Svt midrange inductor, diy?

[Pedjoh]

Hi, nice forum!

Just wonder if it's at all sensible to try to wound an inductor yourself?

I mean, what kind of ferrite's should be used, and what specs should the wire have?

Really greatful for answers!


/pedjoh

[mooreamps]

If you mean for a tone circuit, it would be alot of turns of 28 or 30 AWG magnetic wire on a toriod core diameter of about 2 inchs ; I'm just guessing of the top of my head. I wind toroids for some of my filament power supply designs, and considering a smaller device for one of my pre-amp stages. But, certainly a technology I am planning to more with inside my builds.

-g

[J M Fahey]

Hi pedjoh.
I *did* wind one, for a rackmount SVT '72 preamp a client wanted custom mad, but I don't temember the turns count now.
Anyway, I had no winding data or pot core specification whatsoever, I doubt even Ampeg themselves had that, I'm sure it's an outsourced part, but I remember I just got the only potcore my wire and iron supplier had at the time, wound , say, 300 turns, connected the capacitor as in the Ampeg schematic and measured the resonant frequency.
Once you have measured some audio band resonance, it's easy to get what you need, remembering that more turns mean lower frequency and viceversa.
In less than an hour you should have wound the exact core you need.
If I remember right, I used a 1 inch diameter potcore, or thereabout.

[Giaime]

You find some info here, on the inductor value and tappings:

Ampeg SVT-VR or SVT-CL Schematics - diyAudio

[octal]

The other thing you could do is just wire "off the shelf" inductors in series to simulate the tapped SVT inductor. Of course, winding your own is more elegant!

[J M Fahey]

Here's my "Fahey-SVT72" Rack preamp, PTP wired, including the handwound inductor I mentioned earlier.
Sorry about the picture quality, but my Agfa306 camera was "good" way back then.
The rack chassis is also handmade, as well as the silkscreening.
It was not worth designing a PCB just for a one-off product.
Besides, "PTP handwired beats PCB", at least on the buyer's mind.

[GainFreak]

This is in russian but it's pretty straightforward.
The line below says 0,23mm copper wire, 18 layers, 46 turns each. Winding height 4mm
On the right side "вит" means turns.
I hope this helps.

[J M Fahey]

Thanks !!!! Great info !!!!!
I wonder how *they*got that data.
1972 was in the middle of the Cold War.
I imagine the scene at some KGB office:
- Comrrrrade Spy, you vill be shot for vringing such useless info !!!!!!!!!!!
- Comrrrade Keneral !!! Tis Ampek SVT poverrfullll veapon !!!! Vrinks down valls !!!!!!!!!!!!
Did I mention I *love* "Class B" Films?

[dai h.]

Here's my "Fahey-SVT72" Rack preamp, PTP wired, including the handwound inductor I mentioned earlier.
Sorry about the picture quality, but my Agfa306 camera was "good" way back then.
The rack chassis is also handmade, as well as the silkscreening.
It was not worth designing a PCB just for a one-off product.
Besides, "PTP handwired beats PCB", at least on the buyer's mind.

wow that looks really good!

[J M Fahey]

Thanks.
Making the rack case was more difficult than the electronics part itself, as everybody knows.

[GainFreak]

Thanks !!!! Great info !!!!!
I wonder how *they*got that data.
1972 was in the middle of the Cold War.
I imagine the scene at some KGB office:
- Comrrrrade Spy, you vill be shot for vringing such useless info !!!!!!!!!!!
- Comrrrade Keneral !!! Tis Ampek SVT poverrfullll veapon !!!! Vrinks down valls !!!!!!!!!!!!
Did I mention I *love* "Class B" Films?

This is actually a DIY version of the coil. The original is wound on a toroidal core.