Solid State Linear Kits.

[W2INR]

Hello all ,

 I am in the process of putting a station together and decided to look for linears on eBay. I ran into these solid state boards that make some great claims and relatively cheap. Wouldn't mind giving one a try but there seem to be many out there.

I was wondering if anyone here has had some experience with these amplifiers and if so any recommendations as to one that may be better than the rest. Concerns including IMD on the amps.

There is a picture of one of the boards being offered attached

tnx

G

[W3RSW]

Woah, long time OM. Good to see ya.

Haven't built anything with these latest offerings, but have lashed up a used TR-7 driver and PA brick on one band.  But I've seen a lot of chatter about these newer, similar from Israel, etc. on other ham sites.

Boards look nice but are probably really rated at half PEP power advertised in any real world heat dissapation scheme and with IM decent products.  If they're 12 volt nominal rail devices , probably marginal for IM etc. as you know.

Then you have to lash up stable bias circuits, protection circuits up the was, T/r and LP filters, probably digitally switchable for each band, read-outs for same and many other operating parameters and on and on.

Then there's the cabinet, LCD screen and all the other fun stuff.
Go for it.

[W1ITT]

The unit you pictured uses a BLF188 device.  If you go to the data sheets, these look useful.  They use a 50 volt supply, and IMD numbers look OK within rated limits, at better than -30db for third order crud, which is about what most of the current run of amateur radio gear runs. If you poof a BLF188 it's about $200 down the drain.  PureSignal with the Hermes/Anan series radios will spiff these numbers up nicely.  The Ruskies appear to have some nicely crafted boards, with the Israeli units not being as pretty.  But they are tempting, especially the Ruskie board with the built-in LPF.
Also on Ebay one will find various Chicom solid state HF amps, claiming from 20 watts to 300 watts in some cases, for little money and cheap or free shipping.  But in all cases where I have compared the claims to the data sheet ratings of the transistors used, it appears that there is much poetic license taken.  I'd expect IMD to be pretty trashy, and mean time between failure to be short.
I also have a Drake TR7 brick that I'm lashing up with an HPSDR setup, to drive a GS35B.  It's elderly but proven, and PureSignal will clean up the chain.

[WBear2GCR]

WA1GFZ has had some interesting things to say on the topic in general. There was a thread recently which pointed to a published article regarding the output transformers and their effect on IM... fwiw.

[KF9CM]

 I too have been constructing a LDMOS amp. I've done a little research and I have found that the  BLF188 is not the FET to use. You should use the  BLF188XR or any LDMOS FET with the XR designator. This offers up to a 65 to 1 SWR mismatch. The most vulnerable part of a LDMOS FET is the gate. It takes a maximum of 4 Watts to drive it. Anything more and it's toast. On my amp I'm going to use a 14 db attenuator (-13.9794db) so I can drive it with 100 watts. These attenuators are capable of handling 100 watts. There doesn't seem to be a 14 db and attenuator so, I'll have to use a 10db and a 4db attenuator in series.

73 de Gary, KF9CM

[PA0NVD]

I made many 1300 Watt 27 MHz amps with the freescale FET equivalent to the BLF188XR. Never could destroy one, full load mismatch, shorting or opening the output at full power etc. It is important to have a fast acting circuit that takes the drive down with high SWR, mine acts in approc 1 mSec.
As told by Gary, excess drive can destroy the FET. Also bad cooling will destroy the FET and bad grounding. Use Indium to couple the FET to a good copper heat spreader. When you have fast acting SWR protection, it is close to indestructable. These FET's have superior IMD than many other transistors and can have very high efficiency. I reach 91%
Further, take care, there is a standard problem in all factory proposed designes.
The balanced input and output transformers do NOT couple when the FET's are in phase. So in this situation the input and output transformers are pure inductances without any damping and the amp may oscillate with the two FET's in phase and can self destruct. This mainly can happen when there is no drive. Put two 5 ohm 1 Watt resistors across the half secundary windings of the input transformer and the problem is solved. .

[flintstone mop]

Go back to the tubes Gary....Solid state is pain..

Fred

[KF9CM]

I already built a 4-1000, 3-500z and a 2 x 572b amp they work great. This intrigued me.

73 de Gary,KF9CM