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i have a f-100 212 combo that i picked up used and the reverb doesn't work. if i physically shake the reverb tank the sound of the springs comes through the speakers but the is no reverb effect when playing guitar. it came with a accutronics 9AB2C1B tank that reads 212ohms at the output and 1ohm at the input. i also tried with a known working tank model # 9EB2A1B which reads 196ohms at output and 56ohms at input. with both i can make reverb like noises by shaking the tank but there is no effect when playing guitar through it. i like the amp and would like it even more if i could get the reverb to work. any help or suggestions are much appreciated. also i dont have the footswitch for the amp but im pretty sure the reverb should be on by default without a footswitch plugged in.
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You need to check the send cable first.
If that checks good, then the next item would be the send opamp.
Is it 'sending' a signal to the tank? (pin 7)
Here is a MEF link to the F-30 schematic.
Link: http://music-electronics-forum.com/t32143/ -
yea i've swapped the cables, with regular stereo rca cables, i got same thing. am i looking for a particular voltage at pin 7 or what? i only have a DMM not an oscilloscope or any thing.Comment
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A meter will do fine.
Look at the schematic.
The signal comes off of V3 through the .02uf capacitor.
From there it goes to the Master Volume and to the Reverb.
The Reverb signal is supposed to come out of Pin 7 of the drive opamp.
Set your meter to read Volts DC & measure Pin 7.
It should be zero or thereabouts.
If it is, send a signal into the amp & measure Pin 7 with your meter set to read Volts AC.
If there is not a signal then you need to back up.
The most likely culprit, other than a faulty IC, is the Jfet.
So measure the gate pin & see if is responding to the Reverb On/ Off switch. (Volts dc)Comment
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If the amp came with a tank that has a 1 ohm input coil, that may have damaged the drive ic. That circuit can't source enough power to drive the 8 ohm impedance of that tank.
Do as Jazz suggests and read the voltages on the ic pins and see if they make sense.Comment
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The correct tank should be 9BB3A1B. As 52 Bill said, the 9AB tank may have damaged the IC. Don't connect the 9AB tank to that amp any more. The 9EB tank should be ok for testing purposes.Originally posted by Enzo
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alright thanks for all the help. yea i didn't think it was the right tank but couldn't find what the right one should be. so i noticed that J175 RM has been removed, there are stumps where someone clipped the leads. would there be any good reason for this or should i definatly go ahead and replace it. pin 7 read 1 mV DC. what is the gate pin? also there is no reverb on/off switch would turning the reverb pot up or down produce the same effect?Comment
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J175 is used in the mute circuit.
It is a Jfet with a normally on resistance of 300 ohms.
It mutes the signal when a channel is changed.
The gate pin should sit at a minus voltage (keeping the Jfet off)
http://media.digikey.com/pdf/Data%20...x,MMBFJ17x.pdf
Someone was obviously in there already.
Did you try measuring the opamp pin #7 for a Vac signal coming out?
If there is nothing there then you need to replace the opamp.
With the jfet removed the circuit should still function.Comment
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