Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on October 29, 2014, 03:16:28 am
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From Fender a bypass on the reverb tank to be used as Boost Trick
K
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Normally, people just put a jumper cable from the Reverb Send jack to the Reverb Return jack.
I tried it once on a '67 Princeton Reverb. Didn't sound too good to me.
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But using a tank bypass cable as you done you have the recovery triode in the path,
doing the connection like Fender the recovery triode is out of the equation, so the situation isn't the same
Franco
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I have a Princeton of a similar vintage that took the signal from the plate of the reverb driver and sent it via a switch to the grid of the mixer tube. At the time, I dubbed it the only good distortion idea that Fender ever had.
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There are more than one Princeton, which one ?
K
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I dunno. It's a silver face named "Princeton Reverb", but I don't see anything that identifies which one. If I saw the schematic, I would recognize it. Does the serial # do you any good?
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Is this ?
http://el34world.com/charts/Schematics/files/fender/Fender_princeton_rev_boostpedal.pdf (http://el34world.com/charts/Schematics/files/fender/Fender_princeton_rev_boostpedal.pdf)
K
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No, but if you took the pedal jack out of it, it would be it.
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This ?
http://el34world.com/charts/Schematics/files/fender/Fender_princeton_rev_II_boost.pdf (http://el34world.com/charts/Schematics/files/fender/Fender_princeton_rev_II_boost.pdf)
K
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I don't see it in the schematic library, but it is identical to that boostpedal one you asked about with the exception of the jack. Take an eraser and erase that jack while leaving everything else intact and you have it.
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OK, thanks
K
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Another trick not regarding overdrive but reverb I read about but haven't tried on Fender reverb amps is running the reverb return to your normal channel giving you tone control over your reverb. It may not be such a good idea becasue I haven't seen raves all over the net about it. Platefire
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Do you mean to the input of the normal channel ? Or before V1a to the TS "input"
Franco
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I think he means, get a RCA to 1/4 cord and go directally fron the tank output to the norm. ch. input.
Not for overdrive but tonal control.
Instead of the reverb knob for reverb normal channel controls adjust reverb.
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Normally, people just put a jumper cable from the Reverb Send jack to the Reverb Return jack.
I tried it once on a '67 Princeton Reverb. Didn't sound too good to me.
Thing I never got about that is:
wouldn't you need an 8 ohm load for the reverb's OT. Inotherwords send jack to return jack AND 8 ohm resistor across jack(tip to ground).
Don't you need that 8 ohm load(weither it be the tank or a resistor) for the reflected impeadence on the OT for the plate load of the 12AT7?
with tank the 12at7 see a 22.5K load
without tank (22.5K/8)*220K=618.75K load
I wonder if you just took an RCA cable and spliced an 8 ohm resistor hot to ground and used that instead of the tank if it would work better than just a jumper??? If you notice on the 1st schematic the tank is still connected to the OT, but with a jumper it's not.
Another idea may be to use the switch to also change the 500pF cap for a thicker sound.
Disconnecting the 3M3/10pF might help too.
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What are we trying to achieve here?
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wouldn't you need an 8 ohm load for the reverb's OT. Inotherwords send jack to return jack AND 8 ohm resistor across jack(tip to ground).
Don't you need that 8 ohm load(weither it be the tank or a resistor) for the reflected impeadence on the OT for the plate load of the 12AT7?
You do if you want maximum power output from the 12AT7.
But you're just using it to deliver voltage amplification to overdrive a following stage. Loading for maximum power output isn't important.
Do a search for "maximum power or voltage transfer". You'll find maximum power transfer happens when output impedance of the source matches the input impedance of the load. But maximum voltage transfer happens when the load impedance is very much higher than the source impedance.