I recently bought a Fender 1967 Showman head off Ebay. When I plugged it in the power was really weak, it didn't seem to have nearly the 85 watts its supposed to put out and the tone sounded thin. I drained the caps and started to check the chassis components. I couldn't find anything wrong. I was going to start with replacing all the caps but I then powered the head up to read the plate voltages. During this investigation I flicked on the standby switch to put the amp into operating mode but the amp did not come on at all this time, it stayed in standby. I toggled the standby switch rapidly, heard a pop and then nothing, the amp was now stuck in standby. I check the switch for continuity and realized it was open no matter the position. I replaced the standby switch and the amp has been working fine ever since. Full loud power and great Fender tone. The bright switches don't seem to do a whole lot but I assume that is due to the original capacitors on board. My question is, is it normal for a faulty standby switch to cause a amp to sound like it has now power? I use amplifier troubleshooting guides to fix tube amps and none of them lead me to check the standby switch for a low sound/power condition.
Faulty standby switch
- Thread starter AlwaysSD
- Start date
Re: Faulty standby switch
I would say:
Pop = yes
Low power = no
If the SB Switch was stuck in the On position...I do not see how the amp could work at all.....much less be ... thin, weak, low power, etc.
That is the whole point of the SB.
You say it works fine now...hard to argue with success as the say, but something still sounds fishy to me. :dunno:
I would say:
Pop = yes
Low power = no
If the SB Switch was stuck in the On position...I do not see how the amp could work at all.....much less be ... thin, weak, low power, etc.
That is the whole point of the SB.
You say it works fine now...hard to argue with success as the say, but something still sounds fishy to me. :dunno:
.......you would think the switch was either on or off.
Rich_S
HomeGrownToneBrewologist
Re: Faulty standby switch
Who knows what goes on with the fiddly little mechanical bits hidden inside that block of bakelite? (Full disclosure: I am an electrical engineer by trade. My first tendency in all troubleshooting scenarios is "blame it on the mechanical stuff.") The switch's ability to make a solid connection relies on spring tension, and when that goes, there could be an in-between state where it provides a poor, high-resistance contact. This would be the equivalent of adding a series resistor in the B+ string, lowering the overall B+ level and making it more "saggy".
In response to the previous answers, I disagree that the switch can cause the symptoms you heard. A good switch provides only two states, on and off. A failing switch can provide that "who knows?" state in between. As you found, a completely failed switch then provides only one state; in your case, off.
Who knows what goes on with the fiddly little mechanical bits hidden inside that block of bakelite? (Full disclosure: I am an electrical engineer by trade. My first tendency in all troubleshooting scenarios is "blame it on the mechanical stuff.") The switch's ability to make a solid connection relies on spring tension, and when that goes, there could be an in-between state where it provides a poor, high-resistance contact. This would be the equivalent of adding a series resistor in the B+ string, lowering the overall B+ level and making it more "saggy".
In response to the previous answers, I disagree that the switch can cause the symptoms you heard. A good switch provides only two states, on and off. A failing switch can provide that "who knows?" state in between. As you found, a completely failed switch then provides only one state; in your case, off.
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