I need an audio output transformer for an NC-120, which I understand is
the same as the military RAO. I have also been told the NC-100 is the
civiliam model. The ROA-2 manual lists the transformer as 36000 ohms to
600 ohms but the NC-100 manual lists it as 5000 ohms to 500 ohms. Is
the 36000 a misprint? The transformer couples the 6V6 to the
loudspeaker. The National number on the transformer can I took out of
my NC-120 is CNA-30884
Thanks

Don wrote:
I need an audio output transformer for an NC-120, which I understand is
the same as the military RAO. I have also been told the NC-100 is the
civiliam model. The ROA-2 manual lists the transformer as 36000 ohms to
600 ohms but the NC-100 manual lists it as 5000 ohms to 500 ohms. Is
the 36000 a misprint? The transformer couples the 6V6 to the
loudspeaker. The National number on the transformer can I took out of
my NC-120 is CNA-30884
Thanks

Hi Don...

It appears to be the same transformer that is used in my RAO-3. The
specs in my manual are identical. The only thing I can figure is that
many shipboard radios were not designed for use with a loudspeaker.
The audio normally went to a distribution panel and was routed to
an amplifier located somewhere else on the ship. This ratio may be
necessary to limit the audio output from the receiver to prevent
over driving the headphones or external amplifier.

73, Roger

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"Don" wrote in message
oups.com...
I need an audio output transformer for an NC-120, which I
understand is
the same as the military RAO. I have also been told the
NC-100 is the
civiliam model. The ROA-2 manual lists the transformer as
36000 ohms to
600 ohms but the NC-100 manual lists it as 5000 ohms to
500 ohms. Is
the 36000 a misprint? The transformer couples the 6V6 to
the
loudspeaker. The National number on the transformer can I
took out of
my NC-120 is CNA-30884
Thanks

The NC-100 has a number of differences from the RAO, for
one thing is has 2 RF stages. The two use different output
tubes which may account for the different transformer. 36K
does sound like a rather high load impedance for a 6K6
though, more typical is around 10K. The only power output
spec I could find is for the headphone jack, which is
parallel with the speaker terminals, 0.3 watt, that's low
for a 6K6, more typical would be around 2 watts.


--
---
Richard Knoppow
Los Angeles, CA, USA

"Richard Knoppow" wrote in message
nk.net...

"Don" wrote in message
oups.com...
I need an audio output transformer for an NC-120, which I
understand is
the same as the military RAO. I have also been told the
NC-100 is the
civiliam model. The ROA-2 manual lists the transformer as
36000 ohms to
600 ohms but the NC-100 manual lists it as 5000 ohms to
500 ohms. Is
the 36000 a misprint? The transformer couples the 6V6 to
the
loudspeaker. The National number on the transformer can I
took out of
my NC-120 is CNA-30884
Thanks

The NC-100 has a number of differences from the RAO, for
one thing is has 2 RF stages. The two use different output
I mean the RAO has the extra RF stage.
tubes which may account for the different transformer. 36K
does sound like a rather high load impedance for a 6K6
though, more typical is around 10K. The only power output
spec I could find is for the headphone jack, which is
parallel with the speaker terminals, 0.3 watt, that's low
for a 6K6, more typical would be around 2 watts.


--
---
Richard Knoppow
Los Angeles, CA, USA

Thanks for the response. Will I run the risk the damaging other
components if I try an audio transformer with a 10,000 ohm primary and
an 8 ohm secondary?
Hi Don...

It appears to be the same transformer that is used in my RAO-3. The
specs in my manual are identical. The only thing I can figure is that
many shipboard radios were not designed for use with a loudspeaker.
The audio normally went to a distribution panel and was routed to
an amplifier located somewhere else on the ship. This ratio may be
necessary to limit the audio output from the receiver to prevent
over driving the headphones or external amplifier.

73, Roger

--
Remove tilde (~) to reply

Remember the USS Liberty (AGTR-5)
http://ussliberty.org/

Don wrote:
Thanks for the response. Will I run the risk the damaging other
components if I try an audio transformer with a 10,000 ohm primary and
an 8 ohm secondary?
Hi Don...

My tube manual lists the load impedance as 7600 ohms for a 6K6 with
250 volts on the plate. The 10k transformer will not provide full
output from the tube but should be substantially more than the
original transformer. No risk of damage to anything but your ears
if you plug headphones in with the volume turned up!

73, Roger


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http://ussliberty.org/

"Roger D Johnson" wrote in message
...
Don wrote:
Thanks for the response. Will I run the risk the damaging
other
components if I try an audio transformer with a 10,000
ohm primary and
an 8 ohm secondary?
Hi Don...

My tube manual lists the load impedance as 7600 ohms for a
6K6 with
250 volts on the plate. The 10k transformer will not
provide full
output from the tube but should be substantially more than
the
original transformer. No risk of damage to anything but
your ears
if you plug headphones in with the volume turned up!

73, Roger

There is some variation from manual to manual depending on
the exact operating conditions specified. For instance the
6K6 page from the RCA Tube Handbook at
http://www.pmillett.com/tubedata/HB-...t_2/6K6-GT.PDF

Shows three values of transformer load impedance:
For 100V on plate and screen grid, 12,000 Ohms for 0.35 Watt
at 11% THD
For 250V on plate and screen, 7600 Ohms for 3.4 Watts at 11%
THD
For 315V on plate and 250V on screen (maximum ratings), 9000
Ohms for 4x5 Watts at 11% THD

I don't see any voltages in the on-line handbook but they
should be easy enough to measure. In any case the
transformer impedance does not seem too critical. Check the
bias voltage to see what it is. You may want to change the
cathode resistor. The handbook gives the recommended bias
value.

Since the headphone jack is just paralleled across the
speaker terminals it might be useful to put a load resistor
across it when using high impedance phones.


--
---
Richard Knoppow
Los Angeles, CA, USA