FatBoy 4 pill HG2879C Amp Review

[NightThumper]

Finally got around to testing out the new FatBoy 4 pill with HG2879C transistors. This is a straight AM only no SSB bias/delay. It did come with a “Remote” connection 1/4 phone jack. WOW! First off the fans all these builders use are CRAP! They don’t even use rubber bushings to stop the vibration. Just cinch the screws down and call it good. I’ve replaced the fans on nearly all my amplifiers except the AL-82 and even then add a 140mm external fan to assist with cooling.

Build quality is about what you’d expect out of these mass produced amplifiers. No doubt two pencil irons on the bench turned to max heat. One iron for the small stuff one big one for everything else. This is no RM Italy amplifier on the inside or Ameritron, Acom, Alpha, OM, Ten Tech or other. Lots of point to point soldering.

Generic Aluminum cases with metal screws to hold it together and slap your logo on it. Although I will give them credit for using what appears to be some kind of pressed rivet nut (someone can enlighten me as to what these are called) to hold the case together. Carl Built and Texas Star just use metal screws which strip out easily.

Performance wise I can’t complain for $530 shipped. A lot cheaper than an AL-82 or AL-80b but then again no filtering whatsoever and a nice glass 3-500z tube.

I was looking for an amp that could take high drive. For me 35 watts input to 150-ish. Didn’t care about SSB as in my opinion it’s a marginal add-on to appease the masses.

Okay so performance wise…using the IC-7300 with 117 watts PEP produced 942 watts PEP output. Using my Galaxy DX99V2 with 50 watts PEP AM produced 665 watts PEP output. The input SWR on the pictures looks great but honestly they are all over the place when modulating. A common mode filter from DXENGINEERING Maxi-Core@20 Baluns and Feedline Chokes DXE-MC20-FC placed on either the input of the FatBoy itself or at the LP-700 input coupler did settle things down although I don’t think the FatBoy liked it as the amp occasionally would not un-key completely leaving me without receiving. A low pass filter placed anywhere had no effect. The SWR meters on the radio’s all said no higher than 1.3 without the Common Mode Filter. Even my cheap MFJ meter read the same. One thing about these cheaper SWR meters is something I think is called “Diode Drop Out.” My terminology maybe incorrect, but it’s the point at which the diode detector can no long function and simply “drops out” resulting in a low SWR reading.

For what this Amplifier is I’m satisfied. I don’t think there’s much of a difference between FatBoy, Carl Built, Hopper or others. They all come in around the same price point so choose your poison.

Will I sell it??? PROBABLY and just spring for another AL-82 or AL-80B. Hey it’s fun trying new things but definitely not cost effective. In my opinion any money spent on 11 meter equipment is a loss. At least with Ham gear one can re-coup more of those losses when it comes time to sell and the market interest is greater.

That’s all folks enjoy the pictures.

Brad
KE0XS
South of Pittsburgh

 

[Crawdad]

Brad
KE0XS
South of Pittsburgh

 

[Eldorado828]

That's a neat 4 pill. They are all similar but in my own experience the TinMan boxes are top notch when it comes to a clean build.

Looks like you'll definitely be heard!

 

[Shadetree Mechanic]

Hey Brad, nice looking station you got there. I have seen the SWR thing on several comp boxes, and it seems that a low dead key makes it worse. A simple pi network with two trimmers and a hand wound coil works wonders on the input tuning. Check out my X Force smoked thread, I also did it to that Carl built too. Most people don't know about the input match and without a meter in line, they will never see it. I really like your dual meter setup, I should do something like that with my Autek meters. And that 900 watts will get you on top of the pile for sure.
Chris

 

[NightThumper]

Chris, you’re right about a low dead key making it worst. I’ve got some Cat-8 Ethernet cables coming tomorrow so I can eliminate any interference between my couplers and meters. The Telepost utilizes CAT cables to relay the information to the display unit. I’ll re-visit your X-Force thread and have a boo. So you were able to tweak the input SWR on CarBuilt as well…that’s fantastic. You wouldn’t happen to have a picture of your pi-network on the CarlBuilt would you?

Thanks for the flowers on my station. Spent some time/thought on how I wanted to lay it out. I’m thinking about another pair of couplers so I can put another amplifier (KL-503HD or KL-703) in line. Each meter has 4 inputs. Right now I’m only utilizing two on each of them. That way I could put one of the RM-Italy’s dedicated to the Cobra 29LTD.

Again you’re right, most people have no idea what their input SWR is. Unfortunately with RF keyed amps I’m unable to use the high SWR/PWR feature of those meters to un-key the amp if the set alarms are exceeded. They have to be keyed by the Telepost to use that feature. All I get now is a audible alarm or the display turns red…better than nothing. A manual keying jack on the otherwise RF keyed would be great but I’d have to use a foot switch or have the relay added to the DX98VHP, DX99V2 and Lincoln. The Cobra29LTD already has one installed. If someone has a solution to that situation I’d welcome your input.

So what trimmer did you end up using…the 464 or 468?

Thanks Again my friend
Brad
KE0XS
South of Pittsburgh

PS: S&W357 has me seriously considering boning up to take my Extra Class Exam. His excitement is contagious.

 

[NightThumper]

Cat-8 Ethernet cable’s installed. Any interference between meters and couplers is GONE!

Also ordered the 464 and 468 trimmers to make a tuned input. Hopefully this weekend

 

[w9cll]

Talk about crappy soldering

 

[NightThumper]

Having had this amp for about 6 weeks now it’s time to update my review. First off I would not purchase HG2879c transistors for any amplifier (maybe a two pill). I don’t believe despite the hype any serious power gain is realized. Yes I’ve had both in a 4 pill box. In addition I don’t believe amp builders are using matched quads. At the most two are matched making them unbalanced. The result is that the 100 ohm resistor on the output combiner gets smoked. Yes I had that happen. Secondly the negative feedback circuit leaves much to be desired and needs to be tweaked. As mentioned in another thread my relay was sticking and not switching back to receive. There were power output spikes as a result of oscillation taking place. This was rectified by modifying the negative feedback circuit. I’m expecting at some point in time the HG2879c will get smoked. It’s not a question of if but when.

Searching the internet for matched quads of 2879c the best I could find is that a pair would be matched and not all four. It appears finding regular HG2879’s in matched quads is easier.

At this point I’m seriously considering replacing the HG2879c with regular HG2879’s. Or just selling the amp at a significant loss. (If your interested PM or email me) Maybe I’ll continue buying amps from other builders…maybe a Hopper amp is next. Then again get another Ameritron AL-82/80b I’ve been talking about or just using my RM Italy 703 or 503HD.

If someone can let me know what needs to be done to make the change over that would appreciated. I think it’s the random luck of the draw to get four HG2879c that are closely matched. Maybe their is an amp builder that pays closer attention to this…who knows unless you pull them and test them yourself.

Edit 07/13/2021: The 104 Capacitors arrived yesterday. They are better tolerance 10% and higher quality. Measured each one before installing so instead of a range from 1050-1175nF they were all 1015-1025nF. They worked great and did slightly reduce output power again. The amp is now definitely stable, more linear and both the input and output impedance improved significantly so there is no longer a need to tweak the input circuit. SWR for input is now about 1.5 which is great. Next step is to measure output with 117 watts PEP and 14.5 volts like I did in the initial review and see how much output power decreased. As it stands right now it has more output than a Texas Star DX500 and will accept high drive input. I feel more confident the smoke will not be let out anytime soon. Then maybe it’s just a mirage in my mind…hahaha

Brad
KE0XS
South of Pittsburgh

On another note updated/upgraded to a newer model Weller soldering station. My older unit is the WESD51. The newer one is the Weller WE1010NA. Also sold the Yaesu FT60r and replaced it with a new FT70DR HT. I will probably put my RM Italy KL-503HD up for sale. Basically it’s new…maybe used 6 times mostly for comparison purposes and two QSO’s.

 

[NightThumper]

Edit 07/13/2021: The 104 Capacitors arrived yesterday. They are better tolerance 10% and higher quality. Measured each one before installing so instead of a range from 1050-1175nF they were all 1015-1025nF. In addition I purchased 5% tolerance 2 watt 100 ohm resistors for the negative feedback circuit. They worked great and did slightly reduce output power again with the Galaxy 99V2. The amp is now definitely stable, more linear and both the input and output impedance improved significantly so there is no longer a need to tweak the input circuit. SWR for input is now about 1.5 which is great. Next step is to measure output with 117 watts PEP and 14.5 volts like I did in the initial review and see how much output power decreased. As it stands right now it has more output than a Texas Star DX500 and will accept high drive input. I feel more confident the smoke will not be let out anytime soon. Then maybe it’s just a mirage in my mind…hahaha

Alrighty here are the same test with the IC-7300. The first picture shows a 90.8 watt PEP input and output SWR of 1.37. Output is 855 PEP and output SWR of 1.14 into dummy load. Definitely a better match.

The second picture shows the original test showing a 117 watt PEP input and input SWR of 1.89. Output is 942 PEP and output SWR of 1.26 into dummy load.

The wattage from the IC-7300 was higher in the first test due to the input SWR being higher. Doing the math, in the first test 8.05 watts output was being produced for every input watt. In the second test 9.4 watts output was being produced for every input watt. That means the improved impedances input/output and better linearity are actually producing higher output than in the first test…interesting for sure.

Definitely think the FatBoy could be a keeper now. Such a shame that amp builders put everything right on the edge to generate better output wattages, when in fact once you reach a certain level of input the output is actually increasing/higher.

 

[dave457]

There are much better builders than fatboy. I would have never chosen them for an amp build
Plenty of good info on this site for which amp to buy

 

[NightThumper]

There are much better builders than fatboy. I would have never chosen them for an amp build
Plenty of good info on this site for which amp to buy

Dave…do make a suggestion sir. I’ve had quite a few different mobile/base amps over the years. I’m all ears buddy. At this point in time the FatBoy is working just fine.

Something more than CarlBuilt, Xforce, GateKeep, DaveMade, Texas Star or HopperBuilt.

 

[Naysayer]

Thumper, I enjoyed reading this thread. Liked all the details including the stuff that did not work out. Tooling small SS amps for efficiency is trying yet fun. Extra & fast PO is useful at times.
Did you ever add a pi input circuit?

 

[575nightrider]

Finally got around to testing out the new FatBoy 4 pill with HG2879C transistors. This is a straight AM only no SSB bias/delay. It did come with a “Remote” connection 1/4 phone jack. WOW! First off the fans all these builders use are CRAP! They don’t even use rubber bushings to stop the vibration. Just cinch the screws down and call it good. I’ve replaced the fans on nearly all my amplifiers except the AL-82 and even then add a 140mm external fan to assist with cooling.

Build quality is about what you’d expect out of these mass produced amplifiers. No doubt two pencil irons on the bench turned to max heat. One iron for the small stuff one big one for everything else. This is no RM Italy amplifier on the inside or Ameritron, Acom, Alpha, OM, Ten Tech or other. Lots of point to point soldering.

Generic Aluminum cases with metal screws to hold it together and slap your logo on it. Although I will give them credit for using what appears to be some kind of pressed rivet nut (someone can enlighten me as to what these are called) to hold the case together. Carl Built and Texas Star just use metal screws which strip out easily.

Performance wise I can’t complain for $530 shipped. A lot cheaper than an AL-82 or AL-80b but then again no filtering whatsoever and a nice glass 3-500z tube.

I was looking for an amp that could take high drive. For me 35 watts input to 150-ish. Didn’t care about SSB as in my opinion it’s a marginal add-on to appease the masses.

Okay so performance wise…using the IC-7300 with 117 watts PEP produced 942 watts PEP output. Using my Galaxy DX99V2 with 50 watts PEP AM produced 665 watts PEP output. The input SWR on the pictures looks great but honestly they are all over the place when modulating. A common mode filter from DXENGINEERING Maxi-Core@20 Baluns and Feedline Chokes DXE-MC20-FC placed on either the input of the FatBoy itself or at the LP-700 input coupler did settle things down although I don’t think the FatBoy liked it as the amp occasionally would not un-key completely leaving me without receiving. A low pass filter placed anywhere had no effect. The SWR meters on the radio’s all said no higher than 1.3 without the Common Mode Filter. Even my cheap MFJ meter read the same. One thing about these cheaper SWR meters is something I think is called “Diode Drop Out.” My terminology maybe incorrect, but it’s the point at which the diode detector can no long function and simply “drops out” resulting in a low SWR reading.

For what this Amplifier is I’m satisfied. I don’t think there’s much of a difference between FatBoy, Carl Built, Hopper or others. They all come in around the same price point so choose your poison.

Will I sell it??? PROBABLY and just spring for another AL-82 or AL-80B. Hey it’s fun trying new things but definitely not cost effective. In my opinion any money spent on 11 meter equipment is a loss. At least with Ham gear one can re-coup more of those losses when it comes time to sell and the market interest is greater.

That’s all folks enjoy the pictures.

Brad
KE0XS
South of Pittsburgh

You don't know crap about radio if you're clueless about SSB

 

[Eldorado828]

You don't know crap about radio if you're clueless about SSB

Hey, I don't understand what you're implying but if it's towards @NightThumper you might take it easy there bud. He's a good guy and at one time very active in this forum.

 

[575nightrider]

Hey, I don't understand what you're implying but if it's towards @NightThumper you might take it easy there bud. He's a good guy and at one time very active in this form

I'm sorry, I hope he can forgive me, I should have just let it go. @NightThumper, pls forgive my ignorance. I am truly sorry and it never will not happen again.