What to build with this PT?

[dartanion]

Hey Folks,

I picked up an old military grade PT that is one of those gray bricks.

195 - 0 - 195 330mA
6.3V 4A
6.3/5V 1.2A

It's a Kenyon from Jersey City.

What should I build with this baby?

[VacuumVoodoo]

You have 5.2k Raa OT laying around?

You can build a true class A PP with 2x6L6GC ,get about 16W. There's a certain beauty to be heard with an over sized PT in class A amp.

Check p2 on the datasheet for operating conditions
Use SS rectification. Enough juice on heater windings to feed a bunch of double triodes - a channel switcher?

[David Root]

Good choice. You could also tape off the CT and use a 4-diode full bridge rectifier to get about 500VDC and a still respectable DC mA rating for just about any two large bottle amp.

I've used the IXYS 1200V 32A bridge rectifier module on a 400-0 PT with success. Soft recovery hexfred technology. It will sound MUCH better than four 25 cent 1N400X ever could (but it will cost you more).

Military PTs are generally rated for continuous 24-7 duty so you can probably abuse it a bit currentwise in intermittent duty.

[tubetek]

Howdy Dart-
First post since my shoulder surgery...(of course, it was worse than we anticipated; required conventional surgery to fix it)
I'd think about doing a doubler PS a la 100 watt Marshall and 2x6550/KT88
in a clean BASS amp. 560V on the plates'll get you near 100 watts from a pair (with the right OT)
tubetek

EDIT> if it is a Mil PT it will most likely be rated for CCS (continuous commercial service) For our purposes ICAS (intermittent commercial / amateur service) the CCS rating can be overloaded substantially (40-50%!)

[skyboltone]

Good choice. You could also tape off the CT and use a 4-diode full bridge rectifier to get about 500VDC and a still respectable DC mA rating for just about any two large bottle amp.

I've used the IXYS 1200V 32A bridge rectifier module on a 400-0 PT with success. Soft recovery hexfred technology. It will sound MUCH better than four 25 cent 1N400X ever could (but it will cost you more).Military PTs are generally rated for continuous 24-7 duty so you can probably abuse it a bit currentwise in intermittent duty.

Heck. I just bought a hunnert 1N4007 Fairchilds for .04 a peace. Or was it .03? What's hexfred?

[David Root]

So you're only out $4!

Hexfred diodes are relatively new (maybe 10 years?) technology. No idea how they work. They are extremely fast but don't produce such large spikes in the rectified DC voltage as the 1N4XXX types. They don't have the grainy kind of tone you get with the older type, sound smoother. Try replacing the old diodes in any BF Fender, you'll hear the difference.

In the individual (or dual) hexfred diodes available now ($2-$5), the Fairchild "Stealth" soft-recovery hexfreds are very good. I use them for bias supply diodes and full wave half bridge (the double diode is real handy here) supplies. The soft recovery characteristic is much more inportant then the speed for audio bandwidths, and the Stealths are at the head of the pack in that respect. They come in TO-220 packages which have to be insulated from the chassis with mica and some thermal grease, or put in their own little heat sinks.

The latest development is taking four of these diodes and putting them in a single module about 1" x 1 1/2" by 3/8" thick to make a full wave bridge rectifier. The back is machined aluminum and they are designed to bolt to the chassis as a heatsink. In these the back is NOT the cathode, unlike the Fairchilds, and is electrically insulated, like a conventional silicon bridge rectifier.

The IXYS is one of these, is relatively new, less than a year I think, made in Germany, costs about $22 in the 1200V 32A size, and is very easy to fit. I put mine on the power end chassis apron with externally flush mounted bolts. No, you don't need 32A but these things are not designed for audio, they're designed for very high speed industrial power applications. Yes you do need 1200VDC if your B+ is above about 400 or so, they do still spike a bit but nowhere like the old ones.

[dartanion]

Here's some photos:

[img:482:363]http://www.nmia.com/~elecsurp/GC4.JPG[/img]

[img:552:450]http://www.nmia.com/~elecsurp/GC5.JPG[/img]

[img:526:505]http://www.nmia.com/~elecsurp/GC3.JPG[/img]

It's about 4 x 4.5 x 6 and weighs a ton.

So I can get 500VDC with what is described huh?

Color me shocked. I was thinking of making a HiFi amp with it. Or a class A PP of some sort. I have some 7591As that I was thinking of Wrecking

[skyboltone]

Plug it in and measure between three and five. Make sure you do have 390. You may have 195. I got on something like that only smaller laying around someplace. I think I was going to do a choke input filter with it. You get .9 that way. With a cap input it's 1.35-1.4 times.
My greatest find, which I haven't made up yet is a custom wound transformer rated at 750ma with one dozen (count them) taps between 150 and 550 with a 0 in the middle. I have always intended to make a big test DC supply with it. It came out of the Hammerlund R&D lab when they closed. It must weigh 25 pounds.
I also found a single ended RCA transformer that's (IIRC) 2700/3.2 ohms. It's big too, like maybe 30 watt size. I wonder what thats for?

[bluefireamps]

If it really is 195VCT, that means it is 97.5 - 0 - 97.5. That means the whole winding is 195 volts center tapped. Measure to know for sure.
Dave

[David Root]

That's right. Notice terminals 3 to 5 connection rated for 270V. That would be with CT not used and 3 & 5 feeding a full bridge rectifier 97.5 x 2 x 1.414 = 270.

So no 500V without a voltage doubler off the bridge rectifier, which will cut your DC mA to about 80 or so, I think.

[klingo]

hello!

with 250V/270V supply and a 8/10K OT you're in the 6AQ5/6005, pushpull, AB1, 10watter territory!

6AQ5 are still cheap and the little chassis standing in his jig close to me sounds good(...more infos will come when able to record).

If you need more than 10W, your PT will stand a double/triple push/pull for 20/30W with a suitable OT and more 7 pins miniature sockets & bottles

If you hesitate...send it to me...I love heavy iron

[dartanion]

So I've got an estimated 270V post full bridge rectification right? Why would I only have 80 mA current left in this arrangement?

[rhinson]

So I've got an estimated 270V post full bridge rectification right? Why would I only have 80 mA current left in this arrangement?

you wouldn't. if you used a voltage doubler circuit on the winding your current rating is cut in half-----so you have 115ma and around 546v n.l. (so probably around 500v-520v under load depending)
don't know exactly what you could do with it in that fashion in terms of guitar amps---the tubes that could take the high voltage require a larger current rating on the hv. sec.

you could just do a normal bridge and get your 270v nl (probably about 230 -240v under load depending) and use 4 smaller power tubes (6v6, 6aq5, etc.) and a few preamp tubes---you have a couple of heater windings there so no problem with that. it would be a little low voltage vintage distorto type amp. rh

[skyboltone]

So I've got an estimated 270V post full bridge rectification right? Why would I only have 80 mA current left in this arrangement?

I don't know where those numbers are coming from. 270 VDC at 330 MA is the way I see it. bridge or full wave with a cap input filter. There are lots of possibilities. Like the man said 6AQ5 is a 7 pin 6V6. Use four of them for a nice 20 watt rig. 5.2k OT primary with four of them.

[David Root]

I think my mental arithmetic was a bit off.

270v @.330A is 90VA right? So however you play with voltage doublers, bridge rectifiers etc., you still end up with roughly 90VA rated load and the current will vary according to the setup.

However, since this is a 24-7 continuous duty rating (military duty) you can probably draw quite a bit more than 90VA in intermittent duty, not sure how much, maybe 120 VA or so?