After running my uBITX barefoot for the past 18 months (with 1700 FT8/FT4 contacts) I decided it was time to add a little more power.  The ever-popular WA2EBY linear amp seemed like a good route, except that nobody offered the circuit board anymore.  On a whim, I sent an email to amateurradiokits.in to see if they had even one board left over.  Sunil, VU3SUA responded that the old boards were gone, but they were just a few weeks away from releasing a totally new board for this design.   I asked to be their first customer, and very shortly had the new board in hand.  Here's my review (unsolicited, uncompensated): 

Having seen pictures of the earlier board in past construction articles, I can safely say the new board is a big improvement.   Cosmetically, it has all the professional elements that were previously missing: plated-thru holes and vias, solder masking and comprehensive silk-screening.   The size is a few tenths of an inch longer and narrower than the original, which turns out to be an excellent match for an inexpensive 150 x 60 x 25mm heatsink that is widely available on EBay as of this writing. 

Before you start building, you need to make two design choices.  First, your input attenuation – pads and traces are provided for a standard pi-network attenuator, but it’s up to you to choose the amount of attenuation needed for your setup and then compute the appropriate size/wattage resistors. Plenty of websites can help with these calculations.  Likewise, space is provided for a single band low-pass output filter, but the L and C values are up to you.  Again, no problem –  go to any WA2EBY article/website/blog published in the past 11 years and you’ll find them listed.

A few notes related to the photo:

•  yes, there are still surface-mount capacitors – 10 of them.  And yes, mounting them seemed scary at first, but turned out to be much easier than I thought.  Plenty of YouTube videos are available to walk you through that process.     
• the IRF510 pins need to be bent up 2-3 mm to allow the MOSFETS to mount flush to the heat sink while still maintaining adequate spacing for the board itself.  
• the board has mounting holes for SMA connectors at the RF input and output.  I don’t generally use SMA’s on my projects, and the holes didn’t match up with the ones in my junk box, so I just soldered some mini-coax directly to the pads.
• two other connection pads allow you to route the input signal to an external attenuator and back, if desired.  Otherwise, these points (J4 and J5) need to be jumpered. 

Because this is a mature design, you’ll find a wealth of published articles available to provide detailed advice on everything from component selection to toroid winding to expected performance.  It’s like having multiple assembly manuals to choose from.  Construction went smoothly, and the amp worked perfectly the first time I applied power.   As always with this design, tune-up consists of simply setting the bias current on the IRF510’s.   Stability is excellent, and very little drive is required to obtain full power out.  At some point I’ll do more comprehensive testing, but for now I’m having too much fun operating with it.
 

As a final note, the original QST articles (Mar, Apr 1999) provide an excellent analysis of the thermal challenges that come with running a pair of IRF510’s at 40+ watts.  Based on this, I've decided to run my amp at 30 watts output for the time being, until I have time to construct a better cooling system.  A couple of dB output power just seemed like a small price to pay to spend my time operating instead of replacing IRF510’s.

The WA2EBY PC Board can be ordered from amateurradiokits.in.  It is currently available as a bare board only, but will eventually be sold as a semi-kit as well.  Until it’s added to their website, you can email an inquiry to the address shown on their Contacts page, they’ll respond with the details.     

Ken,

  It looks like a nice board, especially if one wants to work with a single band.  The original amp project has two boards - one for the amp (with the same input attenuator option - add resistors or jump), and a second board for the lowpass filters for 160 thru 10 meters.

   The good news is that Far Circuits still has the boards available.

http://www.farcircuits.net/rfpa2.htm
https://www.farcircuits.net/ARRL%20Handbook.html

Broadband HF amp, ifr510's 1w in, 40 w out (two board set)

$19.50 Set

  KC0WOX did a full build and test manual that's a nice addition to the ARRL articles originally penned by WA2EBY:
http://golddredgervideo.com/kc0wox/wa2ebyamp/index.htm

  I love mine!  I run it from both 13.8 and 28 VDC.  I found a heatsink that's very closely sized to the part originally specified by WA2EBY and find that it doesn't generate much heat even when running 28V and sending out a 2 minute WSPR 'shout'. hihi  I'm guessing that the heatsink you found will do even better than the smaller one originally spec'd.

  73, Andy, KG5RKP

Gah - forget the best part:  Diz at kitsandparts.com has a toroid kit for the WA2EBY amp.

https://www.kitsandparts.com/WA2EBY_toroidkit.php

73, Andy

Diz at kitsandparts.com has a toroid kit for the WA2EBY amp

About 20 years ago when I made my amp and manual I asked Diz if he would make up a torroid kit and he did. It simplifies obtaining the torroids. I'm amazed that his kit is the same $6.00 that it was about 20 years ago. The web page gets several hundred hits a month.
Leonard
KC0WOX

So I have you to thank?
I built this amplifier a few years back, and the availability of the toroid kit made thins so more convenient. Even with shipping across the pond it was still very reasonably costed.
/ Gerry

Mike Kossar, wa2eby, Is who you want to thank. He designed the amplifier. All I did was write an assembly manual. and component location chart.
Leonard
kc0wox.com

Leonard - your manual was among the best guides that I found while researching and eventually building the amp.  I think I've still got a browser tab opened to it on my shack computer.  Kudos & 73,

Ken 

Andy, 
Regarding the multi-band LPF board - I needed one that was PC-controllable because I mainly operate remotely (shack is upstairs, PC is in family room).   So I designed my own board, which uses relays to switch the LPF's in and out for each band.  It can be controlled from a simple contact closure (e.g. an Alexa-controlled relay) or via digital outputs from an Arduino. 
 


Also - you're right, I should have mentioned the toroid kit - it's super convenient.  I decided not to buy it because I already had some of the cores on hand.

Can I buy somewhere this marvelous amp? Does it work in 50V PSU?

Cheers,
Rafael PU2UIT

The bare board should be available on www.amateurradiokits.in  in a few days.  A kit with most of the components will be available later.  

50V is too high - 28V is the absolute max.  It requires at least 4A. 

Hi,

It does look nice for single band use as it looks like Sunil has added a spot for a single LPF on the amp board.  Probably it's set up for 10m now, but you could choose a lower band as desired.

73,  Mark

Hi Ken,

  I like your filter board!  I've had the "it would be cool if the µBITX could change bands on the amp" thought in my head for a while but haven't gotten farther than that.  Nice work!

Leonard - you did more than that.  You've also answered frantic questions from RF noobs that helped them know for sure that their new creation was working correctly.  Thanks again, Sir!

  FWIW, this is the heat sink I'm using.  It was the closest size match I could find to the part WA2EBY specified in his article.  It's 61 x 116.8 x 38.1 mm (L x W x H).  
   https://www.mouser.com/ProductDetail/TDK-Lambda/HAF15T?qs=%2Fha2pyFadujYuVZC2e13mzcrXnoEzMiZDtNhiwH3OfQ%3D

   Andy

The Linear Boards WA2EBY are available on our website.

https://amateurradiokits.in/product/linear-amp-pcb-wa2eby/

Ken,

Any chance you might make the design files available (or even just the gerbers) for that LPF? Looks pretty nice!

73
Mark
AJ6CU