[Phil_S]

Well, this certainly gives one an appreciation for the sublime. It's a good
thing wire is cheap ;-}

I chose 22AWG for the secondary and barely fit 152 +/- turns, with taps at
76 and 104. I was thinking this would result in 8K to 4-8-16. That was the
plan.

I hand wound the secondary. I found that it is very difficult to keep track
of turns. I did, however, accurately figure that I could get 38 turns in a
layer. In practice, due to my lack of manual skill, I ended up with about
35 turns per layer and wound 4 layers. At first, I thought I had badly lost
track. I did loose it somewhere, but it wasn't all that bad. It is also
hard to do this neatly.

I saved the fish paper for the primary and put it back. Actually, it was
probably from the secondary, but I used it to cover the primary. I used
green high temp polyester (?) tape (stuff meant for this sort of thing) to
wrap outer layer of the secondary. It all barely fit on the tongue of the E
lams. I chose to leave the existing gap, which mic'd at about 0.6mm.

I think the most significant error was my estimate of primary turns. I
believe now that primary turns are approximately 3800 and the primary wire
gauge is 39AWG. I bought a surprisingly nice digital caliper on eBay for $8
and its measure says the wire is #39. The number of turns makes sense with
the DCR of the winding.

Assuming that I did wind 150 or so secondary turns -- I think I did -- these
are the test results from the 3 taps:

10225:16 ohms, turns ratio = ~25
9544:8 ohms, turns ratio = ~35
10000:4 ohms (exactly, oddly enough), turns ratio = 50

The 16z and 4z taps both suggest primary turns are around 3800; the 8z tap
must be in the "wrong" place, as it suggests primary turns are around 3500
and the primary z is "low".

I have no idea if I will ever use this OT. It will go on the bone pile for
some future project, or not.

It was educational. I had some fun. I learned more than I bargained for.

Many thanks to Patrick and Flipper for informing me along the way.

Regards,
Phil

[Big Bad Bob]

On 11/08/10 22:59, flipper so witilly quipped:

A note on the 40VA. They're not current limited but internally FUSED.
I had to crack one open and 'repair' it due to a fumble fingered
boo-boo.

I have nothing but unkind things to say about the person that came up
with 'fused' transformers. I could go on but it may be OT.

[mick]

On Tue, 09 Nov 2010 15:03:33 -0500, Phil_S wrote:

snip

I've got a PT that's 280-0-280 @ 40mA and 12.6vct @ 1.5A. You think
this is useful? I'm not quite sure how to deal with the 12.6v filament
supply. Two 6.3v tubes in series and one 12v tube in parallel to that?
Can I do that? I had bought this originally for the concept of an all
12V tube amp, probably 12AX7 + 12AU7, but didn't get to it just yet.

I've also got one that's 114-114 (no CT) and It seems to have held up to
testing at 85mA. The 6.3v winding capacity is unknown, but I imagine it
can handle 1.05A, which is what's needed for a 6AQ5 + two 12AX7's.

Anyhow, getting a PT is not a challenge. Low mA/ low VA types pop up on
eBay cheap every day -- and easier than trying all that back to back
stuff.



Just to but in with something that may be of interest regarding heaters
following the Mullard/Philips designations:

Type numbers Exxxx with 6.3v heaters have variable current (but you knew
that!). They are intended for parallel connection.

Type numbers Uxxxx all draw 100mA and have variable voltage and are
intended for serial connection. Many of them also have quite high h-k
breakdown voltage just because of this.

Type numbers Pxxxx all draw 300mA - once again for serial connection.

More he http://en.wikipedia.org/wiki/Mullard...be_designation

back to lurking

--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.