Looking to find a reliable PA

[G8DGN]

Almost as soon as I started on QO-100, having got my H265 just right, my "cheap" Chinese PA has failed. It is an Acasom jam043850s2 which was sold as 60W capable, although I could never get it to draw more than 48W. It had a massive heatsink so never overheated. The GaN output device (PA0453) seems to be biased at -2.54V on its gate, so I gather these are depletion mode devices. The quiescent current of the PA as a whole is approximately half of the "driven" current (when it worked). So I'm assuming the output device and its biasing is ok.
I've taken some voltage measurements and just discovered what the problem is by burning my finger on the HTN7G38S007P driver chip. Did it jump or was it pushed? This seems to be an under-run 7W device, hence no heatsink. I'll order a couple from Aliexpress but I'm not confident fitting this type SMT chip.

With my dish setup I need about 40W of RF for 333k. Any suggestions for a source of a better PA or components to build one?
Thanks,

[g0mjw]

Bypass it?

[G8DGN]

That's a great idea. I'd have to find something to drive it, as well as providing impedance matching. Maybe I'll try that if the replacement chip fitting does not go well.

In parallel, I'm still interested whether there are any sources surplus used kit that can be re-purposed as a 2.4GHz PA.

[radiogareth]

You might consider this https://www.ebay.com/itm/135542314735?i ... SwQytnqE5g as this is a trusted seller and the two amps I have bought from here delivered what was promised. The 50W is probably a CW rating but with my smaller amps they have delivered 50% of DVBS2@333kS with good linearity. It also does not need a predriver and the seller often takes offers at -20% of listed.
There are a range of similar/smaller amps well worth a look at too.
Article probably upcoming in CQ-TV about them.
Gareth

[radiogareth]

By the way, I THINK what you describe as a VCO is actually a temperature compensated -10dB attenuator. Met something similar on a 3.4GHz big PA I was looking at.
Gareth

[g0mjw]

I think the VCO, if it is one, is part of the linearising - a sample of the RF is demodulated and sent back to the driving hardware and used to inform the pre-distortion to correct for non-linearity.

Alternatively, given Ascom also make jammers - draw your own conclusion why there may be a VCO.

[g4saq]

You could try giving Jim, G7NTG, a try. He is a whizz with SSPAs and has supplied many surplus pallets and complete PA's. I use a pallet supplied by Jim and I copied his design for my PA. A very helpful chap.
73,
Russ.

[G8DGN]

@garethradio, Thank you for the link, I hadn't thought of trying eBay.com. I'll keep an eye out for the next CQ-TV.

@g0mjw, As a jammer it was not efficient at all;) the spectrum was quite pure - when it was working..

[G8DGN]

Hi Russ,

I am reading Jim's posts at this moment.

Thanks