COHERENT transformerless 81mHz amplifier schematic ?

[dreamth]

I'd be interested in the schematic for any of  their 40w+ CO2 laser transformerless(no ferrite core)  amps like this one:

/>I used to fix their lasers 12 years ago and i remember that kind of amplifier being their last embodiment which blew me away at the time.Looks like their RF manufacturer is alpha telecom apparently doing the amps for yaeshu...I'm not knowledgeable in rf field although i used to have a HAM radio operator licence, but i'd like to learn a bit more on that.

[Da_Stier]

Hi,

this amplifier is a very typical implementation of a propably push pull amplifer architecture.
Most datasheets contain a typical implementation.

Take a look at this for example:
MRFE6VP8600H.pdf

Transformerless is not quite true, but you already stated this by adding the without ferrite.
The transformers in this case are the transmission line transformers, realized as coax cable.
(The impedance is most of the time .5 or 1.5 times the system impedance.)

A very fascinating topic to read for sure.


Greetings,
Michael

[dreamth]

Thank you Sir! You've been really helpfull.Never found the time in the last 12 years to go back to lasers altough i still have tons of optical things around me from that era.I think i saw some similar rf amplifier in some Siemens RMN machines two years ago.I knew it was coax coupled , i just wanted to say it doesn't use ferrites indeed.Maybe one day i'll build a 40w co2 laser for myself.I fixed everything in those coherent lasers except the rf units as i didn't have the experience, nor i did have the theoretical background to go there.At the time i was servicing two generations of co2 lasers and the older one used tons of ferrites at 81mHz while this one at 100Mhz scraped them all together.
Is this some Yagy baloon circuit or similar? How is it called technicaly?

[Da_Stier]

Hi,

great to hear that my response was of use. 
This might be a stupid question but what use does an RF amplifier have for a laser?
... I know of Q-switching, which uses a RF power supply in the 13.556MHz ISM band. (around 40W I believe)

The RF transformers (the ferrite ones) are pretty typical of lower frequency designs (for example HAM operators use them)
The higher frequency stuff uses hybrid couplers, most of the time done in microstrip technology.
A good example for that are the cellular amplifiers.
The coaxial variant is a typical transmission line transformer or more precisely a "coaxial transmission line transformer".

The 80 to 100MHz band is kind of an interesting region since there are designs for every style of transformer available, mostly depending on the use case.

There are some pretty good chinese linear amplifier kits out there in all kinds of frequency ranges from 1MHz to 430MHz, which are a nice starting point if you want to experiment with stuff like this without paying a lot of money. 


EDIT:
something like this is pretty similar to the amplifier you postet, minus the preamp of course.
https://www.ebay.de/itm/170W-FM-VHF-80Mhz-180Mhz-RF-Power-Amplifier-Board-AMP-KITS-For-Ham-Radio-DIY-New/264031224310?epid=20025692155&_trkparms=ispr%3D1&hash=item3d797cc1f6:g:ttYAAOSwUfNXR7YQ&amdata=enc%3AAQAFAAACcBaobrjLl8XobRIiIML1V4Imu%252Fn%252BzU5L90Z278x5ickkXKoKcbeZcOrOku%252BoOBl%252BS0PezCOyyZpfhQ24odXGrpqjDbJ1mIZ3VHPcAlDnA8Mx1yz3TvOcUXHmeM6ZPxXLoB5bQ2LRVLSN%252BEz0C7lsUqBXM3YfRPRLW3bwHE6GCEEQ3rkTT3MEhLzgXE%252BiAhqX2JZcMcL0YfC9T4pXO%252BzSmD9non3PbxOY4EO3Ve8sWgVxgCvRLkbdS2wjXw%252FuEmsTCLOKC4rMoA99BxsGTfxA9GQkOD0B29uRCoOhdhQj8KBy7wkiz98bcShJGie2ZQwL4vHcJQqR%252BZ6CXeXqGCgezT12aAYHTP5%252BSbHz5KEvgcFhUcIxUuso6SVb%252FakN7i%252F8UVrvAKJyQwBEY7dUJY4CokWafV%252FYBC1Ag23FHWNb5O8c7BPtNJDTXYjZCMPgCYnFdMO9d%252FnCFheO35ZLMt2bI4NCRMnrw13fHSP4KK%252BJoRJ9WqcgUxq%252BFCwUSSdFa58qyHOkHHDlVGW1G45hjOIBMHLVhdAiwAURaBf6%252FZB0QxLDrxiwFOy40Q%252BEYhA1VAOGbsDLXdZrt8wmeD%252B%252BcwePKBWd0Y2Vzt0j%252BdAjH6BT5tV%252BdKIiDrkVToVpqSbw9pOQoMcxCn1r%252F2nE30p16i%252Fjh1llwHAATrkl0%252FFNgH8rE5%252BoLRA8vGqZuBl7zYltJW7IuaVdP1Us1USko2SKKYcISpIOAeziZREyteJMMe0%252FsF%252BDMb4hIymXhxZ1o6FEfWL2VT5DEvuSufZnP%252Fo5MqOV%252BUWJJZcoKrdmk0ZZO0igafRj5WcJhJS9fM0NegsTyaWxXw%253D%253D%7Ccksum%3A2640312243109176a1e7908f401ba0ade85a8e7fa924%7Campid%3APL_CLK%7Cclp%3A2334524#rwid


Greetings,
Michael

[dreamth]

Cool, now i know the name so i can download some tech papers to maybe understand that better.
The history of RF pumped lasers starts with UK based AEA technology bought probably by  Rofin Sinair and implemented in their  transverse gas  flow lasers too  which used  parallel anodes placed at about 2mm one from another working as a capacitor which was in series with some paralleled inductors resonating at a fixed frequency delivered by this amplifier in short PWM bursts up to 100khz.With the help of a UV ionizing lamp or a secondary RF amplifier the laser discharge was initiated.This system provided a very high quality laser compared with other pumping methods. You can check their early patents:
https://patents.google.com/patent/US4288756
https://patents.google.com/patent/US4077018
Not really sure about the whole history, but transversal flow was better to be used with an RF pumping system.
COHERENT , based in the US used same technology later , got better bussiness and a few years ago aquired its mother company, Rofin which had better but more expensive technology.
The second patent is the origin of later circular flow Trumpf lasers in Germany which integrated very precise CNC in their machines.
You can check any patent linked to rf  pumped transverse flow lasers online like this going to Raytheon:
https://patents.google.com/patent/US4651325
I'm probably  wrong about who's the true inventor of this tecnology, but that's not really important today.

[johnf]

That amplifier topology was invented by Helge Granberg at Motorola in the early 1990s
They look like 9:1 transformers in this case if tyhey have 3 layers of coax each side 2 layers = 4:1 3 9:1 4 16:1 coax impedance has to be the arithmetic mean of the two impedances involved so different designs use 25 ohm 15 ohm and 10 ohm semirigid coax.
 Helge did reccommend that the input transformer was ferrite loaded due to the increased gain at low freqs to help stability

look up mid 90's motorola RF databook MRF141G MRF151G application notes the G suffix indicated Gemini package for push-pull applications

[dreamth]

That amplifier topology was invented by Helge Granberg at Motorola in the early 1990s
They look like 9:1 transformers in this case if tyhey have 3 layers of coax each side 2 layers = 4:1 3 9:1 4 16:1 coax impedance has to be the arithmetic mean of the two impedances involved so different designs use 25 ohm 15 ohm and 10 ohm semirigid coax.
 Helge did reccommend that the input transformer was ferrite loaded due to the increased gain at low freqs to help stability

look up mid 90's motorola RF databook MRF141G MRF151G application notes the G suffix indicated Gemini package for push-pull applications

Thank you Sir!

[Da_Stier]

@dreamth:
interesting, I didn't know that there are RF pumped lasers.
Very fascinating, I guess I have something to read now. 

@johnf:
interesting to know, where it comes from.
The datasheet for the MRF141G is very intereting, they provide some nice pictures of the transformers.


Greetings,
Michael

[dreamth]

Never thougt about rf amplifiers as modulated resonant converters working at high frequencie,  but i never dived into it too much.I was mostly a low noise audio geek, but it looks like  everything is nature, art  and science is  resonant
https://www.ab4oj.com/dl/eb104.pdf
https://www.rf-microwave.com/app/resources/uploads/transistors/Motorola_AN758.pdf

[johnf]

Yes that amp looks like about 1.2kW of RF out maximum
I few years ago I built this for my HAM hobby in this case the BLF188XR is soldered to the heatsink to get very good thermal performance as this little FET consumes 50 volts at 55 amps and will give about 1.3 kilowatts out although I have set the ALC now to 1000 watts as this is my second fet. I forgot to put the antenna on one night and tried to put 1.3kilowatts into an open circuit and I punctured a few of the paralleled fet inside the package