GPT-750 power supply

[stevef]

So I have the HV transformer from a GPT-750 (bought from Barrie a couple years ago by the way).  I was hoping to build a big power supply around it and learned from some of ye on this forum that it requires a choke input.  I was wondering how much the current rating should be on the choke?  Should it be equal to the transformer current rating (750 mA) or should it be somewhat higher?   Big chokes seem to be as rare as big mod trannys.

The intended use of the power supply would be as a backup for my linear amp, and a future supply for a AM big rig.

Tnx,
Steve KK7UV

[N2DTS]

The choke needs to be good for the current you are going to use.
I have 500ma chokes but the rest of the supply is good for much more.

Brett

[ke7trp]

Pick up the ARRL handbook from the 50s or 60s.  Every answer to any question you have is in that book on power supplys.

You can use MUCh smaller chokes if you put them in the negative line instead. This was popular at one time. There is a chapter in the handbook on this subject. I have a 5000 volt 1 amp supply here that has the chokes in the neg lead. Its protected and works fantastic.  Very low ripple and clean output. It was built in 1962 this way.

I purchase transformers and chokes from Robert W0vmc.com.  He seems to have a large stock of big power supply parts. Give him a call or send him an email. I just got a fantastic plate trans out of a gates BC rig for a great price from him. He probably has the chokes you need laying around.

Clark

[The Slab Bacon]

Be careful with negative lead filtering, I learned the hard way. Putting the choke in the negative lead raises the secondary center tap to the full ripple voltage above ground.

Many older transfomas weren't rated for this and cant take it without breaking down.
If the transfoma is rated for FWB rectification you'll be ok. If not, you'll learn the hard way like I did.

Put the choke in the positive lead, and if you're afraid of the choke having a voltage breakdown, set it up on insulators for good luck.

Also chokes with a higher than required current rating will usually have a lower DC resistance, thus giving better regulation under load.

                                                     The Slab Bacon

[WD8BIL]

Putting the choke in the negative lead raises the secondary center tap to the full ripple voltage above ground.

What if the winding doesn't have a center tap? (HI Frank)

[W2VW]

Most xfmrs over a couple kvolts rated for FWB do not have a centertap in the first place.