Those old Jensen paper voice coils will eventually give up the ghost. The curved hotdog shaped cuts in the frames with transformer mounts are usually indicative of it being a Jensen. Weber & modern Sica Jensen uses similar frames but without the rather large universal drill pattern transformer mounting pads. The Modern Jensens kinda suck. (Just my personal opinion.) CED's Mod 50s sound better to my ears and they cost less.
@@Satchmoeddie I have modern alnico P12N's in my twin and they don't suck IMHO. I did have to tweak the voice of the amp for them though (mainly cut the low frequencies a fair bit). They also took a LOT of breaking in.
Yep, the first stage filter caps are 20uf 525v on the larger AA763 amps. I can find the Showman(which should be identical)and Super schematics, this Twin is very rare. I 💯 agree that the ceramic caps are important to the original design and sound. They can sound really hi-fi or “sterile” if they’re over filtered and over film capped.
Wow!! This is a beautify & so well kept, likely loved by it's owner. The rarity of the circuit only makes it more valuable. Thx for the look & tour through a piece of Fender & amp history.
So, your telling us that that if they haven’t nailed the speakers to their perch they would be pushing up the daisies? Love your vids and enjoy some more time off….
Thank you for taking the time to make your tutorial videos, they are really interesting and you present them in a professional fascinating way. This one is absolutely no exception to your high standard. Great stuff. Paul in the U.K.
What an ultra cool amp! My '67 Deluxe is about as clean and original too (though thankfully my Jensen speaker works!) I love your clear respect and admiration for these old amps!
Sprague did make 20 uf at 600 volts, for the main filter caps,... might be nice to have a little safety factor there, if they are still available. Is it possible the tech who changed caps, etc, used lead free solder? Those previously reflowed solder joints don't look that great. I especially agree that the mica across the plates of the PI should be removed. I am pretty sure those speakers are not C -12 N s, The basket belongs with a C 12 R or Q which had the concentric radiating narrow lozenge cut-outs in the frame. i wonder if the speakers had been replaced earlier with one of the two possible lower powered models, as the N series was usually shipped with the Twin. The "N" speakers have trapezoidal cutouts extending from the magnet, and bell to the outer frame. One wonders how they both blew simultaneously, perhaps the second owner cranked them past five or so and the rest of their history was toast?
I guess both speakers didn’t fail at the same time. Maybe one failed first and the owner was playing with one without noticing. When the second failed he did noticed😁
What a bewdy amp! 😎 Thanks so much for sharing this. Really interesting. I only was able to find schematics for an AA763 Super Reverb and an AA763 Tremolux. The Super Reverb looks exactly like an AB763 including voltages. The Tremolux has a .047 mid cap instead of .022 and it’s voltages are lower throughout the amp. 410 volts on power tube plates vs. 460 for AB763 version. Also only 16uf filter caps with 2 in parallel for reservoir cap. You’ve got 20uf in parallel and plate voltages in between the two.
First time I ever saw C12N speakers using that closed hotdog frame, usually they use the open Celestion type frame, but Jensen would switch things up sometimes. The C12R in my 1960 GA-20 (one of the first versions) uses the open frame, when they usually always use the closed hotdog frame. Ted Weber always said to recone old Jensen speakers, rather than buy one of his new versions, he really liked them. I'm not so fond of the "r" sized, don't like the "S" size with tiny magnet, but "Q" is better, "P" like the P12P in my '58 GA40 is great, and "N" size is my favorite. C12N, P12N, C10N are my favorite Chicago Jensen speakers.
Yeah I was thinking,,,, how similar that circuit is to the showman?? I just watched uncle doug repair an AA763 showman and he went through the differences. Nice amp.
Please update us when you get your hands on the AA763 Twin schematic. Going by the changes on the Super, I'd expect the AA to have parallel caps on primary filter and a 100k plate resistor on the driven side of the PI. It would be interesting to see if there are additional differences.
Looking at the AA769 vs AB763 both show 70mfd stacked as first cap with the 220k bleeders so 40 is close to (35) the value of the stacked caps on first. They both look very much the same from what I see. the AA769 has lower voltage front end phase splitter and output about50 v lower on the AA769 405 vs 460 for the AB763.
Ken- interesting to note that I have a 1963 Concert Amp, all dates match and it has a AA763 Circuit with an original P.T. #125P19A which charts show it goes to a Fender Twin Reverb with 7591 Tubes, I also have a 1964 chassis date Band Master with all Tranies and components dated 1963 that is also a AA763 circuit, schematics are available for cross referencing.
7591's behave very similarly to 6L6GT's . i can't remember off hand ,.. but I think the pinouts are the same or there is a slight difference about something, maybe the screen grid resistor, or recommended bias point.
19:21. I have a theory that Fender intentionally called the Strat vibrato a tremolo to differentiate it from a bigsby. Probably suggested by the marketing team. Note that Fender's first amp with tremolo was the Tremolux, but they then had to differentiate the amp effect from the vibrato on the guitar. 60+ years on and we're still confused over terminology...🤦♂️🤪
Fender did make a few amps that actually introduced a small amount of pitch fluctuation, along with the pulsating amplitude (temolo) rather than the two stages of variable phase shift coming from a cathode output and a plate output from the same tube , selected with variable resistance like in the Magnetone amp or some of the vibrato circuits in Hammond or other electric organs (and I don't mean the leslie speaker), the Fenders that did create a little pitch fluctuation , had the low frequency oscillator, supply variable bias to the PI input. Because the bias point can move up or down more than the max amplitude of the signal waveform, the distance between zero crossings as the modulating waveform moves up are further apart than when the modulating waveform moves downward in which they are closer together. The biased based vibrato/tremolo is a much more interesting sound , than the variable volume type tremolo with the neon light / cadmium photo resistor.
@@Geopholus you are talking about what fender called "harmonic vibrato". It sounded quite different from all other types Some tremolo circuits varied the negative bias to the output tubes. I think that this style sounds a little smoother than optical type tremolo. Optical tremolo is more choppy, but it's more effective than other types at higher speeds.
Trem is a score term seen on string parts to denote a volume modulation only through bowing and muting. Going by that, I have always thought tremolo is exactly the correct term for a volume modulation effect on guitar amplifiers. Vibrato is universally regarded in score nomenclature as pitch modulation. Music gets it right every time. Fender, in covering their butt legally, caused decades of confusion.
@@stevem.1853 Yes exactly! I can imagine they called it harmonic vibrato because the harmonic content also changed (a little) with the variable bias. Tremolo is one of those things that most guitarists do not rely on, a lot, but if You play in a cover band with a lot of '60's material it can be indispensable for certain songs.
I have had on my bench many years ago a Showman AA763 amp. With the exception of the reverb the amp was very similar, even C1 and C2 being 20uf caps. The biggest difference being the power tubes were 7355. I’m wondering if this Twin reverb also used 7355 originally. The possible conversion being done at time of recapping. 7355 are extremely hard to find and expensive making 6L6GC conversions common.
I would love to get in touch with you as I have also acquired a 1964 AA763 (tube chart stamped NA) twin that had seen some better days and I am in the middle of resto-modding it. I may be over my head, but I would love your input on a few things concerning this amp.
I had a 1970 Silverface Twin - pre-master volume. I blew the Jensen speakers - the amp volume was maybe on 6. A friend convinced me to replace the speakers with JBL D-120s. In hindsight, the Twin was a bad choice for me (it was also recommended by a different friend.) It was way too loud for 99% of my playing situations - although it had no problem hanging with a full Marshall stack. I also couldn't get anywhere close to my "ideal" tone without melting my face. A Vibrolux, Pro Reverb, or Bandmaster would have been a better choice. (There weren't many other options in 1970...)
I could be mistaken but I'm pretty sure that Twin Reverbs produced between 1963-67 all used the AB763 circuit. The AA763 circuit was used in the earliest Super Reverb amps, which have the same tube complement as a Twin. The Fender tube charts often have a different circuit number than the actual circuit used. I have a '65 Blackface Bassman and it has a tube chart for the AA864 circuit even though it's the AB165. That was Leo Fender being thrifty and not wasting anything. But this amp is obviously one of the earliest examples of a Blackface Twin, as they were first produced in September of 1963, which the speaker date codes confirm. Is there a date code on the tube chart?
Yeah, I'll post a photo when my back agrees to the angle required. Stamp on the chassis says '64, all component/speaker date codes say '63. This is an early rare bird. Given the parallel first stage filters this is an AA763.
@@PsionicAudio Thanks, Lyle. There are definitely some strange and often un-noted variations in circuits during the time that Fender was transitioning from the Brown/Blond amps to the Blackface amps. Thanks for documenting this.
Thanks. Aside from the parallel filters and I suspect (haven't confirmed) possibly a lower HT secondary PT the rest seems like the AB763. No dual 100K PI plates, tail resistor is 22K, mids caps are 47nF.
I have used MOV's from computer power supplies for some mods in which the filament voltage is especially high. They work great, and also good if You want the first pair of filter caps to do more filtering (like 220 uf/350 V pair) in order to avoid destroying tube rectifiers or diodes.
I just recapped a '64 (March). That circuit threw me (and my current limiter when I capped it as an AB763)! The serial number says it is 201 which makes me think it was the 102 one built in that year? Owner wants to sell; go figure!
The Jensens are C12Ns from the 37nd week of 1963. And they are really most sincerely dead. Pending the owner's approval they will be reconed.
Sad to hear that. I had my fingers crossed it was just a failure in the tinsel leads.
Those old Jensen paper voice coils will eventually give up the ghost. The curved hotdog shaped cuts in the frames with transformer mounts are usually indicative of it being a Jensen. Weber & modern Sica Jensen uses similar frames but without the rather large universal drill pattern transformer mounting pads. The Modern Jensens kinda suck. (Just my personal opinion.) CED's Mod 50s sound better to my ears and they cost less.
@@Satchmoeddie I have modern alnico P12N's in my twin and they don't suck IMHO. I did have to tweak the voice of the amp for them though (mainly cut the low frequencies a fair bit). They also took a LOT of breaking in.
They suck compared to the old Jensens. Mid 1960’s Jensens are the best speaker I’ve ever played by a long shot in a blackface circuit
@@cgavin1 I had a P12N in my Deluxe Reverb clone, which sounded great, but when I changed it out to a Weber 12F150 it sounded even better!
Great that you explain a lot on your repairing the amps....almost like watching Hickok45 on a 'Sunday morning shoot-out'......LIFE IS GOOD ;-))
Yep, the first stage filter caps are 20uf 525v on the larger AA763 amps. I can find the Showman(which should be identical)and Super schematics, this Twin is very rare.
I 💯 agree that the ceramic caps are important to the original design and sound. They can sound really hi-fi or “sterile” if they’re over filtered and over film capped.
Wow!! This is a beautify & so well kept, likely loved by it's owner. The rarity of the circuit only makes it more valuable. Thx for the look & tour through a piece of Fender & amp history.
The speakers are "pining for the fjords" ROFL... love your vids, informative and entertaining.
Monty Python reference noted - PININ' for the FJORDS?!?!?!? THIS IS AN EX-PARROT!! LoL.
In early '64, I bought my first amp ... a new Super Reverb ... still got it!
Wonderful!
@@PsionicAudio Thanks! Love your videos. Just wondering why you didn't go into radio ... Dude. You got THE voice!
Nick Grabien is a legend, he has helped me out with some great info in the past.. very knowledgeable
A well maintained Twin is a thing from heaven. Highly dynamic bell-like tone so sweet. But it should come with a roadie for weight reasons :)
So, your telling us that that if they haven’t nailed the speakers to their perch they would be pushing up the daisies? Love your vids and enjoy some more time off….
Thank you for taking the time to make your tutorial videos, they are really interesting and you present them in a professional fascinating way. This one is absolutely no exception to your high standard. Great stuff.
Paul in the U.K.
What an ultra cool amp! My '67 Deluxe is about as clean and original too (though thankfully my Jensen speaker works!) I love your clear respect and admiration for these old amps!
Really cool specimen! Thanks for sharing this rare amp with us and man that was a great tip on using a know good speaker/load for troubleshooting.
Sprague did make 20 uf at 600 volts, for the main filter caps,... might be nice to have a little safety factor there, if they are still available. Is it possible the tech who changed caps, etc, used lead free solder? Those previously reflowed solder joints don't look that great. I especially agree that the mica across the plates of the PI should be removed. I am pretty sure those speakers are not C -12 N s, The basket belongs with a C 12 R or Q which had the concentric radiating narrow lozenge cut-outs in the frame. i wonder if the speakers had been replaced earlier with one of the two possible lower powered models, as the N series was usually shipped with the Twin. The "N" speakers have trapezoidal cutouts extending from the magnet, and bell to the outer frame. One wonders how they both blew simultaneously, perhaps the second owner cranked them past five or so and the rest of their history was toast?
I guess both speakers didn’t fail at the same time. Maybe one failed first and the owner was playing with one without noticing. When the second failed he did noticed😁
What a bewdy amp! 😎 Thanks so much for sharing this.
Really interesting. I only was able to find schematics for an AA763 Super Reverb and an AA763 Tremolux. The Super Reverb looks exactly like an AB763 including voltages. The Tremolux has a .047 mid cap instead of .022 and it’s voltages are lower throughout the amp. 410 volts on power tube plates vs. 460 for AB763 version. Also only 16uf filter caps with 2 in parallel for reservoir cap. You’ve got 20uf in parallel and plate voltages in between the two.
Pining for the fjords indeed!
I'm excited to hear this one when it's completed.
Interesting stuff, looking forward to part 2
Great video, thanks for sharing.
First time I ever saw C12N speakers using that closed hotdog frame, usually they use the open Celestion type frame, but Jensen would switch things up sometimes. The C12R in my 1960 GA-20 (one of the first versions) uses the open frame, when they usually always use the closed hotdog frame. Ted Weber always said to recone old Jensen speakers, rather than buy one of his new versions, he really liked them. I'm not so fond of the "r" sized, don't like the "S" size with tiny magnet, but "Q" is better, "P" like the P12P in my '58 GA40 is great, and "N" size is my favorite. C12N, P12N, C10N are my favorite Chicago Jensen speakers.
Glorious amp......just wow.
Man I really feel like checking for DC on the speaker output for peace of mind..
Yeah I was thinking,,,, how similar that circuit is to the showman?? I just watched uncle doug repair an AA763 showman and he went through the differences. Nice amp.
wow------- beautiful!
Please update us when you get your hands on the AA763 Twin schematic. Going by the changes on the Super, I'd expect the AA to have parallel caps on primary filter and a 100k plate resistor on the driven side of the PI. It would be interesting to see if there are additional differences.
Looking at the AA769 vs AB763 both show 70mfd stacked as first cap with the 220k bleeders so 40 is close to (35) the value of the stacked caps on first. They both look very much the same from what I see. the AA769 has lower voltage front end phase splitter and output about50 v lower on the AA769 405 vs 460 for the AB763.
Ken- interesting to note that I have a 1963 Concert Amp, all dates match and it has a AA763 Circuit with an original P.T. #125P19A which charts show it goes to a Fender Twin Reverb with 7591 Tubes, I also have a 1964 chassis date Band Master with all Tranies and components dated 1963 that is also a AA763 circuit, schematics are available for cross referencing.
7591's behave very similarly to 6L6GT's . i can't remember off hand ,.. but I think the pinouts are the same or there is a slight difference about something, maybe the screen grid resistor, or recommended bias point.
19:21. I have a theory that Fender intentionally called the Strat vibrato a tremolo to differentiate it from a bigsby. Probably suggested by the marketing team. Note that Fender's first amp with tremolo was the Tremolux, but they then had to differentiate the amp effect from the vibrato on the guitar. 60+ years on and we're still confused over terminology...🤦♂️🤪
Fender did make a few amps that actually introduced a small amount of pitch fluctuation, along with the pulsating amplitude (temolo) rather than the two stages of variable phase shift coming from a cathode output and a plate output from the same tube , selected with variable resistance like in the Magnetone amp or some of the vibrato circuits in Hammond or other electric organs (and I don't mean the leslie speaker), the Fenders that did create a little pitch fluctuation , had the low frequency oscillator, supply variable bias to the PI input. Because the bias point can move up or down more than the max amplitude of the signal waveform, the distance between zero crossings as the modulating waveform moves up are further apart than when the modulating waveform moves downward in which they are closer together. The biased based vibrato/tremolo is a much more interesting sound , than the variable volume type tremolo with the neon light / cadmium photo resistor.
@@Geopholus you are talking about what fender called "harmonic vibrato". It sounded quite different from all other types Some tremolo circuits varied the negative bias to the output tubes. I think that this style sounds a little smoother than optical type tremolo. Optical tremolo is more choppy, but it's more effective than other types at higher speeds.
Trem is a score term seen on string parts to denote a volume modulation only through bowing and muting. Going by that, I have always thought tremolo is exactly the correct term for a volume modulation effect on guitar amplifiers. Vibrato is universally regarded in score nomenclature as pitch modulation. Music gets it right every time. Fender, in covering their butt legally, caused decades of confusion.
@@stevem.1853 Yes exactly! I can imagine they called it harmonic vibrato because the harmonic content also changed (a little) with the variable bias. Tremolo is one of those things that most guitarists do not rely on, a lot, but if You play in a cover band with a lot of '60's material it can be indispensable for certain songs.
I have had on my bench many years ago a Showman AA763 amp. With the exception of the reverb the amp was very similar, even C1 and C2 being 20uf caps. The biggest difference being the power tubes were 7355. I’m wondering if this Twin reverb also used 7355 originally. The possible conversion being done at time of recapping. 7355 are extremely hard to find and expensive making 6L6GC conversions common.
Hot damn ! Nice amp. :-)
That amp was cleaner then Martha Stewarts pantry drawer...
I would love to get in touch with you as I have also acquired a 1964 AA763 (tube chart stamped NA) twin that had seen some better days and I am in the middle of resto-modding it. I may be over my head, but I would love your input on a few things concerning this amp.
I had a 1970 Silverface Twin - pre-master volume. I blew the Jensen speakers - the amp volume was maybe on 6. A friend convinced me to replace the speakers with JBL D-120s. In hindsight, the Twin was a bad choice for me (it was also recommended by a different friend.) It was way too loud for 99% of my playing situations - although it had no problem hanging with a full Marshall stack. I also couldn't get anywhere close to my "ideal" tone without melting my face. A Vibrolux, Pro Reverb, or Bandmaster would have been a better choice. (There weren't many other options in 1970...)
I love your passing Monty Python comments. Pining for the fjords.
So what are "class 2" ceramic caps? I've never heard the differentiation before.
nice amps
Love your videos, but please use a pointer stick so your fingers/hand doesn't block the view
Safety first.
Is that board phenolic? Haven’t seen one of those in a while.
Wonder if the badge was added?
I couldn't make it out in the video, but I'm curious if the resistor into the reverb mix stage is 3M3 (like all the AB763s) or 4M7 like the AA763 DR.
3M3
I could be mistaken but I'm pretty sure that Twin Reverbs produced between 1963-67 all used the AB763 circuit. The AA763 circuit was used in the earliest Super Reverb amps, which have the same tube complement as a Twin. The Fender tube charts often have a different circuit number than the actual circuit used. I have a '65 Blackface Bassman and it has a tube chart for the AA864 circuit even though it's the AB165. That was Leo Fender being thrifty and not wasting anything. But this amp is obviously one of the earliest examples of a Blackface Twin, as they were first produced in September of 1963, which the speaker date codes confirm. Is there a date code on the tube chart?
Yeah, I'll post a photo when my back agrees to the angle required. Stamp on the chassis says '64, all component/speaker date codes say '63. This is an early rare bird. Given the parallel first stage filters this is an AA763.
Tube chart date is NA which is January 1964.
@@PsionicAudio Thanks, Lyle. There are definitely some strange and often un-noted variations in circuits during the time that Fender was transitioning from the Brown/Blond amps to the Blackface amps. Thanks for documenting this.
Thanks. Aside from the parallel filters and I suspect (haven't confirmed) possibly a lower HT secondary PT the rest seems like the AB763.
No dual 100K PI plates, tail resistor is 22K, mids caps are 47nF.
Do you ever utilize in-rush devices for these vingage amps to help lower wall voltage?
I have used MOV's from computer power supplies for some mods in which the filament voltage is especially high. They work great, and also good if You want the first pair of filter caps to do more filtering (like 220 uf/350 V pair) in order to avoid destroying tube rectifiers or diodes.
I re-cone every morning
Typed in ‘aa763 schematic’. Bam there it is
Super Reverb and others, not the Twin Reverb. But I can extrapolate.
I just recapped a '64 (March). That circuit threw me (and my current limiter when I capped it as an AB763)! The serial number says it is 201 which makes me think it was the 102 one built in that year? Owner wants to sell; go figure!
I don't know if the SNs have any correlation to when an amp shipped. I rather think not.
3:44 The reservoir caps are both facing the same way. Bad? I dropped this comment at this point lol
Watch on.
Great amp if you're playing outdoors in front of 2000 people lol
drool...