Over the weekend I built another JBOT 5 watt linear amplifier (design by Farhan). I used a nice piece of copper-clad board that Dave, W8NF, sent me (thanks again Dave). This time I chickened out regarding the possible conductivity of the anodized heat sinks. I didn't have any trouble with this on my first JBOT, but I worried that if the anodized layer gets flaked away, a heat sink might short one of those collectors to ground. To be on the safe side, I put small squares of Gorilla Tape on under the heat sinks. (PLEASE don't tell me that Gorilla Tape is conductive!)
For T1 and T2 I used FT50-43 toroids instead of the TV baluns used by Farhan. He had recommended FT37-43's as an alternative to the TV baluns, but I went with the slightly larger toroids. For T3 I rolled my own binocular core using four FT37-43 toroids stacked 2X2.
The amplifier has passed the smoke test. Next I have to put in the low pass filter (Steve Smith: Please note that I have left space on the board for the filter.) Then this version will face its real test when it goes into the 17 meter Azores SINGLE sideband rig.
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Nice build OM. Here's hoping for amplifyin' and not oscillatin'!
ReplyDelete73
Mike
K2MTS
Sure, sure. I'll believe that when I see it (the filter). :-)
ReplyDeleteSeriously, nice build there, OM. This one looks much neater than its predecessor.
73.......Steve "Just call me 'Thomas'" Smith
"Snort Rosin"
Bill,
ReplyDeleteI looked closely at your photographs after reading your description and there's just one thing I don't understand: What is that core to the right of your output transformer. It looks like a large bead.
73.......Steve Smith WB6TNL
"Snort Rosin"
Good eye Steve! Yes, that is a large ferite bead. It it on the wire from the PA's RF choke to the center tap on the transformer. That line carries the 12 volts DC to the 4 final transistors. During the debugging of my first JBOT, putting a bead there seemed to help stabilize the amplifier. So I threw one in on this one too. I may also put a bit of shielding between the LP filter and the final transistors -- this too seemed to help last time around.
ReplyDeleteLP filter will be finished tomorrow.