100w amp

[Spokes]

Does anyone have any files on a reliable 100w amp that requires no more than 1w to drive it? Something that if built correctly outputs clean signal but don't cost a great deal to slap together!

[teckniqs]

There's loads of cheap 100w amp kits on eBay but unfortunately they are 1.5-3w drive.

Give HF-Electronics NL a try.

[Spokes]

To be fair I've had one of those and it was absolute shite! Even my engineer who is reputable on this forum said he was getting nothing out of em, didn't really want to buy an assembled one wanted to etch up a board and build from scratch

Cheers anyway mate!

[Dai Pole]

Rig Doctor had a schematic on the old forum for a 150W amp, and I believe a PCB layout too. I've "lost" all the files I downloaded from the original Radionecks, so can't help you out - but I'm sure someone here will have them. Although not many here will recommend building high power amps without an analyser.

[teckniqs]

To be fair I've had one of those and it was absolute shite! Even my engineer who is reputable on this forum said he was getting nothing out of em, didn't really want to buy an assembled one wanted to etch up a board and build from scratch

Cheers anyway mate!

I've built 4 of them and they all worked first time, ranging from 110-130w.
No good if you're not SMT savvy.

[Spokes]

I've built 4 of them and they all worked first time, ranging from 110-130w.
No good if you're not SMT savvy.[/quote]

Did you find your schematic was back to front to the board one of the ones I had made no sense at all

[Spokes]

Rig Doctor had a schematic on the old forum for a 150W amp, and I believe a PCB layout too. I've "lost" all the files I downloaded from the original Radionecks, so can't help you out - but I'm sure someone here will have them. Although not many here will recommend building high power amps without an analyser.

I love the way everyone dives on the old analyser chestnut...that would be the last thing I would do although if I was successful with the build it would certainly go on one and be given to someone with more knowledge to go over it...think of this more as a little project just for fun but working to the beat of its ability!

[teckniqs]

Did you find your schematic was back to front to the board one of the ones I had made no sense at all

I found it straight forward enough but did had to double check a couple of things with a pal who'd built one before me. If you need any assistance with yours I'll be glad to help.

[Dai Pole]

I don't care personally what someone does with a schematic - you've got to learn somehow. I mention it only to suggest the answer to your request may not be immediately forthcoming.

[Spokes]

Did you find your schematic was back to front to the board one of the ones I had made no sense at all

I found it straight forward enough but did had to double check a couple of things with a pal who'd built one before me. If you need any assistance with yours I'll be glad to help.

I will dig it out tomorrow and send you some pictures and show you what I mean about back to front, but nice one if your confident this is a little gem then the help will be much appreciated mate!

[teckniqs]

Did you find your schematic was back to front to the board one of the ones I had made no sense at all

I found it straight forward enough but did had to double check a couple of things with a pal who'd built one before me. If you need any assistance with yours I'll be glad to help.

I will dig it out tomorrow and send you some pictures and show you what I mean about back to front, but nice one if your confident this is a little gem then the help will be much appreciated mate!

They are good little amps and work very well. They barely get warm too and would probably run happily without even running a fan but I always do, of course.

I can help you with the correct lay out no problem. Provide pictures of mine or anything you need, just ask.

[Albert H]

I love the way everyone dives on the old analyser chestnut...that would be the last thing I would do although if I was successful with the build it would certainly go on one and be given to someone with more knowledge to go over it...think of this more as a little project just for fun but working to the best of its ability!

Without an analyser, you're building "blind". A 100 Watt amplifier is powerful enough to cause plenty of interference, and without a careful check on an analyser, you're unlikely to be able to find out if you're generating crap. That won't matter too much if you're just feeding the signal into a dummy load (you've got one of those too, haven't you?), but it will need a careful check over before being connected to an antenna.

Why 100 Watts? It's a strange power output these days. You could use an MRF317 driven by an MRF134 - that would be around a Watt in for 100 Watts out.

[teckniqs]

Are you sure an MRF134 would be powerful enough to drive an MRF317 to full output? MRF136 would probably be better for driving that?
I've got some MRF134 and they are only rated at 5w, I've built an amp with an MRF317 and it needed at least 10w drive for full output (12w or so).
I also used the MRF314 (not 134) with SD1407 but I think that would be too high output for an MRF317.

[Spokes]

Nice one teck I'm gonna dig her out in a bit and ping you over some pics

Albert I do have pretty much everything other than the analyser and would not be putting this on a tower block to fuck with the airplanes, it will be fed into a dummy load, if I needed something new to be on air with it would be bought from the right places but this is just for fun by all means I would have it checked by someone to check if it was clean or not and if it was then who knows one day what may happen with it, but the likelihood is it will probably stay in shed lol

[Albert H]

Fair enough. As a good basic check for harmonics (but not close-in crud) you can use an Absorption Wavemeter - easy to build, too.

[Albert H]

I've got a PA here with a 134 driving a 317 to 98 Watts at 98MHz

[teckniqs]

I've got a PA here with a 134 driving a 317 to 98 Watts at 98MHz

Did you build it in '98 too?

That's pretty good going. My power amp section is broadband in and out so that won't help with the gain.
I'm getting around 125w with 12w drive from a Motorola M2518 (12v) on 88MHz.

[Albert H]

No - it was built quite a lot earlier than that! I got a batch of MRF317s from my pals at TRW, and I built lots of stuff with them. One of them got used in a Channel 3 (VHF) TV transmitter, as a linear, with envelope feedback to improve the video linearity.

The 317 is a very rugged transistor if you keep the drive down and don't ask for too much power out. On the bench I've wound one up to about 165 Watts, but it would die if anyone coughed! At 95 - 110 Watts, they're pretty unburstable, and Stephen fired one up (without damage) for several minutes before realising that it had no load!

It was the last generation of the bipolar RF transistors. The MRF317 was very similar (functionally, not in package) to the TP9381. For a bipolar, it has pretty good gain (typically 12 - 13dB at 100MHz in Class C). If you shop around, you can still find them quite cheaply. You can also pair them up, but you have to match them carefully.