Fender AB1263 Tremolux schematic needed

[Matthews Guitars]

More info on the amp: (Got to the shop this evening for a bit.)
Headshell tube chart shows
Model "TREMOLUX-AMP. AB763"
Production......#2

Code "OI" low to the right of Fender Musical Instruments (this shows 1965, October, which does not match the amp by serial number.)

Stamped chassis serial no. 05059 which falls into the blonde time period, 1963, 6G9 circuits.

Power transformer markings: TR-80 1052-6950 Can't identify
Output transformer markings: 125A-6A 606-246 Shows correct
Choke markings: 125C3A 606-3-06 Shows correctd


So...cabinet is 2 years younger than the chassis.
Board is 6G9-B or C. Chassis has AA763/AB763 features and 6G9 range serial number.

PT may not be original.

[sluckey]

All the tremolo circuit has been removed.

[pompeiisneaks]

As far as I know that board is original to this chassis. So...still thinking it might be transitional. Late 6G9-B/early AA763.

Does that seem possible? Would Fender have released an amp that was transitional between old and new versions?

Fender did this a ton. They used up the stock they had on hand but built other things inside them etc.

~Phil

[Matthews Guitars]

At the time that photo was made, I had not done much to the amp. I got it in a mostly stripped condition. I've since repopulated the board and completed MOST of the job of wiring it back into the chassis. It now has its tremolo circuit back, along with everything else.

I've got to wait a few more days to get the new tapped treble pots. Once that's done I'll be able to complete the circuit and test it. After sorting out any issues, I'll then take another sweep through it and make it as "correct" as i can, plus a couple sensible upgrades. (Such as using shielded cable for the input and volume lines.)

I'll also have to take out those original Whale dual 25 capacitors and check their values. I found an extra one in a bin of parts and measured it. It's supposed to be dual 25 uF and it read as dual 400 uF on two different cap meters. So clearly that's drifted a lot. Since those are used as cathode bypass capacitors it means the amp would pass every frequency from subsonics to bat sounds.

If they're still good, I'll use them. But if they've drifted more than 10 percent, I'll put in F&T dual 25s that I've got in stock.

[Matthews Guitars]

The status of the amp as of this evening: Excuse the mess, I get it running first, tidy it up later.

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[The Ballzz]

The status of the amp as of this evening: Excuse the mess, I get it running first, tidy it up later.


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You do make the rounds of all the cool guy hangouts, dontcha!

Nice To Se Ya,
Gene

[martin manning]

I've got to wait a few more days to get the new tapped treble pots...

Neither the AA or AB76 Tremolux layout shows tapped treble pots, but 6G9-B does. I guess that's consistent with the board being 6G9-B. You chassis doesn't have them, so I wonder what happened there. I don't know what you found for those, but if you want something that looks more like the original, here is a very close substitute: https://ampgarage.com/forum/viewtopic.p ... 34#p193334

[Matthews Guitars]

I found the correct tapped treble pots. Studio Sound Electronics has them. I ordered a few extras because that's what a prepared amp tech should do.

I got this amp, or what was left of it, in a pile of old projects that I "inherited" from my friend and local amp guru who died in mid 2021. I handled his final affairs, and he had already given me his wish list as to whom gets what. He knew that his health was bad and he wasn't likely to outlive me. So after handling the distribution of property this big pile of junk was left over. So with there being no objections I took it over. This nearly empty Tremolux chassis was in the pile. But it had its boards, its transformers, and most of its controls in it, so of course that's rebuildable.

I've rebuilt amps starting with less! Like a '69 Marshall Superlead that featured its original chassis, perf board, and choke...and that's about it. Now it's running and more or less correct.

[martin manning]

I found the correct tapped treble pots. Studio Sound Electronics has them.

Those are a usable replacement, yes, but not the original 1" diameter tapped pots. With the faux tap you have a similar appearing result with a commonly available full-size pot plus a couple of resistors.

[Matthews Guitars]

That's all it needs to be. A functional replacement. Sometimes you just have to deal with the fact that some parts are no longer available in their original form factor.

I'd have no idea where the original pots went to. Maybe I've got them in a box of random parts. And I DO have a box of accumulated random parts that I "inherited" out of this deal.

I've found a lot of odd but useful parts in there already. Including all the correct screws required to reassemble this amp.

[Matthews Guitars]

I just wasn't paying enough attention.

Now I understand the discrepancies. I was completing the rebuild today when suddenly I saw it:

The standby switch hole is off center and not labelled ON as is the power switch on the back panel.

It was added after the fact.

Then I looked at the bias pot. Took it out of the chassis. That hole it's in is MUCH fresher than any original hole,
and isn't even plated. So my friend who worked on it last added those later features to what would have been an original and correct 6G9-B chassis.

In fairness to him, he probably started modding that amp so far back in the past, I'd say at least 15 years ago, that collector's value on this model hadn't taken off yet.

No matter what I do this won't ever be an original and highly collectible amp. I know that. But if I can make it look good and sound right, and be mostly correct as far as the build spec, that'll do.

Just for fun I took a few minutes to randomly test resistance values on some of my Ohmite Little Devils CC resistor kit stash, and sure enough, they've ALL drifted higher in value. I found a few that are still barely within tolerance but most of them are at least the next standard resistance value above what they should be. I found NONE that were below their indicated value.

[martin manning]

Well, that explains things. Not to say that Fender didn't make a hybrid now and again, especially in that brown/blonde era.

[Matthews Guitars]

Regarding those tapped pots that I bought and mentioned recently, via Studio Sound Electronics:

They have a few issues you would want to know about.

The shaft length is too long and has to be cut down to fit cupcake style knobs correctly.
The shaft diameter is 6mm, while the cupcake knob takes a 1/4" shaft. This means the knob will visibly wobble when turning it, unless you insert a shim to fill in the gap.
The bushing thread is metric. The CTS nuts won't work.
The bushing is SHORT. You may have to skip the lock washer or use a very thin lock washer. Otherwise, the stacked thickness of the brass ground plate, steel chassis, and aluminum faceplate will run you out of room and you won't be able to get a nut on it and tighten it down.

But it can be made to work.

And now I have something to consider that I just thought of: The 6G9-B circuit has no bias adjustment, being a fixed bias design, and the tremolo circuit uses the bias modulation scheme rather than the optocoupler. So I need to ask if I want to install adjustable bias, and if I do, figure out how that will interact with the bias modulating tremolo circuit. Is this even a workable combination?

[martin manning]

Regarding those tapped pots that I bought and mentioned recently, via Studio Sound Electronics:

They have a few issues you would want to know about.

The shaft length is too long and has to be cut down to fit cupcake style knobs correctly.
The shaft diameter is 6mm, while the cupcake knob takes a 1/4" shaft. This means the knob will visibly wobble when turning it, unless you insert a shim to fill in the gap.
The bushing thread is metric. The CTS nuts won't work.
The bushing is SHORT. You may have to skip the lock washer or use a very thin lock washer. Otherwise, the stacked thickness of the brass ground plate, steel chassis, and aluminum faceplate will run you out of room and you won't be able to get a nut on it and tighten it down.

But it can be made to work.

But all good reasons, IMO, to go with a standard 500k, 1" diameter, 3/8" bushing pot and use the option linked above (https://ampgarage.com/forum/viewtopic.p ... 34#p193334)

And now I have something to consider that I just thought of: The 6G9-B circuit has no bias adjustment, being a fixed bias design, and the tremolo circuit uses the bias modulation scheme rather than the optocoupler. So I need to ask if I want to install adjustable bias, and if I do, figure out how that will interact with the bias modulating tremolo circuit. Is this even a workable combination?

No problem; keep the 6G9-B circuit. Bias modulating trem sounds great. You're just making the raw bias voltage feeding the bottom of the intensity pot adjustable.

[Matthews Guitars]

Today I got the amp up and running. After initial startup, there ware a few issues to sort out and I got them handled in good time.

The tremolo circuit seems to be less intense in its range of volume than a "bug" circuit tremolo. It doesn't come close to hitting zero volume during the cycle.

Is that normal for this circuit? I have no personal prior experience with it.