Discussion in 'Amateur Radio Amplifiers' started by WA6MHZ, May 26, 2012.
I'm sure you could use any 70 (68 or thereabouts) PF cap that will handle the current.
After seeing this bidding war, I'd reconsider doing anything other than restoring it. As of now, one bidder will win it and FOUR bidders won't. It's up to $405 and the auction still has one day to go. That would buy a lot of parts with which to build an amplifier...
Just dont holler too much when it takes off and the tube goes with it....thats a real hack mod.
I just got the parts in from Digikey, but most are for the Power Supply rebuild. That shouldn't devalue it too much. Maybe I oughta keep it stock after all. I STILL want to build a 6M kilowatt though! Maybe I can find something at the Chino Hills Swapmeet.
I will put in the new Electolytic caps, new 1N5408 diodes, bleeder resistors, and Glitch circuit. Also a Soft Key circuit
I don't know that I'd make any changes unless a sale depended on it. I say sell it for megabux as it is, and build yourself an amplifier that'll loaf along at 1500W at 100% duty cycle.
If you use a separate HV supply, you can use it with multiple RF decks with the use of HV relays. That'll cut down some of the cost. I'm impressed with the work W5JGV has done on a HV SMPS... using NO heavy (and expensive) iron. HV is regulated, too.
Today, (Saturday) I shined on the VHF CONTEST and came into work to work on the SB-230. Today I was going to make my first PC Board in probably 30 years! And, yes, I would do it the OLD FASHIONED Way!
First the SB-230 was openned up and the Electrolytic caps pulled. Unlike the SB-200, these are mounted individually using bolts and nuts; and no PCB is used. I would be changing that as there was no practical way of mounting the new caps and bleeder resistors any other way.
Carefull measurements were taken on where the bolts all went for the 6 caps. A template was made to use the exisiting bolt holes (12 of them!!!)
I went in the back and cut out a precise piece of doublesided PCB and sanded it down to a bright copper finish. Now, the hole pattern was drilled and the board checked for proper alignment. Always hafta file a few holes!
The new caps were laid out along with the resistors on the PC Board and holes drilled. Now, I used both a Sharpie Magic Marker and NAIL POLISH to cover where I wanted pads and traces. I will be etching it in Circa 1980 FERRIC CHLORIDE!!! I bet the EPA has banned this stuff and U can't even buy it anymore. Anymore, people use photoresist and make FANCY PCBs. But I am using 1970-1980 Technology, to match the age of the amp!
It would take a half hour to etch the PCB, and, yes, I DID get it all over my hands and shirt! Messy yellow stuff!
But after the etching and cleanup, it looked BEAUTIFUL!!!
It was time to mount the parts. Note the topside traces too.
I mounted it in the Chassis and started to wire it up
But as I started to wire it, something was not right. OH SH******!!!!!!!!!! I put the topside traces on the wrong pins!!!!!!!!!!!!!!!! REWORK TIME!!!!
I removed the board and 2 of the caps. The clads between the 2 were peeled off the board. I will go back to using JUMPERS the way Heathkit did it. Also, the board was 180 degrees outta phase. So I had to reverse the board in the chassis and do more hole filing. Well, you expect these kind of things!
Time to wire up the bottom.
This time, the wiring was CORRECT, and I added the 22 ohm 10W GLITCH resistor and 630mA fuse.
This fuse may blow, so I might hafta delete it. Atleast the Glitch resistor is there.
So now on to the Rectifier board, which was broken up in the chassis due to GORRILLAS tossing it around. I will make ANOTHER PC Board for it as well. The Sharpie worked out fairly well, but the Ferric Chloride might be getting weak. Will take alot longer to etch it this time. STAY TUNED for the next adventure in SB-230 Restoration! I hope this Capacitor board was an UPGRADE!
Ferric Chloride is awful to use because, as it gets used up, it becomes opaque -- you can't tell when your board is etched. It's still available but gawd knows why anyone would WANT to use it.
I've used amonium persulfate in a homebrew heated & aerated vertical tank. I run the heater at around 95°F (35°C), and it speeds it up a bunch. As it gets used, the etchant turns transparent blue. Sodium persulfate works well, too, and is compatible with Sharpie etch resist. Both come in crystaline form and store well -- just mix with water. MG Chemicals makes both. It's been ages since I used the photoresist method (coated my own boards, etc), back in the 1980s. With ANY etchant, you need to take precautions. I would wear (at least) suitable gloves and eye protection.
It will be cool to see it work....
I think I would think twice about modifying this amplifier for six...
Once would do it for me, too.
My concern is the availability of the tubes.
Allthough with a socket change Pat could use 8560s which are more available.
The problem being the 8560s are tetrodes and would put him back to using a 4CX-250 family tube.
I do like the idea of building a good power supply and several single band amplifiers for the VHF bands he likes to work. Put them all in a rick together and he is good to go.