super original 64 vibrochamp recap??

[bullkelp]

Hi all
Im lucky enough to have scored this delightful little amp.
I was told it was an AA764 64 Vibrochamp.
Apart from the power cord, to me, it seems unbelievably clean and original.

Im posting to get a feel for what I should or should not do. I reaaaallllyy want to keep it the museum piece that it is. But I also believe these things should be played.

For what its worth ive made some recordings of how it sounds. For a bit of fun ive also used my 1964 Jag. Lovely to consider they left the factory the same year :)

I propose:
1. Changing the cap can to a new one. Now the AA764 calls for 20/20/20 but I see a 40/20/20 in this, which the ab764 schematic calls for. I have in my parts drawer a CE 30/30/30 and a CE 40/20/20/20
The otehr thing I notice is scuff marks by the soloder joints of the cap can to chassis. Did fender do this?? Or does this suggest the cap can has been replaced.

2. Im going to order an ESR meter but id have to assume the board electrolytics are done for after 60 years. IF i do go about replacing them I want to use the mallory tubes to house them. What is the most sensitive way to do this? Is there a way to leave all exteranl elements intact (board solder joint etc) and conceal everything inside?

OR...should I leave it alone and pop it on the shelf...?

Thanks!

[bullkelp]

[bullkelp]

You can see the scuffs my the solder on the cap can to chassis connections

[bullkelp]

[bullkelp]

Clean/verb

Loop plus some clean boost

Crankypants

Tremolo

[SEL49]

OR...should I leave it alone and pop it on the shelf...?

YES! I'm a firm believer in "Don't fix it if it ain't broke."

You'll likely have to change caps at some time, but not today.

[Willabe]

Nope, I'd change every ecap in a heart beat.

They're too old, and if 1 of the big caps in the can shorts, it could take out the PT.

Standard preventive maintenance.
 

[bullkelp]

Nope, I'd change every ecap in a heart beat.

They're too old, and if 1 of the big caps in the can shorts, it could take out the PT.

Standard preventive maintenance.

Yep I tend to agree tho it does pain me …
I did put back up diodes on the rectifier before I played it for any length of time just in case

I’m certainly going to do the cap can. Just deciding on configuration
It’s a 5y3GT in there . I think I’ll use one of the cans I have

[Latole]

Check if the main and only fuse is the right one.

[bullkelp]

Check if the main and only fuse is the right one.

Yep done , and it is

[acheld]

Maybe I'm wrong, but it looks like one of those Mallory caps might be leaking.  Can't tell for sure from the picture.

[Latole]

Maybe I'm wrong, but it looks like one of those Mallory caps might be leaking.  Can't tell for sure from the picture.

If they are not leaky, the value could be wrong .

It is a good thing to replace them. And keep the old ones.

[bullkelp]

Righto
I’ll get it back on the bench this arvo and test my nerves with ‘stuffing’ a cap inside the casing of a Mallory
I have a CE 40/40/20/20

Shall I use that but leave out one cap obviously
Would you make the 40 the revise cap or one of the 20s (keeping in mind I have a 5y3GT rectifier)
Thanks !

[mresistor]

Are you planning on keeping the amp? If so use both 40s for the first two nodes.  Some also ad a new ps node up front off the rectifier which helps eliminate noise but if you are only playing it through the 8" speaker then the noise won't be bothersome.

[mresistor]

Here you can see later VCs used a 40uf reservoir cap  https://el34world.com/charts/Schematics/files/Fender/Fender_vibrochamp_ab764.pdf


You'll need a big 75-100W soldering iron to remove the cap can.

[Calboy]

I say play it as is and build a vibrochamp clone.

[Willabe]

The time to change the ecaps in that amp 20+ years ago.

And adding an extra B+ filter stage before what's in their stock is getting to be a standard mod.

[HotBluePlates]

... Im posting to get a feel for what I should or should not do. I reaaaallllyy want to keep it the museum piece that it is. But I also believe these things should be played. ...

I agree with SEL49:  I would leave all caps exactly as they are, and play the amp.

   - I didn't hear hum in your clips, telling me the filter caps are good enough.
   - The amp sounds good, so the preamp electrolytic caps are doing well enough.
   - In Fender amps, I usually prefer the sound of 1-2µF cathode bypass caps over the stock 25µF (that can be boomy/muddy), and this is where they tend to go when the cathode bypass caps age/change-value.


I have experienced removing electrolytic caps from 1960s amps, only to find they test as-good or better than modern replacement filter caps.  While the knee-jerk "replace them all" advice comes from a well-meaning place, I don't think it's as absolute as often presented.

... Im going to order an ESR meter but id have to assume the board electrolytics are done for after 60 years. ...

ESR meters are "meh" to me.

I much prefer the Sencore LC75 I got a few years ago.  It places as much as 600vdc across the cap, then measures leakage current in µAs.  That tends to correlate well to performance of filter caps, etc.

[bullkelp]

... Im posting to get a feel for what I should or should not do. I reaaaallllyy want to keep it the museum piece that it is. But I also believe these things should be played. ...

I agree with SEL49:  I would leave all caps exactly as they are, and play the amp.

   - I didn't hear hum in your clips, telling me the filter caps are good enough.
   - The amp sounds good, so the preamp electrolytic caps are doing well enough.
   - In Fender amps, I usually prefer the sound of 1-2µF cathode bypass caps over the stock 25µF (that can be boomy/muddy), and this is where they tend to go when the cathode bypass caps age/change-value.


I have experienced removing electrolytic caps from 1960s amps, only to find they test as-good or better than modern replacement filter caps.  While the knee-jerk "replace them all" advice comes from a well-meaning place, I don't think it's as absolute as often presented.

... Im going to order an ESR meter but id have to assume the board electrolytics are done for after 60 years. ...

ESR meters are "meh" to me.

I much prefer the Sencore LC75 I got a few years ago.  It places as much as 600vdc across the cap, then measures leakage current in µAs.  That tends to correlate well to performance of filter caps, etc.

This is reassuring
I have put rectifier diodes in place as a back up
You’re right, it has no hum, I would say the low end farts out a bit and isn’t all that stout but I wouldn’t expect it to be . Would be nice to compare it to another but that’s not gonna happen .

You’re right, there isn’t much noise floor / hum.

So this is the core of what I’ve been throwing around in my head . Leave it be or ‘fix’ her up.

The old if it ain’t broke don’t fix it etc

If I were about to rely on it for gigging or receding daily then maybe I should done in there . But in reality this might get played once a month as a bit of fun. I have other amps that are old and non original that are my go to for playing .

Is it worth doing some measurements for DC leak etc ?

[HotBluePlates]

Is it worth doing some measurements for DC leak etc ?

If you measure DC Volts on each tube pin, you will see whether any grid has something other than 0vdc.  That's good enough.

However, the coupling caps in your amp generally are not known for leakage.

[bullkelp]

I see or hear nothing wrong so there is no reason to change anything.  I say play it as is and build a vibrochamp clone.
When the time comes change what is needed.


Did you miss reply #6?

Yes sorry! for some reason is goofy when I try and use this on my phone

[Latole]

Here you can see later VCs used a 40uf reservoir cap  https://el34world.com/charts/Schematics/files/Fender/Fender_vibrochamp_ab764.pdf


You'll need a big 75-100W soldering iron to remove the cap can.

I have this powerful iron,
I found it is easier( and faster )  to break the tab and pull it off them with pliers. 

[Latole]

The old if it ain’t broke don’t fix it etc

They are very very old , put new F&T caps. if you don't want to do the job in......like 1 or 2 years.
You have your hand inside now

[tubeswell]

If this was my amp, and I didn't want to flick it on as an unmolested vintage amp - but instead wanted to keep it for playing, I'd replace the filter cap can (and maybe the 5Y3). If you burn up the original PT, the replacement/repair PT won't be original either. I bet Leo never intended the original cap can to last forever.

[scstill]

If this was my amp, 
I'd replace the filter cap can (and maybe the 5Y3). If you burn up the original PT, the replacement/
repair PT won't be original either.

So understand replacing the old electrolytes, but in my Silvertone 1484 I kept the original red Planet electrolytes because it sounds really good (I play it often) and they look kind of cool. Why (if at all) could a faulty Electrolyte be risky to the amp?

I also prefer to use vintage tubes including rectifier tubes. Is this risky to the amp? Should I be installing SS diodes as backup to the rectifier tube??

[tubeswell]

If this was my amp, 
I'd replace the filter cap can (and maybe the 5Y3). If you burn up the original PT, the replacement/
repair PT won't be original either.

So understand replacing the old electrolytes, but in my Silvertone 1484 I kept the original red Planet electrolytes because it sounds really good (I play it often) and they look kind of cool. Why (if at all) could a faulty Electrolyte be risky to the amp?

I also prefer to use vintage tubes including rectifier tubes. Is this risky to the amp? Should I be installing SS diodes as backup to the rectifier tube??

No biggie. YMMV

[Latole]

If this was my amp, and I didn't want to flick it on as an unmolested vintage amp - but instead wanted to keep it for playing, I'd replace the filter cap can (and maybe the 5Y3). If you burn up the original PT, the replacement/repair PT won't be original either. I bet Leo never intended the original cap can to last forever.

I agree !

[Latole]

If this was my amp, 
I'd replace the filter cap can (and maybe the 5Y3). If you burn up the original PT, the replacement/
repair PT won't be original either.

So understand replacing the old electrolytes, but in my Silvertone 1484 I kept the original red Planet electrolytes because it sounds really good (I play it often) and they look kind of cool. Why (if at all) could a faulty Electrolyte be risky to the amp?

I also prefer to use vintage tubes including rectifier tubes. Is this risky to the amp? Should I be installing SS diodes as backup to the rectifier tube??

New F& T filter caps may make the amp sound better.
A shorts 'lytics may destroy the PT in the worst case.
Rectifer tubes ,vintage or new are same ; they have nothing to do with sound.

[tubeswell]

Rectifer tubes ,vintage or new are same ; they have nothing to do with sound.

Yeah if the rectifier tube works fine, no problem.

[Latole]

Many enthusiasts are interested in tubes, but often through ignorance or lack of knowledge of a good tech, neglect the other parts of the amp and more often the bias.
Good tubes ( or NOS tubes ) can be a waste of money if the amp's other components are not in good condition.
Just as “modern” tubes can give a better result in an amp in good condition.

This text is not mine but that of someone who knows a lot about amplifiers and I fully share his opinion.
______________

I will warn you about fake NOS tubes being sold widely.
NOS = New Old Stock (new UN-used tubes are the only real "NOS" tubes.)

But many vendors have been selling old used (beat to death) tubes, and calling them "NOS."
Don't fall for it.

This tube "tests NOS." Don't fall for it.

Just about 80% of all of these old used tubes which supposedly "test NOS," are defective.

The best way to avoid being scammed: Buy only NEW tubes from highly reputable dealers.

Yes, there are REAL NOS tubes.
But these tubes are new UN-used tubes. And these tubes are mostly very expensive.
If you insist on buying "NOS" tubes, be very cautious about where you are buying them from.

[scstill]

I don't look for NOS
Just good vintage tubes.
Big plus if the lettering is good.

I have been into 12AU7 lately especially with clear glass on top.
Looks really good when operating.

[HotBluePlates]

It's not common for electrolytic caps to fail suddenly as a short-circuit.  Normally leakage increases over time and/or the capacitance falls away & the amp starts humming.

A scenario has been raised of, "What if the filter caps fail & smoke the power transformer?"

   When I was new to amp-tinkering, I tried the "Transformer Shunt Method" of measuring power tube idle current.
   The meter is configured to measure current, where the meter does its best to be a short-circuit (to route current through the meter).

   When I got done measuring tube idle current, I forgot to re-configure the meter for measuring Volts.  I poked the B+ and short-circuited the power supply.

   One time I blew the meter's fuse, and the other time I blew the amp's fuse (I'm not the Brightest Bulb in the Box).


Point being if the amp has a fuse & it's properly-sized, we expect it will do something to prevent a catastrophic event.

I'm not against replacing the filter can, but the rigid dogma seems unwarranted when an amp demonstrates it is performing well (and my unexpected experience measuring <3µA of leakage on a 60-year-old filter cap with 400v present taught me this "rule" isn't as strict as we might believe).

[mresistor]

To illustrate what HBP talked about - I'm currently working on a 1967 Deluxe Reverb. The owner wanted the reverb fixed.  I did a cursory power up and check out and sure enough when I turned up the reverb there was nasty hum like a choirboy that doesn't know the words to the song. 120Hz hum.
So I shut it off drained the caps, flipped it over and took off the doghouse cover. Someone had previously serviced the amp and installed 3 16uf F&T caps and two apparently used grey IC caps. Of course the cap feeding the B node was the culprit. I pulled it and measure it. It measured 34pf.  That cap is definitely bad, but the circuit was still working, albeit with loud hum.     I have no idea why someone would install only 3 nice caps and two dogs..

[Latole]

I don't look for NOS
Just good vintage tubes.
Big plus if the lettering is good.

I have been into 12AU7 lately especially with clear glass on top.
Looks really good when operating.

 A tube which tests 100% good can fail after it warms up. No BS.

Consumer Tube testers are not accurate. Tube testers will miss about 6 out of potential 10 problems.
Tubes which are pre-screened by professional tube labs are far more trustworthy.

According to me: the best way to test a tube is in the actual circuit. I don't trust tube testers unless it's done by a tube testing lab.