A client brought in a late 70s (pull boost) DR that he got cheap because it sounded horrible. It had been hot rodded in a really bad way, after someone else, presumably years before, had blackfaced it.
Anyway, the tremolo circuit had been oddly modified at some point. If you look at the picture, you can see I drew two red circles. The lead from the Intensity pot was moved to the bias connection at the power tube grid load resistors--and the original bias connection is still there, too.
Also, a 0.1 mF cap had been soldered between the 10M resistor and ground at the side of the trem bug.
I think this was an attempt to convert it to bias modulating trem, but in the late DRs, this is death to the power tubes, as they are run really hot to bring the plate voltages down. Seems to me that when the trem cuts them off the plate voltage will spike way over 450VDC.
My guess is that the extra cap was an attempt to quiet the thump the trem induces into the signal with this mod.
Has anyone seen this sort of thing before?
Oddly modded Deluxe Reverb tremolo
Moderators: pompeiisneaks, Colossal
Oddly modded Deluxe Reverb tremolo
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Rich Gordon
www.myspace.com/bigboyamplifiers
"The takers get the honey, the givers get the blues." --Robin Trower
www.myspace.com/bigboyamplifiers
"The takers get the honey, the givers get the blues." --Robin Trower
Re: Oddly modded Deluxe Reverb tremolo
That seems to be a ill considered way to implement 'bias vary' trem, as the variation in 'bias' will only be between normal and hot, rather than oscillating around normal?
My band:- http://www.youtube.com/user/RedwingBand
Re: Oddly modded Deluxe Reverb tremolo
I agree. In the few amps that used bias-vary trem, the intensity pot lead was the source of the bias voltage. I'm going to restore the thing to normal tonight.
With so many years/owners in them, you just never know what you're going to find in an old Fender like this. For example, the trem wasn't affecting the sound at all when I got it. I checked the bias (someone had previously put the 1Ohm Rs on the cathodes), and the power tubes were drawing only 7 mA! Once I dialed the bias up, the trem began to work, but it thumps. But since the later Silverface DRs had beefed up PTs for more headroom, letting the plate voltages run up so high will kill the 6V6s.
After undoing the other stupid mods in the amp and taking out the ridiculous boost circuit, the thing is incredibly sweet sounding. Given that he spent only $300 on it, I'd say he got a great deal!
On mod I will do, though, is to replace the boost footswitch jack with a stereo (TRS) 1/4" jack and jumper over the verb/trem connections from the RCA footswitch jacks. this will allow the verb/trem to be footswitched with a more modern switch if so desired.
With so many years/owners in them, you just never know what you're going to find in an old Fender like this. For example, the trem wasn't affecting the sound at all when I got it. I checked the bias (someone had previously put the 1Ohm Rs on the cathodes), and the power tubes were drawing only 7 mA! Once I dialed the bias up, the trem began to work, but it thumps. But since the later Silverface DRs had beefed up PTs for more headroom, letting the plate voltages run up so high will kill the 6V6s.
After undoing the other stupid mods in the amp and taking out the ridiculous boost circuit, the thing is incredibly sweet sounding. Given that he spent only $300 on it, I'd say he got a great deal!
On mod I will do, though, is to replace the boost footswitch jack with a stereo (TRS) 1/4" jack and jumper over the verb/trem connections from the RCA footswitch jacks. this will allow the verb/trem to be footswitched with a more modern switch if so desired.
Rich Gordon
www.myspace.com/bigboyamplifiers
"The takers get the honey, the givers get the blues." --Robin Trower
www.myspace.com/bigboyamplifiers
"The takers get the honey, the givers get the blues." --Robin Trower
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Stevem
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Re: Oddly modded Deluxe Reverb tremolo
I do not know why folks do trem mods like that ?
I get asked a lot to slow the trem down a lot of times by Rhodes piano players or swamp rockers and kicking up the 3 caps in the osc circuit gets that done quick!
I get asked a lot to slow the trem down a lot of times by Rhodes piano players or swamp rockers and kicking up the 3 caps in the osc circuit gets that done quick!
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: Oddly modded Deluxe Reverb tremolo
Last night I got the tremolo completely squared away by restoring the connections to normal. I cured the ticking by gathering up all the leads to the trem tube and moving them away from V4. I zip tied them up to the filament leads. Now the tremolo works and sounds great.
Folks like Gerald Weber who say the later CBS amps have crappy lead dress were certainly right about this one. Changing the dress certainly helped this amp work better.
Folks like Gerald Weber who say the later CBS amps have crappy lead dress were certainly right about this one. Changing the dress certainly helped this amp work better.
Rich Gordon
www.myspace.com/bigboyamplifiers
"The takers get the honey, the givers get the blues." --Robin Trower
www.myspace.com/bigboyamplifiers
"The takers get the honey, the givers get the blues." --Robin Trower