Chasing Mystery Noises | '79 Fender Super Reverb

[@Burgschall]

Funny to see this GND issues on that 7ender as I am currently working on an 82 JCM800 which had „mystery noise“ and it turned out that the tooth washers under the GND connections of the HT Caps had corroded and where causing contact resistivity…unscrewed GND, cleaned Chassis, new tooth washer, noise gone…

[@PsionicAudio]

Yeah, that's SOP here on old Marshall grounds. Will be showing that (again) next week on a 2204.

[@edwardhannigan6324]

Nice beast..Great walk thru and tech tips..look forward to finished repair..Ed...uk..😀

[@BradsGuitarGarage]

You had me at "non combative situation".

[@TheBoss1597]

Thanks Lyle! Understand that u need a brake (who wouldn't) just want to say that the solder sucker I mention is great , but it do get quickly clogged but otherwise it's great!

[@fiddlix]

Great informative content as usual. Keep up the excellent work..!

[@DROPTUNED]

Thanks for your wisdom ❣️

[@brianm9282]

I recently scored a 1976 Super Reverb from the son of the original owner for $150. The cabinet was pretty water damaged on the bottom and would have had to be replaced. I put it a $100 used, empty head shell so now it's a head that runs at 2 ohms but I recently picked up a 2x12 VHT cabinet that I loaded with 8 ohm Jensen Mod 12 speakers. The cabinet runs at 3.2 ohms mono so I don't think I'll have any problems with it. I just need to do a cap job on it.

[@Splattle101]

I reckon the blow that bent the front of the chassis probably had something to do with the deformation around the PT. It must be really nice to open an amp and think, "That looks like my work," and then find the details in your records.

[@PsionicAudio]

Maybe. But I've seen similar chassis deformations around the PT in plenty of mint examples. It's just a matter of weight and time. In my own builds I reinforce the chassis at PT hardware connection points with SS fender washers. Spreads the stress over a wider area and doubles the thickness at the points of contact. But I still don't use transformer hardware for grounds.

[@goodun2974]

Keps nuts, having their own built-in star washer (acting as a lockwasher) are excellent for purely mechanical fastening, but not so great for tightening down against a ground-lug terminal, especially a terminal with its own internal-tooth star washer, because as you tighten the Keps nut it tends to make the ground lug spin, and you essentially have two built-in star washers at that junction which are gonna make it difficult to get the ground lug to really bite into the chassis, and perhaps prevent it from being completely tightened. This might be why somebody soldered, or tried to solder, the ground lug to the chassis. Add the weight of the transformer and the torsion of the chassis from transporting the amp, and it's no surprise that grounding points fail. Better to either solder the wire(s) directly to the chassis, or drill a hole (as amps go, this one isn't that collectible) and put in a separate bolt and nut to hold the ground lug. You can solder a plain lug to the chassis if you like, but it isn't necessary if the metal is clean and the connection tight. A lug with integral star washer doesn't need soldering to the chassis, and I'd skip the Keps nut ---- a plain nut and a flat washer followed by a dab of Loctite or glyptol lacquer on the threads where they meet the nut is sufficient. The teeth on the lug will bite into the chassis for a low resistance connection.

[@TheBoss1597]

Understan what u mean about silikon vs hot glue, obvious if I just have thought i about it....thnx

[@stevebeck3164]

3W screen grid resistors? Aren't they kept to 1W as sacrificial component when/if a tube shorts, instead of having nearly infinite current on the output xfmr?

[@elwrongo]

That's interesting about the pot taper. Can I ask what audio taper/pot specs we should be looking for to replicate the blackface pot action?

[@PsionicAudio]

Look at the Treble and Volume pots on the AB763 schematics. See that 2-25 written beneath the value? They mean a 25% taper pot, so J taper vs standard "log" A taper (which is 10%). tubesandmore.com sells 250K and 1M J taper pots.

[@waynegram8907]

Would using lead free solder be better when soldering ground wires direct to the chassis metal because lead free doesn't cause any oxidation and the oxidation will add resistance causing grounding noises? Correct me if I'm wrong

[@PsionicAudio]

Lead free solder is never better.

[@ekimnavillus4452]

What would be the possible cause(s) of the volume getting loud so quick? My dads 1990’s 65 twin reverb clean channel volume got loud very quick like this amp. The pot was replaced with an OE fender direct replacement and he keeps swearing that they were all like that back in the day. All the other reissues ive played or heard do not jump up on volume so quickly.

[@jackbirth7087]

Hello, Do you know a Person in Ireland you can recommend to me please to Service a fender base head please. Kind regards, Jack,

[@PsionicAudio]

I’m sorry, no.

[@mattjohnson6916]

What is the story behind those two large ceramic resistors?

[@PsionicAudio]

One is replacing a choke and the other is to load the preamp nodes to Fender's desired B+ range. The '70s man...

[@mattjohnson6916]

@@PsionicAudio All that's missing are the bellbottoms!!

[@goodun2974]

@@mattjohnson6916 , not just bell-bottoms, but "hot pants"! Mine were red white and blue!

[@zbaby82]

What's the best metal to make a chassis from?

[@PsionicAudio]

Steel or aluminum are both great, if the guage and construction methods are suitable. You can make a bad chassis from either. If I were to have whatever I wanted in a custom chassis I would want the nickel coated steel like the mid '60s Fenders. That stuff is lovely. But not if I have to drill into it. ;)

[@Strumbum01]

Hey Lyle, are 70’s Fender amps, like a Vibrolux Or Deluxe Reverb, worthwhile, or too many possible costly issues? Thanks in advance!

[@PsionicAudio]

Very much worthwhile, but know four things: The glued/dadoed baffles after '72 are harder to replace when needed (and the particle board baffles often need replacing). The heavily waxed boards after '73 usually need to have all the wax removed as it becomes conductive. Many models had circuit changes like the push-pull boost master that most players don't really like,, pot values changed in some bad ways, and some models went to ultra linear output sections for more clean gain. Which many players don't like. Not to mention the white thick spaghetti wiring and poor lead dress. So it can take $300-600 to get them sounding as good as the pre-'72s.

[@Strumbum01]

@@PsionicAudio I remember you dealing with the wax issue on one of your other videos. Great info here, thank you very much for your response!

[@danielsaturnino5715]

Sounds like an easy fix :)

[@PsionicAudio]

Yes. But I have to do this relatively easy fix to almost every post '65 Fender. And never* on the pre-CBS amps. *Sometimes the wires from the board to the brass panel pull out of the solder joint on those. But it's less common than issues with the transformer hardware grounds.