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Amp repair help
Amp repair help
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Old 18th May 2006, 07:39 AM   #1
2SickBassist is offline 2SickBassist  United States
diyAudio Member
Join Date: May 2006
Default Amp repair help

Hey guys. Im new to the forum but I was hoping you guys could lead me in the right direction to fix this amp. Ok my girlfriend was given a Peavey Rage 158 Transtube amp that didnt work. After investigation, I realized that the power transformer was burnt up on one side. There was no power to the other side. So I replaced it with a transformer from radio shack (I know) to see if it mayb worked until I could get a better one. The back of the amp says that the original transformer put out 7.7v rms at 4 ohms and 15 watts. After hooking up the new transformer I tested it with a multimeter and got that it was running at 8v at around 4-4.5 ohms which should put out abt 14-16 watts.

Well after hooking everything up and powering the amp on, I used a computer for a test signal. The sound was very low even at full volume on the knob and was very distorted. Does anyone know why the amp is doing this? could I have measured the values on the multimeter wrong or is it more likely another problem? Any help/suggestions would be much appreciated. Thanks.
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Old 18th May 2006, 07:52 AM   #2
AndrewT is offline AndrewT  Scotland
Join Date: Jul 2004
Location: Scottish Borders
I think you have put in the wrong transformer.

Is it the mains transformer or an output transformer or something else?

Those figures you quoted sounded more like the amplifier output, not the transformer output.
regards Andrew T.
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Old 18th May 2006, 08:44 AM   #3
Enzo is offline Enzo  United States
diyAudio Member
Join Date: Sep 2004
Location: Lansing, Michigan
It is a small solid state practice amp, but it does actually sound pretty cool. The only transformer in it is the mains tranny. it is identical to the Blazer 158, except the Blazer has a small reverb added. Same board.

First, you are confused. On the rear panel it says 7.7vRMS into the 4 ohm speaker. That is not the transformer voltage, that is the voltage the amp puts out into the 4 ohm speaker load. That voltage across a 4 ohm speaker yields about 15 watts of audio.

Either call Peavey or email parts@peavey.com and request the schematic. Ther have been a few variations on the RAge, so make sure to include the entire name, meaning the Transtube and the 158. Even include your serial number if it is still on there.

Peavey is an extremely customer friendly company. They will email it back to you.

You can also order the proper power transformer from them. It will have the right voltages, and it will fit in the space where it belongs.

The transformer puts out about 20VAC, not 8, so I don't doubt it sounds bad. The main power rail in it will be +28VDC. The preamp is transistor, not op amps, and it runs on 25VDC. The stages use power supply derived bias voltages of 1.5v and 3vDC. None of those supplies will happen with an 8v transformer.

While the transformer might have just failed on its own, it is also possible that there is something else wrong in there - and that possible caused the transformer failure.

As with most all little practice amps, the most common failure is the TDA2040 power amp chip - it drives the speaker.
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