Blown tubes...is this the truth??

I just dropped the head off with a electronics dude and he thinks the tubes may be blown (he kept repeating "man..these tubes are EXPENSIVE").Yeah, if you hear your dentist saying "Hmmm" or "Uh oh" when he looks in your mouth, or your mechanic uses either of those phrases when he looks under your hood . . .
But if the tech guy hasn't quoted a price yet, it may turn out to not be as bad as it sounds.
The inside was black and he pointed out this sort of halo of white material around a darker circle in the middle of the tube as an example of the fact that it's probably blown.That doesn't sound real promising, but I s'pose you could get a second opinion, maybe from somebody who doesn't keep mentioning how "EXPENSIVE" the tubes are.
It's quite possible somebody here will say the appearance you described is a definite sign that the tubes are toast, but it's the "probably" part that I don't quite get. If the outward signs aren't definitive enough for him, then he should fire up the ol' tube tester (if he's got one) and "rule in or rule out."
I'm not familiar with guitars and amps, but being a Geek I do know about collectibles and classic cars and that keeping items as close to their original condition as possible helps to retain their value. Okay, but which is more valuable to you, a working amp with non-original internal components, or an amp with authentic but dead parts?
If you could find out what tubes are in it, they may not be as "EXPENSIVE" as he says, or there might be some substitutes that will cost less but work so well that nobody can tell the difference. If you can find replacements that won't cost "an arm and a leg," you may be able to replace them yourself. Just pay heed to whatever the other guys here say about biasing and things like that.
Good luck with it.

Disclaimer: Any or all of the above comments may be dismissed as being merely .

start educating yourself on the details as soon as possible. search for the parts on the web, schematics, replacement tubes, prices, etc.
:wink: forwarned is forarmed :wink:

Some tubes are expensive. It all depends on the tube and where you get it. Sounds to me like your amp tech is going to charge you a lot. :shock:

I often recommend Bob at Eurotubes. His tubes are very good, his prices are great (some of the lowest you'll find anywhere), and his service is excellent. Bob will always take the time to answer your personal e-mails.

He will more than likely know exactly which tubes your amp takes.

Eurotubes

If you know for a fact that the only problem with this amp is old blown tubes, buy them yourself and install them. It is normally a very simple procedure. If you can see the tubes, then it should be simple.

ALWAYS EXERCISE CAUTION TO AVOID ELECTRIC SHOCK.

sounds to me like the tubes are shot. even if they aren't, it's probably a good idea to replace them if they are from the 70's. they aren't hard to change by yourself, at least i don't think so. i have an all tube amp, but havne't had to change a tube yet. pretty sure it should be just a "plug in" type thing. also, since you're worried about it not being original, i highly doubt that the tubes that were in it were the original tubes anway, so i wouldn't worry too much about it. you could always keep them in a box somewhere so if you ever decide to sell it and the peron wants the original tubes, you'd be able to give them to that person.

Just as a sidenote to what Wes just said, if you put the tubes in yourself, check the fuse, too.

thanks for the replies everyone. He's got the amp and he's going to take a look at it, let me know what the problem is, and then I'll have to decide what to do. I just feel like that old amp shouldn't be wasted sitting around here doing nothing, especially since I've decided to take up the guitar anyway. It also has an alleged interesting history. It's supposed to have belonged to Pete Townsend's brother, but that could just be a story my brother told me.

that's cool. old ampeg's are usually pretty good amps. anything vintage is usually pretty good. the old saying "they don't make them like the used to" usually applies to guitars and equipment. you'll have to let us know how things turn out. and make sure to ask on here before he puts any expensive parts on the amp.

You cannot test a tube by looking at it!
(Unless the glass is broken)

Burn marks are completely normal for tubes.

The best way is to use an old tube tester.
Find a repairman that has one (it's a sign of a specialist)!!!
(They do sell them on Ebay)

Have you (or your tech) tried plugging the amp in and strumming a few chords?
Often bad tubes will still work - they just sound bad, or only one channel will work.

Those amps are a part of guitar history. They were very reliable.

Was it even plugged in before it was taken it apart?

Here's a great site with information. Ampeg v4.com

Joe

As a former owner of a V-4 half stack, spend the money. The sound will be well worth the expense.

Of course, this same half stack started my love affair with small, LIGHT combo amps after having to do a series of gigs at a club where we had to load in three flights up a fire escape.

V-4's are HEAVY, man :shock:

Your tech doesn't know what he's talking about.

The only ways you can look at a tube and know it's "blown" are if there are obvious cracks or breaks in the glass, there are pieces obviously loose and rattling around inside, or if that dark "getter" deposit on the glass has completely turned into white powder.

Having a shrunken getter with a halo of white around it doesn't mean that tube's gone bad. It means that the getter's been doing its job of reacting with traces of air that have infiltrated into the tube over the years, keeping the vacuum up. If there's still a good sized dark spot left, the tube may be a bit "gassy" when first turned on, but as it warms up the getter (a thin film of barium metal deposited from vapor when the tube is manufactured) will activate and "clean up" the gas.

NOS tubes, which are much prized by many, will often show this, just as used tubes that have been out of service for many years will. I have tubes that look like what you've described serving quite satisfactorily now. I have many old used tubes on hand and often use them as replacements.

I would never change out all the tubes in an amp "just because." It's a bad idea for preventive maintenance. The highest failure rate for tubes is when they're new. Once they pass 100 hours or so in service they're unlikely to fail catastrophically, and they'll likely go on working for a long time. It's common for "power tubes" to work well for 1000-2000 hours, and "preamp tubes" to last through several sets of "power tubes." Rectifier tubes have the hardest service and often are the first to go.

You need spare tubes on hand, whether you choose to replace the ones you have or not.

Some Ampeg amps use unusual tube types that have been quite hard to find and expensive, like 7591s. They were unobtainable for a while, after a Japanese man bought up all that were available in the US at the time in the early '90s. But now ElectroHarmonix and JJ both have new 7591s available. A lot of things have come back on the market like that. I think some of those use 7199s, too. Old ones are scarce and pricey. Sovtek has new ones, quite reasonably priced.

(I've got a Hammond H-182 organ that uses some of those oddball '60s hi-fi tube types, so I've looked into those pretty closely.)

Ah, I went to the Ampeg site above and took a peek at the schematic. The output tubes are 7027s. Same tube as the 6L6GC. The ONLY difference is that the 7027 has a dual connection to the screen grid on both pins 1 and 4, whereas the 6L6 has only pin 4 connected to the screen grid. A 6L6 should plug in and work fine in place of the 7027.

Some idiots have built 6L6 amps using the Pin 1 tab on the socket as a tie point for things like screen grid resistors. One wired like that (such as my Pignose G40V) would run a 7027 tube too "hot" and would put +425V on the shell of a metal 6L6 tube. That's dangerous, and a liability risk for the amp builder.

But you can buy good quality 6L6s and plug them right in where your 7027s would have gone, as long as there's a screen grid connection to Pin 4 of the socket, as there certainly should be. If they wired it backward with a single screen connection to Pin 1, it's an easy fix to move it to Pin 4, or solder on a jumper to it (in which case you'd have to post a warning on the amp to NEVER use a metal 6L6 in that socket!)