Is this amp "redplating"?

[Structo]

Was that your amp?

[dartanion]

I hear you on reliability and replacing caps with high quality, low ESR caps, but do you measure them before installation? I mean, value and ESR. I can't measure ESR, yet. However, I do measure all the cap values before I install them and with that said, I have seen lots of "new" high quality caps that are OOS. Besides, an electrolytic can blow up at any time. New, old, teenager, etc. If you cannot see any physical damage, and it measures and performs fine in the circuit, tell me how you will know that a cap is going to give up the farm?

Another example. I just did a repair for a client that has this unique and rare amp (no not a Dumble or Wreck) that had a nasty hum to it. The owner brought it to another shop 3 times and they couldn't fix it. The first time in they replaced all the PS caps, with mostly good quality caps, and the owner stated the hum was worse after the new caps were installed. Hmmm...interesting. Well, they replaced all the tubes in the next visit, then gave up on the 3rd visit. When it came to me, I measured the PS caps and 2 were OOS, but not enough to matter. It turned out to be a leaky coupling cap in the preamp, which negated the replacement of all the PS caps. The owner was quite upset that this other place yanked out perfectly good parts that were original to the amp, including the original tubes (mostly UK Mullards). They gave him new, microphonic as hell Sovtek 12AX7s, and a pair GT 6L6GTs that one was on it's way out (flashing was turning white and flaking off).

So, for us as amp builders, it's no big deal to swap parts. For owners of tube amps that are not technically astute, it's rather a big deal. They don't know if they are getting screwed or legitimately getting their amp fixed for issues as such.

[jelle]

Another +1 on replacing old electrolytic caps. And yes, if I would own a tweed deluxe for my personal use, I'd replace all electrolytics before I would switch it on.
These caps are good for about 10 years.

I love the car analogies...would you go on a vacation driving 2000 miles in your 64 chevrolet that still has the original tires on it?

[dartanion]

Another +1 on replacing old electrolytic caps. And yes, if I would own a tweed deluxe for my personal use, I'd replace all electrolytics before I would switch it on.
These caps are good for about 10 years.

I love the car analogies...would you go on a vacation driving 2000 miles in your 64 chevrolet that still has the original tires on it?

Hey Jelle,

If the tires are in perfect condition, no dry rot, no bulges, etc. Then yes indeed I would drive it. There is no way to tell that they WILL blow out on the trip.

Would you drive that same 64 Chevy with replacement tires from China 2000 miles on a trip?

So, would you change the electrolytics in an 80s Dumble if the amp is working perfectly? I bet not, unless you had exact replacements, which even if they're NOS would still be "OLD".

Yes, replacing them is a good practice, but not always necessary.

[jelle]

Yer not giving up aren't you!

I have a box full of those caps. And in certain spots, old e-caps sound better, to me at least.

BTW, did you see my email with the XLS file?

[dartanion]

Yer not giving up aren't you!

I have a box full of those caps. And in certain spots, old e-caps sound better, to me at least.

BTW, did you see my email with the XLS file?

Hey Jelle,

Thanks for sending the file, and I will be working on in over the next few days.

I don't give up on things easily

[Cliff Schecht]

Yer not giving up aren't you!

I have a box full of those caps. And in certain spots, old e-caps sound better, to me at least.

BTW, did you see my email with the XLS file?

Hey Jelle,

Thanks for sending the file, and I will be working on in over the next few days.

I don't give up on things easily

I don't blame your for not giving up, you're also correct in many ways and obviously have experience to back up your talk. I tend to give recommendations based on an engineers standpoint instead of a collectors standpoint because I'm not big on collecting vintage gear, everything I build/use is meant to be played and abused. I agree that recapping a working amp is not necessary, especially on a collectors item, but it's almost always good practice on a working man's amp. In the case of the Montgomery Ward amp, they weren't exactly known to use good parts.. I have a 1954 Silvertone that aside from the replaced electrolytics is completely original and I found that changing the E-caps didn't change the sound, they just made the amp work!

Something else to note about the Montgomery Ward amp posted here is that the caps are the large can electrolytic types which seem to last quite a bit longer. I finished a SE harp amp recently that used all older metal can type caps and haven't had a problem with that amp at all yet, at least in the power supply section.

[Structo]

Heheheh, some might call it Russian roulette.

[img:640:480]http://i23.photobucket.com/albums/b392/ ... C01890.jpg[/img]
This was a Marshall amp and it is a cap can that blew up.
Of course that is a worst case scenario.

The guy that owns it said he was aware of it needing to be replaced but decided to postpone it for whatever reason.
He said it sounded like a gun went off!

When I was young and dumb we used to take smaller electrolytic caps and run a zip cord to them with a knife switch on one side.
Plugged it into the wall then closed the switch.
It was like a firecracker going off!
We did it a bunch until my dad caught us doing it......

[Richie]

Of course that is a worst case scenario

Not really, but different amps i've seen much worse, Multi section Oil caps, yikes !!
plus coupling caps like the one used as the death cap,those can make a huge mess, some of what you see there in that pic,just not as much, along with a bunch of black smoke residue. I don't know if i still have it,but i used to keep those,just to show people. You look at it, and think no way that little cap made that much of a mess.

[Sirca]

Update...

Replaced the 150 ohm/10 watt cathode resistors with a couple 200/10. I also have a pair of 250/10, but tried the 200 first since they have to same form factor as the originals.

I also swapped out the original Siemens 50uF 50V filter caps for a pair of CDE 50uF 50V caps (though the schematic calls for 35 uF).

Plate voltage is 460 vdc and only one pair of tubes were redplating. But I don't have any audio output for some reason (and it's the head as the same i/o with my vox head is fine) so I only had it powered up a minute or so. Will have to sort that out first.