Just about to do some bias testing on this guy before I solder in the big transistor.
Built off of this website's info:

https://xtronic.org/circuit/amplifier/p ... lifier-fm/

Looking for some insight into performance and any issues faced while building/tuning.

This has been a distraction project from the stentor.....

Yes me and it is god enough .But i was searching for the same or other design on this transistor with easy tune one variable capacitor or even a no tune design is it possible ?
this is npn type transistor no Bias voltage at base only neutrodynage with vk200 and some 68 pf x 4 because like i said a tuneable design
BTW why you put big capacitor at input and little variable cap that i think they cannot handle such power and will melt atoutput pink cap
i get about 22w in that time driven with 1w veronica type
the good thing is that came with lf that is good not test on spectrum because not having one in y hand

Yeah I had though about the cap situation and your probably right. I have some hi voltage blue caps that might end up being swapped in. Not a whole lot of info on the site to build it and your the first guy I have found that actually built one. I built it with the electrolytic at the input as the original schematic called for. I need to build a 1w driver to run it unless I can dial down my stentor to 1-3w

in my opinion a well tuned driver will just need 1w at 15volts and transistor work well but a close picture to me see that is it a genuine transistor ? if u could find a way to meake it easy tune or even to combine two pallets of theses is well
when i guet picture i will post

NOT my work thoses kepted from the net

radium98 wrote: ↑Wed Oct 18, 2017 9:12 am NOT my work thoses kepted from the net

I'm pretty sure its a genuine 1946, I paid decent money for it and it came from a reputable RF part company in the U.S.
That second pic looks like hivoltage on the input and standard ceramics on the output?

I have hi-volt blue caps to replace the following:

100PF
220PF
470PF

Those 3 values are 60% of the board.

I have some 18PF silver micas, could they replace the 27PFs on the output and LPF? Also have some green 22pf NPO caps that might work?

I don't have anything close to the 56PF value in a hi-volt cap, nor the 47PF that are on the LPF.

Am I going to hurt something if I replace everything I can with hi volt stuff and end up cooking the lower rated ceramic caps during the initial testing ?

I can do some digging in my sizable pile of scrap electronics and look for some hi-volt caps in the 56 and 47PF values. I'm thinking there might be some in a fluorescent light ballast......

As I Promised the working PA @ 25w

radium98 wrote: ↑Thu Oct 19, 2017 8:42 am As I Promised the working PA @ 25w

That kinda looks like a stentor driving that guy! I'm assuming the TO220 hanging off of it is for a 78xx power supply? What did you turn the stentor down to in order to not overdrive the 1946P PA? 3W?

That looks like exactly the setup I'm trying to build, I want to mount mine in a .50 cal ammo box and run it off a mobile @ 13.8VDC.

It is coming from db exciter board few mw trough bfr96 to c1971 po 3w to the c1946
I would like that amp will be no tune design

Just replaced every cap on the board with at least 500V units, most are 1kv and 4kv caps. I'm gonna drive with a CZH turned down to 1W.

Here she is sitting on the heat sink. I'll either leave it full size if I can't run a fan or cut it down to 6" OAL instead of 10" OAL if I will run a fan. It came from a 600W car amplifier that had (4) TO-220 mosfets attached to it.

Here's some new pics of the new caps. Gonna coat the bottom in heavy polly or hot glue before final mounting to eliminate any shorting concerns.

Morning.
Two tips. In my opinion it is wrong to add extra solder on those traces on board, if you don't know what you are doing. That practice is used on parts of boards where there is a lot of current flowing.
That amplifier have a few coils that are made from PCB traces and when you add solder on them you are changing ( lowering ) their inductivity, since you are making them thicker with that solder.

Another thing. I see that you are changing those bypass capacitors to much higher voltage. In my opinion you dont need to go that high with voltage, because on the input side low power is present, 2-3 W max. Ordinary ceramic caps 50V is fine there. On the output side 30 W is still not huge value so you don't need to worry much. It don't hurt if you already replaced them, but keep it in mind for future works.

Radio Garfield wrote: ↑Wed Oct 25, 2017 8:21 am Morning.
Two tips. In my opinion it is wrong to add extra solder on those traces on board, if you don't know what you are doing. That practice is used on parts of boards where there is a lot of current flowing.
That amplifier have a few coils that are made from PCB traces and when you add solder on them you are changing ( lowering ) their inductivity, since you are making them thicker with that solder.

Another thing. I see that you are changing those bypass capacitors to much higher voltage. In my opinion you dont need to go that high with voltage, because on the input side low power is present, 2-3 W max. Ordinary ceramic caps 50V is fine there. On the output side 30 W is still not huge value so you don't need to worry much. It don't hurt if you already replaced them, but keep it in mind for future works.

I appreciate the input.

I ended up adding the solder because I used 1/2 oz PCB instead of 1 oz. At 25W, it probably would have been fine as is. Radium's board was either tin dipped or had the same thing done to it, have to ask him.

I just got the driver going today, I should have some real testing done on this by Saturday......ish.

radium98 wrote: ↑Thu Oct 19, 2017 5:04 pm It is coming from db exciter board few mw trough bfr96 to c1971 po 3w to the c1946
I would like that amp will be no tune design

Radium,

What kinda SWR will this thing tolerate? I just got it mounted in a box and after some issues with the power connector, fed power and RF to it for the first time. My CB RF power/SWR meter showed almost exactly 25W and the SWR side shot right to the far right (indicating 4:1+ if it was a CB). I know the meter isn't the best for measuring FM, but I am a bit concerned about frying the big pill before I even get a chance to play with it.

So far I'm liking what I'm seeing
EDIT:

I should also mention that when I saw the SWR peak, I shut off the 1w exciter. The SWR side of the meter fell to 0 but the watt side read about 10w. I removed power from the amp within a second or three after. Is this residual energy in the big input cap or just my exciter slowly powering down? Its a CZH ST-7C set on low.

Just swapped CB meters for my more reliable Workman P5000. It showed 8w out until I played with the caps. I started with input and moved through the circuit to the output. I was able to get 'er up to ~33W, but backed down the last cap to make it read 25W for fear of over driving it. The SWR at 8w was about 1.7:1 , the SWR at 25W was right around 3:1.

Please forgive any stupid assumptions I am making, I'm still learning all this stuff.

EDIT: I haven't felt the 1946 get over room temperature during any of my 45 second test runs. I think this is a good sign.\\\

EDIT #2: Sounds pretty good based on reports from a local, apparently it's a tad clearer with just the driver running.

I'm thinking the CB meter isn't giving me any near an accurate reading on power out. I finished lining the box with copper tape, and built a wire dipole within 1/4" of my frequency. At the cap settings I originally had it set at, it was showing 60w. I turned the final cap down until it displayed 25w, then let it play for 5 minutes. At the end of the test, power output had dropped to 22w, and the 1946 was just above comfortably warm to touch for more than 3 seconds.

I think I need to buy a meter designed for the band.......

Hello Mountainman!
Not sure if I understood correctly? But heres my concerns
Your SWR readings seem way too high? 2:1 max if you can, anywhere in the red area and youre in trouble!
You seem to be using the trimmer caps to control the power? You should be tuning to get max power and lowest transistor temperature! Use your driver power control for adjusting the amplifier output power!
Also you mentioned the amplifier still giving out 10watts with driver power off? this is usually a sign of self oscillation? Try powering up the amplifier alone with no drive connected? (Keep dummy connected to the amplifier just to be safe) You should read no output power?

nice look at first to me
i agree with sinus trouble look let say drive ure pa with the exciter first dummy load connected at output then switch off the exciter and remove it totaly from input but keep the linear powered and see do u still have any output rf sign if yess you should change one or more of ure capacitor and are making self oscillation
dont worry to much c1946a is a very good transistor hard to find nowadays and there are plenty of fake from this good boy but once i forget to connect my aerial to up to 15 minutes with 14,5volts and the transistor still alive
i have little ask how can i combine two boards in parrallels using a DIY wilkinson or just some 1/4 coax transformer ? but prefer a diy wilkinson

Sounds like I need to run a small resistor from the input pad to ground? Or a variable pot? One weird thing I noticed is that I have a computer fan hooked up to the same wires that are feeding the amp, when rf input is turned off the fan turns but as soon as the RF input is turned on, the fan stops turning. I'm assuming I need a diode on the ground side of the power going into the amp so that the amp does not back feed power through the ground into the fan? I'll mount a variable pot on the input pad to ground and see if I can use that to limit the input feed going to the amp.