50's 5E5A - Repairs for Reliability

[Robert Technology]

Hello!

A buddy of mine has a 50's Fender 5E5-A that I've done some work on before (just the minimal amount of changes to keep it up and running), but now wants me to "do whatever I need to in order to make it reliable."

He's had this amp since he was a kid and is never going to sell it or be concerned with re-sale value; he simply wants it to be as reliable as possible so that he can use it for playing shows without any concern.

My current plan of attack is to replace all of the jacks (some have already caused issues after losing their ability to close all of the way. I've burnished and flexed them into place in the past), check and replace any drifted resistors, as well as any that appear to have partial heat damage, and replace the selenium rectifier in the bias stage while also adding an adjustable bias control. I've already changed Filter caps and any caps with notable DC leakage, and installed a 3-prong power cable.

What do people tend to do when replacing the Selenium rectifier in these amps?? I've seen some mixed information online about whether a dropping resistor is needed, or if you can simply drop in a 1N400X diode or two.

When I've worked on it before, I did the bare minimum, wanting to maintain the "integrity" of its vintage, but with his latest statement I'm tempted to simply replace all of the coupling and bypass caps. Will I be kicked out of the forum if I pull Astron caps from an amp like this, even if they test with minimal DC leakage??

Fender-Pro-5E5A-Schematic.pdf

[Leo_Gnardo]

All of that sounds like a good plan, along with the things you've already done. Maybe one more, remove the "death capacitor" from AC line to chassis, if you already haven't. Since you're putting in a bias adjust pot, there may be no need to do anything else to transition from selenium to silicon rectifier. At most, maybe change one resistor so that the bias is within range. You'll notice a slight increase in bias voltage when you go silicon. Install your adjustment pot, then evaluate whether you need to make any further change.

No you won't get launched outta here for replacing Astrons. The bypass caps must be on their last legs, going for 60 years old. Coupling/eq caps, you may leave in place but they are similarly aging. To be reliable - to add "in the future" seems redundant - I'd swap in Mallory 150 film caps but you may choose whatever you like. Any mica caps (treble control mostly) need to be considered too. I've seen these "super reliable" caps go bad in aging amps. What's worse, one customer brought in his expensive boo-tiki amp where the builder had installed NOS mica. It was making a symphony of awful rackety noises. Guess what - mica! Heck I've even seen new-ish less than 20 year old silver micas go bad. Not that there's a rash of that. OTOH I've never had a regular 1000V rated disc cap go bad yet in the treble function.

[Robert Technology]

Thank you for the response!

I forgot to add that I removed the "death cap" when changing the power cable the first time this amp was brought to me.

I hadn't even thought about the mica caps, so thank you for pointing those out! I'll plan on replacing any of those out as well and will size my limiting resistor for the adjustable bias as needed to get within the proper voltage ranges.

This amp really is something special... The owner has had it since it was new and he is one hell of a player, so he really just wants it reliable and playable without any concern. I've gotten to play it at a few shows and it sounds INCREDIBLE as is, but it really is too nice of an amp to not be played.

[Justin Thomas]

I'd question the original speaker if it's still in... invest in a fine vintage-style replacement and box the original for safekeeping. Or if he's genuinely not concerned about resale value, play it to it blows... one option is to keep the speaker detachable, so he can just plug into a cab if desired and save the original for extra-special occasions...

Justin

[Robert Technology]

I'd question the original speaker if it's still in... invest in a fine vintage-style replacement and box the original for safekeeping. Or if he's genuinely not concerned about resale value, play it to it blows... one option is to keep the speaker detachable, so he can just plug into a cab if desired and save the original for extra-special occasions...

Justin

This is an excellent point. I'll make sure to ask if he has any concerns about the original speaker being gigged regularly, although I suspect he'll want to play it until it blows.

Are the Weber replacements still the go-to replacements for something vintage? I've always deferred to those or Celestions for personal use, but honestly don't have much experience with newer Jensen speakers.

[Leo_Gnardo]

Are the Weber replacements still the go-to replacements for something vintage? I've always deferred to those or Celestions for personal use, but honestly don't have much experience with newer Jensen speakers.

That's a Tweed Princeton, right? I think that's an 8 inch speaker. My customers & I have been happy with the Weber ceramic mag 8, still cheap just over $30 if I recall. In fact probably the cheapest of all the 8's. So called "reissue" - Recoton - ceramic mag Jensens, MOD series, also good, but don't tell Weber that, they have a feud going on.

[Enzo]

About "out of tolerance" resistors. That sounds great, but sound is the issue. He is used to hearing the amp with the resistors at current values. Out of tolerance won't hurt the amp. But if some resistor has gone from 100k up to 140k, well he likes the sound of that, and you stick in a nice new fresh 100k part, and the amp is changed. 1950s amps were made with 20% resistors anyways.

[Justin Thomas]

Leo,

That's a Pro.
1 - Champ. 2 - Princeton. 3 - Deluxe. 4 - Super. 5 - Pro. 6 - Bassman. 7 - Bandmaster. 8 - Twin. 9 - Tremolux. 10- Harvard. 11- Vibrolux. 12- Concert. 13- Vibrasonic. 14- Showman. 15- Reverb Unit. 16- Vibroverb

Justin

[Robert Technology]

That's a Tweed Princeton, right? I think that's an 8 inch speaker. My customers & I have been happy with the Weber ceramic mag 8, still cheap just over $30 if I recall. In fact probably the cheapest of all the 8's. So called "reissue" - Recoton - ceramic mag Jensens, MOD series, also good, but don't tell Weber that, they have a feud going on.

This model is actually the "Pro" with a 15" speaker if I'm remembering correctly. It may be a 12, but I'm pretty sure it had a 15" last time I worked on it.

[Leo_Gnardo]

This model is actually the "Pro" with a 15" speaker if I'm remembering correctly. It may be a 12, but I'm pretty sure it had a 15" last time I worked on it.

Woops, I should'a looked up the Fender model number.

[Robert Technology]

About "out of tolerance" resistors. That sounds great, but sound is the issue. He is used to hearing the amp with the resistors at current values. Out of tolerance won't hurt the amp. But if some resistor has gone from 100k up to 140k, well he likes the sound of that, and you stick in a nice new fresh 100k part, and the amp is changed. 1950s amps were made with 20% resistors anyways.

Thank you for pointing this out Enzo!

I should have written this out when I'd had more coffee in my system. When I said that I would change any out of tolerance resistors what I meant to say was only those that seemed as though they were on the verge of failure or could cause issues for the amp. If something has drifted a bit I'll leave it in to maintain the sound. My intention is to change as few parts as possible in order to change the sound as little as possible, while still making it as reliable as possible for regular gigs.

What's the consensus on too much drift? An order of magnitude? My gut is saying it's more complicated than a "one-size-fits-all" answer and that I would have to look at whether the drift in resistance then caused a voltage that would be too high for the component (resistance drifting high), or alternatively too much current (resistance drifting low). I suppose in extreme cases I'd also have to consider how an increased voltage or current would affect associated components and stages as well!

[Enzo]

Resistors almost never drift low.

Current is not often the issue. Imagine say 220k grid resistos on a power tube. No current runs through them. Likewise a plate resistor on an input stage. Stock values in amps prange from 100k to 470k, so if your 100k rises to 200k, so what, there is only maybe a milliamp in the circuit. Up in the B+ supply is the place to think about current and resistors getting hot.

[Mick Bailey]

The issue with replacing parts is where to stop before you end up with an original chassis and a load of replacement parts. Reliability, like durability, is a retrospective view. You already know how long the original parts have lasted, but there's no certainty that anything you put in there that's brand-new today will last as long. Equally, the remaining life in existing components is difficult to predict or estimate.

Electrolytic caps aside, unless there is a good reason to replace a part, my view is to leave it alone if it's working fine. I always advise customers to work out a backup plan in case an amp fails. A brand-new amp can fail just as easily as an old one so it doesn't matter what you have - you need a plan B, even if it comes down to an FX unit with a speaker-emulated DI out that can be run through the PA.

So how far do you go? Jeff Beck's main Marshall amp was checked every day when on tour, but he still couldn't rely on it not to fail - neither did his amp-tech. So he had another one powered at all times which could be switched over instantly (hot standby) and in case there was a supply surge there was another one that wasn't connected to the mains (cold standby).

[Robert Technology]

I totally agree with this sentiment! When a problem is not as clear as a specific bad component how far do we go? When is a compromise too much? How long is a piece of string?

The last time I worked on this amp I did my best to change as little as possible while still sending the amp out the door stable and ready to be played. Unfortunately, the owner has said it has been problematic on occasions, and I never seem to be able to simulate any of the issues at my bench that he is having at home. He is not a guy that is going to bring a backup rig (other than potentially a DI where it would be appropriate to do so), and honestly, the gigs he's playing probably don't demand it either way.

However, he has asked that I make the amp as reliable as possible so there's a good chance that those coupling caps are going to get pulled. I've tested them for DC leakage in the past and left any that tested good, but I suspect they are part of the issue. I understand that there are no guarantees that any new part I put in won't fail prematurely, or that it will even last as long as the original, 60-year-old part, has.

There is a risk to all things in life, and uncertainty in everything (sorry if my personal existential crises is bleeding through here... we are all just floating through the void attempting to repair as many amps as possible while there). My intention is to minimize those risks of component failure to the best of my ability, so that this guy can happily play his amp, and maximize the time between now and the next component failure!

I really do appreciate all of the opinions and insight you are all providing, so please keep it coming if there is anything else I should consider!!

[eschertron]

Unfortunately, the owner has said it has been problematic on occasions, and I never seem to be able to simulate any of the issues at my bench

So how far do you go to ensure his patch cords, stomp boxes, etc., are 100% reliable while you are working on his amp? Certainly inspect resistors, sockets, etc., but leave them in if not obviously damaged. Caps, yeah, why not? Maybe test the coupling caps for value after pulling, so you can hand-pick values that will retain the 'mojo'.
As you understand, there is always a risk of failure. Get the amp to "as reliable as possible" and let the owner know there are still things out of your (and their) control. My advice is to feel existentially OK with the work you've done to the amp, and pass that sense of assurance on the the customer.