The AM Forum

I got these 560uF/450vdc electrolytics and I'm not sure about the positive lead(s).  The negative side is clearly marked and is off by itself.  I thought that the 3 other prongs were the positive lead in-common, but they don't have continuity between them.  Do I parallel the 3 on each capacitor anyway?  

This is for my 20 meter single 3-500 linear amplifier.  It's light duty so all the components are small.  I'm actually using a voltage doubler and using a Viking Valiant plate transformer as the B+ supply.

Jon

put it in series with a speaker. The terminals that pass audio are the cap terminals.

     I remember those caps, the Plus is opposite the Negative strip mark.   The other two are for mounting strength.  You can
float or tie them to the negative lead (per cap).   They are little monster caps, not sure what the series resistance is on them but should power a 3-500z well!   post pics of your project pse!

That all makes sense.  Thanks!

Yeah, I'll post pictures as it comes together.  I have all the parts, so it's just a matter of building it. 

When I was in Vegas, I picked up a Drake 2-A receiver with matching speaker pretty cheap off of Craigslist.  I re-sold it and bought another 3-500 to replace the one that I dropped.  I opened this one very carefully.

I had to walk down the strip quite a ways to get the receiver back to my hotel room.  I was really concerned about raising awareness of myself carrying this big electronic "thing".  My worst fear was getting tazed or something.  "Don't taze me bro!  Hear me out... it's a radio."

Jon

In the 80's I hand carried a solid state 2 channel 60MHz +delayed oscilloscope on a plane. A bit of an arm stretcher but a bench scope about the size of a Tek 2210. My uncle up North had given it to me to take home to TX. The security people at first were suspicious but when I plugged it in to show them what it was for they were more like fascinated and respectful. Hah that 'respectful' portion is all gone now. Move along cattle! Mooo!

These are caps with a common neg lead and three positive leads.

Each positive lead may have a different Max voltage rating so be careful. Hopefully, all positive posts have the same voltage rating.

Copy the cap numbers and go online to determine the cap specification.

Below is a pdf file showing what I think you have.


Phil - AC0OB

I've attached a photo of the capacitors that I got from eBay that shows the information on the side. 

I wired the rectifier board and I've attached a photo of that as well.  I just used the center positive contact.  I couldn't fine any good data sheet on the caps by Googling it.  I'm still open to suggestion if I should parallel the 3 or leave it as-is.

Jon

I do not know if these are similar to what you have or not, but United Chemi-Con makes capacitors that look the same.  The data sheet for them shows the option of the four pin contacts, and it specifically says that the extra two are for mounting only and should not be connected to either the positive or negative terminal.  You may want to be cautious in any event.

http://chemi-con.com/upload/files/3/3/48990562506224c250b19.pdf

Good luck with the project!

Dean

That seems to be the consensus.  I'll leave it as-is. 

I mounted everything to the HV shelf.  Just a little more wiring and then I can move onto the RF deck.

Jon

The bottom rack space will be the HV power supply and a blank front.  The control/meter panel will be the next up rack space (it's shown in the picture).  The rack space above that will be the RF deck.

Mounted inside the cabinet will be a bathroom fan blower with the output PVC piped directly to the bottom of the tube socket. 

This amplifier design is totally enclosed, so there's very little danger for my kids.  However, the switches are absolutely within their reach.  They could wreak havoc with the tube by turning on high voltage without the filaments being on (they don't care about switch sequencing).  I've put the fuse holder on the front panel so that I can remove the fuse when not in use. 

Jon

Removing the fuse holder may not be a good idea.  The kids may put something metal or even their fingers in the empty holder.  A key lock switch may be better if you can find one.  Auto parts stores have switches that use keys.

Fred

Good point.  I do have my radio room locked and the power strip that the amp is plugged into has an on/off switch.  I'll keep it under control.

Apparently that was the right pin for the capacitors.  I turned it on and got 4300 volts unloaded.  And, it actually did store power because it decayed slowly.  

I'm guessing a Valiant plate transformer will have enough current for this project.  I'm using a voltage doubler so the current will be halved.  My goal is about 500 watts CW, so we'll see.

Jon

Good on you for locking the room for childrens' safety.

If you are not into actual key switches but will use a low voltage coil relay on the mains input, there are a lot of simple or no-cost things you can do such as:
 
- a 1/4" audio jack with a shorted plug, or use a reed switch behind the aluminum panel and you place a magnet in a little plastic tray in front of the spot or slip part way into a hole, etc. and keep the 'key' on a short lanyard conveniently high up on a hook on the wall.

- a small push button in a corner of a panel that has to be pushed to enable a latching relay that receives coil power only when you flip the filament switch. It'll come on only if the push button is pressed while you flip the switch.

I suggest you try and wire it so the fil must be turned on and the soft start must be un-bypassed before the plate can be turned on. Any little mistake could be otherwise costly with the tube. Using DC control voltage and some diodes and a relay can get you quite a bit of reliable logic!



Very nice cabinet and power supply BTW. Is that white panel a modified cutting board?

Actually, my current setup has some value.  If I start to forget to operate the switches in the correct sequence, it'll tell me that it's time to hang it all up, start watching re-runs of Matlock and wait out the duration.  Actually, your magnet idea could serve the same purpose.  If I forget what the magnet does, well, I couldn't even turn it on in the first place. 

However, if things start to get that bad, my open frame class E rig would've given me multiple RF burns on my hands. 

You know, mental note:  In another 30 years, I'm going to do ham radio (safe) pissed-off old buzzard style.  I'll get a wiz-bang SSB commercial transceiver and a 75 meter dipole. 

Anyway, the teflon is from a cutting board that I got from Fry's.  It's pretty big and thick for $10.  It's nice... I can buy my transistors and kitchen supplies in one-stop-shopping.

Jon
Jon

Getting close to completion on the RF deck.

Jon

Almost done except for piping the cooling air and waiting for the plexiglass viewing window to arrive.  

There turned out to not be much room for the blower, so it had to go where it sits.  Consequently, there's no direct path for cooling air to the tube, and there'll be a few 90 degree bends in the path.  There still should be plenty of air though for CW service.  

Also, not shown in the picture is an angled air deflector (or, a kitchen cooking pan bolted to the front and angled about 30 degrees) above the RF deck.  It blows all the hot air out the back, sort of like Taco Bell.  Otherwise, all the hot air would heat up other equipment higher in the rack.

Jon

Done!  I just need a 10' RG-8 jumper and I can test it.  That'll be in shortly.

Jon

...and I couldn't wait to do an initial test without RF drive.

Idling figures are:


Eplate = 3600 vdc

Iplate = 114 mA
(actually, that figure is total cathode current.  I didn't separate grid from plate current)

I expected more of a voltage drop to around 3000 vdc.  Apparently that Valiant plate transformer is more robust than I thought.  I didn't put much bias in the cathode (I think 6 or 7 diodes) so that's about 4.5 volts.  It could stand to be higher to limit idling current.  

I've got the DX-60 set to 10 watts output when I do a power output test.  

Jon

Why wait???  Get some zip cord and test away.


Its the right thing to do.

KLC

Actually, I just ordered more of the same diodes from DigiKey that I used in the cathode.  I'm going to bias it around >15 volts.  It'll take a lot of diodes to do that though, so I'm back to adding another Teflon cutting board near the RF deck.  This time, I shopped at Ikea for my cutting board. 

Zip cord is ok, but RG-174 is funner.  Hit transmit and run!

Jon

Well, there you go.  I put an additional 20 diodes in the bias string to give me about 18 volts, and the resting current is very minimal.  Once I go to TX and bypass the 5K bias resistor, the plate meter moves just a tiny bit. 

I just put it on the air at the 500 watt level and talked to a guy in Arkansas.  I had a few good long transmissions (in CW) and you have to look very closely to even notice a change in color on the plate.  I'm probably not driving it hard enough. 

But, I did look in the backyard and nothing is on fire.  The cat is sleeping in the chair next to me, so nothing went "BANG" or anything like that.  Sounds like success to me!

Jon

Pretty cool!
Is that an audio amp in the middle as a modulator? How is it with the heat of the tube under it?

It is a solid state audio amp. I have a heat shield beneath it angled upward toward the back of the rack. Most of the hot air is deflected out the back of the rack.

I'm debating taking out that audio amp and class E transmitter and replacing them with my ARC-5 and power supply (which I need to build). That would make the rack my "tube" zone.

Jon