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Callins capacitor?...

P

piglet

Guest
On 12/12/2020 4:49 am, Don wrote:
The earlier Callins link was only for reference to give people an idea
of the price and physical characteristics.

My questions actually pertain to a 100 μF 6 V Callins, which looks
identical. It\'s used in a PAIA VCO module from the 1970s. The
schematic\'s shown here:

https://crcomp.net/paia/2720-2A.png

C7 is the Callins. C6 is a plain vanilla electrolytic in a can. They
both have a value of 100 μF.

Although the simpleminded answer goes through everyone\'s mind first, it
doesn\'t add up. Why pay more for a Callins back in the day? Why not buy
twice as many electrolytics in cans to get a better price break?
Or, if Callins was the cheap alternative back then, why pay more
for electrolytics in cans?

Perhaps the answer\'s as simple as the late John Simonton inheriting a
pile of Callins. It\'s too late to ask John, but there\'s a PAIA forum,
which may supply some answers, provided they process my registration.
For the time being, the Callins will be substituted with a new
electrolytic in a can.

Danke,
I have some similar epoxy sealed aluminum electrolytics from the mid
1970s made by Roederstein (now incorporated into Vishay). At the time
they cost only a few percent more than metal can/elastomer seal
capacitors. There is absolutely nothing special about the electrical
characteristics needed of C6 and C7 in that unsavoury circuit and my
guess is that the assemblers just randomly picked that brand.

piglet
 
D

Don

Guest
In sci.electronics.design legg <legg@nospam.magma.ca> wrote:
On Sat, 12 Dec 2020 07:56:15 -0000 (UTC), \"Don\" <g@crcomp.net> wrote:

Phil Allison <pallison49@gmail.com> wrote:

the Callins is in an epoxy sealed container

Interesting, but it doesn\'t answer my question:

Why was the circuit designed to use a Callins in C7?

If it was designed to use a Callins cap, then Callins
would show up on the schematic and BOM.

As it is, specifying a 6V electrolytic to filter a
6.2V reference is probably a mistake.
Excellent observation! There\'s actually a 25 V Callins on the board
itself. So, there\'s definitely a mistake on the schematic.

Danke,

--
Don, KB7RPU
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.
 
D

Don

Guest
In sci.electronics.design piglet <erichpwagner@hotmail.com> wrote:
On 12/12/2020 4:49 am, Don wrote:
The earlier Callins link was only for reference to give people an idea
of the price and physical characteristics.

My questions actually pertain to a 100 μF 6 V Callins, which looks
identical. It\'s used in a PAIA VCO module from the 1970s. The
schematic\'s shown here:

https://crcomp.net/paia/2720-2A.png

C7 is the Callins. C6 is a plain vanilla electrolytic in a can. They
both have a value of 100 μF.

Although the simpleminded answer goes through everyone\'s mind first, it
doesn\'t add up. Why pay more for a Callins back in the day? Why not buy
twice as many electrolytics in cans to get a better price break?
Or, if Callins was the cheap alternative back then, why pay more
for electrolytics in cans?

Perhaps the answer\'s as simple as the late John Simonton inheriting a
pile of Callins. It\'s too late to ask John, but there\'s a PAIA forum,
which may supply some answers, provided they process my registration.
For the time being, the Callins will be substituted with a new
electrolytic in a can.

Danke,


I have some similar epoxy sealed aluminum electrolytics from the mid
1970s made by Roederstein (now incorporated into Vishay). At the time
they cost only a few percent more than metal can/elastomer seal
capacitors. There is absolutely nothing special about the electrical
characteristics needed of C6 and C7 in that unsavoury circuit and my
guess is that the assemblers just randomly picked that brand.
Thank you for confirming my suspicions. It turns out there\'s a typo on
the schematic. The actual Callins capacitor on the board is 25 V.

As an aside, perhaps the circuit\'s relaxation oscillator looked a little
less unsavory back in the hazy 1970s, back when Woz won Bushnell\'s
bonus to minimize the chip count. :)

Danke,

--
Don, KB7RPU
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.
 
D

Don

Guest
In sci.electronics.design Tim Schwartz <tim@bristolnj.com> wrote:
Don,

If you look closely at the photo showing the cap on its side, you\'ll
see a row of \"+\" marks, so this is a plain old polarized electrolytic
capacitor, are are both C6 and C7 on the schematic diagram you provided.
Perhaps one of them had been replaced over the units history. One is
marked 100uf/10V and the other 100V/6V, so maybe it is what the
purchasing department was able to get a deal on.

My experience with those encapsulated Callins caps is that they are
awful. I am NOT a fan of changing every electrolytic capacitor over 3
months old, which seems to be popular on internet forums, but I might
make an exception for the Callins caps. A couple of years ago I got a
lot of surplus caps, including dozens of Callins, all of which tested
bad even after being give a while to form up on my trusty Heathkit IT-28
\"capacitor checker\".

AR and KLH seemed to use quite a few of them in some models.

Maybe they are charging so much because they are the only good ones
left on the planet?
People get nostalgic about all sorts of things. And it\'s OK with me if
they spend good money to make the object of their obsession a perfect
replica in every way. Some people pay a lot more for questionable fine
art.

It turns out there\'s a typo on the schematic. The actual Callins part is
rated at 25 V. Regardless, thank you for taking the time to confirm my
suspicions about it.


Danke,

--
Don, KB7RPU
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.
 
S

server

Guest
On Fri, 11 Dec 2020 19:31:10 -0500, legg <legg@nospam.magma.ca> wrote:

On Fri, 11 Dec 2020 08:55:19 -0800, jlarkin@highlandsniptechnology.com
wrote:

On Fri, 11 Dec 2020 16:13:22 -0000 (UTC), \"Don\" <g@crcomp.net> wrote:

Greetings,

Why do Callins capacitors command such a high premium:

https://richelectronics.co.uk/product/callins-300uf-25v-audio-capacitor-vintage-low-esr-ol0382b

What\'s so special about them?

What\'s a good substitute?

Danke,

Is that a non-polar electrolytic? Looks like two regular caps potted.

What use is a 300 uF non-polar \'lytic?

Crossover network?

I also saw something of a similar value in a Hafler preamp parts list,
(and another smaller value) though I couldn\'t locate it on the
schematis..

RL
The old bakelite Black Beauty film (or maybe paper?) caps are highly
prized/priced because some people can hear the difference.

If I paid $25 for a 0.022 uF cap, I bet I could hear the difference.

I wonder how many of these sorts of things are Chinese fakes.







--

John Larkin Highland Technology, Inc

The best designs are necessarily accidental.
 
S

server

Guest
On Sat, 12 Dec 2020 13:25:26 +0100, Arie de Muynck
<no.spam@no.spam.org> wrote:

On 2020-12-11 17:55, jlarkin@highlandsniptechnology.com wrote:
On Fri, 11 Dec 2020 16:13:22 -0000 (UTC), \"Don\" <g@crcomp.net> wrote:

Greetings,

Why do Callins capacitors command such a high premium:

https://richelectronics.co.uk/product/callins-300uf-25v-audio-capacitor-vintage-low-esr-ol0382b

What\'s so special about them?

What\'s a good substitute?

Danke,

Is that a non-polar electrolytic? Looks like two regular caps potted.

What use is a 300 uF non-polar \'lytic?

The second picture (un)clearly shows + + + marking.
I think so. So it\'s one ordinary cap potted.



--

John Larkin Highland Technology, Inc

The best designs are necessarily accidental.
 
S

server

Guest
On Sat, 12 Dec 2020 07:56:15 -0000 (UTC), \"Don\" <g@crcomp.net> wrote:

Phil Allison <pallison49@gmail.com> wrote:

the Callins is in an epoxy sealed container

Interesting, but it doesn\'t answer my question:

Why was the circuit designed to use a Callins in C7?

Danke,
Was it designed that way?

That circuit was barely designed at all. What\'s it supposed to do?



--

John Larkin Highland Technology, Inc

The best designs are necessarily accidental.
 
S

server

Guest
On Sat, 12 Dec 2020 09:18:09 -0500, legg <legg@nospam.magma.ca> wrote:

On Sat, 12 Dec 2020 07:56:15 -0000 (UTC), \"Don\" <g@crcomp.net> wrote:

Phil Allison <pallison49@gmail.com> wrote:

the Callins is in an epoxy sealed container

Interesting, but it doesn\'t answer my question:

Why was the circuit designed to use a Callins in C7?

Danke,

If it was designed to use a Callins cap, then Callins
would show up on the schematic and BOM.

As it is, specifying a 6V electrolytic to filter a
6.2V reference is probably a mistake.

RL
Lytics usually have a pretty good overvoltage tolerance, and a little
leakage wouldn\'t do any harm in a power supply filter. It may have
failed by drying out over the years and been replaced by whatever was
handy.





--

John Larkin Highland Technology, Inc

The best designs are necessarily accidental.
 
D

Don

Guest
In sci.electronics.design jlarkin@highlandsniptechnology.com wrote:
On Sat, 12 Dec 2020 07:56:15 -0000 (UTC), \"Don\" <g@crcomp.net> wrote:

Phil Allison <pallison49@gmail.com> wrote:

the Callins is in an epoxy sealed container

Interesting, but it doesn\'t answer my question:

Why was the circuit designed to use a Callins in C7?

Was it designed that way?

That circuit was barely designed at all. What\'s it supposed to do?
Your question restates the gist of this thread.

How can you know the circuit was barely designed at all if you don\'t
even know what\'s it supposed to do?

Danke,

--
Don, KB7RPU
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.
 
J

John Robertson

Guest
On 2020/12/12 8:44 a.m., Don wrote:
In sci.electronics.design legg <legg@nospam.magma.ca> wrote:
On Sat, 12 Dec 2020 07:56:15 -0000 (UTC), \"Don\" <g@crcomp.net> wrote:

Phil Allison <pallison49@gmail.com> wrote:

the Callins is in an epoxy sealed container

Interesting, but it doesn\'t answer my question:

Why was the circuit designed to use a Callins in C7?

If it was designed to use a Callins cap, then Callins
would show up on the schematic and BOM.

As it is, specifying a 6V electrolytic to filter a
6.2V reference is probably a mistake.

Excellent observation! There\'s actually a 25 V Callins on the board
itself. So, there\'s definitely a mistake on the schematic.

Danke,
Engineers make mistakes? Never!

(ducking)

John :-#)#
 
S

server

Guest
On Sat, 12 Dec 2020 17:54:08 -0000 (UTC), \"Don\" <g@crcomp.net> wrote:

In sci.electronics.design jlarkin@highlandsniptechnology.com wrote:
On Sat, 12 Dec 2020 07:56:15 -0000 (UTC), \"Don\" <g@crcomp.net> wrote:

Phil Allison <pallison49@gmail.com> wrote:

the Callins is in an epoxy sealed container

Interesting, but it doesn\'t answer my question:

Why was the circuit designed to use a Callins in C7?

Was it designed that way?

That circuit was barely designed at all. What\'s it supposed to do?

Your question restates the gist of this thread.

How can you know the circuit was barely designed at all if you don\'t
even know what\'s it supposed to do?
Because it\'s full of trimpots and selected values. It was probably
futzed until it worked. What\'s it supposed to do?



--

John Larkin Highland Technology, Inc

The best designs are necessarily accidental.
 
P

piglet

Guest
On 12/12/2020 6:19 pm, jlarkin@highlandsniptechnology.com wrote:
On Sat, 12 Dec 2020 17:54:08 -0000 (UTC), \"Don\" <g@crcomp.net> wrote:

In sci.electronics.design jlarkin@highlandsniptechnology.com wrote:
On Sat, 12 Dec 2020 07:56:15 -0000 (UTC), \"Don\" <g@crcomp.net> wrote:

Phil Allison <pallison49@gmail.com> wrote:

the Callins is in an epoxy sealed container

Interesting, but it doesn\'t answer my question:

Why was the circuit designed to use a Callins in C7?

Was it designed that way?

That circuit was barely designed at all. What\'s it supposed to do?

Your question restates the gist of this thread.

How can you know the circuit was barely designed at all if you don\'t
even know what\'s it supposed to do?

Because it\'s full of trimpots and selected values. It was probably
futzed until it worked. What\'s it supposed to do?
My guess is it was some kind of analog synth VCO, inputs EFG are summed
and make the ramp, square and triwave outputs at jacks HDJ.

Dig the 3.6V D3 zener in the path, the 3.9Meg and 680R R19 R20 and the
kooky voltage follower Q3 Q11 Q4 - the unijunction Q2 is probably the
least nasty part of it all.

Thats why I used the word unsavoury!

piglet
 
L

legg

Guest
On Sat, 12 Dec 2020 09:23:52 -0800, jlarkin@highlandsniptechnology.com
wrote:

On Fri, 11 Dec 2020 19:31:10 -0500, legg <legg@nospam.magma.ca> wrote:

On Fri, 11 Dec 2020 08:55:19 -0800, jlarkin@highlandsniptechnology.com
wrote:

On Fri, 11 Dec 2020 16:13:22 -0000 (UTC), \"Don\" <g@crcomp.net> wrote:

Greetings,

Why do Callins capacitors command such a high premium:

https://richelectronics.co.uk/product/callins-300uf-25v-audio-capacitor-vintage-low-esr-ol0382b

What\'s so special about them?

What\'s a good substitute?

Danke,

Is that a non-polar electrolytic? Looks like two regular caps potted.

What use is a 300 uF non-polar \'lytic?

Crossover network?

I also saw something of a similar value in a Hafler preamp parts list,
(and another smaller value) though I couldn\'t locate it on the
schematis..

RL

The old bakelite Black Beauty film (or maybe paper?) caps are highly
prized/priced because some people can hear the difference.

If I paid $25 for a 0.022 uF cap, I bet I could hear the difference.

I wonder how many of these sorts of things are Chinese fakes.
I recall there being an oversupply of non-polarized electrolytics
at one time, mainly because of their perceived mark-up value.

The value was due to their predominant sale to low-volume hobbyists.

The Callins part is polarized and of no special importance to the
circuit in which it was employed.

The Hafler circuit was the DH110, which used descrete transisators of
both polarities in complimentary pairs. I still don\'t see the C109
part in the schematic.

RL
 
J

Jeroen Belleman

Guest
On 2020-12-12 19:46, legg wrote:
On Sat, 12 Dec 2020 09:23:52 -0800, jlarkin@highlandsniptechnology.com
wrote:

On Fri, 11 Dec 2020 19:31:10 -0500, legg <legg@nospam.magma.ca> wrote:

On Fri, 11 Dec 2020 08:55:19 -0800, jlarkin@highlandsniptechnology.com
wrote:

On Fri, 11 Dec 2020 16:13:22 -0000 (UTC), \"Don\" <g@crcomp.net> wrote:

Greetings,

Why do Callins capacitors command such a high premium:

https://richelectronics.co.uk/product/callins-300uf-25v-audio-capacitor-vintage-low-esr-ol0382b

What\'s so special about them?

What\'s a good substitute?

Danke,

Is that a non-polar electrolytic? Looks like two regular caps potted.

What use is a 300 uF non-polar \'lytic?

Crossover network?

I also saw something of a similar value in a Hafler preamp parts list,
(and another smaller value) though I couldn\'t locate it on the
schematis..

RL

The old bakelite Black Beauty film (or maybe paper?) caps are highly
prized/priced because some people can hear the difference.

If I paid $25 for a 0.022 uF cap, I bet I could hear the difference.

I wonder how many of these sorts of things are Chinese fakes.

I recall there being an oversupply of non-polarized electrolytics
at one time, mainly because of their perceived mark-up value.

The value was due to their predominant sale to low-volume hobbyists.

The Callins part is polarized and of no special importance to the
circuit in which it was employed.

The Hafler circuit was the DH110, which used descrete transisators of
both polarities in complimentary pairs. I still don\'t see the C109 [...]
^^^^^^^^^^^^^^^^^^^^
Every time I see that, a vision of them congratulating each other
comes to mind.

It\'s complementary.
-

Jeroen Belleman

P.S. Oh, and \'discrete\'.
 
D

Don

Guest
In sci.electronics.design jlarkin@highlandsniptechnology.com wrote:
On Sat, 12 Dec 2020 17:54:08 -0000 (UTC), \"Don\" <g@crcomp.net> wrote:

In sci.electronics.design jlarkin@highlandsniptechnology.com wrote:
On Sat, 12 Dec 2020 07:56:15 -0000 (UTC), \"Don\" <g@crcomp.net> wrote:

Phil Allison <pallison49@gmail.com> wrote:

the Callins is in an epoxy sealed container

Interesting, but it doesn\'t answer my question:

Why was the circuit designed to use a Callins in C7?

Was it designed that way?

That circuit was barely designed at all. What\'s it supposed to do?

Your question restates the gist of this thread.

How can you know the circuit was barely designed at all if you don\'t
even know what\'s it supposed to do?

Because it\'s full of trimpots and selected values. It was probably
futzed until it worked. What\'s it supposed to do?
It\'s the VCO module from an old synthesizer. It has three triangles on
its face-plate and it\'s right above the left hand side of the keyboard
in the first image shown here:

http://www.johnnypumphandle.com/johnny/Paia/paia.htm

Danke,

--
Don, KB7RPU
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.
 
L

legg

Guest
On Sat, 12 Dec 2020 19:53:22 +0100, Jeroen Belleman
<jeroen@nospam.please> wrote:

On 2020-12-12 19:46, legg wrote:
On Sat, 12 Dec 2020 09:23:52 -0800, jlarkin@highlandsniptechnology.com
wrote:

On Fri, 11 Dec 2020 19:31:10 -0500, legg <legg@nospam.magma.ca> wrote:

On Fri, 11 Dec 2020 08:55:19 -0800, jlarkin@highlandsniptechnology.com
wrote:

On Fri, 11 Dec 2020 16:13:22 -0000 (UTC), \"Don\" <g@crcomp.net> wrote:

Greetings,

Why do Callins capacitors command such a high premium:

https://richelectronics.co.uk/product/callins-300uf-25v-audio-capacitor-vintage-low-esr-ol0382b

What\'s so special about them?

What\'s a good substitute?

Danke,

Is that a non-polar electrolytic? Looks like two regular caps potted.

What use is a 300 uF non-polar \'lytic?

Crossover network?

I also saw something of a similar value in a Hafler preamp parts list,
(and another smaller value) though I couldn\'t locate it on the
schematis..

RL

The old bakelite Black Beauty film (or maybe paper?) caps are highly
prized/priced because some people can hear the difference.

If I paid $25 for a 0.022 uF cap, I bet I could hear the difference.

I wonder how many of these sorts of things are Chinese fakes.

I recall there being an oversupply of non-polarized electrolytics
at one time, mainly because of their perceived mark-up value.

The value was due to their predominant sale to low-volume hobbyists.

The Callins part is polarized and of no special importance to the
circuit in which it was employed.

The Hafler circuit was the DH110, which used descrete transisators of
both polarities in complimentary pairs. I still don\'t see the C109 [...]
^^^^^^^^^^^^^^^^^^^^

Every time I see that, a vision of them congratulating each other
comes to mind.

It\'s complementary.
-

Jeroen Belleman

P.S. Oh, and \'discrete\'.
I flipped a coin with complementary. Discrete has no excuse.

It was the DH100, not 110, using ICs, that had the C109 issue in it\'s
docs. If I had a board, I\'d make the schematic alteration.

Looks like all pns 100+ were added post-design. Stuff like RF
filtering on inputs, belt and braces decoupling, grounding leakage
paths etc. Most show up.

RL
 
T

Tauno Voipio

Guest
On 12.12.20 6.49, Don wrote:
The earlier Callins link was only for reference to give people an idea
of the price and physical characteristics.

My questions actually pertain to a 100 μF 6 V Callins, which looks
identical. It\'s used in a PAIA VCO module from the 1970s. The
schematic\'s shown here:

https://crcomp.net/paia/2720-2A.png

C7 is the Callins. C6 is a plain vanilla electrolytic in a can. They
both have a value of 100 μF.

Although the simpleminded answer goes through everyone\'s mind first, it
doesn\'t add up. Why pay more for a Callins back in the day? Why not buy
twice as many electrolytics in cans to get a better price break?
Or, if Callins was the cheap alternative back then, why pay more
for electrolytics in cans?

Perhaps the answer\'s as simple as the late John Simonton inheriting a
pile of Callins. It\'s too late to ask John, but there\'s a PAIA forum,
which may supply some answers, provided they process my registration.
For the time being, the Callins will be substituted with a new
electrolytic in a can.

Danke,
There must be some audio magic inside the Callins, but I see
it difficult to get any advantage in a power supply filter.
If you\'re not happy with a garden-variety aluminum, get a
tantalum one, and please, with a little more than 6V rating,
as the power line is nominally 6V.

--

-TV
 
L

legg

Guest
On Sat, 12 Dec 2020 14:12:05 -0500, legg <legg@nospam.magma.ca> wrote:

<snip>
It was the DH100, not 110, using ICs, that had the C109 issue in it\'s
docs. If I had a board, I\'d make the schematic alteration.

Looks like all pns 100+ were added post-design. Stuff like RF
filtering on inputs, belt and braces decoupling, grounding leakage
paths etc. Most show up.
I\'m a dolt.

C9, C109 set the LF gain corner of the first IC\'s gain stage.

Part numbers above 100 are right channel, not repeated in schematic.

.. . . Q has hovered for some decades in rubbish area of skull.

RL
 
T

Tauno Voipio

Guest
On 12.12.20 19.34, jlarkin@highlandsniptechnology.com wrote:
On Sat, 12 Dec 2020 07:56:15 -0000 (UTC), \"Don\" <g@crcomp.net> wrote:

Phil Allison <pallison49@gmail.com> wrote:

the Callins is in an epoxy sealed container

Interesting, but it doesn\'t answer my question:

Why was the circuit designed to use a Callins in C7?

Danke,

Was it designed that way?

That circuit was barely designed at all. What\'s it supposed to do?
Agreed.

There is a voltage-controlled UJT sawtooth generator, with
outputs sent to three places:

- direct output,

- a differential pair-rectifier to cut it at the
middle for a (maybe) symmetric triangle,

- a Schmitt-trigger to create a variable width pulse

There is plenty of opportunity for improvement even when
using the block diagram (and forgetting the UJT).

--

-TV
 
D

Don

Guest
In sci.electronics.design Tauno Voipio <tauno.voipio@notused.fi.invalid> wrote:
> On 12.12.20 19.34, jlarkin@highlandsniptechnology.com wrote:

<snip>

Was it designed that way?

That circuit was barely designed at all. What\'s it supposed to do?


Agreed.

There is a voltage-controlled UJT sawtooth generator, with
outputs sent to three places:

- direct output,

- a differential pair-rectifier to cut it at the
middle for a (maybe) symmetric triangle,

- a Schmitt-trigger to create a variable width pulse

There is plenty of opportunity for improvement even when
using the block diagram (and forgetting the UJT).
You seem to know what you\'re talking about. :)

Although its ramp and triangle outputs are now restored, the Schmitt
trigger\'s still a work in progress. It\'s (manually transcribed from a
PDF and as typo-free as possible) Design Analysis is shown below. The
last paragraph in the analysis leads me to believe the Callins capacitor
was plausibly used by design.

DESIGN ANALYSIS

The central feature of the 2720-2A VCO is the self-zeroing, summing
voltage to current converter comprising of IC-1, Q1 and associated
components. Unlike the more conventional inverting summer, the feed
back voltage does not come directly from the output of the amplifier
but rather from the emitter of the current source transistor Q1. In
operation positive voltages applied to one or more of the summing
resistors (R1 - R3) force the output of the amplifier to go to
whatever negative voltage is necessary to make the same voltage
appear at both the inverting and non-inverting inputs of the op amp.
Feedback circuits are always a balancing act and the balanced point in
any linear operational amplifier circuit is reached when the two inputs
are at equal voltages. Since in this case the non-inverting input is
grounded (0v.) the inverting input must also go to zero volts.

Since the base emitter junction of Q1 is inside the feedback loop of
the summing amplifier, both the natural non-linearities and constant
voltage drop of the junction are eliminated from the response of the
current source. Both sets of resistors that serve as emitter resistances
for the current source (Range trimmer R7 in series with R6 both
paralleled by R4) terminate at ground and a virtual ground so that for
zero control volts input the source must generate zero current.

The output of the current source charges capacitor C1 which in
conjunction with Unijunction Transistor (UJT) Q2 forms a relaxation
oscillator. As increasing voltages are applied to the control inputs,
the current supplied by Q1 increases causing C1 to charge more rapidly
thereby increasing the frequency of the oscillator.

The ramp waveform that appears across C1 is applied to the input of the
darlington emitter follower consisting of Q4 and Q11. The high input
impedance of this emitter follower is important in presenting
negligible load to the timing capacitor C1. A second emitter follower Q4
in conjunction with zener diode D3 performs a level shift so that the
ramp is transposed to slightly above ground potential while a third
emitter follower (Q5) provides a low output impedance buffer to couple
the signal to the rest of the waveforming circuitry.

The ramp waveform is used three ways. First, it is applied to the
voltage divider string consisting of R11, R24, R23 and R22. Between R11
and R24 the string is capacitively coupled through C5 directly to the
\"RAMP\" output jack J1 where it becomes available as a signal source.

Secondly, the ramp is applied to the Schmitt trigger composed of Q9 and
Q10. A Schmitt trigger has a low output or a high output depending on
whether the input voltage is above or below a pre-set design level. As
the ramp input to the trigger begins to rise the output remains low
until the voltage exceeds this level and then abruptly changes to the
high state. The output of the trigger, then, is a rectangular pulse at
exactly the frequency of the ramp input. By varying the amplitude of the
ramp you regulate the duration of the pulse by changing the relative
point at which the trigger changes state.

Finally, the ramp is applied to the input of the differential pair Q6
and Q7. In the differential configuration the voltage at the collector
of Q7 is in phase with the input ramp and the voltage at the collector
of Q6 is inverted. The diodes D1 and D2 \"select the higher of the two
collector voltages and apply it to the base of emitter follower Q8.
During the lower half of the input ramp\'s excursion Q6\'s collector
voltage is higher and that section of the ramp is presented in an
inverted form to the base of Q8. There is a slight rounding at the
bottom of the wave during the cross over between Q6 and Q7 and a slight
pip at the top during the ramp \"flyback\" but neither of these
imperfections are audibly noticeable.

The most voltage sensitive portions of the circuit are powered from the
simple series voltage regulator consisting of zener reference diode D4
and pass transistor Q12. Less critical parts of the circuit are powered
by the decoupling networks R33/C6 in the positive supply line and
R35/C8 in the negative supply.

Danke,

--
Don, KB7RPU
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.
 
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