Peavey MP400 power xformer

[Davo]

Hi guys,

Is anybody familiar with the MP400 PA?

I'm looking to replace the power tranny and am looking for a voltage on the secondaries.

Thanks!

 

[JohnRoberts]

Hi guys,

Is anybody familiar with the MP400 PA?

I'm looking to replace the power tranny and am looking for a voltage on the secondaries.

Thanks!

Besides the voltages on the schematic you posted?

JR

 

[Davo]

I'm seeing 120 on the primaries and then it looks like +/-33v on the secondaries....  bit tough to read

Thanks!

 

[psych60s]

Take care of the VA rating of the transformer you will install, too.

 

[JohnRoberts]

Have you tried Peavey service?

JR

 

[Khron]

With only one pair of output transistors, it won't be able to handle a whole lotta power without burning up anyway. 
Even the datasheets for the 2SA1941 / 2SC5198 say "Suitable for use in 70-W high fidelity audio amplifier’s output stage".

I'd reckon something in the region of 100VA or so would be plenty (if not even a slight bit "overkill").
+/-33VDC rails would need a 2x23VAC secondary; 2x24VAC, or 48V center-tapped is more "standard" (ie. easier to find).

Take care of the VA rating of the transformer you will install, too.

 

[psych60s]

With only one pair of output transistors, it won't be able to handle a whole lotta power without burning up anyway. 
Even the datasheets for the 2SA1941 / 2SC5198 say "Suitable for use in 70-W high fidelity audio amplifier’s output stage".

I'd reckon something in the region of 100VA or so would be plenty (if not even a slight bit "overkill").
+/-33VDC rails would need a 2x23VAC secondary; 2x24VAC, or 48V center-tapped is more "standard" (ie. easier to find).

You're right, it is not a monster amp and size of the new transformer is something to verify too.

 

[Davo]

Awesome, thanks guys, I appreciate the replys!!

 

[WA2BXY]

The transformer on mine has an open primary fused thermal protection link. I'm guessing either the 20 watt drivers shorted (obselete for 5 years) or the 100 watt power transistors gave out. One of them is obsolete, also. My verdict: scrap it.

 

[JohnRoberts]

The transformer on mine has an open primary fused thermal protection link. I'm guessing either the 20 watt drivers shorted (obselete for 5 years) or the 100 watt power transistors gave out. One of them is obsolete, also. My verdict: scrap it.

The MP400 was Peavey's entry level (first) topbox powered mixer. As I recall they were pretty popular, packaged with some small 2 way speaker systems.

Have you tried contacting Peavey's customer service?

If the transformer has an open primary it is toast (not user serviceable). New comparable entry level top box units are not that expensive, while shipping cost back and forth to get a broken one repaired could be significant.

There are probably sundry power transformers out in the world that might be substituted, if you are willing to invest some time tinkering.

JR

 

[tkaz]

I have a Peavey Classic 30 where the thermal fuse died. I unwrapped the transformer enough to get to it and removed it.
Still working fine after 10+ years.

 

[JohnRoberts]

I have a Peavey Classic 30 where the thermal fuse died. I unwrapped the transformer enough to get to it and removed it.
Still working fine after 10+ years.

I hope you at least replaced it with another thermal fuse...

The safety agencies don't add those for chuckles.

If transformer primary side insulation breaks down, it could energize the chassis...

JR

 

[tkaz]

Hopefully the fuse blows quickly in that case. I've never had that happen even with 70 year old amps.
Unless transformers are not made as well now?

 

[JohnRoberts]

Hopefully the fuse blows quickly in that case. I've never had that happen even with 70 year old amps.
Unless transformers are not made as well now?

It depends on how the insulation fails... winding to winding shorts (shorted turns) should trip a fuse-breaker. A winding to core/chassis short could energize the chassis. In a properly ground bonded outlet that should also trip the breaker. In the real world bad things could happen.

If you are going to play fast and loose with human safety, you can buy GFCI outlet strips that will trip before dangerous amounts of mains current escape into the wild.

JR

PS: Many people who should know better suffer harm from depending on their own personal anecdotal experience. Safety agencies operate from the collective experience of all product failures that cause human harm. UL was a PIA to satisfy, but a worthwhile partner when SH__ happens. Peavey had UL sitting with us in court when we got sued by the family of an electrocuted guitar player (our product was exonerated, his house was condemned over dangerous wiring faults).

 

[tkaz]

Good advice. I will follow that in future.