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Vintage threads from the first ten years

Reverb on Normal Channel

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9/22/1999 2:01 PM
GaryP	Reverb on Normal Channel Hi Everyone, I'm sure this has been asked many times before, but how can I mod my SF Deluxe to get Reverb on to the Normal Channel as well? Thx

9/23/1999 5:19 PM

The is the way I do it:

Jumper pin6 of V1B to pin6 of V2B with a piece of insulated wire. The outputs of both preamp tubes will now go through the reverb circuit before reaching the phase inverter.

Both preamp tubes are supplied from the same B+ point in the power supply, so it's ok to connect the plates directly.

Remove the coupling cap (.047uf?) coming from the plate (pin6) of V1B. It's in series with a 220k signal summing resistor, whose other end connects to a similar 220k resistor on the component board. You can leave the resistor in place, open-ended, or remove it if you like. (I like to leave it in place for an easier return-to-stock wiring locator.)

If the sound seems brighter or thinner than before, you can exchange the loose .047uf coupling capacitor for the .022uf one connected to pin6 of V2.

Hope this helps.

9/23/1999 8:37 PM

quote:
"Remove the coupling cap (.047uf?) coming from the plate (pin6) of V1B"

I didn't remove that cap, just disconnect the wire. May it be a problem?

Thank you

Giacomo

9/23/1999 8:56 PM

The least amount of stray grid signal pickup will result by removing the wires and unused components. If you prefer to delete the wire, keep the .047uf cap on the board, then also be sure to remove the 220k resistor between the .047 and the other 220k resistor (which stays).

If you only disconnect the wire, but leave the cap & resistor hanging there open ended and connected to a grid, you have the makings of a pretty good antenna, which means hum pickup and possible oscillation.

9/24/1999 3:20 AM

Doc:

You can leave the resistor in place, open-ended, or remove it if you like. (I like to leave it in place for an easier return-to-stock wiring locator.)

Or you can bend the 220k resistor over and solder it in parallel to the other 220k resistor for a stronger signal going to the PI. (That tip is from the Dan Torres book of VG reprints.) I believe I have a scan of the appropriate pages on my site (something like "both_rev.gif"). Dan's instructions are a little bit different, but along the same lines I believe...

Thanks!

Steve Ahola

P.S. Although not confirmed by sufficient experimentation, I have felt that an unconnected cap (like the 0.047uF) will have some effect on the signal even though the circuit is not completed. The analogy that comes to mind would be an air chamber in house plumbing to eliminate the hammering noises when you turn a faucet on or off. It just seems like some of the signal goes into the cap enough to muddy the sound up a bit... (I *think* noticed the effect in a tone stack, where a very subtle change can make a difference that you can hear or feel. I doubt if you would notice it with the 0.047uF coupling cap. But maybe all of that was just the dreaded "Placebo Effect".)

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