Koss.Rek-O-Kut Model X Electrostatic Speakers...

[Peter W.]

Just to make it clear, these are Acoustech Model X *Solid State* self-powered electrostatic speakers, about two meters high (more than 6\') and just under 75 cm wide.

They are silent. As in not even a pop, click or hiss. They have been so for ten (10) years.
-Fuses are good.
-Capacitors are good under LV test.
-Relay is good.
-Power Transformer is good.
-Transistors are good.
- There is no evidence of physical, water, or similar damage or abuse.

These were my brother\'s who used them for many years until he stopped. He just moved into a rather small apartment, and they had to go.

There are two (2) potted transformers that feed from the driver section onto the speaker itself. Seven (7) leads connect to the speaker. From the back left-to-right:
1. Silicon Red wire to larger potted tranny
2. Silicon Red wire to larger potted tranny
3. Small yellow wire to smaller potted tranny
4. Small blue/black wire to smaller potted tranny
5. Small black wire to smaller potted tranny
6. Small black wire to smaller potted tranny
7. Silicon Red Wire to Fat Flat Wire on speaker to smaller potted tranny

I can get continuity from 1-2 that makes sense.
I can get continuity from 3 - 6 that also seem to make sense.
I cannot get continuity from 7 to anywhere either on the chassis, other transformer leads nor any other point that I can trace.

I have a very bad schematic from HiFi Engine that speaks to a shield. But its origin(s) and destination(s) are not clear.

This condition is extant on both (2x) speakers.

Any one out there who has had experience on these beasts? Any thoughts? If not, I will treat them as landfill and flog them as-is and with a very accurate description on the usual auction site, pick-up only. Otherwise, if there is hope, I am up for the work.

Thanks in advance!

Peter Wieck
Melrose Park, PA

 

[Phil Allison]

Peter Wanker dribbled:

=================:

Just to make it clear, these are Acoustech Model X *Solid State* self-powered
electrostatic speakers, about two meters high (more than 6\') and just under 75 cm wide.

----------------------------------------------------------------------------------------

** The model was marketed briefly by Koss in *1965*.

Each speaker was bi-amped - at a time when most SS amps used Germanium transistors.
Each amplifier feeds an output transformer, to boost the voltage maybe 100 times.
If the HT ( 2kV at least) supply fails, an ES speaker goes silent.

Moisture and dust ingress destroys ES speakers over time.


...... Phil

 

[Phil Allison]

Peter Wanker dribbled:

=================:

Just to make it clear, these are Acoustech Model X *Solid State* self-powered
electrostatic speakers, about two meters high (more than 6\') and just under 75 cm wide.

----------------------------------------------------------------------------------------

** The model was marketed briefly by Koss in *1965*.

Each speaker was bi-amped - at a time when most SS amps used Germanium transistors.
Each amplifier feeds an output transformer, to boost the voltage maybe 100 times.
If the HT ( 2kV at least) supply fails, an ES speaker goes silent.

Moisture and dust ingress destroys ES speakers over time.


...... Phil

 

[Peter W.]

a) All the transistors are silicon. The output devices are in-place are 2N4348 in a TO3 package. https://alltransistors.com/crsearch.php?mat=Si&struct=NPN&pc=120&ucb=140&uce=120&ueb=7&ic=30&tj=200&ft=0.8&hfe=15&caps=TO3
b) There are three (3) transformers: the main power transformer being one and verified as having no open coils and no internal shorts.
c) There are two (2) potted transformers commonly connected to the main board through a single eight (8) conductor plug (Cinch-Jones).
d) Of these two transformers, one appears to be HV only (two red silicon leads to the speaker).
e) The other has five (5) leads to the speaker, one of which is also red silicon. And that is the one that is floating as far as I can test.
f) The available schematic does NOT show a diagram of the potted transformers. If I had that, I would not be here.

Again, before I apply power for the first time in over ten years, I would like to understand what is connected to which and to explain the 7th speaker connection with no discernable \'\'other end\".

Peter Wieck
Melrose Park, PA

 

[Rob]

Peter W. <peterwieck33@gmail.com> wrote:

a) All the transistors are silicon. The output devices are in-place are 2N4348 in a TO3 package. https://alltransistors.com/crsearch.php?mat=Si&struct=NPN&pc=120&ucb=140&uce=120&ueb=7&ic=30&tj=200&ft=0.8&hfe=15&caps=TO3
b) There are three (3) transformers: the main power transformer being one and verified as having no open coils and no internal shorts.
c) There are two (2) potted transformers commonly connected to the main board through a single eight (8) conductor plug (Cinch-Jones).
d) Of these two transformers, one appears to be HV only (two red silicon leads to the speaker).
e) The other has five (5) leads to the speaker, one of which is also red silicon. And that is the one that is floating as far as I can test.
f) The available schematic does NOT show a diagram of the potted transformers. If I had that, I would not be here.

Again, before I apply power for the first time in over ten years, I would like to understand what is connected to which and to explain the 7th speaker connection with no discernable \'\'other end\".

Peter Wieck
Melrose Park, PA

I would recommend to first forget about those transformers and their
connections and focus on the power supply and amplifiers. Unless there
are blown fuses, the transformers are likely OK, but the power supplies
and amplifiers could suffer from bad caps or other component failure.

Likely best is to isolate the poweramp from the transformer (unplug it
and replace with a resistive load, like 50 ohms) and run the amplifiers
separately, watching their output on a \'scope.
Check for DC setpoint of the amplifiers and see if they output the audio.
When that is OK, connect the transformers and measure on their output
(being careful because of the HV)

 

[Rob]

Peter W. <peterwieck33@gmail.com> wrote:

a) All the transistors are silicon. The output devices are in-place are 2N4348 in a TO3 package. https://alltransistors.com/crsearch.php?mat=Si&struct=NPN&pc=120&ucb=140&uce=120&ueb=7&ic=30&tj=200&ft=0.8&hfe=15&caps=TO3
b) There are three (3) transformers: the main power transformer being one and verified as having no open coils and no internal shorts.
c) There are two (2) potted transformers commonly connected to the main board through a single eight (8) conductor plug (Cinch-Jones).
d) Of these two transformers, one appears to be HV only (two red silicon leads to the speaker).
e) The other has five (5) leads to the speaker, one of which is also red silicon. And that is the one that is floating as far as I can test.
f) The available schematic does NOT show a diagram of the potted transformers. If I had that, I would not be here.

Again, before I apply power for the first time in over ten years, I would like to understand what is connected to which and to explain the 7th speaker connection with no discernable \'\'other end\".

Peter Wieck
Melrose Park, PA

I would recommend to first forget about those transformers and their
connections and focus on the power supply and amplifiers. Unless there
are blown fuses, the transformers are likely OK, but the power supplies
and amplifiers could suffer from bad caps or other component failure.

Likely best is to isolate the poweramp from the transformer (unplug it
and replace with a resistive load, like 50 ohms) and run the amplifiers
separately, watching their output on a \'scope.
Check for DC setpoint of the amplifiers and see if they output the audio.
When that is OK, connect the transformers and measure on their output
(being careful because of the HV)

 

[Peter W.]

I would recommend to first forget about those transformers and their
connections and focus on the power supply and amplifiers. Unless there
are blown fuses, the transformers are likely OK, but the power supplies
and amplifiers could suffer from bad caps or other component failure.

Likely best is to isolate the poweramp from the transformer (unplug it
and replace with a resistive load, like 50 ohms) and run the amplifiers
separately, watching their output on a \'scope.
Check for DC setpoint of the amplifiers and see if they output the audio.
When that is OK, connect the transformers and measure on their output
(being careful because of the HV)

a) No blown fuses. Fuses are not new.
b) I have not yet plugged them in. I am generally resistant to plugging in a stranger until I understand its functions and antecedents. If I were to have a diagram of the potted transformers, I would be much more sanguine about applying power.
c) I can isolate the potted transformers from the rest of the system. Theoretically, I could then determine if the amps are passing audio.
d) But I would REALLY like to know what is going on inside all that elephant snot....
e) And the main power transformer shows no shorted windings or internal shorts, and the secondary windings make sense as to the schematic.

Peter Wieck
Melrose Park, PA

 

[Rob]

Peter W. <peterwieck33@gmail.com> wrote:

I would recommend to first forget about those transformers and their
connections and focus on the power supply and amplifiers. Unless there
are blown fuses, the transformers are likely OK, but the power supplies
and amplifiers could suffer from bad caps or other component failure.

Likely best is to isolate the poweramp from the transformer (unplug it
and replace with a resistive load, like 50 ohms) and run the amplifiers
separately, watching their output on a \'scope.
Check for DC setpoint of the amplifiers and see if they output the audio.
When that is OK, connect the transformers and measure on their output
(being careful because of the HV)

a) No blown fuses. Fuses are not new.
b) I have not yet plugged them in. I am generally resistant to plugging in a stranger until I understand its functions and antecedents. If I were to have a diagram of the potted transformers, I would be much more sanguine about applying power.

Power them up with a light bulb in series with the mains.

I have made a special wiring harness with a male and female mains
plug and a standard E27 lamp socket that allows me to insert a
light bulb (40, 60, 100W) in series with any device, to reduce the
maximal current.
When available, use a VARIAC to slowly increase the voltage and
have a multimeter attached to some point of interest (e.g. the DC
output of the powersupply) to see what happens.

 

[Rob]

Peter W. <peterwieck33@gmail.com> wrote:

I would recommend to first forget about those transformers and their
connections and focus on the power supply and amplifiers. Unless there
are blown fuses, the transformers are likely OK, but the power supplies
and amplifiers could suffer from bad caps or other component failure.

Likely best is to isolate the poweramp from the transformer (unplug it
and replace with a resistive load, like 50 ohms) and run the amplifiers
separately, watching their output on a \'scope.
Check for DC setpoint of the amplifiers and see if they output the audio.
When that is OK, connect the transformers and measure on their output
(being careful because of the HV)

a) No blown fuses. Fuses are not new.
b) I have not yet plugged them in. I am generally resistant to plugging in a stranger until I understand its functions and antecedents. If I were to have a diagram of the potted transformers, I would be much more sanguine about applying power.

Power them up with a light bulb in series with the mains.

I have made a special wiring harness with a male and female mains
plug and a standard E27 lamp socket that allows me to insert a
light bulb (40, 60, 100W) in series with any device, to reduce the
maximal current.
When available, use a VARIAC to slowly increase the voltage and
have a multimeter attached to some point of interest (e.g. the DC
output of the powersupply) to see what happens.

 

[Peter W.]

I have a very nice metered Variac. https://www.byan-roper.org/steve/steve-at-play/antique-electronics-and-2/heathkit-ip-5220-variable.html like that.

Again: I do not understand clearly what is going on or should be going on. And all I have is the nameplate in terms of anticipated current. I am trying to get to where I can align the actual current to the anticipated current before I apply power.

Related: I just heard from David Janzen, the son of the designer of these beasts, and still in the business. He is looking to see if he has a diagram of the potted trannys. That will be immensely helpful.

Peter Wieck
Melrose Park, PA

 

[Peter W.]

I have a very nice metered Variac. https://www.byan-roper.org/steve/steve-at-play/antique-electronics-and-2/heathkit-ip-5220-variable.html like that.

Again: I do not understand clearly what is going on or should be going on. And all I have is the nameplate in terms of anticipated current. I am trying to get to where I can align the actual current to the anticipated current before I apply power.

Related: I just heard from David Janzen, the son of the designer of these beasts, and still in the business. He is looking to see if he has a diagram of the potted trannys. That will be immensely helpful.

Peter Wieck
Melrose Park, PA

 

[Jeff Layman]

On 18/07/2021 21:15, Peter W. wrote:

Just to make it clear, these are Acoustech Model X *Solid State* self-powered electrostatic speakers, about two meters high (more than 6\') and just under 75 cm wide.

I have a very bad schematic from HiFi Engine that speaks to a shield. But its origin(s) and destination(s) are not clear.

This condition is extant on both (2x) speakers.

Any one out there who has had experience on these beasts? Any thoughts? If not, I will treat them as landfill and flog them as-is and with a very accurate description on the usual auction site, pick-up only. Otherwise, if there is hope, I am up for the work.

If you haven\'t already done so, is there any point in contacting Koss? I
can\'t see them having any spares from that time with which they could
charge an exorbitant repair fee, so maybe if they\'ve got the service
manual and/or circuit diagram, perhaps they\'d let you have a copy.

--

Jeff

 

[Phil Allison]

Peter Wanker is 100% NUTS !!
=========================

a) No blown fuses. Fuses are not new.
b) I have not yet plugged them in. I am generally resistant to plugging in a stranger until
I understand its functions and antecedents.

** How bizarre !


> If I were to have a diagram of the potted transformers, I would be much more sanguine about applying power.

** FFS why ???????

c) I can isolate the potted transformers from the rest of the system. Theoretically, I could then determine if the amps are passing audio.

** Really? What if the transformers are push pull output ?


> d) But I would REALLY like to know what is going on inside all that elephant snot....

** Where - inside you fat head ?


....... Phil

 

[Phil Allison]

Peter Wanker is 100% NUTS !!
=========================

a) No blown fuses. Fuses are not new.
b) I have not yet plugged them in. I am generally resistant to plugging in a stranger until
I understand its functions and antecedents.

** How bizarre !


> If I were to have a diagram of the potted transformers, I would be much more sanguine about applying power.

** FFS why ???????

c) I can isolate the potted transformers from the rest of the system. Theoretically, I could then determine if the amps are passing audio.

** Really? What if the transformers are push pull output ?


> d) But I would REALLY like to know what is going on inside all that elephant snot....

** Where - inside you fat head ?


....... Phil

 

[Phil Allison]

Peter Wanker hasLOST IT !!!

==================

Again: I do not understand clearly what is going on or should be going on.

** Hmmmm - nothing new there ....


> And all I have is the nameplate in terms of anticipated current.

** Then use that info.

> I am trying to get to where I can align the actual current to the anticipated current before I apply power.

** Not even faintly possible .



...... Phil

 

[Phil Allison]

Peter Wanker hasLOST IT !!!

==================

Again: I do not understand clearly what is going on or should be going on.

** Hmmmm - nothing new there ....


> And all I have is the nameplate in terms of anticipated current.

** Then use that info.

> I am trying to get to where I can align the actual current to the anticipated current before I apply power.

** Not even faintly possible .



...... Phil