There are some pretty amazing engineers, and technicians in this group, that go above and beyond. I started this project because I knew I could use the learning experience. Thanks for the help. 

Hi Scott,

For increasing power on the upper bands you should check the Wiki on this group's site.  Easy parts for that to get on Mouser or Digikey are the bfr106 and the 2n2222a.  I think both are available in SMD versions.

73,   Mark

I'm anxiously waiting on the slllooooowwww shipping.  I've received some parts from Mouser and was wondering it there's any other common replacement / upgrade parts I might want to round up while I wait for my delivery.  I'd like to protect the rig from any strong RF I generate on other setups as well as make some mods to increase power at the upper bands (20M, 10M),   I'm willing to make simple changes to get more power on 10/20 .   I've got plans and parts for smaller dipoles to start my journey into HF.   If I need to reverse or alter simple mods to keep things in spec on the lower freq bands in the future that's ok.

This order wasn't all uBITX related but I have these pieces on hand now.  First post - hopefully this works.   

Thanks

I doubt that cap failed because of a power surge (by that I assume a voltage spike).
A 0.1uF cap in a 1206 package should be rated for 25v, maybe 50v.
If that 3.3v rail saw over 25v, the whole raduino would be a smoking crater.

Rough handling could fracture it, perhaps tapping it hard with a screwdriver.
Maybe flexing the board.
Or it's a cap from a low budget manufacturer with a significant failure rate.
Or bad luck.

We haven't seen many bad caps reported here.
Though I did have a short on the 0.1uF 1206 cap at C107 on a Bitx40 four years ago.
    https://groups.io/g/BITX20/message/22764

I doubt this problem was self inflicted, and I doubt it will come back to haunt you.

Jerry, KE7ER

Thanks Evan!!
--
 

73
Mick VA3EPM 

Hi,

Concerning the amp.  As the finals are MOSFET's (like the IRF510's in the uBitx and WA2EBY amp, etc) they each have different turn-on voltages.  This means that there is really no set voltage, even if they write one in the schematic.  And also since they each have a different turn-on voltage, they each must have their own bias supply.  I would just copy the bias setup used in the WA2EBY amp.  Any cheap amp from eBay etc, that uses individual MOSFET's but only has a single bias supply needs to be fixed.

It was mentioned above in the thread that the finals were getting burned out.  With a single bias supply one of the final transistors will most likely always get turned on too much and the other too little, so one transistor will run a high standing current with more heat and more likelyhood to burn out.

Also, with uneven bias, the cancellation of even harmonics will be reduced and the output will be more dirty than necessary.

73,  Mark

Photo of the PA + ATU100:

Mine got with unmarked FETs.
They are probably IRF530 which I already killed some due to overheating, so fan in addition to good heatsink is highly recommend.

I also had to change R7 to 220 Ohms in order to get about 3.7V bias to drive about 400mA.

I also purchased and built the ATU100 antenna tuner by N7DDC.      The kit is less than 30USD with amazing performance.

I plan to integrate it with the uBitx, PA, LPF and use its display for Po/SWR.

Mick,
That is a very similar schematic to the kit that I purchased on ebay.  Here are some articles that I found useful:
http://pa-11019.blogspot.com/2016/11/diy-kits-70w-ssb-linear-hf-power.html
https://ea8arx.blogspot.com/2018/06/minipa-70-step-by-step.html

In reading the article again, The 4 3 watt resistors are overkill for power.  I did not have one in the resistance range listed.  It did drop the power output to 45 watts for me as well.  Of particular note is the comment in the second link to set the bias by the current draw rather than the voltage listed.  When I tried that I could not get the current up to that value.  I had to change R7 on the attached schematic to get to even 500ma.


Here is a picture of the amp before I added the 4 resistors with the added LPF:


Hope this helps
73
Evan
AC9TU

It is all about of having fun by DIY and information sharing.

and...  There is no business model for our hobby other than enjoy it :-)

I already have 3 commercial iCom/Yaesu HF radios, but I must say I enjoy much more working with self made toys like uBitx.

Zvika

Thank you. I'm not a technician, or engineer, and I was confused.  Thank you for the help. 

Mick,
You have the correct labeling.  I agree that Ashhar Farhan did use none standard numbering for this relay depending on the relay selected.  I am sure it was because of the model he used in the board layout software.

The diodes go between your numbers 4 and 8.
 
73
Evan
AC9TU                     

I haven't studied exactly where your traces go, but that looks about right.
There was some discussion about relay pin numbering in the forum
a year or two ago.  The alternate numbering scheme just flips the 
relay end for end.  The relay fits in a standard 16 pin dip pin pattern
on 0.1 inch centers, but not all the pins are populated.

Jerry, KE7ER

Didn't see the post where you had already removed the Si5351  before my previous reply.
That bad cap is probably just bad luck, seldom happens.

Evan is right, putting down an Si5351 should not be too bad, yet another learning experience.
You are right to be concerned about the pads, the glue that holds them to the board can
give up in the face of all that heat and lift off the board, but if really careful they are
still usable even in that state.  If they break off, you should be able to patch that trace to the pad
with a scrap of very thin bare hookup wire. 

The old Si5351 is probably fine, but you could just wait for the new ones to arrive.
I find adding extra flux helps a lot when soldering small pins, gets the solder to flow better.
Wash off that flux with alcohol, especially if you have a water soluble flux as that can be very corrosive.
Then let the board dry before powering up, perhaps helping the process with a little heat.

At worst, get that Adafruit breakout board.  It has a 3.3v regulator on it so you could power it
directly from 5v.  It doesn't have the series caps at C4,C5,C6, so make use of the ones on
the Raduino board.  But it does have pullup resistors like R13,R14, you could remove
one set of them.  It also has level shifters to protect the Si5351 SDA and SCL pins if using
it in a 5v environment, those can be left in place.   You might want that Adafruit board anyway,
that and a Nano can be very useful as a signal generator..

Jerry, KE7ER

Evan,
Thanks for the pic.
Below are the pin outs for K1 which is incorrectly marked (I think) on the schematic. See below and let me know if I am incorrect on this.

Correct schematic labelling


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73
Mick VA3EPM 

Evan,
Thanks for the info, really informative. I noticed my PA has a 75 ohm 3w resistor across the input transformer secondary, this wasn’t on the schematic they provided and I was wondering why it was there. I could try changing the value and see what happens .
I did check the harmonics of the PA with and without the LPF using an SDR, I didn’t document the results but I was satisfied with the results at the time.
FYI my PA schematic