REDDI DI

[MicDaddy]

you are the Man!

thanks again, Harry,  ;D

that is indeed the 100 EI lam, sq stack,

big enough to be a OPT for a pair of EL 84 tubes, sheesh,

average turn for 100 EI is 14.5 cm = 5.7 inches,

we are running 16 ma plate current,

#38 good for 15.7 ma,

lets bump up to #36 which handles 25 ma just to be safe and calculate turns based on DCR, turn length, and ohms per 1000 ft for #36,

ohms per 1000 ft of #36 is 415 at sea level, 

957 ohms pri / 415 ohms per 1000 ft = 2.3,  2.3 *1000 = 2,300 feet of #36,

convert to inches and divide by turn length, 2,300 * 12 inches = 27,600 inches

27,600/5.7 = 4,842 turns,

winding area for a 100 EI bobbin is  1 1/4" by 3/8"  = .4687 sq in.
copper area is split between pri and sec, and we need room for tape since this thing does 60 k hz which translates to about 7 sections of coil, 

0.492/2= 0.246 sq inches, subtract for tape and call it 0.2 sq inches for pri  wire,

#36 = 31,000 turns per sq inch, so we have room for .2 *31,000 = 6,200 turns,

we guessed 4,842 turns based on DCR and 6,200 turns based on wire size,

let's call it 5000 turns and see what the Henries are for a gapped 100 EI core,

might be 4000 turns looking at how full the bobbin is,

for a 10 mil gap we get 37 Henries, for a 5 mil gap we have 50 Henries pri L,

50 Henries @ 20 Hz = 6.28 * 20 * 50 = 6 K pri Z, if 10 mils then 4.7 K,

if turns ratio is 3:1, then Z ratio is 9:1,

6K/9 = 667,  4.7/9 = 522 ohms, seems ballpark to me,

gauss is 500 AC and 1000 DC, total flux is 1500 gauss so we are loafing on a steel core,

sec turns will be 5000/3 = 1667,

1667 * 5.7"  = 9500 inches  9500/12= 792 feet of wire,

what size?

132 ohms, 792/1000 = .792,  try #32, ohms per 1000 = 163,

0.792 * 163 = 129 ohms, Bingo!  so 5000 T #36 and 1667 T #32 on a 100 EI,

Garry, if you have time, measure AC current at 100 hz, this will tell us inductance,
then we can see how close we are to guessing turns,

should be about 13 VAC/6.28*100(f)*50 (Henries)
=
13/628*50=13VAC/31,400 Z-ohms = .000414 = 414 uA

thanks!  test procedure below>

be damned if I wasn't dreaming this stuff last night...

CJ I'm following your math but have one question (perhaps mundane/obvious)...

"0.492/2= 0.246 sq inches, subtract for tape and call it 0.2 sq inches for pri  wire,"

Where does 0.492 come from?

 

[CJ]

probably meant .4687, some weird rounding process going on, 

 

[MicDaddy]

Thanks CJ, 8) was chasing my tail for many hours on this one

Is there something about this "rounding process" one should know or is this a rabbit hole I don't care to venture down?

I'm trying hard to keep up with you guys, the struggle is real.

Ever tried Foremostplastic for bobbins? 

 

[dirty1_1garry]

Good news.
Just lunched new full version of predi'ct. Yappi!
All characters are good, voltages ok, no noises.
Tried with both edcor CSXE5 transformer and my custom made. Sounds gooood.
Check the video (75Mb) here:
https://yadi.sk/i/S7-Ui87ibiCbD

I think that I will be ready to take an orders on this week. I just want to finally proof that all Ok, will made a sound samples and documentation for building.
`

 

[dirty1_1garry]

Here is an iron

 

[MicDaddy]

Here is an iron

Are you winding these in house?

 

[My3gger]

That is some real diy i'm missing so much, congratulations I'm curious why you used C core, is it easy to get it where you live, you found some real advantages over EI, somethings else?
Don't mind which core this trafos have as long as they sound and measure good. Pcb is also nice for those who need it. Please post some results as time permits, this is very interesting because diy gapped trafos are so rare. Thanks for bringing this to us.

 

[dirty1_1garry]

Here is an iron

Are you winding these in house?

No, this transformer was made by my friend who is transformer guru and have made a lot of them for hi-fi tube amps

 

[dirty1_1garry]

That is some real diy i'm missing so much, congratulations I'm curious why you used C core, is it easy to get it where you live, you found some real advantages over EI, somethings else?
Don't mind which core this trafos have as long as they sound and measure good. Pcb is also nice for those who need it. Please post some results as time permits, this is very interesting because diy gapped trafos are so rare. Thanks for bringing this to us.

I just bring idea of creating this trafo to my friend who is transformer creator and after researching schematic and his available parts we decide to made it in C-core. It works and sounds good so I can't see any bad aspects of using it in this situation.

 

[ungifted]

C core is very popular amongst trafo gurus here in Russia.  I've got some TRIAD HS-52 based transformers for Fairchild 670 style compressors  in stock - same C core used (little bit smaller size) . Many Hi-Fi enthusiasts use this good quality old iron.
Sorry for ad.

 

[My3gger]

I thought availability was part of decision for C core. I don't care what it is as long as it sounds good.
The other day i found some remarks about V series stuff, same amps didn't have same cores..
About availability; in our parts (eastern Europe) people mostly wind toroids and small EI's. It is actually quite hard to get good EI winder where i live, at least for simple audio because we never had thin lams. Even many audiophiles have toroids for their OT's. Still didn't try toroid line OT, it costs like 15eur here...
Btw, Pikatron and several other German companies used toroids for at least line level, they got very good specifications.

 

[theokbird]

1 x pcb, 1 x iron, please!  very excited about this project!

 

[dirty1_1garry]

Hello everybody!

Ahhh, just finished full pack of documentation for the project!
Will create separate  build tread in next days. Two kits will be available.
PM me if you in interest of purchasing pcbs and kits with transformers.

Here is an image of fully tested and worked unit. Two pcbs was tested. Both work great.

 

[abbey road d enfer]

After nearly 300 posts on this project, wouldn't it be time to move it to another section?

 

[theokbird]

Hey all,
first, i just want to say thank you to everyone who made this project possible, simplifying it enough for me to feel comfortable taking it on

i apologize in advance, as i'm fairly new to all this but i was thinking i'd take a chance and see what anyone else has to say on this subject:

i'm interested in adding a balanced xlr input to this design, possibly with a variable impedance, what would be the best way to go about doing that? 

i assume i need to convert the unbalanced signal to balanced, and there's a few ways of going about that, but what would work best in this design? add an input transformer? is this a terrible idea considering there's not much gain to be had from this circuit anyway?


thanks

-Adam

 

[abbey road d enfer]

i'm interested in adding a balanced xlr input to this design, possibly with a variable impedance, what would be the best way to go about doing that? 

i assume i need to convert the unbalanced signal to balanced, and there's a few ways of going about that, but what would work best in this design? add an input transformer? is this a terrible idea considering there's not much gain to be had from this circuit anyway?

It would be easy to add a step-up xfmr (1:10 or 1:15) with the secondary connected to the grid. It would probably work somewhat. It would not have much gain, but would be usable on hot sources. The variable impedance part is easy, you just connect a 10k log pot (wired as a rheostat) across the input and you're good.

Before undertaking such a project, I think you should think about what you want to achieve.
The nice thing is that it's very easy to do. You may find little practical use for it, but it's the fun of DIY.

 

[dmp]

I am building up a pair of these with added input transformers, just like you describe.
Could use them as "ribbon boosters".
Up the gain of a low output mic.
I was going to use the Neutrik combo jacks that take an XLR or a 1/4" jack, and have switching contacts.

 

[abbey road d enfer]

I am building up a pair of these with added input transformers, just like you describe.
Could use them as "ribbon boosters".
Up the gain of a low output mic. 

Beware that you'll be challenged in terms of optimizing the noise performance. Cleanliness of B+ and heater voltage is paramount, as well as shielding of both input and output xfmrs.

 

[theokbird]

i'm interested in adding a balanced xlr input to this design, possibly with a variable impedance, what would be the best way to go about doing that? 

i assume i need to convert the unbalanced signal to balanced, and there's a few ways of going about that, but what would work best in this design? add an input transformer? is this a terrible idea considering there's not much gain to be had from this circuit anyway?

It would be easy to add a step-up xfmr (1:10 or 1:15) with the secondary connected to the grid. It would probably work somewhat. It would not have much gain, but would be usable on hot sources. The variable impedance part is easy, you just connect a 10k log pot (wired as a rheostat) across the input and you're good.

Before undertaking such a project, I think you should think about what you want to achieve.
The nice thing is that it's very easy to do. You may find little practical use for it, but it's the fun of DIY.

Ah yes, i figured it would be easy, yet not too beneficial in the end!  however i think i'll give it a go anyhow... would this transformer work?
https://www.edcorusa.com/mx12cs
it's copper shielding is crucial, and i should use high quality shielded cable for the connections, i assume.  should i be worried about it's position in the case?

thanks!

 

[theokbird]

I am building up a pair of these with added input transformers, just like you describe.
Could use them as "ribbon boosters".
Up the gain of a low output mic.
I was going to use the Neutrik combo jacks that take an XLR or a 1/4" jack, and have switching contacts.

i apologize if this is really obvious, but..

whats your wiring scheme for this?  this is exactly what i had in mind.  thinking about using the edcor mx12cs

cheers,
adam