The Benson 300 I'm working on is #32, it has reverb and tremolo but no distortion circuit. As reported to me by the owner, last year Ron Benson replaced the A/C cord with a modern 3 wire version and replaced the volume control input jack #2 with a bight switch but it does not seem to do much at all (it's the big red button where the volume control use to be on the panel). The tremolo makes a loud motor boating sound when engaged. The speed and intensity controls work. I replace the old RCA 12AX7 with a known-good new tube and it make the motor boat sound a little louder but did not stop it. Any ideas about how to repair the trem circuit?
Thanks for your help.
Benson 300
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sixstringer
- Posts: 186
- Joined: Wed Feb 03, 2010 11:13 am
- Location: SoCal
Benson 300
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Re: Benson 300
Interesting amp!
Poor trem performance could certainly be caused by the ancient electrolytics.
Poor trem performance could certainly be caused by the ancient electrolytics.
I build and repair tube amps. http://amps.monkeymatic.com
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Stevem
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Re: Benson 300
X2 on ALL the lytics! Yup even all those blue ones!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Benson 300
So it uses a light bulb and photocell for the tremolo?
Sort of like the Fender bug but not shrink wrapped.
Sort of like the Fender bug but not shrink wrapped.
Tom
Don't let that smoke out!
Don't let that smoke out!
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sixstringer
- Posts: 186
- Joined: Wed Feb 03, 2010 11:13 am
- Location: SoCal
Re: Benson 300
That's correct, the lamp and photo cell are in the tremolo circuit, I'm thinking now that the tremolo was working when i received the amp. It was weak, but it worked, now that's out of the cabinet, it just make the popping, motor boat sound. Maybe the photocell is overloaded with ambient light while out of the cabinet? I'll test it in the dark.....
Did Gibson use this sort of circuit for tremolo?
Thanks for your help and advice.
Did Gibson use this sort of circuit for tremolo?
Thanks for your help and advice.
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sixstringer
- Posts: 186
- Joined: Wed Feb 03, 2010 11:13 am
- Location: SoCal
Re: Benson 300
With further checking, it seems that that motor boating sound only comes on when the reverb intensity is turned up, with the intensity set to zero, there is no motor boating, so maybe it is indeed an oscillation. Switching the reverb and tremolo on and off with the foot switch has no affect on the motor boating. The speed of the noise is controlled by the speed of the tremolo. The reverb works and would sound good if the oscillation was not on top of it. The tremolo also works, but it's not very strong, even with a new tube.
Your help is most appreciated.
Your help is most appreciated.