Parts List for Twin Reverb - AB763?

[Chemo64]

Hello, does anyone have (or know of a source for) a parts list for the AB763 version?

Also, beyond the component values, I'm trying to determine the exact types as originally used. I do realize that certain components are simply no longer available in their 50's/60's form, but I'm searching for as close of a match as possible. Suggestions?

Any assistance is greatly appreciated.
Bob

[gregarious]

Hoffman springs to mind... http://www.el34world.com/Hoffman/ab763parts.htm

AB763 is an early 60's circuit, and while the exact original components may not be available, there are plenty to choose from to build the circuit.

The original components were primarily mylar (polyester) coupling caps and carbon comp resistors. Some research will support that Fenders were built to cost as opposed to the components being selected to optimize the tone of the circuit.

There are plenty of examples of almost original AB763's as well as present day interpretations using modern components which can be viewed on the web. It gets down to where you want to take it.

[Richie]

If you can find one,The old fender service mauals list all parts and part numbers. Schematic on one side, and the parts list on the other.

[Chemo64]

Thank you gentlemen. These are helpful.
The end state I am trying to achieve is to recreate the sound produced from this early circuit. I don't have a timeline set, so I'll take all the time I need, and plan to stockpile components one-by-one. I am finding that resisting the call of better designs, mods, and/or components is a constant battle. Truth be told, I ultimately plan to recreate the sound that Luther Perkins had (with Johnny Cash) in the early 60's. More for my own enjoyment than anything else.

[Phil_S]

www.tedweber.com publishes a BOM Excel file for all of his kits. This is a pretty good starting point. In the end, no matter what you do, I think you will have to take a schematic and tick off all the parts for correct value and type. Then you will need to figure out what's needed that doesn't show up on the schematic, as there are bound to be "assumed" items. An example might be tube socket shields.

[Chemo64]

www.tedweber.com publishes a BOM Excel file for all of his kits. This is a pretty good starting point.

Thank you, this is quite helpful. Just did a quick once-over and see that the pots, bias pot and the few caps I looked at match up. I may have to settle for a list of this type vs. a fender produced one.

In the end, no matter what you do, I think you will have to take a schematic and tick off all the parts for correct value and type. Then you will need to figure out what's needed that doesn't show up on the schematic, as there are bound to be "assumed" items. An example might be tube socket shields.

Yes, I agree. I've done this and am now looking for the "official" parts list to cross reference and to spot mistakes I've made.

I believe the more difficult phase of parts gathering is identifying component types and trying to find the closest match (from a material and composition stand point). I'm trying to resist going the easy route and simply matching values. Quite the scavenger hunt.

[b24warbaby]

I believe the more difficult phase of parts gathering is identifying component types and trying to find the closest match (from a material and composition stand point). I'm trying to resist going the easy route and simply matching values. Quite the scavenger hunt.

I use www.partexpress.com for the inventory. get 10x each component
for about $1 . caps too. double up on common values: 100k, 1.5, 2.k, 68k,
22uf., 001, 0022, You will end up with a nice stash of parts afterwards.

[b24warbaby]

I believe the more difficult phase of parts gathering is identifying component types and trying to find the closest match (from a material and composition stand point). I'm trying to resist going the easy route and simply matching values. Quite the scavenger hunt.

I use www.partexpress.com for the inventory. get 10x each component
for about $1 . caps too. double up on common values: 100k, 1.5, 2.k, 68k,
22uf., 001, 0022, You will end up with a nice stash of parts afterwards.

my ab763: http://www.freewebs.com/willispage6/ab763b.htm

[benoit]

I've made up a couple of BOMs for other things and I've found that usually it takes less time to do it yourself than to try to scare up one of someone else's, not to mention that it gets you better acquainted with the schematic/layout. I'm not trying to talk you out of looking - I'm sure someone's got one, just throwing it out there as an option.

That said, I just realized I have a BOM. It's got sources and part numbers for a some of the components. I never actually got it built but It should be pretty accurate. As far as checking it, you shouldn't need the fender parts list if you've got a schematic and layout. Print them out and circle each component after you've checked it.

[CaseyJones]

I hear you're still undecided about what type of parts to use, on the one hand you can use PIO caps and audiophile grade resistors OR new stuff like carbon films OR the exact vintage components.

Any time I work on an old Fender I use Allen Bradley carbon comp resistors as per the original. Clark Amplification has a good stock of carbon comps.

http://www.clarkamplification.com/Parts ... 0Index.htm

I use carbon comps because carbon films can be unreliable in a high voltage application. Having said that Xicon carbon films can reduce hiss compared to carbon comps when used as plate resistors. If you use carbon film double the original wattage rating, use 1 watt resistors in place of half watt resistors.

Xicon makes 1/2 watt carbon comps that can be an affordable alternative to Allen-Bradleys, TRWs, Ohmites and the like.

Good luck finding the original '60s "Blue Caps" used as coupling caps. I have a shoebox full of them removed from customer's amps when they insisted on a "complete and total cap job". I test them and use them for customers who insist on total originality.

Use either Sprague 715Ps or 716Ps for coupling caps. The capacitor discussion is almost as broad as the "which tubes?" of the "which speakers?" discussion, it usually turns out that the guy with the most contrary opinion has musical tastes opposite mine, plays a different guitar then I do, etc, etc. Buy some caps, Git 'R' Done! Do they say "Git 'R' Done!" in Germany?!

Electrolytics: You can't go wrong with Vishay "Sprague Atoms" in a Fender or a Fender replica. The cathode bypass caps aren't very expensive, the filter caps are getting pricey. I'm experimenting with other brands under the "doghouse" although nothing else has Sprague's proven track record. Don't waste your time with old electrolytics.

Don't ignore the sockets. I avoid ceramic sockets no matter how good they look, the market was flooded with cheap imported sockets over the last couple years. The quality ranges from usable down to absolute junk, for instance one recent batch of imported octals has a center reference pin hole large enough that the tube can be inserted eight different ways! I use NOS Cinch bakelite sockets. You may be able to find Omron octal relay sockets in Germany, those are good.

[benoit]

Deleted: bad info.

[Firestorm]

I'll weigh in here because I must have restored close to 50 amps from this era. The tone and coupling caps are pretty key to the sound of these amps and you definitely want the blue Mallory caps IF you can find them. A lot of "techs" have parted out these amps over the years so you can sometimes find used caps on eBay (in fact, here's a current item #: 120218941484). Don't worry about them being used -- I've NEVER seen one go bad (but do check). If you go with modern versions, I suggest the 225P or 418P type caps (which are polyester film and foil like the Mallorys) instead of the 715P or 716P (which are polypropylene).

An argument can be made that the cloth covered wire is part of the sound. I won't get into that, but you can get vintage-style push-back wire from folks like Doug Hoffman. You want the push-back wire (two layers of fabric insulation -- not the plastic insulated, cloth covered wire). A VERY significant consideration is lead dress (including which leads route under the board). You'll need to have a stock example or photo to follow -- the published chassis layout doesn't cut it.

The resistors are all carbon comps. In a blackface, most are 1/2 watters, and only a few are subjected to voltages over 300VDC, so you can use inexpensive 1/2-watt Xicons nearly everywhere (most of them could have been 1/4 watts, but in the 60s 1/4 watt resistors actually cost more than 1/2 watt resistors). THE EXCEPTIONS: screen resistors (470 ohms/1 watt); main filter balancing resistors 220K/1 watt); power supply dropping resistors 1K/1 watt and 4K7/1 watt); the plate resistor on Pin 1 of V5 (220K/ 1/2 watt, but at 458 volts); the plate resistor on Pin 6 of V5 (10M/1/2-watt, but also at 458 volts); and ALL of the 100K preamp plate resistors, which were originally 1/2 watt, but really should be 1-watt unless you want the amp to start sounding like a bowl of Rice Krispies from "shot noise."

For the screens, I prefer the 2-watt ceramic versions since they behave like carbons but hold up better in the high-heat tube socket environment. For the rest, 1-watt Allen Bradleys are great if you can handle the price. 2-watters are fine too but won't fit everywhere (like in the power supply where you can have 5 leads in one eyelet!).

The Vibrato/Tremolo "roach" (LDR) can be a little problematic because not all of the available replacements give you the same depth as the originals. I'm afraid I don't have a definite recommendation here. Also in the phase lag loop for the oscillator circuit, use at least 1KV (2KV or 3KV, even better) CERAMIC caps (one .02 and two .01s). If you find the tremolo to be too fast, change one the .01s to .02 to slow it down.

For trannies, obviously you can go with Mercury and get real good iron. I don't know how the various "replacement" transformers from other sources compare.

Speakers were typically Jensen C12Ns and I really like the current Recoton-made versions in this application, but opinions differ. A little later, JBL D120Fs were available as an option. These sound great but different.

Sorry for the long post. I've got Fenders in my blood.

[Chemo64]

Thank you all for the thoughtful and insightful suggestions. You've given me more to consider than I imagined.
I'll begin the scavinger hunt and will report back once I'm finished.

I hadn't considered the push-back wire and lead-dress at all, thanks Firestorm for the tips (as well as sharing your obvious experience).

Can you point me to a source for a stock underside photo? I bought Tino Zottola's Amp Book (vol II) which I am hoping includes this info, but will have to wait until it arrives to be sure.

FYI, I'm a US soldier stationed in Germany, not a German. And since I hail from Texas, I can assure you that 'Git her done' is often said here in Deutschland!

[Firestorm]

Chemo64--

I've got Twin Reverb from March 1965. Give me a day or two and I'll pop it open and shoot some pics for you. I think I modified the reverb circuit slightly and may have coax from one of the inputs, but everything else is intact and you should be able to pick up the needed lead sress tips.

And BTW, thank you for your service.

[Chemo64]

Thank you Firestorm, that is very kind of you. I look forward to seeing the pics.
Bob