Any ideas on mods for '63 Vibroverb reissue?

[ER]

I was looking at the tone lounge "odds and odds" page and he has a mod for adding gain at the expense of less reverb, well that sounds like just the ticket for my Vibroverb, I could use more gain and can't run the reverb above 2 without getting seasick.

The '63 RI curcuit looks a little different from what he describes and I couldn't figure out how to accompilsh this. Any other mod ideas?

See a related posting in the general topic forum under "the one that got away".

-Erik

[billyz]

I posted this earlier but it has disappeared ?

1. Changed the V1 cathode resistor to 820 ohms. one of my favorites, modest affect.
2. you can increase the Plate load resistor. ex. to 120K, 150K all the way to 220K and beyond. watch out this can get serious and I would leave the cathode at 1500.
3. change the "Middle " Resistor to 10K-25K . I like this one.
4. Change the negative feedback, increase the 10k resistor to say ,68K , + to 100K. or even disconnect it.

There are many other "mods" , but these don't require any circuit changes.

Do them one at a time, so you know what did what. I would not do them all or just a modest adjustment of each. For example. 1. do the 820 cathode. 2. Middle resistor to 10K. 3. NFB resistor to 47K.

I did not address the Reverb, you can try a 12at7 or even 12au7 tube to reduce the drive to the Verb . You change the mix resistor too. I never do this so I don't have an opinion what is most affective.

good luck and let us know what you end up with.

[ER]

Thanks Billy-

Those seem reasonable and easy, I'll give them a go.

-ER

[Darkbluemurder]

To tame the reverb, a 12AU7 (aka ECC82) is a good way to go. I did this to my Vibroverb 63 RI and it really helped. I no longer have the amp though.

[Andy Le Blanc]

my favorite is to rewire the recovery stage as a grounded grid, you ground
the grid and use the cathode as the input, it drops the gain and acts as an
electronic shield, tones not bad either.