Ampeg B500DR bass head solid state

gcb34 · 1st December 2011, 12:09 PM

First off thanks for any help you can offer. I have a Ampeg B500DR bass amp that won't get put out any bass guitar sound. When I turn up the volume the fuzz gets louder but no signal output. There is a relay I was tapping on and after a few taps I resistor in the power section fried. I attached the block diagram but could really use the schematics if anyone out there has them.

indianajo · 1st December 2011, 06:27 PM

What does the DVM (volt-ohmmeter) say the speaker leads read on the low ohms scale? Should be 4 ohms or above. Calibrate the meter with a known resistor, when meter batteries go weak this is the first scale to read the wrong numbers.
If that is okay, how old is the amp? Does it have IC's on the heat sink or Transistors. How old are the electrolytic capacitors? (25 years is too long).

gcb34 · 3rd December 2011, 01:28 PM

Transistors on the heat sink the unit is 18 y.o.

indianajo · 3rd December 2011, 06:15 PM

Well, if your speaker or wires are not messed up, (test above) check to see if there is DC coming out of the speaker hot terminal on and idle. If so, one or more output transitors are bad. Then if none of that, check your power supplies that they are about 80% of the capacitor rail voltage. Checking rail voltage while playing into 4 ohm resistor (watt rating >amp rating) would be a better test.

gcb34 · 3rd December 2011, 09:58 PM

The speaker and wires are good. The weird thing is when you turn up the volume you can here it increase but nothing from the bass guitar comes out.

gcb34 · 3rd December 2011, 10:29 PM

I plugged a preamp in the poweramp input and did get sound.

indianajo · 4th December 2011, 08:11 PM

If you take any of the measurements I suggested, I will comment about the results.

1st December 2011, 06:27 PM	#2
indianajo diyAudio Member Join Date: Jan 2010 Location: Jeffersonville, Indiana USA	What does the DVM (volt-ohmmeter) say the speaker leads read on the low ohms scale? Should be 4 ohms or above. Calibrate the meter with a known resistor, when meter batteries go weak this is the first scale to read the wrong numbers. If that is okay, how old is the amp? Does it have IC's on the heat sink or Transistors. How old are the electrolytic capacitors? (25 years is too long). __________________ Dynakit ST70, ST120, PAS2,Hammond H182(2 ea),H112,A100,10-82TC,Peavey CS800S,SP2-XT's, T-300 HF Projs, Steinway console, Herald RA88a mixer, Wurlitzer 4500

3rd December 2011, 06:15 PM	#4
indianajo diyAudio Member Join Date: Jan 2010 Location: Jeffersonville, Indiana USA	Well, if your speaker or wires are not messed up, (test above) check to see if there is DC coming out of the speaker hot terminal on and idle. If so, one or more output transitors are bad. Then if none of that, check your power supplies that they are about 80% of the capacitor rail voltage. Checking rail voltage while playing into 4 ohm resistor (watt rating >amp rating) would be a better test. __________________ Dynakit ST70, ST120, PAS2,Hammond H182(2 ea),H112,A100,10-82TC,Peavey CS800S,SP2-XT's, T-300 HF Projs, Steinway console, Herald RA88a mixer, Wurlitzer 4500

4th December 2011, 08:11 PM	#7
indianajo diyAudio Member Join Date: Jan 2010 Location: Jeffersonville, Indiana USA	If you take any of the measurements I suggested, I will comment about the results. __________________ Dynakit ST70, ST120, PAS2,Hammond H182(2 ea),H112,A100,10-82TC,Peavey CS800S,SP2-XT's, T-300 HF Projs, Steinway console, Herald RA88a mixer, Wurlitzer 4500

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3rd December 2011, 01:28 PM	#3
gcb34 diyAudio Member Join Date: Jan 2008	Transistors on the heat sink the unit is 18 y.o.

3rd December 2011, 09:58 PM	#5
gcb34 diyAudio Member Join Date: Jan 2008	The speaker and wires are good. The weird thing is when you turn up the volume you can here it increase but nothing from the bass guitar comes out.

3rd December 2011, 10:29 PM	#6
gcb34 diyAudio Member Join Date: Jan 2008	I plugged a preamp in the poweramp input and did get sound.

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