ShoeHorn Job !! How many parts CAN you get on a PC board???

[steve_qix]

Well, the time has come to lay out a PC board for the so-called "Simple" Class H modulator (it is quite a bit simpler than the other ones have been).

This one incorporates about half of the overload shutdown board into its circuitry, which added a bit.

The goal here is to use ExpressPCB's "MiniBoard" service, which is very inexpensive - and with no setup charge (a big charge, usually).  They also have MiniBoard Pro, which includes the silk screen and solder masks..  This for less than $30/board shipped.  Yes, you can do better in large quantities because the setup cost is divided between many boards, but I'm not ready to make that "investment" yet  

Here is the schematic:



And, here is the board:



The board will handle up to 2 MOSFETs in each bank - this is about 150 watts of carrier power delivered to the class E RF amplifier, max.  For those who want more, simply outboard the MOSFETs and run as many as your power supply will handle.  PWM highly recommended above 300 watts.

Regards,

Steve

[KF1Z]

Nice....

Sure does look like a good candidate for mostly surface mount devices though!

That would really save some room....

[steve_qix]

This would be a good surface mount job, but old guys like me would have trouble building it 

Oh, the actual size of the board is 3.8 x 2.5 inches - so the picture of the board above is MUCH larger than the actual board.  This picture of the board is 300 pixels wide.  At 72 pixels per inch, it would be about 273 pixels wide.



There is absolutely no real estate available on that board for anything else 

[KA8WTK]

That's a pretty packed board!

[WA1GFZ]

Steve, Check app notes on the TL074 driving a high C load. U3-1 might oscillate driving that high value cap. 

[steve_qix]

Steve, Check app notes on the TL074 driving a high C load. U3-1 might oscillate driving that high value cap. 

Hi Frank,

I use the same value in another circuit, however if it starts complaining, I'll just reduce the cap value and up the resistance !!  Either way, the time constant will be similar.  The base current of the transistor driving the LED is small, but not 0, so eventually, no resistor at all would be needed.  I'll still leave one in place to ensure a more constant draw-down.

[Opcom]

Nice job!  I'd ask what you are going to mount on the other side but I don't like hand-building with SMT either.

[w3jn]

Suggestion - leave out all the LV PS components, that'll save a ton of room (as well as some heat generating components on the board), and those caps won't have to hang their asses off the board    Any hamfest will cough up nice Lambda or other small PSs with the required outputs for a couple bux.  For those in an area bereft of hamfests, they're also available from many of the online surplus dealers for not much more than the price of the 3 regulators, chips, etc.

The compactness of that board will make it quite a bit more difficult for the ham-handed (like me!) to stuff the components.  Too, there's little space for substitution of on-hand parts that may differ a bit from the norm.  But truly a remarkable accomplishment, Steve!

[steve_qix]

Hi !

I made some modifications to the layout and got about 1 extra square inch per board.  This allows the power supply components to hang over less, leaves more room for good ground connections to the board, and a bit less tight component spacing 



In past designs, I did have the power supply off-boarded, and this saves a little space (the diodes, regulators and big caps move off the board).  If the builder uses sufficient skill, it works well    Ground loops, RF and other problems can develop if not !!

These boards do give the impression that they would be hard to build, but in actuality, they are not!  Here's a section of the modulation monitor layout, and approximately the same section assembled.  It looks real crowded on the layout, but there is actually plenty of "air" in final assembly.

The board:


The assembled unit:

[KF1Z]

Yeah, that board isn't so bad...

Full, yes, but not hard to build.

What would take the longest is picking and placing parts.

Might take 1 1/2 to 2 hours to build the first one. 



If one wanted to seperate this into 2 boards... the low volt supplies AND the HV  rectifiers/filters, and relay could probably go off on another board...

But, in a small run of boards, that doubles the cost (of course) but to a pretty high amount...

[steve_qix]

If one wanted to seperate this into 2 boards... the low volt supplies AND the HV  rectifiers/filters, and relay could probably go off on another board...

But, in a small run of boards, that doubles the cost (of course) but to a pretty high amount...

Relay... Hmmmmm... The relay is already off the board (there is a connection for it provided. Look for RLY in the lower left portion of the board).  I did have the relay on the board for a while!  Took up about 1/3 of the board 

[KF1Z]

That's what I mean... IF there was a second board...

There would be a place to mount the relay, low-volt power supplies and HV rectifiers/filter caps....

Just one of those "IF"s  Steve..   
In reply to W3JN's post about leaving the LV supply components off the board...


Not saying there should be another one... but would neaten up a build if there was.

[WA1GFZ]

Steve, I agree with John. CTR Surplus on ebay has a pile of cheap linear power supplies. I've bought a few. Lamda modules are very clean. I used them in my HPSDR. Just a 1uf on each rail should do it.
I have seen op amps take off with a few hundred pf and crosstalk to other amps on the same substrate. You can get around it with a series resistor but that will hurt the charge time. I was thinking you would be better off with a dual time constant integrator and I bet the same part count.
We had problems driving shielded cable hanging off an op amp. The cable was maybe 30 feet long so I bet under 470pf. There are apps to deal with it though.

[flintstone mop]

Nice....

Sure does look like a good candidate for mostly surface mount devices though!

That would really save some room....

WHEW!
And your post Steve,
I was worried how you were going to fit a lot of thru hole devices on the board shown.

Fred

[K1JJ]

Steve -  Does this mean you're ready to start on the greatly anticipated MOSFET direct coupled audio driver for us plate modulated tube schleppers?  

T

[WBear2GCR]

Waaaa waaaa waaaa! 

nice board, but no dual opamps...

Steve you must have bought an awful lot of TL074s...?

(Steve's gonna be mad at me for floggin this horse)

                     _-_-bear

[steve_qix]

Waaaa waaaa waaaa! 

nice board, but no dual opamps...

Steve you must have bought an awful lot of TL074s...?

(Steve's gonna be mad at me for floggin this horse)

                     _-_-bear

Oh Bear oh Bear oh Bear - for this application the TL074s are JUST FINE.  If I were designing an AudioPhool amp that needed a 100dB or better S/N ratio, I would use something else.  And, one quad takes up less room than two duals    And boy, is room at a premium on THIS board 

This modulator sounds incredibly good !!