AB763 Super - no 5U4GB?

[fdesalvo]

Just a curious observation -

I have seen some Fender schematics/layouts showing the AB763 Super with a 5U4, whereas on other sources, I see that they were produced with the 5AR4.  Was there a transitional period between the Blackface and Silverface Supers where the AB763 circuit started to integrate the stiffer rectifier?  

[Ed_Chambley]

I've got 4 of them.  One which is said not exist, a 66 blackface.  Inside joke of a friend because he said he has never seen it.  It was bought new by my father and never left his house.  We were not allowed to touch it.  Everyone says I need to go through it and do a cap job and check all the resistors.  Not a single cap is leaking or has a blister.  It looks brand new.  I think I will keep it as is.

I have 2 dripedges, one pre AA1069 and the other is aa1069 both of them are halfbreeds and show parts from 1969.  Then I have a 1973 silver.  Everyone of the except the 1973 has a the tube sheet inside calling for a GZ-34. the 73 has a 5u4gb on the sheet, but I have the original tube and it is a RCA something like 4011 on.  I know that is not right, I just cannot remember.  Anyway it is just a 5u4gb when cross referenced on my tube tester.

They are all now AB 763 and have real 7025's and Winged "C"s except for the 66 which is all original, even down to the Victoria luggage cover.  Best I know is they were GZ-34 until CBS.  I am not certain, but I think the first ones arrived in late 64, at least I read that.  After 73 they began doing all kind of things to them.

The best sounding one I have is the 73.  It has weber alnicos on top and weber ceramics on the bottom.  Disconnected NFB.  Mercury OT.  Reverb with added Dwell.  Single wire reverb to add to the normal channel.  Switched on the tremolo for gain boost.  AB 763 with Mallory caps and Sprague Atoms.  It has a RCA 5U4GB.  In G Webers book he has 10 mods for supers. 4 of them are really great.  I've tried a few MV's and took them back out.  Doesn't need one.  The amp just sounds great at any volume.

Sorry to ramble, but you hit on my favorite topic.  The best amp ever made.

[fdesalvo]

NOT a ramble - and also one of my favorites.  I've been studying Weber's book and just finished the section with the top 10 Super mods :).  Which mods did you keep?  I see two of them.

Just a curiosity - I guess it doesn't matter which recto they used as long as the voltages lined up.

Regarding the =C=, I can't say I'm sold on them just yet.  I bought real Ruskie ones and brought them up to ~45ma and find them missing a little something compared to the JAN/Philips 6L6WGB - then again it's probably how the circuit should sound stock.  I just can't stop evangelizing the goodness of these Philips in this circuit! 

[Ed_Chambley]

NFB Removal, Change in cap values.  Can't remember, but I will look.  One of them made my Tele feel connected to the amp.  Like it was one single thing.  I did not like losing any channels as I like to use Humbuckers as well as Single coils.

There is a friend of mine who sells amp tubes here in Atlanta.  I go to his shop and he hand picks the C's.   Now done get me wrong, I have a lot of RCA black plate 6L6's which are great.  I have used the Phillips as well.  These amps are played a lot, so I don't roll tubes much  You gotta consider the preamp section.  A real 7025, which is hard to get, makes a bigger difference than most people realize in a super.  They are very low monophonic so you can hit v2 harder.  I run the bias colder and hit the front end harder.  Right now I am using an Exotic RC Booster in front of my supers.  I am biased a little over 60%.  Brings the tonestack really alive.  It gives me a great tone at any volume.

The SR is the clean of clean and has the most responsive bass control of any amp I have ever played.  That is what I use them for.  That's why the Winged C.  To me they are chording amps.  Plug in a good Gibson Hbucker and you will get Sunday afternoon all day.  It's all in what you are using them for.  I know people who use them for blues and want that singing solo sound from a strat.  I do not even own a strat.  I sat in with a friends band the other night and played his strat through a cranked super.  We did things like Red House and it sounded great.  The thing was screaming.  Sovtek 12AX7 and Sylvania Clears.  It was nasty good.

I'm a different breed.  If I got a gig that is mostly blues I carry my plexi and a Les Paul.  I realy like the Allman Bros tone as opposed to SRV.

[fdesalvo]

Hotlanta, huh?  Love the place.

I do lean more towards the SRV side of the tonal spectrum, but have been loving the circuit with a JB/Jazz combo in a mahogany bodied strat. 

I'll try to find a real 7025 to see what the fuss is about - interested.  I've recently discovered that I can't live without my JHS Morning Glory - it's basically an optimized BluesBreaker pedal - very, very transparent and dynamic.  It sounds exactly like my amp, but cranked up - so impressive.  If I want a fat lead tone, I hit the G2D Cream TOne - which as it's own tone, but it's very pleasing. 

[alerich]

The stiffer GZ34 came first as Ed_Chambley noted. Looking at the schematics only the AB763 shows the GZ34. All the subsequent prints show a 5U4GB (or solid state rectification for the 70W UL version). Schematic Heaven has all of these prints. I had a 1972 SF SR that I have now come to believe was the AA270 schematic. I did not even know that version existed until today so thanks for bringing this topic up. I don't recall seeing the schematic online when I owned the amp. I probably just overlooked it.

I made a number of mods to my SR while I owned it. Rewired the Normal channel for trem and reverb. Changed the vibrato channel coupling cap from .022 to .047 to match what is in the normal channel. Changed the PI coupling cap from .01 to .001 (all but the AA270 already have this so that's why I now suspect mine was the AA270). Added a trem disconnect to lift the trem intensity pot from ground for a little clean gain. NFB disconnect switch. Split the V1B/V2B cathode resistor/bypass cap to dedicated resistor and bypass caps. Added fully adjustable bias and 1 ohm sense resistors.

Used the old three position ground switch (disconnected that and removed the "death cap") to add two caps to the trem circuit for variable levels of trem "slow motion" - very cool effect. Also did this to my Vibro Champ that I still own. Tried the "Raw" control in the ground path of the tone stack but never really bonded with that mod. A little was ok but I found the value most guys use (250K) to be too much. 50K might work for me. I made a few tweaks to the power supply dropping resistors but ended up putting it back stock. I always ran a GZ34 in mine or sometimes a solid state plug-in. I liked to have as much clean headroom as possible. I love the classic Fender clean tone but I'm not so much for their overdriven tones, at least for personal playing.

The mod I liked most was changing out the reverb pot from linear to audio taper. Made the reverb much more controllable and usable. No more "on / off" syndrome when the dial got to about 2.5 or so.

Tonally the SR is my favorite Fender configuration as long as I did not have to move it. I only ever owned that SR and a few Twin Reverbs as far as full sized Fender amps go so I don't have much personal experience with a wider variety of Fender amps. I never played in a band where the SR (or any Fender amp, for that matter) would have been a good choice since I loathe pedals for overdrive. Was always more of a Marshall man at heart but nonetheless I sometimes miss that old SR and wish I still had it to strum around on here at the house.

[HotBluePlates]

I used to have a '67 Super Reverb. The amp and tube chart were both GZ34.

[Tyrannocaster]

Disclaimer: I have never owned a Super Reverb (although I do own a '70 Dual Showman Reverb that somebody put in a Twin cab with 2 12s; it has the old Blackface trannies, more proof that Fender used whatever was lying around) but I would think that disconnecting the NFB would have a more dramatic effect and all the other mods put together. I'm pretty sure that for me, that's all it would take (I'd put it on a switch) to make a SR the most awesome of all Blackfaces. My main gripe about the Twin and the SR is that they are just so damn hard to haul around.

[fdesalvo]

Alerich - loved your post, man.

HBP - That sounds like one of those "kick yourself in your own @ss moments" hehe.  I let go of some great amps, myself.

Tyranocaster - That's a really simply mod to implement, can't hurt!  I'm waiting for a head cab so I can haul my lil AB763 clone around.  Should be 19" x 8" X 9" after all is said and done, so Im looking forward to having a little grab-n-go rig.  I'm trying to phase out my boogie halfstack and at first my bandmates thought I was crazy until I plugged the chassis into the 412 and they quit whining :).

[phsyconoodler]

Doesn't matter what rectifier it has,it's all about the voltage.If it's more than 460v on the plates it likely has the wrong rectifier.The power transformer they used was the deciding factor there.
  So next time you pop in and check the voltages see if you have more than 470v.If so,change the GZ34 to a 5U4.It's as simple as that in the transistion year Fender amps.

[Dave]

The PT's weren't exactly the same size. The CBS (5U4) PT was taller and heavier. If you don't have one of each to compare, then it won't be much help, but if you have one of each, the easiest way to tell would be to see whether its the tall PT or the short one.

Dave

[Ed_Chambley]

The PT's weren't exactly the same size. The CBS (5U4) PT was taller and heavier. If you don't have one of each to compare, then it won't be much help, but if you have one of each, the easiest way to tell would be to see whether its the tall PT or the short one.

Dave

You are absolutely correct and I found is one of the reasons (among others) why they had a much cleaner tone at higher volumes.  Sort of bright, but some really like the true silver sound.  You can get a fairly good surf sound from them.  The one I replaced on my 73 is smaller and came from Mercury which I thought was strange, but it is a toneclone for a Blackface.  I never thought about that.  I still have the original, wonder what the difference is?  Great observation.

[phsyconoodler]

The major reason for a silverface to sound cleaner is not voltage,it's the phase inverter values.
  Again,you need to know what the voltages of the amp are.
Good call on the height of the PT but don't rely on that alone.
  The larger PT put out more voltage so they needed a 5U4 to tame it down.

[HotBluePlates]

HBP - That sounds like one of those "kick yourself in your own @ss moments" hehe.  I let go of some great amps, myself.

I've had a lot of very good, very different amps. I suppose I don't really regret getting rid of any of them, but a few I'd like to have back for a few days.

[Fresh_Start]

Another big difference between the 5AR4 (GZ34) and 5U4GB tubes is the heater current required.  The 5AR4 filament only draws 1.9 amps, but the 5U4GB requires 3.0 amps.

Thought it was worth mentioning for anyone building a Super Reverb clone so that you can make sure the PT can handle your rectifier's heater current.

It might not be a good idea to put a 5U4GB in an older SR which came with a 5AR4/GZ34 originally.

Cheers,

Chip