BLW60

[shuffy]

Hi guys... what's the furthest anyone's pushed a BLW60? I've used a few of these in PAs over the years, sticking to 45W out with about 4-5W drive at no more than 14V and never pushed one further. By chance though, I've got one here that's doing around 55W at just over 15V, probably with about 5W of drive. It doesn't seem to be complaining - does/has anyone else ever run them around this set of conditions - or more? Cheers.

[Analyser]

Yes, I've had (IIRC) about 70W out of one of these with an 18V supply. It worked fine on the bench but was "extremely intolerant" to a less-than-optimal SWR in practical use.

I wouldn't push it.

[teckniqs]

Just under 80w with around the same voltage and about 8w drive lol.
....I was using a modified circuit that you originally gave me Analyser about 20 years ago with BLY88/89 etc.

[shuffy]

I knew it would be you two! Thanks a lot. Doesn't sound like I'm stressing it much then, but as you've said (and in line with my own experience) SWR is the killer when you're operating above the "line". Obviously SWR on the bench is one thing but when deploying, it's quite another. I'm probably going to turn it down a tiny bit. Cheers!

[Analyser]

I knew it would be you two! Thanks a lot.

Hmmm, Busted!

[Analyser]

....I was using a modified circuit that you originally gave me Analyser about 20 years ago with BLY88/89 etc.

Err, perhaps, maybe. Or something.

I quite like all those old school BLY devices, they were pretty easy to get working and with a few watts input from your SD1127/ MRF237/ BFQ43 you could get a nice little 50W rig.

A friend of mine still has a box of BLY89 which he wants to make some RSL-type PAs with. I'll give him a hand designing one when I get some time, just for nostalgic purposes.

[teckniqs]

....I was using a modified circuit that you originally gave me Analyser about 20 years ago with BLY88/89 etc.

Err, perhaps, maybe. Or something.

I quite like all those old school BLY devices, they were pretty easy to get working and with a few watts input from your SD1127/ MRF237/ BFQ43 you could get a nice little 50W rig.

A friend of mine still has a box of BLY89 which he wants to make some RSL-type PAs with. I'll give him a hand designing one when I get some time, just for nostalgic purposes.

Now I've that Gerry Rafferty old song going through me bloody head!

Yeah another popular one was the 2SC1947, the old board you knocked me up had SD1127 driving it.
....I've got an old BW unofficial 150w amp with a BFQ43 driving the SD1480 somewhere.

Around 15 years or so ago NRG had the BLW60 for £9.95 so I ended up buying a few, they also had the TRW PT31963 which was good for around 30-40w at £6.95 each.

[Albert H]

Stephen and I tried all sorts of tricks with the BLW60 and the BLW60C (a fractionally different beast). We found that any of them were good for 50Watts at 15V with 4.5W of drive. This was using a single variable trimmer in the output match - we found that this tuned fairly broadly. We had some success with a fully broadband design, but the gain was significantly lower, and we never got more than about 30W for 4W drive.

At 40W, the devices were pretty much indestructible, so the PA was designed for this power level when coupled with the PLL Pro III. It always proved very difficult to persuade the average numpty transmitter buyer that the difference between 40 and 50 Watts was negligible!

That's why the next PA was at 120W - it was an BLF177 running at 42V, set up to be broadband. It used the 4 Watt drive from the PLL Pro III and delivered 120 Watts of very clean power into almost any load - again, it was (pretty much) unbreakable.

[teckniqs]

That's why the next PA was at 120W - it was an BLF177 running at 42V, set up to be broadband. It used the 4 Watt drive from the PLL Pro III and delivered 120 Watts of very clean power into almost any load - again, it was (pretty much) unbreakable.

Around 1999/2000 time I remember seeing a Veronica PLL Pro 150 with an MRF150 output, the TX was in quite a large vinyl coated box and considerably larger than the usual Maplin style box which was popular back then. ...since then I've seen plenty of MRF151, BLF177, SD2931 but never MRF150.

[Banus_radio]

they also had the TRW PT31963 which was good for around 30-40w at £6.95 each.

As it happens ive got about 8 of them in my tray.. They are black with a stud mount. Good little transistor.

[shuffy]

I prefer some things about bipolar PAs, especially for middling output power like this. Slightly less efficient on air but simpler circuits in general. Obviously though, FETs win for gain and power these days.

Anyway - I turned the supply down a little on this PA (it's a 2 stage design so that also reduced the drive) and now getting 46W at 14.1V with around 4.5W drive. I would have left it alone but I don't think the eventual users will be able to guarantee perfect SWR, so playing safe. Thanks everyone for the input.

[Albert H]

That's why the next PA was at 120W - it was an BLF177 running at 42V, set up to be broadband. It used the 4 Watt drive from the PLL Pro III and delivered 120 Watts of very clean power into almost any load - again, it was (pretty much) unbreakable.

Around 1999/2000 time I remember seeing a Veronica PLL Pro 150 with an MRF150 output, the TX was in quite a large vinyl coated box and considerably larger than the usual Maplin style box which was popular back then. ...since then I've seen plenty of MRF151, BLF177, SD2931 but never MRF150.

Stephen and I bought a strip of MRF150s. They really would do 175W for about 10W in, but the biasing was incredibly critical. We fed them from TP1028 or 2N6081 drivers. When they were used up, we abandoned them in favour of the BLF177, which was a lot less critical.

There was another device we used - SRF1616 as I recall - which came as a batch from Thomson in France, which I managed to get up to about 200W for 5W drive, but these turned out to be very touchy, so we went back to the BLF177.

We built even several units in 19" cases with four BLF177s in parallel for the final, which we rated at 500W output. Two of these are still in use in Eastern Europe!

[teckniqs]

There was another device we used - SRF1616 as I recall - which came as a batch from Thomson

Possibly SRF1818? .....Are you sure they weren't Motorola?

[Analyser]

Most SRF things are Motorola AFAIK.

I don't like the MRF150 either, I found the output matching to be awkward and the gain was nowhere as good as the MRF151.
This may be one of the reasons why you see many more of these going cheap on the second-hand market and hardly any '151s or '177s.
The Chinese have cottoned on to this and remark all the MRF150s as 151s or 177s.

Crafty buggers.