6104	2011-04-13 14:31:10	Edson	Output transformer for push-pull MOSFET final RF amp
Message	Date	From	Subject
Hello, I am searching for a 100W RF linear amplifier project and am having difficulties in finding the ferrite core for the output transformer. Since old tube-based linears seldom use ferrite cores, I wander if would there be a way to use an air core transformer. I haven't seen much literature about this. Does anyone on the list have any experience or suggestion in this regard? 73, -- Edson, pu2mwd
6105	2011-04-13 14:47:13	Chris Trask	Re: Output transformer for push-pull MOSFET final RF amp
> > I am searching for a 100W RF linear amplifier project and am having > difficulties in finding the ferrite core for the output transformer. > Since old tube-based linears seldom use ferrite cores, I wander if > would there be a way to use an air core transformer. I haven't seen > much literature about this. Does anyone on the list have any > experience or suggestion in this regard? > Trask, C., "Designing Wide-Band Transformers for HF and VHF Power Amplifiers," QEX, Mar/Apr 2005, pp. 3-15. Chris Trask N7ZWY / WDX3HLB Senior Member IEEE http://www.home.earthlink.net/~christrask/
6106	2011-04-13 14:57:14	Tim	Re: Output transformer for push-pull MOSFET final RF amp

6107	2011-04-13 15:00:45	Edson	Re: Output transformer for push-pull MOSFET final RF amp
Hi Chris, Your paper is very interesting, but it focuses
6108	2011-04-13 15:11:37	Chris Trask	Re: Output transformer for push-pull MOSFET final RF amp
> > Hi Chris, > > Your paper is very interesting, but it focuses on RF transformers using > ferrite cores. This is exactly what I am trying to avoid. Have I > misunderstood your article? > No, you haven't. I don't know as I have ever come across an article where air-cored transformers were used for solid-state power amplifiers. The low impedances of solid-state power amplifiers, meaning much lower than would be seen in vacuum-tube power amplifiers, makes some form of flux (ferrite or iron core transformer) or TEM (transmission-line transformer) necessary to get good coupling. Chris Trask N7ZWY / WDX3HLB Senior Member IEEE http://www.home.earthlink.net/~christrask/
6109	2011-04-13 15:36:12	Tim	Re: Output transformer for push-pull MOSFET final RF amp

6110	2011-04-13 16:29:41	kb1gmx	Re: Output transformer for push-pull MOSFET final RF amp

6111	2011-04-13 16:38:13	Chris Trask	Re: Output transformer for push-pull MOSFET final RF amp
> > > I don't know as I have ever come across an article > > where air-cored transformers were used for solid-state power amplifiers. > > It depends on how many watts you need for "power" but before ferrite > transformers took off in the early 70's, most QST solid-state transmitter > construction articles were using air coupled output transformers. e.g. > W1CER in June 1967 QST, K2HXE in May 1964 QST. > > That wasn't the only way of course. Others used pi networks or simply > tapped down on the PA transistor's tank. e.g. WA6UVR in the August 1964 > QST. Whatever became of him? :-) > I was still doing tubes into the early 1970s as they were cheap, so I missed those. > > > The low impedances of solid-state power amplifiers, meaning much lower than > > would be seen in vacuum-tube power amplifiers, makes some form of flux > > (ferrite or iron core transformer) or TEM (transmission-line transformer) > > necessary to get good coupling. > > Typical link-coupled tuners have coupling coefficients for the inductors, in > the 0.1-0.5 range. > Ouch! That's disgusting. I wouldn't consider using a transformer that had a coupling coefficient of less than 0.95. Chris Trask N7ZWY / WDX3HLB Senior Member IEEE http://www.home.earthlink.net/~christrask/
6112	2011-04-13 17:02:27	kb1gmx	Re: Output transformer for push-pull MOSFET final RF amp

6114	2011-04-13 17:08:27	Tim	Re: Output transformer for push-pull MOSFET final RF amp

6115	2011-04-13 17:12:32	kb1gmx	Re: Output transformer for push-pull MOSFET final RF amp

6116	2011-04-13 17:46:51	KK7B	Re: Output transformer for push-pull MOSFET final RF amp
There is a really outstanding collection of good information on this subject in the book: John L.B. Walker, Daniel P. Meyer, Frederick H. Raab, and Chris Trask, "Classic Works in RF Engineering: Couplers Transformers...etc." Amaz
6118	2011-04-13 18:25:49	Chris Trask	Re: Output transformer for push-pull MOSFET final RF amp
> > There is a really outstanding collection of good information on this > subject in the book: > > John L.B. Walker, Daniel P. Meyer, Frederick H. Raab, and Chris Trask, > "Classic Works in RF Engineering: Couplers Transformers...etc." > > Amazon has copies listed at gasp-inducing prices. I paid considerably > less than that a few years ago for a new copy at one of the on-line > technical booksellers. If you have access to a good technical library > it's worth a close look, but after leafing through the pages you may > want your own copy. > > Obscure classic works by Guanella, Reed Fisher, and others are reprinted > alongside recent applications by Granberg, and new notes by the four > authors. It's one of the more important references in my library. > > Yep, same Chris Trask... > Yes, indeed it is. :{) Chris Trask N7ZWY / WDX3HLB Senior Member IEEE http://www.home.earthlink.net/~christrask/
6123	2011-04-14 04:25:53	Tim	Re: Output transformer for push-pull MOSFET final RF amp

6128	2011-04-14 14:55:05	kb1gmx	Re: Output transformer for push-pull MOSFET final RF amp