UPDATE: PT help needed

[Geezer]

I have a PT (drawing attached) that I need to find the "start" of the winding........how do I this?
Is it possible to do (I think I used to know how(?))

Could I measue resistance between the 45v tap & each 660v (or 720v) tap & the one with the smallest resistance is the "start"?

TIA, G

[sluckey]

Could I measue resistance between the 45v tap & each 660v (or 720v) tap & the one with the smallest resistance is the "start"?

That should work. If the difference in resistance is too small to be obvious, try measuring voltage between the bias tap and the red leads. Smallest voltage would be your 'start'. And if that still won't get it, I can tell you how to find it with a scope.

[jjasilli]

Curious: Is this a polarity issue?  Why does it matter?  How do you plan to use all those volts?

[Geezer]

Curious: Is this a polarity issue?  Why does it matter?  How do you plan to use all those volts?

Glad you asked....

See this PT>>  https://taweber.powweb.com/store/PTGPsch.jpg
It uses different combinations of taps to generate different voltages.

I have the (before posted) 360-330-45-0-330-360 PT right here, but the voltage is too much for the project I am working on.

My plan is to use the 330v & 45v taps (highlighted in red above) to achieve an effective output of 285v-0, then use a bridge to rectify.

Is this approach feasible?
How much current rating will I lose, if any? The PTGP unit claims 150mA at all voltages, using any tap combination.
Since I'm only using ~~1/2 of the winding (or less), will my current rating be "de-rated" in proportion?

I don't have an extra $75-100 bucks right now & would really like to use this PT if I can possibly do so.

G

[Geezer]

try measuring voltage between the bias tap and the red leads. Smallest voltage would be your 'start'.

That's what I need to do....measure the voltage between the 45v & each of the 330v taps until I find my ~~285v. The "wrong" combination will yield ~~375v.
I wasn't thinking clearly this A.M.

Thanks

[PRR]

You don't need the phasing. Measure from Blu/Red to either Red/Wht to find 285V (as you say). Or for safety, apply 6V AC to the 120V side, look for the 14V.

> will my current rating be "de-rated"

Yes.... but the CT connection is un-thifty. Moving to the full-wave Bridge uses half the winding about 1.5 times better. I'd load it with 150mA. Power a pair of bottles with 390V 150mA and you can load in 5K CT (4K-8K no great difference).

[Geezer]

You don't need the phasing. Measure from Blu/Red to either Red/Wht to find 285V (as you say). Or for safety, apply 6V AC to the 120V side, look for the 14V.

> will my current rating be "de-rated"

Yes.... but the CT connection is un-thifty. Moving to the full-wave Bridge uses half the winding about 1.5 times better. I'd load it with 150mA. Power a pair of bottles with 390V 150mA and you can load in 5K CT (4K-8K no great difference).

Excellent! 150mA is EXACTLY what I was hoping for! I'm running a quad of 16GK6's (EL84) & a 4k-ish load.

Thanks for the confirmation & all the help!

Geezer

[Geezer]

OK, an update:

Got the PT wired, running 4x 6005w's (6AQ5A's, small bottle 6V6-type) along with 3x 12A_7's, a 5654 & a 5879.
It works perfectly, voltages are exactly where I expected, AND the PT runs cooler than it ever did before when using the full winding (330-0-330).
When I ran 2x6L6's with this PT, it ran pretty hot. Now it isn't even warm after an hour or so.....pretty cool, indeed!

Anyway, I hope this gives more options for different voltage choices to those who may have similar PT's on the shelf.

Thanks again for everyone's help & input.

Geezer

[stingray_65]

Cool stuff Geezer!

I was envying Buttery and Iso's proto type board and was thinking how neat it would be to have a few multiple choice taps for a HV power supply.

Your PT would eliminate the need for a variac and give quite a few practical choices.

Ray

[DummyLoad]

I was envying Buttery and Iso's proto type board and was thinking...

what we do is use any old tranny that can supply the current connected to a variac and use on-board filament transformer. we check the fil. ckts. and warm them up prior to doing a new start-up with a lamp limiter - saves much grief and time. to make mods to ckt after initial smoke test, we turn off main power, swap components with fil power left on. saves a lot of time on warm-ups. once we are satisfied, we order or have wound a PT that we believe will give similar results - we get pretty close in most cases.

 

[jojokeo]

Geezer, did you use the taps I drew in the pic below rather than the earlier posted pic? Would this be the "more preferred" connections to make or does it matter?

[Tone Junkie]

Cool I have one of those and wanted to use it also, what are you working on my friend.Bill

[Geezer]

Geezer, did you use the taps I drew in the pic below rather than the earlier posted pic? Would this be the "more preferred" connections to make or does it matter?

Which side of the CT you are on makes a difference.......if both taps are on the same side of the CT, then the voltages are subtracted from each other (330v minus 45v = 285v).
Once you cross over to the other side of the winding, then the voltages are additive (330v plus 45v = 375v).

I used the "hybrid" bridge arrangement (see below) so I can sub different tube rectifiers for the "forward" diodes, thus being able to further control the B+ voltage.

BTW, used the amp on a 4hr gig last night & while getting fairly warm to the touch, it was by no means "hot" (ie: I could easily leave my hand on the unit indefinately without burning).

G

[jojokeo]

BTW, used the amp on a 4hr gig last night & while getting fairly warm to the touch, it was by no means "hot" (ie: I could easily leave my hand on the unit indefinately without burning).

That's again some creative "forward" thinking like your diodes Geezer! It's a wonder you get enough time to practice & play~

[Tone Junkie]

I was so tired when i looked at this the other night I thought you were talking about this transformer when you said trying to get to 285 volts. this is what I have and was going to try and use for 6aq5,s.

[jojokeo]

...this is what I have and was going to try and use for 6aq5,s.

Keep it in past tense - too much transformer for 6aq5s 

[Tone Junkie]

I have actually 8 6005w which i thought was basicly the same thing as 6aq5 I shouldnt visit auctions  . Bill

[jojokeo]

I believe they are the same Bill. But either way w/ only .45A & 250V max for each, that tranny would seem to be rather large, heavy, and better used for it's upper range capacity. I was thinking when I posted that you may have some large number of tubes-type of amp conceived which would make more sense if that was in fact the case?

[DummyLoad]

I have actually 8 6005w which i thought was basicly the same thing as 6aq5 I shouldnt visit auctions  . Bill

for a single pair 6005/6AQ5 - hammond 269GX w/ 6CA4/EZ80 recto.  ~~270-280V B+
hammond 1608 OT. 

should sound nice.

i've run them at 280V w/o any problems.

[jojokeo]

i've run them at 280V w/o any problems.

As have I but my point is starting out @ 280v w/out much load on that PT gives a pretty high end result voltage w/ a lot of wasteful amperage plus it's large size & weight. Why pay & transport a large suitcase around when a small backpack will do? 

[Tone Junkie]

The reason i pulled that transforer out was I get them fairly cheap and havnt treied them for anything yet I bought two couldnt beat the price. they say there made for a bridge rectifier though. at least thats what it says and they had a tap set up that was at 280 volts .
Bill

[Tone Junkie]

I bet this PT would be better for a pair of 6005w. the problem I have is I have two amplifiers in my amp stands right now. I have the board for the blues miester almost done this evening and im daydreaming about my next build after that. I think Im addicted (LOL).
Thanks Bill
                    

[PRR]

> they say there made for a bridge rectifier though. at least thats what it says

I'm sure it was MADE for a 2-diode rectifier, and the order got SCREWED-UP. That the taps got connected wrong.

I'd guess the mistake was not discovered until a ton of transformers were shipped across an ocean, re-working would cost more than making-new, so Weber decided to offer them as "oddball" stock at lower price. And since there is no "center" anywhere in that mess of leads, only a FWB will work correctly.

> run them at 280V

Then with an ideal FWB you'd want 200VAC, maybe 230VAC to cover filters and bias. There is a 210V section. But that is a third of the total winding, two-thirds is wasted. That's OK if the part is very cheap (it's priced low) AND if your roadies work very cheap (or you never go anywhere).