Rockmaster preamp power transformer?

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wireman75
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Rockmaster preamp power transformer?

Post by wireman75 » Sat Jul 22, 2017 12:18 pm

Hi guys, One of my Rockmaster preamp's seems to need a power transformer. Looking for info on where to find the correct replacement.

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Pappy B
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Re: Rockmaster preamp power transformer?

Post by Pappy B » Sat Jul 22, 2017 2:12 pm

Call, not email, call Peavey. If they don't have it I bet they can advise you on a replacement. Make sure you know it's bad before spending money on a new one.
The more I learn the more I realize how much I don't know.

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Enzo
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Re: Rockmaster preamp power transformer?

Post by Enzo » Sat Jul 22, 2017 4:39 pm

Agree.

And just how did you determine it needs one? I have no idea your experience, and transformers are the single most over-diagnosed part in a system. Transformers are the most reliable of parts, and so is the last thing on the failure list, while to novice techs it is usually the first thing on their list.

wireman75
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Re: Rockmaster preamp power transformer?

Post by wireman75 » Sat Jul 22, 2017 10:44 pm

My amp tech says the transformer is getting 20 volts on both taps. From my understanding the secondary tap should be 200+ volts. I will give peavey a call on Monday.

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Enzo
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Re: Rockmaster preamp power transformer?

Post by Enzo » Sun Jul 23, 2017 4:00 am

I am concerned with "both taps". That makes me think the reading was taken to ground. The high voltage winding is a single winding with no taps, including no center tap, so readings to ground are not valid. I don't know what B+ is in this amp, but with 500v caps I will guess 400v or more. And that means 300vAC from the transformer as a reasonable guess. That is measured wire to wire, NOT to ground.

On the other hand there is a low voltage winding that IS center tapped, and either end of that ought to measure around 20vAC. It provides power to the heaters and relays.

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Pappy B
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Re: Rockmaster preamp power transformer?

Post by Pappy B » Sun Jul 23, 2017 1:37 pm

I hope his meter was set to volts and not ohms when he took those readings.
The more I learn the more I realize how much I don't know.

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