I bought a pile of books recently and among them was the Ed Romney
"Fixing Up Nice Old Radios" book which you may be familiar with. For
those not familiar he reprints the ARRL Handbook two-tube regen set
which uses plug in coils. There is choke coupling to the audio amp with
a 750 Henry choke.


I suppose I could get Sowter or Jensen to wind one, but is there an
off the shelf part that will sub for this unobtainable little bugger?

Bret Ludwig wrote:
I bought a pile of books recently and among them was the Ed Romney
"Fixing Up Nice Old Radios" book which you may be familiar with. For
those not familiar he reprints the ARRL Handbook two-tube regen set
which uses plug in coils. There is choke coupling to the audio amp with
a 750 Henry choke.


I suppose I could get Sowter or Jensen to wind one, but is there an
off the shelf part that will sub for this unobtainable little bugger?



I don't have that book but you can use the winding of an old audio
interstage xfmr in most of the ckts where such a choke is called for.
That will be in the 10-30 H range and should work just fine. I've had
good luck even using the little 200mw $1.99 transistor interstage xfmrs
from Mouser. Don't know how many henries they represent but compared to
the coil+resistance in a set of old 1920s phones that served exactly the
same function in similar ckts it seems roughly equivalent....on the
order of 3-10 H wouldn't be atypical according to the measurements one
fellow made.

The National SW-3 uses such a 750H choke and you can also find one of
several hundred Henries in the old BC-221 freq meters.

The audio will be down only slightly using a smaller value but quite
honestly I don't see why they used such high values.

-Bill

Bill wrote:
Bret Ludwig wrote:
I bought a pile of books recently and among them was the Ed Romney
"Fixing Up Nice Old Radios" book which you may be familiar with. For
those not familiar he reprints the ARRL Handbook two-tube regen set
which uses plug in coils. There is choke coupling to the audio amp with
a 750 Henry choke.


I suppose I could get Sowter or Jensen to wind one, but is there an
off the shelf part that will sub for this unobtainable little bugger?



I don't have that book but you can use the winding of an old audio
interstage xfmr in most of the ckts where such a choke is called for.
That will be in the 10-30 H range and should work just fine. I've had
good luck even using the little 200mw $1.99 transistor interstage xfmrs
from Mouser. Don't know how many henries they represent but compared to
the coil+resistance in a set of old 1920s phones that served exactly the
same function in similar ckts it seems roughly equivalent....on the
order of 3-10 H wouldn't be atypical according to the measurements one
fellow made.

The National SW-3 uses such a 750H choke and you can also find one of
several hundred Henries in the old BC-221 freq meters.

The audio will be down only slightly using a smaller value but quite
honestly I don't see why they used such high values.

What I figured I'd do is just tap off a small practice guitar
amplifier for B+ and heater power (it's a homebrew with excess to
spare) and use it for audio too. So I shouldn't need too much audio
output.

The other question I have is, what relatively common miniature tubes
would be good to sub for the 5 and 6 pin ones in this circuit?

Bret Ludwig wrote:


The other question I have is, what relatively common miniature tubes
would be good to sub for the 5 and 6 pin ones in this circuit?

I don't know that particular ckt, what tubes is it using? Can you post
the schematic or is it on the web somewhere?

-Bill