Schem questions...

[trem]

...sorry, buy I have to ask.
1. Is the Reverb unit using a half wave rectifier.? I just see that one diode with the bypass cap across it.
2. What is V3B doing.?
Thank You

http://www.el34world.com/charts/Sche...b_sf_schem.pdf

[Enzo]

Yes, that is a half wave rectifier. There is no power amp dragging boo coo current from it, so it is sufficient.


V3b may be drawn kinda funny, but it is just a cathode follower driving the dry signal into the mix pot. That prevents the mix pot loading the input signal

[trem]

Great...Thanks.
Gotta ask just one more (maybe it is in Merlin's book, but I have your ear...) what exactly is that 0.002 cap across the recto diode doing.?
Thank You

[R.G.]

It's snubbing the "snap-off" that some junction rectifiers do. It helps suppress a squark of RF that can make the wires ring every time the diode turns off, and sound like buzzy hum. It would be better if it had a small resistor in series with it, but the cap itself helps some.

[trem]

Once Again.....Thank You

[isaac]

If it were me, I'd probably go with a schematic of the reverb circuit in a twin reverb, and then just make a couple changes to accommodate the differences of having it in a separate FX unit, instead of built in. It seems it would be easier. I assume that the earlier versions of this reverb unit, 50's (?) and 60's. Were simpler in design, and I wouldn't doubt they sounded better. As with a pretty good amount of silverface era stuff, that looks like it has a lot of unneeded stuff in it. Like a master volume twin with a pull boost. All that stupid crap..... Maybe I'm wrong, but I'd look for earlier designs. That looks too "new."

BUT if thats what you want, good luck building it, assuming you are building it... And post clips and photos.

[trem]

http://www.el34world.com/charts/Sche...EVERB_6G15.pdf

Hey Isaac -
Above is the "original".
I was just curious about some of the things I saw.
So here is another question then.....On the latter schem...there is (I think) a parallel dual-triode at the output...that the older schem does not have. I am wondering why that was Added/Needed.?
Thank You
btw...no, I am not building one (not yet anyway) I was just curious about some of the differences.

[isaac]

I would guess on the later one, that they needed another 12ax7 triode for the end, but didn't want to waste the second one, so they paralleled them, but there are also good things about paralleled triodes. They reduce output impedance by halp I think, and they reduce noise due to phase cancellation. I believe that's most of what they do, but you can read more on that anywhere. Looking at an original schem for the 6g15, I'll make some notes in a second.

In the old one, there is no triode to boost the signal right after the tone control, in the new one there is, and I assume they didn't want to waste a triode so they paralleled them, as stated above. Also, besides to boost the signal after the tone control, I assume that that last two triodes in parallel might help mix the signal after the mix pot a little bit.

If you ask me, I would only build the 6g15, for one because its much more like the ab763 type of reverb design which is simpler, and the fact that it is the original, I'm guessing it'll sound better than the later one with a zillion extra parts, and wires that seem to go there because they had nowhere else to put them...