Picked this up off a friend as he's unsure as to what's up with it due to some components missing on the amplifier side - TR5 and C28.
C28 is slightly to the right of TR5.

I've researched the MRF240, and as it's rated at 40W surely the heatsink on this is far too small? Does anyone have a schematic for this to decipher the missing parts, and also, was this mainstream as I don't remember it being sold?

Further images...

For C28 you can use between the 10-22PF
TR = 2N4427 (motorola)
not seen this board many times only ready built in box and sold as 10W transmitter

I think Stephen originally designed this for something like a BLY88 in the final, though having said that, you probably wouldn't get 10W out of it driving with a 2N4427 as the BLY88 didn't have quite enough gain (although IIRC it was the most gainy of the BLY87 - BLY90 family). As you say the MRF240 is a 40W device with 9dB nominal of gain, so you might approach 10W (and that's with a genuine 4427 driving it) but nowhere near 40W. I suspect someone's tried to modify the board to get more than 10W out. Good luck to them I say

... and if that 2N4427 magically transformed itself in to a MRF237?

MiXiN wrote:
I've researched the MRF240, and as it's rated at 40W surely the heatsink on this is far too small?

If it's only operating at around 10w it should be fine with that heatsink.

Thanks for all the help.

Seems I have the exact same thing as Sinus Trouble has.

Further info has come in, and my pal says that he's found out that a 2N3553 was used in the TR5 position according to the person he bought it off a while ago.

I have some genuine ST and Motorola 2N4427s here and 18pF Capacitors for the TR5 and C28 that are strangely missing, so I'll fit them sometime tomorrow and see if we have lift off.

I briefly connected it to a PSU earlier and the driver stage is tuning from 88 > 108 no problems, so it's a good start.

Sorry about the no doubt basic question, but does anyone know what this copper foil is all about?

It's soldered to the PCB ground but is hanging loose.

Sent from my SM-G900F using Tapatalk

Analyser wrote:... and if that 2N4427 magically transformed itself in to a MRF237?

Well, Mr. Clever Clogs Steve had a design where he drove the MRF237 with a 2N4427 after his balaced oscillator. He rated the board at 5W out of the final, suggesting that the 4427 wasn't being driven into much of a sweat.

On this board though, I don't know what's driving the missing transistor... it doesn't look like anything particularly powerful. So if the 2N4427 magically changed into an MRF237 and we assume (optimistically) that the circuit can drive a 2N4427 to 1.1W, and 12dB gain from your MRF237, that would mean the MRF240 is seeing 1.7W which means... 13.5W out. Which is better than a kick in the rocks I suppose!

2N3553, by the way, is a 28V device.

MiXiN wrote:Sorry about the no doubt basic question, but does anyone know what this copper foil is all about?

Could be a variety of things, looks like a strap to fasten the ground plane of the board to something else... box? Adjacent board? other side of the PCB?

shuffy wrote:

Analyser wrote:... and if that 2N4427 magically transformed itself in to a MRF237?

Well, Mr. Clever Clogs Steve had a design where he drove the MRF237 with a 2N4427 after his balaced oscillator. He rated the board at 5W out of the final, suggesting that the 4427 wasn't being driven into much of a sweat.

On this board though, I don't know what's driving the missing transistor... it doesn't look like anything particularly powerful. So if the 2N4427 magically changed into an MRF237 and we assume (optimistically) that the circuit can drive a 2N4427 to 1.1W, and 12dB gain from your MRF237, that would mean the MRF240 is seeing 1.7W which means... 13.5W out. Which is better than a kick in the rocks I suppose!

2N3553, by the way, is a 28V device.

The buffer stage (I think that's what is called) after the oscillator uses 2 x MPSH10 in parallel on mine, but I'm not sure what output power they'd provide?

Sinus Trouble has the exact same NRG board as me, but in place of the MPSH10 Transistors that are on mine I read his are BF199. I'm thinking the BF199 are meant to be used, as if you look at my example the Transistors are a different way around.

MiXiN wrote:The buffer stage (I think that's what is called) after the oscillator uses 2 x MPSH10 in parallel on mine, but I'm not sure what output power they'd provide?

I'd guess maybe 250mW. Following the same logic as before, with an MRF237 and your MRF240, could give you just under 30W out.

Hello Mr Mixin!
There is very little info on this board? as far as i know it was an experimental prototype that steve made but never released!
I believe the PA section was loosely based on these!
I managed 14watts @ 88mhz with this baby but it got quite hot without extra heatsinking!
TR5 was a 2N4427 and C28 is a 15PF

Steve had his own reasons for rejecting this??? My personal view on this board is that it seems too be struggling to get the most from a VFO? Dont get me wrong? its performance seems clean and VERY stable when tuned up correctly, however! i found mine would go into some strange oscillation or drop drastically in power if not aligned using a scope to monitor it
Most likely an error in my RF competence? but thats my opinion lol!

I will post some more detailed images if you need them?

shuffy wrote:

MiXiN wrote:The buffer stage (I think that's what is called) after the oscillator uses 2 x MPSH10 in parallel on mine, but I'm not sure what output power they'd provide?

I'd guess maybe 250mW. Following the same logic as before, with an MRF237 and your MRF240, could give you just under 30W out.

That's a bit more like it!

The MPHS10 transistors shouldnt be an issue, assuming they are not damaged?
Steves PA sections were generic and could be adapted to suit a wide range of configurations!

Stephen really hated being called "Steve"!

We got a batch of MRF240s from a dealer in France. We tried them out with various drive stages and even prototyped a dual 240 PA which gave about 90 Watts out at 13.8V supply when 9 Watts was shoved in, and the tuning was critically tweaked. Unfortunately, the 240 was abandoned for several reasons: they were erratic (some had much more gain than others), they drew huge currents at higher powers because of the low supply voltage, they were relatively inefficient so they tended to run very hot (heatsinking was a nightmare), they were "fragile" and quite intolerant of poor operating conditions (contrary to the Motorola blurb), and worst of all - they were relatively expensive.

I managed to secure a good supply of BLW60s and that was what was used at 10 - 40 Watts since they were so cheap and had so much gain. We also found that they were robust and efficient. I still have our dual BLW60 PA here somewhere. It did 105 Watts at 16V!

Albert H wrote: I still have our dual BLW60 PA here somewhere. It did 105 Watts at 16V!

Would be interested to see a picture of that...

I'll dig it out and photograph it. It's just a pair of BLW60s with hairpin output coils feeding an impedance converting tuned match, into a lowpass filter. The input stage used the usual couple of caps and a coil to each transistor base. RFC and caps from bases to ground and a resistor between bases. As I remember, we found that we had to use '60s from the same batch to prevent "current robbing" by one higher gain device over the other. I think that we did actually match them for Hfe as far as I remember. It was built on a 4" square piece of copperclad and had a big airspaced output trimmer! I'll dig it out when I get home.

Albert H wrote:Stephen really hated being called "Steve"!

Soo sorry! my deepest respects for Mr Moss!