1959 Premier 71...MINT! change wax caps?

[O-Fuzz]

Hello all,
Been a while, but another jem has graced my bench...this 1959 Premier Model 71 in near MINT condition. The amp had never been opened before. As of now I've added a 3-prong, and changed out the can-cap.
Question - should I automatically change out all of those original wax caps??

Please note, I couldn't find the schem for a Model 71, but I included one for the Model 76, which I believe is quite similar.

THX!
O.

[AlNewman]

Question - should I automatically change out all of those original wax caps??

Yes.  Especially at ground connections with high voltage.  And the bumblebees as well, which I believe are also paper in oil.  Once you start changing them out, measure the capacitances.  I doubt any would fall into a 25% tolerance, and most would be at least double the capacitance they're rated for.  That's my experience, anyways.

[roarshock]

I'm just a garage amp builder, but I'd recommend asking your customer what they want and moving forward with that.  Some collector types may allow workable tolerances for the aesthetic and others, like a performing musician, may want every part possible replaced.  The owner knows, none of us do.

[Latole]

I will not replace coupling wax caps if they don't leak .

I will replace all 'lytics caps mostly filters caps

[shooter]

I'm in the "don't fix it if it ain't broke camp"  especially vintage original.


do all the DC checks, bust out the scope, chase signals through noting "oddities"
play it long time joe, evaluate what you find
talk with customer; "Is this an investment amp, a play it like you stole it amp....."

[AlNewman]

I have to disagree.  Some of them could make a real mess if they went.
There's a death cap, 2 caps on the power rail, a coupling cap off of 4A which could potentially take out the transformer, a coupling cap from 2A to the grid of the PI, the 2 PI coupling caps feeding the grids of the power tubes...

[Latole]

Hello all,
Been a while, but another jem has graced my bench...this 1959 Premier Model 71 in near MINT condition. The amp had never been opened before. As of now I've added a 3-prong, and changed out the can-cap.
Question - should I automatically change out all of those original wax caps??

Please note, I couldn't find the schem for a Model 71, but I included one for the Model 76, which I believe is quite similar.

THX!
O.

[Latole]

I have to disagree.  Some of them could make a real mess if they went.
There's a death cap, 2 caps on the power rail, a coupling cap off of 4A which could potentially take out the transformer, a coupling cap from 2A to the grid of the PI, the 2 PI coupling caps feeding the grids of the power tubes...

These are not coupling caps  in my book

[O-Fuzz]

Thank you all for the feedback!

I should mention that the amp sounds really great, articulate, and warm and chimey - strong tremolo...but after about 30-40 minutes it starts to develop audible noise particularly while rolling the pots...i'm thinking as the unit heats up, already leaky caps start to leak more DC to ground, thus the noisy pots. I'm starting to lean towards changing out the wax caps...

I know this would be to the chagrin of many purist, with such a pristine example of an amp, but I'll have afurther conversation with the owner and go from there...stay tuned for an update!

THX!
O.

[Latole]

Thank you all for the feedback!

 i'm thinking as the unit heats up, already leaky caps start to leak more DC to ground, thus the noisy pots. I'm starting to lean towards changing out the wax caps...

 
THX!
O.

The coupling cap can't leak  to ground, you talk about decoupling caps.  Not same .

Your issue is from the 2 coupling caps I show one with the picture.

The side from the tube plate may have 300 volts , the other side must have : 0 volts
You may read few volts that is why volume are scratchy .

[AlNewman]

I have to disagree.  Some of them could make a real mess if they went.
There's a death cap, 2 caps on the power rail, a coupling cap off of 4A which could potentially take out the transformer, a coupling cap from 2A to the grid of the PI, the 2 PI coupling caps feeding the grids of the power tubes...

These are not coupling caps  in my book

Actually, I'm pretty sure the ones I identified as coupling caps are indeed coupling caps.
I did mislabel the choke as a transformer, so you can get a gotcha on that.

[O-Fuzz]

Sorry Guys, I just don't know my way around these forums quite enough to 'quote' correctly...

But both @Latole, and @AlNewman,
You fellas bring up great suggestions, points and perspective...
Clearly you are both more skilled than I am in regards to tube amp circuits. I'd love to speak to either or both of you directly specifically about this amp. Does the forum allow direct phone communication between members??

THX!
O-uzz...

[Latole]

Sorry Guys, I just don't know my way around these forums quite enough to 'quote' correctly...

But both @Latole, and @AlNewman,
You fellas bring up great suggestions, points and perspective...
Clearly you are both more skilled than I am in regards to tube amp circuits. I'd love to speak to either or both of you directly specifically about this amp. Does the forum allow direct phone communication between members??

THX!
O-uzz...

PM send

[HotBluePlates]

...this 1959 Premier Model 71 in near MINT condition. ...
Question - should I automatically change out all of those original wax caps??
...

... I know this would be to the chagrin of many purist, with such a pristine example of an amp, but I'll have afurther conversation with the owner and go from there...

As you said, this amp is mint and it belongs to someone else.  That changes the calculation.

I would measure DC Volts at all tube pins.  If you have evidence of DC-leakage from any cap (due to DC Volts on tube grids, or low DC Volts due to leakage to ground), then know which to replace.

Your customer might want a replacement that "looks original" at which point you consider whether it's possible to cut an original cap in half, to re-use as an outer shell for a modern polyester cap (which will generally be much smaller).


There are tools you can use that can measure whether a cap is leakaging & quantify the leakage current.  Sometimes you find 60-year-old electrolytics that are just as good as a modern cap, in spite of all forum-wisdom to the contrary.  A challenge is you'll need to remove the cap from the circuit to make the measurement.

If you have a museum-piece, sometimes a collector will not want it tinkered, even if that is required to make it functional or playable.  I own such a museum-piece, which looks the same as the day it was made in 1962 (even has the shipping box, with the list price written on the side by the store that received it).  If I had to replace anything in it, I'd make every possible effort to make it appear as though nothing had been changed.

  - I own the Impedance Meter linked above.
  - Even before using it, I would guess 95+ percent of all the wax caps leak DC, based on prior experience.
  - But my experience owning a museum-piece amp teaches me to tread with caution, especially when it's someone else's amp.

[Latole]

Very good advice HotBluePlate.

Where I disagree is with the advice to cut off old capacitors and use them to hide new ones.
I prefer to keep old capacitors whole in a safe place. They're valuable to collectors.

[AlNewman]

I do a lot of radios, and they're all unique in their cabinets, glass, etc.  In my experience, the electronics aren't normally considered as far as collectible desirability.

Maybe there's a museum market for a radio that won't work due to wax caps, but I think most collectors want to be able to turn on the power without their sphincter tightening.

Any radio I've ever rebuilt with original wax caps will not work properly until I replace every essential cap.  Guitar amps don't have the same tolerance, so they will still work with some leakage and capacitance differences, although likely not as designed.  That being said, I've never come across a guitar amp that uses wax caps, that technology was likely 20 years behind most factory built amps that we're used to seeing.

Every time there's a major fault in radio that I've seen from the early 20th century has almost always been due to a capacitor.  Mainly output transformers, but other faults as well, including pretty much any inductor or transformer, as well as otherwise fine carbon comp resistors.

I've thrown away hundreds of wax capacitors, and will likely throw away hundreds more.  I'd be happy to send them out for the price of shipping for anybody interested in trying to convert them to a museum presentable piece.

Those were all my radios though, and as mentioned earlier, your customer's needs are 1st priority.

[O-Fuzz]

Thank you all for the feedback!

 i'm thinking as the unit heats up, already leaky caps start to leak more DC to ground, thus the noisy pots. I'm starting to lean towards changing out the wax caps...

 
THX!
O.

The coupling cap can't leak  to ground, you talk about decoupling caps.  Not same .

Your issue is from the 2 coupling caps I show one with the picture.

The side from the tube plate may have 300 volts , the other side must have : 0 volts
You may read few volts that is why volume are scratchy .

[O-Fuzz]

Hello All,
First off...thank you for such pointed advice and suggestions.

So clearly I'm going to go slow with this one - I should also say that I am NOT a fully trained or qualified amp repair technician...But I am learning...and often need a little help...but, I am also not necessarily a beginner.

OK, feeding on Latole's note about starting with the de-coupling caps - just want to be sure i'm on the right track. Please see pics attached - I believe these are the bypass caps (de-coupling caps) (circled in RED)- the larger, .05u goes to pin 6 of V1 and the smaller, .022u goes to Pin 1 of V1. They then go to that socket (circled in green), which connects to a wiring harness to the control panels volume and tone pots. I suppose the fact that though the schematic shows both of those as .022u, that has to do with the fact that my amp is a model 71 and the schem is for a model 76 - similar, but not the same.

OK, next is to get some reading on those caps voltages - but alas, that will ahve to wait till tomorrow.

-Cheers all!
O-Fuzz

[rake]

To me the most important part of an amp like this is what's the owner looking for?
If it's a collectable closet queen just to show off to other old amp nerds then originally is definitely paramount.
But, if the owner plans to gig with this amp and wail on his mouth harps in clubs for $$$$ then sound & reliability
are the top priority. Always have a real good sit and bullsh*t session with the owner / end user.
Either way never, ever, EVER throw away any replaced OEM components! Bag them up and give them back to the owner.
If he doesn't want them, stash then in your vintage parts drawer. IMHO, it's not an amp if it doesn't work!

But, she's definitely a looker!

[Latole]

I do a lot of radios, and they're all unique in their cabinets, glass, etc.  In my experience, the electronics aren't normally considered as far as collectible desirability.

What I meant to say was that a future amp buyer/collector, who would pay a high price, would appreciate having these old parts at the time of purchase. the parts alone are, in fact, worthless.

[rake]

If the amp is going to be a "full time player" it's usually best to fire the "cap cannon" at it even if some of the parts are "still good". 
Sometimes even the "resistor cannon" is needed. 

The used parts are only "worthless" until you need one to save an "all original" amp for the collector market.   

[bmccowan]

So, I am assuming that you talked with the owner and he says to get it working proper. Good decision IMO. After all, that's why you replaced the power cord and the filter cap can, eh? And last I checked there are not many amp museums out there. Although PRR located a hammer museum so
Doing a good job replacing point-to-point caps is not as easy as it might appear. Sometimes the leads, which are much heavier than modern cap leads will be wrapped tightly around tube socket terminals and tag strips. Protecting with a heat sink and removing all old solder from the connection will make for a neat job. A vacuum type desoldering iron is rather expensive, but when I finally got one, I kicked myself for waiting. Also, planning carefully where you place a hot iron will keep you from burning the insulation on nearby wires. I would choose tubular replacements, as orange drops will look modern IMO.
My apologies if you know all this. 

[mresistor]

The Jupiter capacitors that Doug sells right here would look right at home in that amp.  If thats out of your budget then the Mojo Dijons would work.

[Dave]

I don't "shotgun" replace anything but E-caps. It might take a little extra time, but verifying the function/leakiness/value of caps before I replace them, I consider to be best practice. In the case of an amp like that, "if it ain't broke, don't fix it" is the approach I would take. Someone suggested replacing all the bumble bees. Again, I disagree. Invariably, some of them will be leaky, no doubt. Some will be fine. The ones that are fine will likely stay that way for a long time to come. Why replace them?


I once built an entire (big/complex) amp using only rescued/repurposed bumble bees. Love that amp.



Dave

[mresistor]

Dave  how long into the future will the bumblebees be "fine"?  On has to consider that aging has results. They've been fine sitting in the amp that wasn't played much but what if the amp gets played regularly?


These are things to consider.   As mentioned above.

[Dave]

Dave  how long into the future will the bumblebees be "fine"?

Good question. Here's the answer.
I don't know.


Here's my logic.
After 70 years of service, many were leaky or out of specs or both. I figure that the ones that weren't leaky or out of specs, or both after 70 years of service are probably going to be alright for quite a while longer.


Am I right?
Who knows. I just play my amp.


Dave

[bmccowan]

I think if working on your own amp, replacing only what has failed makes sense. But if working on a customers amp, it is important to consider the longevity of the amp as it is returned to the owner. Presumably they expect it to perform well for a significant time period before it again needs service. I no longer play gigs, but when I did, the last thing I wanted was an amp going off song.

[O-Fuzz]

Hey All,

OK, so first - thanks for all of the great advice and commentary....I take all of it to heed...

So here's the update...I had a conversation with the owner, who intends on playing the amp very little, who is not a working stage or studio musician, but does want the amp to sound as good as possible when he does play it for an hour or so, every now and then.

The bottom line, all of the wax caps with the exception of the bypass cap on the instrument channel, tested well. We decided to change out that one cap, and the amp sounds fantastic!

At the end, a changed power cord (upgraded to 3-prong - brown cloth covered for the look), removed death cap, replaced filter cap can, replaced one bypass cap...all original parts are saved and kept with the amp...done...

[rake]

There you go. If another cap should fail down the road it's not as big of a deal as it's not a gigging amp.
And, maybe you get to service it again! 

[HotBluePlates]

Dave  how long into the future will the bumblebees be "fine"?  ...

Just as there is more than one kind of "orange drop," there is more than one kind of Sprague cap with the "bumblebee" appearance.

Some have paper dielectric, and will very certainly become leaky.  Others are "di-film" types with both paper and plastic (the new "Mylar") dielectric, and tend to last & last.

The non-nostalgic Radio Guys immediately rip & replace all wax & paper caps without testing.  They don't care about what the radio looks like inside.  But Guitar Amp Collectors care about originality (the vintage guitar collectors & repair guys are looking at every solder joint to discern whether they're factory-original).

So there's a tension between Collector Value and "make it work."  A true Time Capsule may be non-functional; making it work might detract from the vintage-value.  So it's wise to be well-versed in the vintage market & know how much of a hit a particular model might take for changed-parts (because it's absolutely not a single answer for all amps/brands/models).

[AlNewman]

The non-nostalgic Radio Guys immediately rip & replace all wax & paper caps without testing.  They don't care about what the radio looks like inside.  But Guitar Amp Collectors care about originality (the vintage guitar collectors & repair guys are looking at every solder joint to discern whether they're factory-original).

Again, I have to disagree.

Most radios I see are basically one-offs.  I am absolutely nostalgic in how I protect the things that can't be replaced.  Capacitors and resistors are cheaper and built better than anything available 100 years ago.  But it breaks my heart to drill holes in a 100 year old chassis to install a non-original transformer.
Even tubes for certain purposes are becoming non-obtainable, and besides a major redesign if an amp has been neglected due to improper service, they become junk.
Maybe it's just that guitar amps are a few years behind.  And, granted, maybe that's a good reason to try and preserve their originality.
On the other hand, I listen to my radios and play my guitar amps all day long.

[bmccowan]

O-Fuzz, you likely had no idea what you started here.
I know no radio collectors, so I will not comment on that hobby.
But, I will comment on amp collecting.

But Guitar Amp Collectors care about originality (the vintage guitar collectors & repair guys are looking at every solder joint to discern whether they're factory-original).
So there's a tension between Collector Value and "make it work."  A true Time Capsule may be non-functional; making it work might detract from the vintage-value.  So it's wise to be well-versed in the vintage market & know how much of a hit a particular model might take for changed-parts (because it's absolutely not a single answer for all amps/brands/models).

I have no doubt that HBP is correct here. But I am hoping that the silly fixation on factory original eases. It makes no sense in the context of collecting hobbies and vintage markets. Consider vintage cars. Whether it's impeccable restorations or "survivors" (both are valuable these days) unless the car runs and drives it does not reach anywhere near top $ value, nor does it get awards at car shows. I've been to the Concourse d'Elegance at Pebble Beach a couple of times and the judges severely downgrade cars that will not start and drive. The day before the judging the cars go on a tour of the area and then park in Carmel so the public gets a chance to walk through and speak with the owners. The highest ranked cars are the ones that are restored to perfection and have "correct" parts, not necessarily original parts. Vintage motorcycles and bicycles are valued the same way.
Guitar amps have one purpose: make an electric guitar useful. They were meant to be played. Capacitors are consumable parts. Leo used eyelet boards both to make assembly modular and also to ease the repair. The excellent book The Birth of Loud  details the amazing amount of time Leo and George spent repairing their amps that were returned by dealers and owners.
So back to O-Fuzz. You and the amp owner did the right thing IMO. It's a beautiful amp - just look at that lovely faceplate with the bakelite knobs. And now it sounds great too. Those combined attributes make it more valuable to me than the same model in perfect original cosmetic shape that snorts and sizzles when someone dares to power it up.
End of rant.
 

[rake]

Mac, My day gig is stringed instrument repairs. Recently had a guy come in with a pre war 000-18 Martin.
It was beautiful but unplayable. The neck block came unglued causing HIGH action and it really needed a fret job.
The owner was worried about originality. I told him he could have an original wall hanger or a playable pre war guitar!
When done it played, looked and sounded superb! Sometimes there are no perfect solutions so we have to take the best solution.
An all original amp that doesn't work may as well be a coffee table!

[HotBluePlates]

I'm not claiming "correctness" but only offering a different perspective.

In fact, I have to consider how to tackle a related issue in my museum Ampeg amp: I think there may be some leaking Astron caps, but this thing is a Time Capsule.  I post a picture later, but the 2-prong power cord hadn't even been uncoiled from how the factory bundled it for shipping (the prior owner replaced it with a 3-prong, but directed the tech not to uncoil the cord).

So a workaround is to replace parts that need replacing, but consider whether the new part could be housed in the husk of the old part.  Yes, it's only value is appearance if someone opens the amp.  But when the amp is near-mint, the market may make the effort worthwhile.

For example, an average Ampeg amp (which tend to be in rough condition) will bring $600-800, while an excellent condition example could bring double that price.  And I've got one where the chrome is perfect, the covering is perfect, the innards are 100% original, and even the tubes are the Ampeg-branded Sylvania tubes installed at the factory.  That thing might be $3k+ in today's market, which has shot up 200-300% since before the pandemic.

OR... the particular amp/model may be unloved, and have no special collector value regardless of perfect condition.  So I advocate "know the market" when it's near-mint, and especially when the amp belongs to someone else.



These guys have a reputation as "price makers" (pricing well above prevailing market-value), but I doubt they would be brave enough to ask $2400 for an amp I paid $700 to get a few years ago if it had been visibly altered from its factory condition.

[shooter]

the only "high-dollar" amp I worked on was a 64 showman?  (can't find the file!)  was listed working, in original condition ~$3k, even found some that sold around that price, so when the owner called, I stepped up with my A-game.
 
He didn't want a 3 prong, didn't want any "typical changes" Ecaps et al.  just stop it from dropping signal.
 one bad solder joint later it was working, biased, all VDC and VAC checks recorded,


but one channel's TS was crap, got the go-ahead, rebuilt, but I cleaned up the 3-4 old parts leads, polished up the 1 pot, put them all in a box, with notes, that way the "next guy" could re-install if someone wanted "vintage original"

[bmccowan]

Given the current start of the collectible amp market, I think HBP is spot on. I am only helplessly hoping that someday soon, collectors give playability the respect it deserves. Not because I want to sell them my ratty amps just because I want people to have the pleasure of playing through a great sounding amp without hurting the value by replacing a few capacitors. I bought Apple stock 20+ years ago. Its up 800% but never sounded all that good.