70 Watt amplifier kit for 23cms coming soon


James Smith
 

I found a source of power transistors and decided to try them using John G4BAO's PCB design which is now public domain. He has unfortunately , run out of boards so I made my own with a scalpel to a similar design to test these transistors. results are very good on the first try - 80 watts saturated 70 watts P!dB and a gain of 14.4dB , 28 volt supply at about 5 amps @ 70W.
I am now building another one to test repeatability and if all is good then I will order some boards and look to selling a partial kit of PCB, transistor and ATC caps. No Idea of price yet. 
Since the supply of reliable MRF286's has dried up , this may help as a stopgap until another design comes along.
With great thanks to John Worsnop G4BAO for having done all the hard work in designing the matching and the rest of the PCB.
I won't say yet what device but will let you know soon.
The device used is a MRF5S9070 and I bought them as new old stock NOS from a UK firm who had them in stock for many years
I will make them available in partial kit form with a PCB made with Rogers 4350 , power transistor and ATC and C0G capacitors and when all the development is finished I will write an article for here and for CQ-TV magazine.
The expected kit price will be £30.00 + postage
See G4BAO amplifier in photos
Email me if you are interested and I will put you on the list.


James Smith
 

more info on DATVPA@groups.io


KENT BRITAIN
 

Hey James, I'm the one that made most of John, BAO's boards.

If you can deal with the older 274D Gerber format, I have Gerbers!
I did make one change, the board is for the more common TO-220
style voltage regulators.    These are on Arlon 25N material.
Which by a strange coincidence has the same electrical characteristics
as Rogers 4350.   Oh that marketing department!!

Maybe a trade of some boards for a device??    Cheers  Kent WA5VJB/G8EMY

On Sunday, June 28, 2020, 3:59:31 PM CDT, James Smith via groups.io <thebigclunk@...> wrote:


I found a source of power transistors and decided to try them using John G4BAO's PCB design which is now public domain. He has unfortunately , run out of boards so I made my own with a scalpel to a similar design to test these transistors. results are very good on the first try - 80 watts saturated 70 watts P!dB and a gain of 14.4dB , 28 volt supply at about 5 amps @ 70W.
I am now building another one to test repeatability and if all is good then I will order some boards and look to selling a partial kit of PCB, transistor and ATC caps. No Idea of price yet. 
Since the supply of reliable MRF286's has dried up , this may help as a stopgap until another design comes along.
With great thanks to John Worsnop G4BAO for having done all the hard work in designing the matching and the rest of the PCB.
I won't say yet what device but will let you know soon.
The device used is a MRF5S9070 and I bought them as new old stock NOS from a UK firm who had them in stock for many years
I will make them available in partial kit form with a PCB made with Rogers 4350 , power transistor and ATC and C0G capacitors and when all the development is finished I will write an article for here and for CQ-TV magazine.
The expected kit price will be £30.00 + postage
See G4BAO amplifier in photos
Email me if you are interested and I will put you on the list.


James Smith
 

Hi Kent
I already have boards on order to John's gerbers using Rogers 4350
I am interested in a deal - how many boards have you got?
How about a swap - 2 devices for 2 boards so I can test them?
email me at thebigclunk@...
Jim G7NTG


Derek Brown G8ECI
 

Hi James

I would be certainly interested in a kit, i have trying to rebuild my old 2C39A EME amp for about 5 years and still no where near to finishing, a sspa and preamp right under the antenna would be briliant. Please put my name and call in the list Derek G8ECI JO03ai

73 Derek G8ECI



Sent from my Samsung Galaxy smartphone.


g3zqu
 

Please put my name down for a kit please.
Martin G3ZQU


Andy G4JNT
 

It's ironic that a switch mode PSU from 12V for 2C39 amps would have been quite a straightforward project.   With only one high voltage to generate at 100 Watts or so, grid bias applied to the cathode derived from the 12V, as well as the heater, and that's all.  No complicated screens, protection, negative supplies all interlocked   AT one point, yonks ago, I had the high voltage supply, near enough to that anyway, built; but that was for another reason altogether.



On Mon, 29 Jun 2020 at 17:01, Derek Brown G8ECI via groups.io <g8eci=yahoo.co.uk@groups.io> wrote:
Hi James

I would be certainly interested in a kit, i have trying to rebuild my old 2C39A EME amp for about 5 years and still no where near to finishing, a sspa and preamp right under the antenna would be briliant. Please put my name and call in the list Derek G8ECI JO03ai

73 Derek G8ECI



Sent from my Samsung Galaxy smartphone.


G0FVI
 

Hi James,
please put me down on the list for a kit too.

Andy G0FVI


Martin <gw3xjq@...>
 

I am interested in this kit. Where/how can I find the photos you refer to?   I am a 'new boy' on this forum and to 23 cms, but have started putting something together. 73 Martin GW3XJQ


Robin Szemeti - G1YFG
 

My half-assed plan is to put a 48V socket on the pack of the 23cm amp, the 70cm amp already has one ... shack use and portable with a genny, I shall use the mains input ... otherwise, I shall lob 4 batteries in the back of the car. to supply the 48v


On Mon, 29 Jun 2020 at 19:14, Andy G4JNT <andy.g4jnt@...> wrote:
It's ironic that a switch mode PSU from 12V for 2C39 amps would have been quite a straightforward project.   With only one high voltage to generate at 100 Watts or so, grid bias applied to the cathode derived from the 12V, as well as the heater, and that's all.  No complicated screens, protection, negative supplies all interlocked   AT one point, yonks ago, I had the high voltage supply, near enough to that anyway, built; but that was for another reason altogether.



On Mon, 29 Jun 2020 at 17:01, Derek Brown G8ECI via groups.io <g8eci=yahoo.co.uk@groups.io> wrote:
Hi James

I would be certainly interested in a kit, i have trying to rebuild my old 2C39A EME amp for about 5 years and still no where near to finishing, a sspa and preamp right under the antenna would be briliant. Please put my name and call in the list Derek G8ECI JO03ai

73 Derek G8ECI



Sent from my Samsung Galaxy smartphone.


G0FVI
 

If I read it correctly the kit will be based on G4BAO's design. You can read about it in 'microwave knowhow' https://b-ok.org/book/1204058/8a19de .


Bob G8HGN
 

Hi James,

Could you put me on the list please, thanks,

Bob G8HGN

On 28/06/2020 21:59, James Smith via groups.io wrote:
I found a source of power transistors and decided to try them using John G4BAO's PCB design which is now public domain. He has unfortunately , run out of boards so I made my own with a scalpel to a similar design to test these transistors. results are very good on the first try - 80 watts saturated 70 watts P!dB and a gain of 14.4dB , 28 volt supply at about 5 amps @ 70W.
I am now building another one to test repeatability and if all is good then I will order some boards and look to selling a partial kit of PCB, transistor and ATC caps. No Idea of price yet. 
Since the supply of reliable MRF286's has dried up , this may help as a stopgap until another design comes along.
With great thanks to John Worsnop G4BAO for having done all the hard work in designing the matching and the rest of the PCB.
I won't say yet what device but will let you know soon.
The device used is a MRF5S9070 and I bought them as new old stock NOS from a UK firm who had them in stock for many years
I will make them available in partial kit form with a PCB made with Rogers 4350 , power transistor and ATC and C0G capacitors and when all the development is finished I will write an article for here and for CQ-TV magazine.
The expected kit price will be £30.00 + postage
See G4BAO amplifier in photos
Email me if you are interested and I will put you on the list.


Chris G0WUS
 

Hi James put me on the list for a kit please

73 chris G0WUS



Sent from my Samsung Galaxy smartphone.


-------- Original message --------
From: Bob G8HGN <g8hgn73@...>
Date: 30/06/2020 7:01 pm (GMT+00:00)
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] 70 Watt amplifier kit for 23cms coming soon

Hi James,

Could you put me on the list please, thanks,

Bob G8HGN

On 28/06/2020 21:59, James Smith via groups.io wrote:
I found a source of power transistors and decided to try them using John G4BAO's PCB design which is now public domain. He has unfortunately , run out of boards so I made my own with a scalpel to a similar design to test these transistors. results are very good on the first try - 80 watts saturated 70 watts P!dB and a gain of 14.4dB , 28 volt supply at about 5 amps @ 70W.
I am now building another one to test repeatability and if all is good then I will order some boards and look to selling a partial kit of PCB, transistor and ATC caps. No Idea of price yet. 
Since the supply of reliable MRF286's has dried up , this may help as a stopgap until another design comes along.
With great thanks to John Worsnop G4BAO for having done all the hard work in designing the matching and the rest of the PCB.
I won't say yet what device but will let you know soon.
The device used is a MRF5S9070 and I bought them as new old stock NOS from a UK firm who had them in stock for many years
I will make them available in partial kit form with a PCB made with Rogers 4350 , power transistor and ATC and C0G capacitors and when all the development is finished I will write an article for here and for CQ-TV magazine.
The expected kit price will be £30.00 + postage
See G4BAO amplifier in photos
Email me if you are interested and I will put you on the list.


Garyov
 

Be interested in a Kit if still available please.
G4BJD Gary


Martin Cranage, G8OFA
 

I would also be interested. 
73, Martin G8OFA

--
Martin, G8OFA


Mark
 

Hi James

If it is not too late, could i also register my interest in the kits


73 <DE> Mark


Bill GM0NRT
 

Hi,

If not too late, please add me to the list.

Thanks,
73 Bill GM0NRT


Alan Beard
 

Hi all,

Looking at the designs around the MRFE6S9160 a low Z stripline transmission line
comes from the FET drain, about 1/4 wave, then a second higher impedance line
also about 1.4 wave to the final 50 ohm output.

Looking for  a five ohm impedance transmission line, can ten pieces of 50 ohm
coax in parallel do the trick? 

Also, I'm loathe to solder the device to a heatsink, can I clamp it on using
a bar across the device also being an earth shield?

Actually, with copper shim under the device lifted each side, gate and drain
with tape so I can solder to the shim, the shields of the above coax.

Note, under the device, only the shim copper and grease. No tape.

Alan VK2ZIW


On Wed, 15 Jul 2020 14:12:32 -0700, BillC wrote
> Hi,
>
> If not too late, please add me to the list.
>
> Thanks,
> 73 Bill GM0NRT

---------------------------------------------------
Alan VK2ZIW

OpenWebMail 2.53, nothing in the cloud.


Robin Szemeti - G1YFG
 



> Looking for  a five ohm impedance transmission line, can ten pieces of 50 ohm
coax in parallel do the trick? 

Possibly, but it is FAR easier to design it as a matching section on PCB material, either PTFE or FR4 substrate.

> Also, I'm loathe to solder the device to a heatsink,

Why? it is simple to do, with nothing more than the kitchen stove and some solder ... W6PQL says he has done "hundreds" without issue, I did my 23cm one and had no problem.  Don't forget the ceramic seals on these devices are fixed in a kiln at silly temeraptures, a little soldering is not going to harm them. I admit I was apprehensive when doing it, but having done one, I plan to use it as a standard mounting technique going forward..
_._,_._,_


Alan Beard
 

Hi Robin,
> Possibly, but

Can somebody answer "yes" or "no"?

There is another reason: The RF field is contained.

Design  may be far easier for you but "I want to do it my way"
and have it done/made now, not several weeks later.

This is a home brew one off.

Alan VK2ZIW

On Thu, 16 Jul 2020 02:48:31 +0100, Robin Szemeti - G1YFG wrote
>

>
> > Looking for  a five ohm impedance transmission line, can ten pieces of 50 ohm
> coax in parallel do the trick? 

>
> Possibly, but it is FAR easier to design it as a matching section on PCB material, either PTFE or FR4 substrate.
>

>
>
>

> > Also, I'm loathe to solder the device to a heatsink,
>
> Why? it is simple to do, with nothing more than the kitchen stove and some solder ... W6PQL says he has done "hundreds" without issue, I did my 23cm one and had no problem.  Don't forget the ceramic seals on these devices are fixed in a kiln at silly temeraptures, a little soldering is not going to harm them. I admit I was apprehensive when doing it, but having done one, I plan to use it as a standard mounting technique going forward..
>

---------------------------------------------------
Alan VK2ZIW

OpenWebMail 2.53, nothing in the cloud.