diytube ST-35 rev D Build

[TomMcNally]

I built this last night. I wanted to try the Edcor output transformers,
the CXPP25-MS-8K/23%, which are 8K, 23% Screen Tap, 4, 8 and 16 ohm
secondary. They are really hefty, in fact, they are the same size as the
XPWR005-120 Power Transformer. Ask me how tight I had one bolted
into the power transformer spot before I realized it. The PT has the
same specs as the Dynaco, but it barely gets warm. If you are using
one in an ST-35 where you parallel both 6.3 volt windings, you'll need
to test for proper phase before finalizing the connection, I just used
two sets of crimp lugs, and left one side of one winding hanging, and
tapped it on, no sparks, so I got it right the first time. The output
transformer phasing may need to be experimented with too, mine
oscillated the first time, so I flipped all 8 leads and it was perfect.
Using the barrier strips on the ST-35 board with spade lugs makes it
an easy fix. See my pix for color coding if you use some. I used
Auricaps because I had them, red leads go to the outside.

Bottom line, Edcor is worth a checking out, OPT's are $ 56.52 each,
and the PT is $ 43.21 ...

Tips ... Don't EVER use a Chinese clone UniBit. Don't mark a black
chassis with a blue flair and expect to see it. Don't tighten the trim
ring on your misplaced power switch with tiny pliers. Black Honda
touchup paint kind of works. Permatex black silicone covers sins.

Bottom line ... as usual, this ST-35 kicks ass.

More pics, taken from flattering angles at http://tmamps.com

[Geek]

Gorgeous, Tom!!!

We should have an Edcor fanclub here or something

Cheers!

[Blooze]

Glad to hear another report of those Edcor OPT's. I haven't got around to finishing my rev.B due to lack of funds, but I'm glad I had Brian put those up on the regular website instead of having to ask for them.

[Ty_Bower]

If you are using one in an ST-35 where you parallel both 6.3 volt windings, you'll need to test for proper phase before finalizing the connection, I just used two sets of crimp lugs, and left one side of one winding hanging, and tapped it on, no sparks, so I got it right the first time.

I'm thinking a safer way to verify phasing of multiple 6.3v windings might be to wire them together in series. Apply power to the primary and check the voltage across the two windings together. If it is zero, you've got them out of phase. Mark one end of each with a dot when you know what they are.

If you parallel windings out of phase, you can draw excessive current and burn out a winding. Hopefully the fuse pops before you toast a transformer.

[Geek]

If you parallel windings out of phase, you can draw excessive current and burn out a winding. Hopefully the fuse pops before you toast a transformer.

Heh, heavy power trannies complain bitterly when that happens... HUMMMMMM and tripping of breakers

Cheers!

[TomMcNally]

If you are using one in an ST-35 where you parallel both 6.3 volt windings, you'll need to test for proper phase before finalizing the connection, I just used two sets of crimp lugs, and left one side of one winding hanging, and tapped it on, no sparks, so I got it right the first time.

Tapping the windings together for 1 millisecond and looking for a spark isn't going to blow the fuse or burn up the winding. Yes, a Nervous Nelly type could go through a more elaborate test, but I don't see it as being necessary.

[paart]

A person on another forum offered a good suggestion about checking transformer phasing. Wire the primary leads to a small AC "wallwart". This will reduce the overall voltage and current enough that the correct and incorrect phasing will still be apparent, but considerably reduce the potential danger. Of course, I was working with a 1:1 isolation transformer, but I think 6.3 volts would still show up with most meters.