As the subject says, I have a Denon PMA 250 with an open circuit mains
transformer primary - no doubt the thermal protection has failed. Can
anyone tell me the secondary voltage?


RonUK


--
Lune Valley Audio
Public Address Systems
Hire Sales Maintenance
www.lunevalleyaudio.com

Ron(UK) wrote in message
...
As the subject says, I have a Denon PMA 250 with an open circuit mains
transformer primary - no doubt the thermal protection has failed. Can
anyone tell me the secondary voltage?


RonUK


--
Lune Valley Audio
Public Address Systems
Hire Sales Maintenance
www.lunevalleyaudio.com



Assuming you have tried excavating into the wrapping to find a th f and not
found it.

Is the secondary wire/s carried out to the terminals ?
Then measure diameter of the wire/s , measure DC resistance of wire/s and
1000Hz inductance, guesstimate the average diameter of turns and find wire
gauge to resistance table and isn't there a formula for the ratings of the
secondary then.

Failing that, try those measurements on some other known or powerable
similar transformer.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

On Jun 5, 10:37*am, "Ron(UK)" wrote:
As the subject says, I have a Denon PMA 250 with an open circuit mains
transformer primary - no doubt the thermal protection has failed. Can
anyone tell me the secondary voltage?

RonUK

--
Lune Valley Audio
Public Address Systems
Hire Sales Maintenancewww.lunevalleyaudio.com

Hmm. I just found a "datasheet" for a Denon PMA250SE. It quotes the
output power as 2x50W into 4 ohms. And I'm wondering: how feasible is
it to "reverse size" a power transformer based on an amp's output
rating? For example in this case, 2x50W = 100W x some_fudge_factor
(to account for losses, powering preamp circuitry, etc.), so maybe a
PT capable of outputting 150W (at a reasonably proper voltage) might
do the trick? Or is there some large loss or conversion factor I'm
ignoring?

"Ron(UK)" wrote in message
...
As the subject says, I have a Denon PMA 250 with an open circuit mains
transformer primary - no doubt the thermal protection has failed. Can
anyone tell me the secondary voltage?


RonUK


--
Lune Valley Audio
Public Address Systems
Hire Sales Maintenance
www.lunevalleyaudio.com

If you can't get a definitive figure for the secondary voltage, how about
the old 70% of the main filter caps' rated voltage, times 0.707
guesstiformula ?

So, for instance, 63v rated caps, times 70% = about 44v, times 0.707 =
about 30v RMS. As for current rating, take output stage efficiency at say
50% so for total output power of 50 watts per channel, stage input power
around 200 watts. With 88v of supply across it, that's around 2.3 amps.

30-0-30 at 2.5 amps sounds reasonable. Just as a matter of interest Ron, why
not a 'genuine' replacement ?

Arfa

Arfa Daily wrote:
"Ron(UK)" wrote in message
...
As the subject says, I have a Denon PMA 250 with an open circuit mains
transformer primary - no doubt the thermal protection has failed. Can
anyone tell me the secondary voltage?


RonUK


--
Lune Valley Audio
Public Address Systems
Hire Sales Maintenance
www.lunevalleyaudio.com

If you can't get a definitive figure for the secondary voltage, how about
the old 70% of the main filter caps' rated voltage, times 0.707
guesstiformula ?

That`s what I`ll do, I was just hoping someone had a service manual to hand.

So, for instance, 63v rated caps, times 70% = about 44v, times 0.707 =
about 30v RMS. As for current rating, take output stage efficiency at say
50% so for total output power of 50 watts per channel, stage input power
around 200 watts. With 88v of supply across it, that's around 2.3 amps.

It`s actually rated at 30 watts p/c, the smoothers are 50 volt


30-0-30 at 2.5 amps sounds reasonable. Just as a matter of interest Ron, why
not a 'genuine' replacement ?

£115+vat is why not The amp's worth about a tenner
Cheers

Ron

"Ron(UK)" wrote in message
...
As the subject says, I have a Denon PMA 250 with an open circuit mains
transformer primary - no doubt the thermal protection has failed. Can
anyone tell me the secondary voltage?

**I only have a manual for a PMA350-II. It is rated at 50 W/ch. Secondary
Voltage is rated 34-0-34. I reckon 30-0-30 sounds about right for your amp.
I had the same problem with a Denon a couple of months back. Bloody potted
toroidals!


--
Trevor Wilson
www.rageaudio.com.au

Trevor Wilson wrote:
"Ron(UK)" wrote in message
...
As the subject says, I have a Denon PMA 250 with an open circuit mains
transformer primary - no doubt the thermal protection has failed. Can
anyone tell me the secondary voltage?

**I only have a manual for a PMA350-II. It is rated at 50 W/ch. Secondary
Voltage is rated 34-0-34. I reckon 30-0-30 sounds about right for your amp.
I had the same problem with a Denon a couple of months back. Bloody potted
toroidals!


Cheers for that, it`s about what I figured using the 70% 'rule'

Ron(UK)