OP
marshalltsl
Well-Known Member
I'm sorry Brother. It's not my amp. My friend don't want fix It. He said It's cheapest buy a reverb pedal.
JCM900 reverb tank
- Thread starter marshalltsl
- Start date
OP
marshalltsl
Well-Known Member
Hi all.
I have had severe health problems but fortunately I'm recovered. Recently a friend came to see how I was doing and told me that his JCM900 was no longer working. I follow this thread because it is this JCM900. No IC was replaced. A reverb pedal was used in the effects loop.
Today I took a look on It. No sound. No noises. No blow fuses. All looks solid on It. I tryed a guitar on effects loop return jack. A good preamp tube on all preamp sockets. I tested HT and bias voltages on power tubes. I test ohms on effects loop stereo pot. Still no sound.
Tomorrow I'll have more time to find out what happen. Could be an output transformer?
No signal on power tubes? Does anyone know what the hell could happen?
Some help is appreciated.
Thanks
I have had severe health problems but fortunately I'm recovered. Recently a friend came to see how I was doing and told me that his JCM900 was no longer working. I follow this thread because it is this JCM900. No IC was replaced. A reverb pedal was used in the effects loop.
Today I took a look on It. No sound. No noises. No blow fuses. All looks solid on It. I tryed a guitar on effects loop return jack. A good preamp tube on all preamp sockets. I tested HT and bias voltages on power tubes. I test ohms on effects loop stereo pot. Still no sound.
Tomorrow I'll have more time to find out what happen. Could be an output transformer?
No signal on power tubes? Does anyone know what the hell could happen?
Some help is appreciated.
Thanks
Last edited:
D
Deleted member 1331
Guest
Tank cable could be shorted out or tank dead. Easy to just replace tank and see.
OP
marshalltsl
Well-Known Member
Reverb tank it's ok. The issue on reverb It's IC3 reverb Drive/return or IC7 reverb control. Reverb cables are ok. If these ICs are completely broken, could the amplifier stop working?
Could be IC8?
Last edited:
D
Deleted member 1331
Guest
I am sorry I did not read completely enough. I thought you had sound sans reverb. I am too dumb to further advise!
Amp Mad Scientist
Ambassador of Heresy
Pull out the power tubes.
Connect DC voltmeter black probe to chassis.
Turn power on, leave standby in "warm-up" position.
Do not turn standby to operate position....
Connect red probe to pin 5 of output tube socket. What is the DC voltage?
Test DC voltage on pin 5 of all output tube sockets. Note the readings.
Set meter for AC volts.
Connect red probe to pin 2 of output tube socket, what is the voltage reading?
Connect red probe to pin 7 of output tube socket,what is the voltage reading?
Set meter to DC volts.
Turn standby switch to "operate"position.
What is the voltage reading of pin 3 on each output tube socket?
What is the voltage reading of pin 4 on each output tube socket?
Amp Mad Scientist
Ambassador of Heresy
Plug a guitar into the effects return, turn up the master volume, get any sound?
OP
marshalltsl
Well-Known Member
Hi.
No sound.
Hi.
I tryed with onother one. No sound.
Thank you so much guys. I apreciated It.
OP
marshalltsl
Well-Known Member
Hi.
I'll report mesurament voltages. I have Bias 34mA per tube. I didn't check pin 2 and 7. I will.
Thank you for help.
D
Deleted member 1331
Guest
Sorry to butt in again. Have you checked to make sure fuse is not blown?
Amp Mad Scientist
Ambassador of Heresy
Follow the measurements in post 26, and we can find out what's wrong.
Do you have a voltmeter?
Do you have a voltmeter?
OP
marshalltsl
Well-Known Member
Yeah. I checked all external fuses (5X20mm). I had HT on It.
Amp Mad Scientist
Ambassador of Heresy
What is the DC VOLTAGE on pin 5?
Don't do the tests with the tubes installed. Take the tubes out.
OP
marshalltsl
Well-Known Member
Yes. I will report It this afternoon. I know that my stupid friend used It with a 4 ohm cabinet into 16 ohms output.
OP
marshalltsl
Well-Known Member
I will. Thank you.
Amp Mad Scientist
Ambassador of Heresy
It may be the low voltage power supply...
Amp Mad Scientist
Ambassador of Heresy
"...I know that my stupid friend used It with a 4 ohm cabinet into 16 ohms output."
Some friend. Is friend paying for the output transformer and power tubes?
Some friend. Is friend paying for the output transformer and power tubes?
OP
marshalltsl
Well-Known Member
I aware him many time.I know him many times. I warned him not to do it
Amp Mad Scientist
Ambassador of Heresy
I often wanted to invent some kind of stupid preventer for tube amps...
Cause no matter how many times you tell people "don't do this...." they go right ahead and do it anyway.
Cause no matter how many times you tell people "don't do this...." they go right ahead and do it anyway.