Need schematic for Heathkit AC-11 FM multiplexer unit

[Roger Jones]

Hi, Vacuumlanders,
I've just found one of these in some "inherited treasures". It's a
black, oblong box-like thing with three 12AU7's from the chassis
numbers (but there's one 12AT7 in mine at the V2 position.) It looks
very clean and may well be in working condition, but not tried yet.
I've just reformed B+ filter caps for now with the tubes out - caps
seem OK, tubes test good.
Can anyone point me to a schematics for this unit? It's not on the
Heathkit archive that I can access, viz: http://www.vintage-radio.info/heathkit/index.htm
Thanks for all replies,
Cheers,
Roger

[William Sommerwerck]

If it's an FM multiplex unit, you'll need to drive it directly from the
output of an FM tuner's detector -- it extracts the subcarrier and recreates
the left and right channels.

It is otherwise of no use.

[Roger Jones]

On Jun 15, 12:55 pm, "William Sommerwerck"

Post by William Sommerwerck
If it's an FM multiplex unit, you'll need to drive it directly from the
output of an FM tuner's detector -- it extracts the subcarrier and recreates
the left and right channels.
It is otherwise of no use.

I know. I have a couple of "non-stereo" tube tuners with MPX outputs.
I want to try it out on them. One concern I have is whether the L and
R audio outputs are at low impedance, i.e. cathode followers, as I
want to drive 47Kohm s/s/ amp inputs.
Cheers,
Roger

[William Sommerwerck]

Post by Roger Jones
I have a couple of "non-stereo" tube tuners with MPX outputs.
I want to try it out on them. One concern I have is whether the L and
R audio outputs are at low impedance, i.e. cathode followers, as I
want to drive 47Kohm s/s amp inputs.

Look at the resistors connected to the cathodes. I forget the formula for
computing source impedance.

Regardless, use low-capacitance cables and keep them short.

[John Byrns]

Post by Roger Jones
Hi, Vacuumlanders,
I've just found one of these in some "inherited treasures". It's a
black, oblong box-like thing with three 12AU7's from the chassis
numbers (but there's one 12AT7 in mine at the V2 position.) It looks
very clean and may well be in working condition, but not tried yet.
I've just reformed B+ filter caps for now with the tubes out - caps
seem OK, tubes test good.
Can anyone point me to a schematics for this unit? It's not on the
http://www.vintage-radio.info/heathkit/index.htm
Thanks for all replies,
Cheers,
Roger

Hi Roger,

I put a copy of the Heathkit AC-11 schematic here:

Loading Image...

I found this somewhere on the internet a while back, I'm not sure where or who
to credit.

[William Sommerwerck]

Post by John Byrns
http://fmamradios.com/stuff/ac11mpx.jpg
I found this somewhere on the internet a while back,
I'm not sure where or who to credit.

I'm trying to decide whether it's a switching or matrixing decoder.
Regardless...

I checked the 4th edition of the RDH. The source impedance of a cathode
follower is the value of the cathode resistor, divided by (the cathode
resistor's value times the tube's transconductance, plus 1).

[John Byrns]

Post by William Sommerwerck

Post by John Byrns
http://fmamradios.com/stuff/ac11mpx.jpg
I found this somewhere on the internet a while back,
I'm not sure where or who to credit.

I'm trying to decide whether it's a switching or matrixing decoder.
Regardless...
I checked the 4th edition of the RDH. The source impedance of a cathode
follower is the value of the cathode resistor, divided by (the cathode
resistor's value times the tube's transconductance, plus 1).

It's a classic GE switching decoder.

I also figured out where I found the schematic, it's on this page along with
dozens of other MPX decoder schematics.

http://pacifictv.ca/wanted.htm

For the many fans of reflex radios there is an interesting schematic of a
Grundig Stereo decoder that with typical German tube frugality uses only a
single pentode in the circuit, with both the 19 kHz and 38 kHz signals reflexed
through the single pentode, which also serves as a cathode follower in the more
common fashion.

[Roger Jones]

Post by John Byrns

Post by Roger Jones
Hi, Vacuumlanders,
I've  just found one of these in some "inherited treasures". It's a
black, oblong box-like thing with three 12AU7's from the chassis
numbers (but there's one 12AT7 in mine at the V2 position.) It looks
very clean and may well be in working condition, but not tried yet.
I've just reformed B+ filter caps for now with the tubes out - caps
seem OK, tubes test good.
Can anyone point me to a schematics for this unit? It's not on the
http://www.vintage-radio.info/heathkit/index.htm
Thanks for all replies,
Cheers,
Roger

Hi Roger,
http://fmamradios.com/stuff/ac11mpx.jpg
I found this somewhere on the internet a while back, I'm not sure where or who
to credit.
--
Regards,
John Byrns
Surf my web pages at,  http://fmamradios.com/

John, outstanding! Many thanks. I've already tried it on a Heathkit
FM-4 that I've just refurbished and a Trio AM/FM tuner I've had for
years (fed from the MPX outputs, of course.) So far, no stereo
separation! Some forensics needed...
Cheers,
Roger