MIL spec PT - 300v-0-300v 0.350A - 290v-0-290v 1.15A - The best use ??

[kagliostro]

Today I got a MIL spec PT

it has

no filament winding

300v-0-300v 0.350A winding

and

290v-0-290v 1.15A winding

so I must use a separate filament transformer and I can get one adequate for any use I can do of the transformer

the question is

Which is the best use for this transformer ?

which final tube and haw many of it do you think I can use as to get the maximum from this transformer

I've some tubes that need a low screen voltage but both the winding of this transformer are near to give the same voltage (also if they has different current abilities)

So I need your councils

Thanks

Kagliostro

p.s.: If I remember well the rectified B+ will have the half of current that is in the AC, is this correct ?

[FYL]

Hmmm. This kind of tranny calls for big bottles with a vastly different screen and plate V.

You could use the 290V winding in a Delon full-wave bridge doubler or a Marshall-style bridge doubler (quite close to the Delon); the 300V winding could be used for screens. Silicon recto.

With app. 800V on the plates and 400V for the screens a quad of KT88's would deliver 250 watts or so thru a 2K OT such as the Hammond 1650W.

Big, bad and dangerous - every component should be suitably rated. For instance a bog standard octal tube base can be OK up to 500 V, it becomes a timebomb at 800 V.



 

[PRR]

Most of your power is in this winding:

290v-0-290v 1.15A winding

This can give 400V at maybe 0.6 Amps.

400V/0.6A= 677 ohms, the OT should be nominal 1353 ohms end to end.

Three pairs of EL34 or 5881/6L6CG or 6550/KT88 will be over 100 Watts output, nearly 150W.

I would even consider exceeding 0.7A with a 1,100CT load.

Yes, you could run 800VDC and 5K load but that's very reckless and an unusual OT spec.

[imaradiostar]

If it's a mil TF make sure it's not designed for 400hz use...that could make for a sad day if you build an amp around it and the PT burns up on first use!

Come to think of it you probably won't be able to use it. I'll be happy to get rid of it for you!! 

Personally...I'd use it with a bridge rectifier and some surplus 450 volt snap-in caps connected FWCT across the whole 290 winding, end to end. The caps would stack and connect at the center tap, automatically balancing the voltage between them. This would give you around 800 volts for the plates and 400 for the screens, perfect for any of a number of large tubes. That should be enough current to supply a 200-300 watt tube amp with 4 KT88's. They'll probably work nicely into a 2-3k load with voltages like that. If you didn't like the sound of that you could try EL34's or KT77's or 6CA7's...but 6 or 8 instead of just four.

Maybe you could try the new KT120 power tube from Tung-Sol? http://www.tubedepot.com/ts-kt120.html With those you should be able to make over 150 watts a pair!

Hammond has in-stock (supposedly) output transformers that are compatible with this sort of thing. They're rated for 280 watts with hi-fi bandwidth. In guitar or bass use you're unlikely to need a larger output transformer, even with your monster power transformer running a mono amp. Even a much less expensive Edcor that's designed for 100 watts of hi-fi audio should weigh in around 12-14 pounds and be good for 200 or so watts of guitar or bass noise!

You can always use multiple smaller output transformers and mix and match signals as needed to get them to do what you want them to.

You'd still have the 300 volt windings to run a preamp or an entire separate 50 watt marshall into a hotplate as an "Effect pedal" for your giant tube amp!

jamie

[kagliostro]

MANY THANKS     TO ALL

for the given help and councils

the transformer is a 50/60Hz 115v-115v primary

some time ago I got a nice unusable Variac, it was rated for 400Hz, so it was of no use

at that time the 400Hz appeared after cleaning the Variac, so now I look well before

(with this transformer there were also some nice little transformers and a unit having inside a nice variac, but all that was rated 400Hz so of no use here)

here a photo of the transformer

Very nice tube the KT120

sometime ago into the web I've also seen KT100, but never able to see a real one

About tubes I've some EL509 and EL519 (sometime ago we discussed about the use of this tubes here in the forum)

I also have think to the new version of the EL509 from JJ  but the KT120 is a surprise

If someone can give me news about the original use of this transformer it will be very nice

I like to discover the use of some nice stuff I find at radio amateur flea markets

many thanks again

Kagliostro

[FYL]

If someone can give me news about the original use of this transformer it will be very nice

I'd say it's a PT for big bad shack transmitters or linear amplifiers.

The pic isn't very clear but I guess that you can read "TO NO. F-1831 COLLINS NO. 672 0393-00". Collins Radio, now part of the Rockwell group, was a large US manufacturer of ham and RF equipment.

[sluckey]

Have you checked the secondary volages? The info I see in the pic indicates a 300VCT which would be 150-0-150, not 300-0-300. Same for the 290VCT winding.

[FYL]

Have you checked the secondary volages? The info I see in the pic indicates a 300VCT which would be 150-0-150, not 300-0-300. Same for the 290VCT winding.

Yup. Or how to stop at details and forget the essential...

[PRR]

290V CT is 145V each side, say 205V DC. I would suspect the "1.15A" is the _DC_ spec; or at least you could pull 1A for several hours a night (Collins stuff often ran 24/7 in hot racks).

The HiPot says you could probably ignore the CT and FWB for 410V 0.5A.

This is four 6L6GC, EL34, etc: the classic "80W-100W" Fenders and Marshalls. Or a bit more. With the 0.35A winding idle it might feed six bottles for 120+W output.

[kagliostro]

Thanks

As you can read

the voltage in the secondary windings are write between the extremes of the windings and (I think you can't read it in the photo) the CT was labeled as GN (for Ground I suppose)

so the first thing I've done when at home was to measure the output voltage

I put in series the 115v primary windings to obtain a 230v primary

I put on my 222v wall voltage and measured the output and they were very close to 290v-0-290v and 300v-0-300v

after we established the real output voltages

if someone knows more about the original Collins apparatus - Welcome

Many thanks again

Kagliostro

 

[FYL]

if someone knows more about the original Collins apparatus - Welcome

There are many wab sites dealing with Collins, check for instance http://www.collinsmuseum.com/collins.html

[andrew_k]

so you're the person who outbid me on that PT...   

[kagliostro]

If you were in Marzaglia (Italy) at the radio amateur flea market in 08/05/2010

YES

 

Kagliostro

[andrew_k]

haha, no!
Wow, exact same unit went on eBay in Melbourne, Australia a week ago. Small world.

[dynaman1]

I've a nice potted milspec filament transformer that will match yours nicely.....

[kagliostro]

I've a nice potted milspec filament transformer that will match yours nicely.....

That is interesting

but I think we are very far each other

(and also need a 230v primary or 115v + 115v primary)

so I hope to find one at the next radio amateur flea market in 05/06/2010 in Mantova (Italy)

anyway THANKS

Kagliostro

[dwp]

someone explain where the 800V's was coming from please? (for the lame of us)

[kagliostro]

300v-0-300v connected without use the CT and rectified (600 x 1.4)

Kagliostro

[dwp]

thanks for the answer. I did not know that.......

so does that mean I can raise my B+ by putting a resistor between the center tap and ground?