Vibroverb Reverb replace trem with overdrive

[Ed_Chambley]

I was asked if you could mod a Vibrolux Reverb aa964 removing the tremolo and using the available tube and pots to make an overdrive.  Since there are 2 pots available would they be useable and could you use the standard footswitch for turning it on and off?

Just some thoughts, ideas or if anyone has done this in a fender as I never have or even considered it until I was recently asked.  I remember in the 70 (i still have one) a thing that plugged into the reverb called an Ice Cube made an awful sounding overdrive and the reverb pot became your overdrive gain.  I have used the reverb circuit to make a overdrive, but never the tremolo.

I attached the schem and layout if someone wants to look.

Thanks in advance for your ideas.

[sluckey]

I was asked if you could mod a Vibrolux Reverb aa964 removing the tremolo and using the available tube and pots to make an overdrive.  Since there are 2 pots available would they be useable and could you use the standard footswitch for turning it on and off?

You could use the tube for an extra gain stage, although the socket location is not optimal. The tremolo pots would not be useful. You could use the foot switch IF you use it to control a relay that does the actual signal switching.

It would be much easier to just cascade the NORMAL preamp into the VIBRATO preamp and use an A/B switch.

[Ed_Chambley]

I was asked if you could mod a Vibrolux Reverb aa964 removing the tremolo and using the available tube and pots to make an overdrive.  Since there are 2 pots available would they be useable and could you use the standard footswitch for turning it on and off?

You could use the tube for an extra gain stage, although the socket location is not optimal. The tremolo pots would not be useful. You could use the foot switch IF you use it to control a relay that does the actual signal switching.

It would be much easier to just cascade the NORMAL preamp into the VIBRATO preamp and use an A/B switch.

That sounds like a much better idea as you would still have the tremolo and much less work.  I generally over-think initially.  I have done something similar using an EF86, but I had major problems with microphonics.  Turned out to be lead dress and not the tube.

Thanks, you have me thinking now.

[jim]

Ed--do the London Power pre-amp mod.  Man,  it is so easy and it sounds fantastic.  Your Fender chime is totally unmolested and the overdrive is very harmonic and focused. You need this:  http://www.londonpower.com/amp-mods/fender-preamp-mod  and this http://www.londonpower.com/channel-switcher/electronic-relay-kit or use his books to build the circuits if you have the parts.  I am doing this more often for Silverface owners as the vintage amp market has been mild the last few years.  The mod is totally reversible as no holes are drilled.  Yeah--you will use a good bit of coax and lead dress skills but it will work.  KOC's instructions are now very detailed and computer drawn (as opposed to his older hand drawn stuff).  Here is a picture from the last mod I finished on a Super Reverb. For this amp I perfboarded the switching circuit and utilized the old bias balance pot hole to secure it to the chassis.  The j-fet channel mutes are hanging on the clean volume and overdrive volume and drive pots. It is foot switchable.  You could use relays instead if you have the stuff on hand.  Its funny...the amp owner kid told me he wanted a "Two Rock" clean sound and a "David Gilmore" drive sound and I though no way but he was totally thrilled with his new amp.  Jim

[jim]

here is the pic.

[Ed_Chambley]

Thanks Jim, I have been looking for a reason to buy one of his books.  I know I have the parts.  I built this amp a couple of years ago, so I will not be molesting anything buy myself.

I looked inside a Fuch Overdrive and have had to opportunity to repair and have a 2 rock for a for a little while and upon inspection they are fender similar clean.  The fuch has a parallel tube that switches to series in overdrive.  2 rock change circuit a tad.

Anyway, thanks for the tip.

Willabe speaks highly of Kevin and the TUT series.  Why buy the fish when you can catch as many as you want.  Are both covered in TUT 1.  Do you thing just buying all the books at once is the way to go since it is cheaper?

This question is for anyone who has the TUT books.

[jim]

Buy "Modifying and Custom Building Electric Guitar Amps" first if you can't buy all of them.  They are all good--not exactly beach reading, very detailed and without hype. Sometimes it may be tough to find specific info because the volumes are a little disorganized.  I had a FUCHS ODS with white silicone slathered all over the preamp circuit but my amps sounds better regardless. And I can tweak the tone because I can.  I really have to put together a sound clip.....Jim 

[tubenit]

I'd try this.   I have used V1 as an OD tube before without oscillation issues.  I realized this seems backwards but I think it would be an easier way to mod the layout board.  I'd use shielded wire if you need to. Essentially, you only have two wires coming from and going to the OD; so shielding those should resolve any oscillation concerns, IMO.

Vibrato channel would be the "clean" & normal would be the overdrive.

(note the vibrato isn't shown because there wasn't room on the schematic page)

I want OD verbed and not reverb OD'd.  (reverb insertion point moved)  Note smaller cathode cap values in the vibroverb preamp to prevent the OD from being too muddy.

With respect, Tubenit

[Ed_Chambley]

I'd try this.   I have used V1 as an OD tube before without oscillation issues.  I realized this seems backwards but I think it would be an easier way to mod the layout board.  I'd use shielded wire if you need to. Essentially, you only have two wires coming from and going to the OD; so shielding those should resolve any oscillation concerns, IMO.

Vibrato channel would be the "clean" & normal would be the overdrive.

(note the vibrato isn't shown because there wasn't room on the schematic page)

I want OD verbed and not reverb OD'd.  (reverb insertion point moved)  Note smaller cathode cap values in the vibroverb preamp to prevent the OD from being too muddy.

With respect, Tubenit

Thanks Jeff, I was planning to make it switchable.  This looks like what was in my mind eye.  I do want to further investigate Kevin O'Conners concept and values as I have heard so much good stuff about it.  I have just gotten to the point where I can look at your drawings and not have to think about it a few days.

HBP told me about your amps and how quite they are.  Coming from him I would have to take your input very seriously.

Thanks for posting.

[tubenit]

Ed,

Here is how you can set up the layout board.  You can always use a terminal strip also IF you need to.

Note that I indicate a 50k trim pot with a 15k resistor to ground on the layout.  On the schematic, it simply shows a 39k to 47k range resistor to ground

BTW, I'd recommend trying either a 5751 or 12AY7 in the clean and then a 5751 in the OD position. I think you'll find a smoother tone in the overdrive and not as much grit/dirt.

With respect, Tubenit

[Ed_Chambley]

This is why I was asking about replacing the tremolo circuit initially.  I have already modded the amp and it is back with the owner as he needed it to play Saturday at a festival.  Cascade with an ABY switch worked well and sounded good.  Doesn't mean I do not want to be able to mod it this way.

We were both looking at this circuit from one of the schematics I had downloaded I and I thought inserting this and removing the tremolo would give a place for both pots.  Is the problem having the reverb prior?

The way the amp was originally the Vibrato channel was an AA964 and the normal was like the 6G16 Bright channel with the 350k with 70ohm tap treble (I had an original one, my last one and I wish I knew where to find some of original type).  In a 2 10's cab this was a cool arrangement, but he is not as vintage as I am and did not like the Brownface setup as well.

I say all this to ask if you were to build a multiple preamp amp and wanted to have Reverb, what would be the best insertion point for a Pentode OD?

On a side note, I tried your overdrive wired for Ef86/6267.  Good stuff.

Basically, the Fuchs Overdrive Supreme 30 with 4x 6v6 uses all 12ax7.  I do not care for the amps as the tone is too modern and the clean is harsh, but those are just preferences.  The idea of the amp I like.  I know it uses a belton reverb brick.

So is the best guideline for placing a overdrive in the amp the same a pedal board whereas dirt before modulation or is it best to use the clean signal in parallel with the OD to use for Modulation and insert both at the Phase inverter?

[tubenit]

OK, you gave more information that is important to know regarding the normal and vibrato preamps.

In any amp that has overdrive, I personally would try the insertion point for reverb to be right before going into the LTPI because I don't want reverb overdriven.

Regarding changing the vibrato section out to be an overdrive section?  Not sure if there would be oscillation issues there or not?  I think that's one of those "try it and see what happens things?". I think it might work?

With respect, Tubenit