run hot and who knows how long they will last. Hope this helps.

@@ElPasoTubeAmps Thanks for the answer. I made a nixie clock with some Russian tubes from the 60s NOS and they have been running 24/7 for 6 years now. However, the power between your 500Z is many magnitudes higher than my little IN-17 with 190 only volts. 🙂

Yes, it is Jennings CSL 2000. I don't remember the lower range in pF but the upper range is 2000 pF and the voltage rating is 2000 VDC. I got lucky and found it on Ebay for $49.95 + shipping. I have recently seen another 2000 pF listing at a starting price of $800.00. Way too much in my opinion. Here is the current Ebay listing - www.ebay.com/itm/JENNINGS-Vacuum-Variable-Capacitor-UCSL-2000-3S-/112252553912?hash=item1a22c60ab8:g:Vt8AAOSwImRYZXSD

TheAudioShop@SBCGlobal.net is my RU-vid email address.

Ten-Tec is in Tennessee and so is Dolly Parton. I guess it has to be... :-)

ElPaso TubeAmps I'd love to see a schematic of this one. The RF amplifier I mean. Well, Dolly, too, if you can find a schematic of her :-|

Copy and paste the text below into Google and it will take you to a site that will download a PDF and does a really good job of calculating the input tuned circuits for the 3-400Z. I use 100 ohms for the input Z of the tube. I just recently built this into the amplifier so it will work on all five HF bands. I do actually draw schematics and put them in an envelope inside the cabinet but I don't have a one full schematic of it. RF Power Amplifier (RFPA) Designing a 'Input Tank Circuit' - AMfone