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...