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 on: Today at 12:14:14 AM 
Started by k7mdo - Last post by K1JJ
Assuming you go with a full wave bridge:

You could add a Variac to have full adjustment of the HV. This is always good for testing and experimenting with parameters. ALL of my power supplies from big to small use Variacs.

Another method would be to use a choke input config and short out the choke with a relay that can handle the voltage across it - when desired to up the HV, making it a cap input filter.  Put as much filter C on the PS output as you can.

You could also adjust the HV by putting the two 115V primary windings in series or parallel for a X 0.5 or  X 1 AC xfmr output. (Assuming it's fed with 115VAC source)

A Variac would do it all, but a combination of the latter two would work and give some more flexibility.

The choke input config would give better regulation than C input - which is what is needed with that class B amplifier current requirements due to peak power X5 or X6 AM audio cyclic drawdown.


 on: Yesterday at 11:47:15 PM 
Started by k7mdo - Last post by k7mdo
Thanks Tom for the thoughts... I only settled on that circuit because I had all the parts in the stockpile. 

I will re-think the circuit in light of your concerns... I had thought the final voltage would be closer to 800 vdc but in reality I would not mind getting rid of the rectifier tubes....

I think I can avoid the high in rush to the transformer easily enough... etc.


 on: Yesterday at 11:21:09 PM 
Started by ka1tdq - Last post by ka1tdq
This is all extra stuff that I had laying around, so I made a go-kit.  Granted, it is a lot of stuff and weight for 3 watts CW.  I also bought an MFJ 20 meter 8' whip for the car.

The kit consists of:

 - Homebrew CW transmitter
 - Laptop for the SDRplay receiver
 - Power inverter to power the laptop charger
 - Vibroplex straight key
 - Antenna switch (household light switch)
 - Headphones

There's a mountain a few miles from my house that has a paved road to the top.  I'm going to give it a whirl sometime.


 on: Yesterday at 11:20:18 PM 
Started by k7mdo - Last post by K1JJ
Hi Tom,

The center tapped 800 V transformer as configured will put out only 400 VAC, or maybe 600VDC under load. The tube rectifiers will drop the voltage even more. The choke will also drop some voltage.

I would use a full wave bridge and get over 1000VDC. The 4D32s need that much to give the peak overhead you desire with that big audio capability the PW rig has.   Otherwise you will be dialing the carrier way back to compensate.

Use solid state diodes for less heat and much better rectifier efficiency. The heat waste comes from somewhere and it's from the voltage drop across the rectifier tubes.  

Also, I would add some more capacitance. 4 uF is barely enough to give you the regulation you desire for a clean class B linear amplifer, especially for a cap input circuit. Good idea using the choke.  Be sure the transformer can handle a fullwave bridge config. Some are not designed to carry the extra voltage when the C.T. is not grounded.

Might as well put the primary 115VAC windings in parallel, assuming they are identical, for less IR drop - can't hurt.


 on: Yesterday at 09:38:02 PM 
Started by KB2WIG - Last post by KB2WIG


 on: Yesterday at 08:01:47 PM 
Started by KB2WIG - Last post by Opcom
Need to come up with a stage name.  might be tough competing with the Bieber if you lead off with the Trololo song. A tattoo or 2 and some body piercings might help. But then again, with the right agent ya never know.


Start a goth band. Goth isn't dead (well technically it is morbid and somber but alive..) Age doesn't matter as much as people think, if over 50 you're just an Elder Goth.. Might get some respect and definitely got 'cred' age wise from being in it in the late 70's -80s when it evolved from punk and old dark hippies, death metal, and contains 2% of lesser ingredients... Don't even have to be good looking, goths tend to let themselves go anyway.. Just make sure you got stunning goth girls/ladies to front at your shows.


 on: Yesterday at 07:54:07 PM 
Started by k7mdo - Last post by k7mdo
Well, I sorted through what I have in the "heavy metal" warehouse.  I have all of the parts shown in the attached schematic.

I think it will be enough for the single 4D32 amplifier discussed in the "PW" thread.

I drew up the schematic and am looking for critics of my handiwork? 

I have a good steel chassis that will hold the transformer... think I will make the power supply completely independent of the amplifier so that if things don't go as planned I can just reuse the supply for some other project.

I also have two choices it seems as I have several 4D22's as well as a couple of 4D32's and filament transformers for either.... not yet sure which one to choose but that will come after the supply is complete.

73, Tom

 on: Yesterday at 07:44:47 PM 
Started by KE5YTV - Last post by Opcom
Mike, I am very sorry to hear about Petey's passing away. I've always kept cats that have come to me by one means or another, and when one of them passes away it always takes my love with it, and leaves its love in my heart. Cats and indeed other animals live their lives as God intended and when we can share a deep friendship with them it is all we can ask. I am not an emotional man but I mourned one cat 3 months. You are not alone in grief for a wonderful old friend. One cat leads to another and when it is time you will know, or a cat may just present itself to you unexpected. That is a gift of the best kind.

 on: Yesterday at 02:23:59 PM 
Started by KD6VXI - Last post by WBear2GCR
I got one on epay... the TNC to BNC adapters cost more than the unit!

More up there now, if anyone is interested... search on the "Zxxxx...." designator on the unit (pic below)

The chinese are selling Low Noise RF amps under $10 on epay, and of course they're not going to be as
good as the Mini Circuits, but I kinda doubt they need to be... Cheesy Going to start with one of them, and
see how I like it. Can always upgrade... will need an enclosure, but, them I've got.

 on: Yesterday at 02:20:03 PM 
Started by KE5YTV - Last post by W3GMS
So sorry for your loss Mike.  As you mentioned, it will take time to adjust to your loss.  Not at all easy and as time passes, all one gets good at, is dealing with the deep loss.


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