Improving the EB104 design

[K9AQ]

I am new to these forums, so this is my first posting.  I have read all of the forums on the pro's and con's of the EB104 amplifer design and circuit board.  I have build one and have been using it for several months.  It works wells but I am always looking to improve it.

From the posts that I have read, the common complaints are: the circuit board, poor RF grounding, and RF harmonics on the traces; and the output transformer design.

I have compared the board to the one used on the ALS1300 and it is quite apparent that there is alot of room for improvement of the EB104 board.  The ALS1300 also uses a different design output tranformer.

My first question is, has anyone designed a replacement circuit board for the EB104 that would have better RF grounding and make the design more repeatable by "average" hams?  If not, would anyone out here with the skills be willing to do so?  I am sure the Fred at Farcircuits would build it and make it available to the ham community.  ( I recently worked with him to build a 1 KW low pass band filter and relay board, but I don't have the skills to redesign the EB104 board).

The other question that I have is about the output transformer.  I have seen postings indicating that the design is not correct, but I have not seen anyone's recommendation on what, if anything, can be done to improve it.  Is there a better design that could be incorporated with a newly designed circuit board.

Lastly, is there a way to imrove the EB104 design without going to all this trouble?  I have found that my amplifier works much better without any capacitor at C11. (I  only operate 40-10).  I have also tried putting metal "hats" over the top of the FETS to improve the RF grounding, as recommended in the EB104 engineering bulletin.  I did not notice any improvement in performance and had to remove them when I accidently destroyed the MRF150's doing another "improvement" mod.  I have new FETS on order and wonder if it is worth the trouble to put the metal hats back on.

I look forward to getting some positive discussion started on this topic.

Don
K9AQ

[K8AXW]

My suggestion is to Google the EB104 and search for posts by some ham in ... I think Belgium....maybe Italy.... who has built several EB104s with great success.  I recall reading his post a couple years ago and was very impressed with his findings and suggestions.

I was going to build the EB104 but gave it up because of age and temperament.  I still have the untouched PCB, pre-made transformers and FETS.  Thanks for the reminder.  Need to get rid of that stuff!

[K9FV]

Don, I've sent you an email.  Have you seen this site? http://www.w6kan.com/ssamp.html

You mention "RF harmonics on the traces" for the EB104 - what portion of the traces are affected? Any idea how they should be changed to reduce harmonics?

Did you use the copper spreader offered by CCI?

I've built a LPF setup for a 400 watt amp I built a few yr ago using 2SC2879 - this LPF is controlled by AVR ATmega168 uC to auto switch bands for Yaesu or ICOM rigs.  The code has KW included, but not been tested on that yet.

I'm VERY interested in adapting this circuit to SD2933 - only because I got a decent price on them last yr.


73 de Ken H>

[K9AQ]

I have googled EB104 many times and was able to find a lot of good information that I was able to use. I got my interest in this project from W6KAN's original article in QST.   I did use the copper heat spreader, that is a must.  I don't believe they are still available through CCI however.  I got my copper plate from Willams Metals http://www.wmwa.net/  It was cheap, $100, but this was the only source that I could find at the time.

W8JI discussed the trace problem on an Eham forum.  I believe specifically he referred to the traces from the drains of the FETs to the T3 output transformer.  I found some photos of the insides of an ALS1300, which included photos of both sides of the PA board and there is RF grounding all around the FETs and much larger traces to the transformer.

I also build an autoband switching LPf relay/filter board, using the CCI filter boards.  I mount 2 on a perf board with the associated relays and then stacked two boards, so I cover 40-10.  I replaced the 500 V mica capacitors with 1 KV ones.  I did this on all board except for 15/17 meters. I subsequently blew these capacitors when I had a high momentary SWR due to RF getting into my autotuner. These to are now. 1 kv. 

I found a very effective, low cost band decoder board from Unified Microsystems.  I drive this with Ham Radio Deluxe's parallel port monitor.

Sorry I can't help you with the SD2933's, I don't know any thing about them.

I would be interested in knowing if anyone has build an EB104 using Microsemi VRF151's.  According to the datasheets they are an electrical replacement for the MRF150, but with a much higher drain-source voltage, 170 volts. 

Don
K9AQ

[N8CBX]

Don- I'm building an EB104 right now and you mentioned the 1kw LPF/relay board that you designed? I need a LPF for my amp, could you say what the name of the board is, or part number at Farcircuits. Also, would you have a bill on materials & schematic of the board so I can see what filter design you used?
Jan N8CBX

[K9AQ]

Jan,

Far circuits isn't done with the board yet, so there is no catalog number or price.  If you drop me an email, I will forward you the information on the board.  I am planning on building a 1 KW amp, using either two EB104 PA's with a combiner, or a new amp based on MRF154's, and I am going to use this filter board with that amp.  It would also be ideal for a single EB104, but you could use smaller torroids and capacitors.  The board is designed to use either hole through the board mica capacitors, or surface mount chips.

If you send me an email, I will send you more information on the board.

Don
K9AQ

[SV1BDO]

As far as I know, Baruch 4Z4RB has made some good improovements to the classic EB104 design. He has a store in ebay, http://stores.ebay.com/4z4rb, but he is very friendly and can give you ideas and solutions. You can contact him also by Skype.

73, Sotiris SV1BDO

[K9AQ]

Thanks for the information Sotiris,

He has some interested stuff on his ebay store.  I wil contact him.

Don, K9AQ

[K9FV]

Victor, A Russian gentleman sent this link where he has built an amp using the SD2933 MOSFETs with the EB104 board.

http://eb104.unoforum.ru/?1-16-0-00000000-000-0-0#005.001

It's in Russian but google translates ok.  Looks like Victor did a good job with his amp - he mentions having to use 4 turns on T1 transformer rather than the 3 turns required by MRF150.  I wonder if he had to change capacitance values?

73 de Ken H>