NRG 40watt amp

[montaylor]

Hi,
i have built both types of nrg 40w amps using the blw60c but i only have one blw60c and dont want to blow it up. what other transistors can i use in this board design? will the MRF2628 work ok to get it up and running albeit its only 15w?

[Albert H]

The inductors would be different values (slightly) for the lower power. You might get away with compressing or stretching the existing coils.

However - the BLW60C design is meant to have 4 Watts of drive. The smaller transistor would certainly need less drive - feeding it 4 Watts would probably destroy it!

These days, I wouldn't build any RF Power Amplifier using old fashioned bipolar transistors - the modern FETs are the way to go. They have spectacular gain, and don't suffer from thermal runaway - as a FET gets hotter, it draws less current, so it tends to self-limit. There are also a range of (relatively) low voltage FETs (the Mitsubishi ones spring to mind), and I've built 12V (battery-powered) PAs up to about 90 Watts with them. I've been pleasantly surprised by their efficiency - I built one recently with a pair of the 30 Watt variety, running at 50 Watts output. It needed about 1 Watt of drive, and was around 85% efficient - ideal for a "hit and run" battery-powered operation! I kept the power down so that an antenna mismatch wouldn't destroy the devices (I couldn't be sure of the people who were going to operate it), and so far it has proved to be entirely reliable.

[montaylor]

cheers Albert, i used to have a 40 nrg amp 10 to 15 years ago and sold just that part to my nrg set up so ever since then wanted to replace it. after trying to find the blw60 for a fair price i understand what your saying about old skool stuff!

what bias do i need to set for the blw60?

[Frequent Lee]

cheers Albert, i used to have a 40 nrg amp 10 to 15 years ago and sold just that part to my nrg set up so ever since then wanted to replace it. after trying to find the blw60 for a fair price i understand what your saying about old skool stuff!

what bias do i need to set for the blw60?

You can use a PT31963 as a drop in replacement of the BLW60 in the NRG design. Stephen used to use them if he didn't have any BLW available. You can get them on eBay for £8

I have a few BLW60 original Philips transistors that I bought off Christine when she was liquidating all of the stock a few years after Stephen passed away. I will sell you a couple of them for £35 including postage if you want them send me a DM

[Albert H]

The BLW60C doesn't get any DC bias - it's running in class C. In this mode, the transistor is switched by the incoming signal. This is (usually) the most efficient mode forr bipolar transistors - typically around 70%.

[montaylor]

cheers guys. thanks for the info