Retube Or Not To Retube

[Matt White]

Here's some basic questions that I have that others might share...

I have an old Peavey Classic VT series combo amp...2 12's....

The volume has started to waver when I use it...starts loud...fades...comes back....

Are the tubes shot? I've had it almost 20 years...never changed the tubes....

Is it easy to change tubes? I read years ago that tubes carry voltage for quite a while & that you can electrocute yourself if your not careful changing them....

What kind of tubes would work well in this amp?

Price range?


It's my first real amp....

[The_KiD]

Matt,

It sounds like the tubes are at the end of their life. What are the replacement tube designations? El34, 6550 or 6SN7s? There are some cool options for playing with the sound by different tubes. NOS stuff is usually the best sounding.. Let me know what tubes fit and I will give you a couple of suggestions...

KiD

[Matt White]

A shot of the tubes....

[The_KiD]

Matt,

Thanks, it looks like they are 6550's but i cannot be sure. Can you pull one out and tell me what is written on the tube?

KiD

[BrownSound1]

Pulling tubes is not dangerous...unless they have just been on, then you'll burn the shit out of your fingers. Capacitors are the components that store voltage, not tubes.

The tubes in that amp are probably 6L6 power tubes. In fact I'm about 100% certain, because that's a favorite of old Peavey amps. No preamp tubes...solid state preamp. I'm not sure about the biasing of that amp, it could be like the 5150 and not have a bias control (which is the stupidest thing I've seen.)

If those tubes are 20 years old, then they definitely need replacing...especially if you played the amp a lot.

[Matt White]

Thanks Kid & Brownie...for dispelling that old wives tale aboot tubes...
And you are right Brownie...the tube is a 6L6...with a GC under that...made in USA........

And the VT series is a Solid State pre amp.....

And...the TUbe looks pretty spent....I'm sure they need to be replaced...
Any Brand sugestions?

What kind of price for 2 new tubes?

Any kind of collectability to these amps?

Will different Tubes change the sound of this amp?

[rustoffa]

Steer clear of the vintage-tube-selling dipshits on ebay. Well, unless you have an EXTREMELY specific need. Those fuckers are dipshits.

Actually, DON'T steer clear of 'em. Send 'em questions about how many shoeboxes' full of them they have. When they reply all pissed? Go, "my bad dude, I fucked up in my watching list." Then, when they reply back again, go "I sold a MARANTZ just like that for eighteen hundred dollars."

Fuck those rip-off dipshits.

[The_KiD]

Matt,

If you do a google search on the 6L6 Tube you will find a ton of information. If I am correct, you can replace the 6L6 tubes you have with 6550s or KT-66 tubes. These tubes will give you slightly more output power and a much fuller tone.

I recommend the Svetlana Winged 6550's or if you are feeling like spending some money, the Tung SoL 6550 are probably some of the best sounding 6550's ever made. These do not come cheap. Make sure you purchase a Matched Pair with Readings.

If you want to stick with the 6L6 designation, I would suggest a pair of the RCA 6L6GC- Black Plates. You can usually find these NOS (New Old Stock Tubes and I believe they sell for around $85.00-$100.00 a pair for a good matched pair.

I also believe Tung Sol made a 5881 which is the equivalent to a 6L6. Feel free to email me with any questions...

KiD

[Matt White]

I bought the Amp used in 1987...for $50.00

Thanks....I'm gonna shop around...

[Cathedral]

Eurotubes

I like those...

[Nitro Express]

EL-34 are the tubes that are really finiky. Marshall even stopped using them because the good sources of EL-34's dried up. They are better now but still not as good at the Mullards.

6L6 tubes were typically used in American made amps. The 5881 tube is a beefed up industrial version of the 6L6. Fortunately, lots of good new tubes being made now by Svetlana in Russia. Many people bash them but I use Sovtek 5881 tubes in my Sovtek MIG 50 amp and my Golden Audio tube stereo amplifier. I think they sound great.

You have two types of tubes in a guitar amplifier. Low voltage preamp tubes (the smaller tubes that plug into the small sockets) and high voltage power tubes (the big tubes in the big sockets).

Preamp tubes last twice as long as power tubes so you don't have to changed these as much. You can change these yourself by simply plugging a new tube in. If you have wierd ghost sounds or microphonic sounds, the preamp tubes are usually the culpret. I use a chopstick to tap the tubes with the amp on, you can hear a bad tube when it's tapped.

The big power tubes are a different story. They run in pairs so you have to change them all at the same time. You also want to buy matched sets of these type of tubes. Matching tubes is when they are tested and put with tubes of simular characteristics. Mismatched tubes with cause your amp to run cruddy because the signal won't be propperly matched across all of them.

Most older amps have a bias control. This is usually a small knob you turn with a screw driver and is usally located inside the amp. You usually have to take the chassis of the amp out of the box to retube power tubes. THIS IS DANGEROUSE if you don't know what you are doing because the big filter capacitors on the power supply hold voltage like big batteries. There's enough voltage to KILL you if you touch the wires comming out of them.

What I do is drain the voltage out of them by taking an insulated screw driver and grounding it out on the chassis. You get a huge pop and it's still scares the shit out of me. I once had a small screwdriver weld itself to the amp chassis grounding out a big capacitor! Theres a lot of voltage and it's dangerouse.

Once that is done. I pull the old tubes and check the sockets to see if there are any black marks from arching or shorting. I then clean the sockets and push the little pin tabs in to make sure I have a good tight conection on the new tubes. I then plug the new tubes in.

Now you plug a load like a speaker into the amp. You don't want to run an amp without a load because you might damage your new tubes and the output transformer!

What the bias does is control how much power the power tubes draw. If you see the tube plates glowing orange or red, they are overbiased. If your amp sounds cold, it may be underbiased (not drawing enough current).

There are sevral ways to set the bias on an amp. For the novice, you can order a device from Musicians Friend made by Groove Tubes that plugs into one of the power tube sockets and you can measure how much voltage is being drawn by the tube plates on a multimeter. There is a list of voltage parameters in the instructions. I highly reccommend buying this device. You then turn the bias knob up or down to get in the propper voltage range.

Then what I do is plug my guitar into the amp and play and tweek the bias knob keeping the voltage in the propper range. Once I have it where I like it, I keep it there. I then turn off the amp and let it cool down completely. Then I bolt it back into the amp box. Remember the capacitors are now recharged and hot again. So handle the amp with care because you can electrocute yourself!

Some modern amps do not have a bias knob which means you cannot tweek the plat voltage. What you have to do is look to see if your tubes are glowing or if they sound shitty, you have to change to a different tube set. That's why some of the newer amps like the 5150 are really tube picky. Most Marshalls can be fine adjusted by using the bias knob.

Bias simply is controlling how much voltage is drawn by the plates and controlled by a little knob. It's not the big mysteriouse thing some people make it to be.

You can retube and rebias your own amp without being an electronic geniouse. You just need to understand the dangers of dealing with the big capacitors and high voltages of tube amps. It's all about not touching the wrong wires with your bare hands and never have both hands in an amp at the same time.

Go to musicians friend and keyword bias and it should bring up the Groove Tube rebiasing kit. That's where I bought mine. The instruction book will tell you how to rebias your amp.

[Nitro Express]

Heres what you need to rebias your amp. The Grove Tube Tube Rebiasing Tool:

http://www.musiciansfriend.com/prod...arts?sku=212003

[BrownSound1]

Marshall never stopped using EL-34s...NEVER EVER. The US distributor back years ago thought that by swapping to 6550s they would have less warranty repairs on tubes. The problem was that the EL-34s were damaged during shipping, as they aren't as robust against physical shock as 6550s. The European Marshalls continued to use EL-34s the whole time. A Marshall with 6550s sounds like total ass, IMO...and apparently Jim Marshall hates the tone as well.

Leave the 6550s for the poor bastards that have to re-tube Ampeg SVTs.

As for tubes for this amp, you can put in 6550s, 6L6s, EL-34s. However, you'll have to change the bias resistor to accomodate the 6550s or EL-34s. I say keep it stock...

I have to discourage the use of a screwdriver to discharge capacitors. A quick discharge like that can damage the caps, and yes you could weld the screwdriver to the chassis. Get a resistor...say a 100k ohm 1 watt, and solder a couple of leads to it with insulated alligator clips attached on each end. Clip one end to the positive side of the cap, and the other to the chassis. This should give a slow bleed off and not kill any components. Oh and be sure to use shrink tubing on the resistor leads so you don't have any way to short it out or touch the bare leads and kill yourself. This is much easier on a Marshall because you can do it on the first preamp tube socket. There's a 100k ohm resistor at pin 1, so you discharge through it.

As far as tube brands I'd recommend JJ/Tesla or Winged C (formerly Svetlana...if you can find them). Svetlana is no longer sold in the US, and it appears that the Winged C brand is gone too. Stay away from Ruby Tubes. JJ/Teslas are pretty good bang for the buck...sound great and not as expensive as some of the others. Prices for 6L6s range from 22 bucks to 70 bucks for a matched pair, depending on the manufacturer.

[Hardrock69]

My Super Lead head uses EL-34s.

I have had the current tubes since I bought the thing about 9 years ago.

When I got it originally it was kinda fucked up, but I took it in to the local Marshall Magician, and he fixed me right up.

Been kicking ass ever since!

[ELVIS]

Originally posted by BrownSound1
Pulling tubes is not dangerous...unless they have just been on, then you'll burn the shit out of your fingers. Capacitors are the components that store voltage, not tubes.

More specifically, filter caps...

Those big can looking things in the amp next to the tubes...

They store a charge like a battery, and in some not so rare instances, they can remember their charge and still have alot of voltage even after being discharged...

[ELVIS]

my dad is an old military electronics technician and he helped me work on amps when I was a kid...

BS is correct...

Do not discharge a filter cap with a screwdriver...

You might end up with the same results as laying a wrench across a car battery...

[BrownSound1]

Originally posted by Hardrock69
My Super Lead head uses EL-34s.

I have had the current tubes since I bought the thing about 9 years ago.

When I got it originally it was kinda fucked up, but I took it in to the local Marshall Magician, and he fixed me right up.

Been kicking ass ever since!

Well they quit putting the 6550s in the US Marshalls back around 1985 or '86. Started the practice sometime in the mid-70s.


One other saftey tip for those working inside their amps. Always use the one hand rule, so you don't get across high voltage and it go through your heart. That's a bad day if that happens.

Take off rings and watches too.

[Hardrock69]

Personally if I need an amp worked on, I take it to the local guru.....though my last guru here in Gnashville retired a couple of years ago....

[Nitro Express]

Have have two books on amp repair. One says to bleed the capacitor using a resistor and the other book (writen by a former Marshall R&D technician) says to use an electricians screwdriver.

I always used the screwdriver method because it's obviouse that the caps are discarged because you can hear it. With a resistor you just don't know for sure and plus you have those leads in the way of things and possibly more wires to get shocked by.

I've never heard of damaging capacitors using the screwdriver trick. I knew an electrical engineer who liked to screw around with old tube amps who did the screwdriver trick.

I was told in the 90's that Marshall had gone to using 5881 tubes in their new JCM 900 line because a source of reliable EL-34s was not available. There was a period where the only good El-34s were new old stock.

But yeah, a bleeder resistor will do the trick.

I think it's best to treat a tube amp just like how you treat a firearm. Even if it's unloaded you treat it like it is because plenty of people have been shot by supossedly unloaded guns. It's the same with those big filter capacitors. Treat them like they are always hot and you won't have a problem.

[Matt White]

Good advice....


TANX

[BrownSound1]

Originally posted by Nitro Express
Have have two books on amp repair. One says to bleed the capacitor using a resistor and the other book (writen by a former Marshall R&D technician) says to use an electricians screwdriver.

I always used the screwdriver method because it's obviouse that the caps are discarged because you can hear it. With a resistor you just don't know for sure and plus you have those leads in the way of things and possibly more wires to get shocked by.

I've never heard of damaging capacitors using the screwdriver trick. I knew an electrical engineer who liked to screw around with old tube amps who did the screwdriver trick.

I was told in the 90's that Marshall had gone to using 5881 tubes in their new JCM 900 line because a source of reliable EL-34s was not available. There was a period where the only good El-34s were new old stock.

But yeah, a bleeder resistor will do the trick.

I think it's best to treat a tube amp just like how you treat a firearm. Even if it's unloaded you treat it like it is because plenty of people have been shot by supossedly unloaded guns. It's the same with those big filter capacitors. Treat them like they are always hot and you won't have a problem.

A quick discharge to ground most definitely can damage filter caps, I don't care what that book said. I've seen it with my own eyes. You might get away with it 4 or 5 times, but it'll eventually get you. Plus, who wants to risk welding the screwdriver to the chassis. Some amps automatically bleed off the caps when you shut it off...and they use a bleed off resistor in the circuit. It doesn't take as long as you think, and if there is any question, then check it with your multimeter. (You shouldn't be probing around in the amp without one)

Now, the EL34 shortage for the JCM900 is probably true...but c'mon a JCM900 ain't a real Marshall. I've seen them with both EL34s and 5881s (6L6..same thing), and it still sounded like ass with either one. The Plexi reissues from that period still had EL34s, so who knows. The first JTM45s had 5881s as did the very first 100 watt amp that Marshall built...complete with dual output transformers.

Nowdays you've got plenty of sources for EL34s, thankfully. No, they aren't as good as those old Mullards, but I think they're much better than the late 80's/early 90's offerings.

[GAR]

Originally posted by ELVIS
More specifically, filter caps...

Good gawd, are you and BS1 the only ones with some kinda common sense in here?

He needs to replace the filter caps. I'd do that before replacing any tubes whatsoever.

Seldom have I ever replaced power tubes. Eddie dropped the voltage input with a Variac because he wasn't deep in the money like Roth and needed to stretch the tube life.

I'd redo the caps and see what happens. I never replaced a preamp tube once I got an amp setup properly and a good set under casual use should last at least 10 years.

Unfortunately capacitors last to spec 7 years at most and it's difficult to explain this to people who think they can just throw a new tube in there when the juice to run it just ain't there off the juice end of the caps.

[Nitro Express]

I got one of those old Philco radios from the late 1930's that is in the big wood box that was suppossed to look like a piece of furniture. It was my grandparents and the only thing it took to get it working was replacing the power cord and new electrolytic capacitors. It has all the original Tung-Sol and RCA tubes that were in it. Of course all the cobwebs and shit were cleaned out of it but it still works and that big ass speaker sounds great.

I don't think anyone will be using my iPod 60 years from now. Got to love tubes!

I was told electrolytic capacitors will last a long time if they are used but if they just sit there unused, they dry out and fail.

I've never done a cap job but I heard you need to bring the new capacitors up slowly with a variac after you install them.

[Nitro Express]

I think the only JCM 900 I've ever heard sound good is the one Henry Garza uses in the Los Lonely Boys. He runs it through a Bogner 2x12. I mean he's using a high gain amp to get a fairly clean Tex Mex sound but it works so what the hell.

[BrownSound1]

Nitro, you're right about electrolytic caps drying out...they definitely will do that. On the variac thing...I know some people say you have to do that, but it is bullshit. The only way I could see you needing to use a variac is if the caps had been sitting up for a long time. You might have to use a variac to reform them. New caps though...forget about it, definitely not necessary. Hell, when most electronic equipment gets manufactured the caps go straight from the box, so to speak, into the unit and fired up to full power. They don't have time to do a slow ramp up.

[Nitro Express]

LOL! The guy that restored that old radio uses a Klein electricians screwdriver to discharge capacitors with a big POP! But he's tottaly anal about using a variac to bring new capacitors up to working voltage.

My head is spinning. Who to believe? LOL!

[Nitro Express]

I've heard stories of capacitors exploding and shit like that. Then you hear the stories of capacitors oozing nasty electrolyte when they are shot. Frankly I've seen none of this.

On really old amps that haven't ran in years, they just don't work or the main fuse blows. I've never seen the oozing and the only capacitors I've heard make loud noises are the ones I've shorted out to ground with a screwdriver. Actually I never liked doing it. It's scary so I guess I sould solder up some bleeder resistors.

[GAR]

Any screwdriver bladed across the capacitors terminals will cause an arc during discharge. They do this to make the piece safe to desolder and remove.

Every tech brings up the voltage on the bench with a new recapping by stepping it up on a Variac.

Just do it. Check mojotone.com for prices maybe you could do it yourself.

[Sleeper Cell]

here are a couple of tube tips I can think of to pass on.

1. Look for discoloration in the plate when the tubes are working--could be a sign of a bad tube

2. Look for burn marks--have you ever heard of anything that looked burnt being good?.

3. Try if you got the means to get a 'matched' set of tubes. This just means that the tubes have been tested and determined to have close to the same break up point and draw.

4. Your amp may need to be bised once you put new tubes in. If you are a novice electrician/tinkerer, do not do this by yourself...

5. Some amps are harder on tubes, and the life is determined by usage, so if you play every day or several times a week, you may get anywhere from 6-12 months out of 'em. My Matchless EATS tubes. I get noticeable loss after about 8 months if i am gigging or playing my usual 1-2 hrs a day.

6. Check the net-there's lots of good tube sites out there full o knowledge.

I am just guessing, but an amp as old as yours probably needs new tubes, especially pre-amp section, but probably all new tunes..

my .02$

[Nitro Express]

What really beats tubes up is the heating and cooling. That's hard on them. That's why they started putting Standby switches in amps to keep the tubes warm during breaks when the amp was going to be used again.

Also bumping tubes when they are hot is hard on them. That's why you should let your amp cool before moving it.

Combo amps are especially hard on tubes because the tubes are usually by a speaker. If you play hard rock and roll with a cranked combo amp, the tubes are being rattled by the speaker when hot and they tend to not last as long. That's why it's better to have the amp sepparate from the speaker.

Maybe Pete Townsend had his Hiwatts off to the side and away from his speakers for a reason.

[Nitro Express]

Theres variouse types of tubes. Consumer grade, commercial, and military grade. The difference is how heavy duty the tube is built.

Take the 6L6 power tube. 6L6 is a consumer grade tube that was popular in America and GE, Sylvania, Tung-Sol made tons of them because they were used in a lot of consumer grade amplifiers.

The 5881 is the commercial variant of the 6L6 which means the components inside the little bottle are beefed up with heavier wire and plates. They have a different sound than the 6L6 as well.

The military version of the 5881 come in a metal case instead of glass. These tubes are made to take a beating and still work.

You can use all of these tubes in the same amp but the sound will differ.

The EL-34 was a European consumer grade tube that was made to be inexpensive. It uses control grids instead of plates like the 6L6. Marshall started using them because they were a lot cheaper than the 5881 tubes that were in the early Marshalls. The EL-34 was just a cheap and highly available tube in Britian. It's sounds wonderful when it's pushed. For some reason this is the case with tubes. The flimbsy ones sound the best when you abuse them. The military ones that can take more of the punishing sound cold.

[Sleeper Cell]

Maybe Pedophile Pete was getting an occurance known as microphonic ringing with his tubes....My amp used to do that. It sounds flippin awfulll when the tubes 'ring'

[Nitro Express]

There's a quick way to find out which tube has gone microphonic. With the amp on and running have someone play the guitar and then tap each preamp tube (the small ones) with a wooden stick (chopsticks work good). You deffinately will hear which tube is bad when it's tapped.