tubular

[cellardweller]

I have an Ampeg tube guitar amp, it's a couple of years old. I read in a previous post, just down the way there, that tube bias is not an issue with mesa boogie amps. I can't find much on Ampeg guitar amps, let alone anything which specifically states whether or not this is a factor. Does the bias issue apply to certain amplifiers of the types of tubes in them?

My amp is starting to exhibit some strange tendencies, which may or may not be human induced, and I'd hate to pay someone for work that was unneeded/unperformed.

 

[volthause]

most tube amps need to be biased manually.

however, unless you have changed your tubes (or performed a modification to the amp circuit) there is no need to worry about having your amp re-biased.

 

[donkeystyle]

maybe you need new tubes. when was the last time u replaced them? if you want your amp to sound it's best, you should replace at least the pre-amp tubes once a year (well if you play every day). i think you can go longer with the power amp tubes, but why not change them both once a year.

 

[AcidRain]

What they've said is true, but I'll just add something... if it doesn't say "bias is not an issue", odds are 99% that bias is an issue. Very few amps are self-biasing or do not require electrical biasing, and it's a major selling point of the amps that do have that feature. So if it doesn't say so, it's safe to assume that biasing's an issue. That said, you probably don't need it biased unless you changed the type of tubes you're using in it...

 

[shortyprs]

Mostly Boogie says you don't need to rebias...if you buy their rated Boggie tubes. Otherwise, I thought Class A el 84 amps were the only ones that didn't need rebiasing if you changed tubes. Even there, I could be wrong. I mean, its the nature of tubes to vary!

 

[cellardweller]

Acidrain, so if I read you right, you are saying that unless you change to a totally different type of tube you should be able to just chuck em' in and go? But then as shortyprs says, it is the nature of tubes to vary, would this variance be cause for biasing?

Last time I had someone replace/rebias tubes was with another amp, years ago, and I felt I was prison sexed. I think it was close to 200$ he charged and that was with me supplying the tubes (I was even younger and more naive at the time). So when my ampeg began acting up I said the hell with it and started using my solid state, but I am tired of dealing with its' limitations now.

What is a reasonable amount to be charged for the biasing, cost of tubes aside?

Also, is it advisable to replace with a like kind of tube? Brand names aside I mean manufacturing specs...

 

[AcidRain]

Acidrain, so if I read you right, you are saying that unless you change to a totally different type of tube you should be able to just chuck em' in and go? But then as shortyprs says, it is the nature of tubes to vary, would this variance be cause for biasing?

You're talking about Ampeg, he's talking about Mesa. What mesa says is, unlike other tube amps where rebiasing is necessary, if you buy a mesa el34, you can drop it in to replace a 6L6. I would highly discourage this if you don't own a mesa, or have not been explicitly told you can do this.

Really, if I were you, I'd email a company like Svetlana, Groove Tubes, etc., tell them what model you have, and whether or not you'd need rebiasing. (keep in mind, they sell tubes... they're gonna tell you to change them, which you may or may not need).

 

[donkeystyle]

you are technically supposed to re bias even if you replace tubes with the same brand and same rating as you had before because as shortyprs said, they will vary slightly.........like with groove tubes 1-10 rating.......there has to be some rounding gong on there.

but most people don't bias everytime. like you said. having work done on ur amp is expensive. i'm pretty friendly with a bunch of the people in one of the local music stores and i was talking about biasing with one of the employees a couple months ago.

he went from groove tubes rated at like a 3 or something to groove tubes rated at a 7........he should have re biased, but he didn't. he said he hasn't noticed any problems. i think that typically all that happens when you don't rebias is tubes don't last as long.

what is your amp doing? that would really help in diagnosing the problem.

if there's a lot of noise or if the volume seems to jump up and down, that can mean you need to get new tubes.

 

[cellardweller]

Exactly...

Yep, that is exactly what it is doing.

All of a sudden, an hour into recording, volume drops 2/3s, and there is an intermitent high pitched sound when nothing in the environment has changed (i.e. walking close with guitar/other, air conditioner kicking on, refrigerator, etc....) I have varified all of these...

Is this noise predictable? Is it as I've said, a slightly varying high pitched sound?

 

[cellardweller]

My reluctance to put out the cash is what prompts me to ask questions I already half know, or at least suspect the answers to...

The tubes are pretty friggin' old!

It has four power amp tubes, I can't see the pre-amp tubes though, I would assume it to have two...

 

[donkeystyle]

well i'm assuming u think it's 2 because it's a 2 channel amp....it's probably not 2 .......it's gonna be more like 4 or more.....i have a 2 channel amp and it's got 5 preamp tubes.........yours may have more.........

preamp tubes are cheap, but it's probably your power amp tubes that are giving you the problem.

it's gonna be around 80 to 100 bucks (including tax) to replace the power tubes. i'm going by groove tube prices....i don't know what you like or will go with. i think they were about 39 bucks list price for a pair......actually now that i think about it, it'll probably be more like 80 bucks to replace em.

the pre-amp tubes don't matter as much and you don't need to get "the best" or most expensive ones........fender pre amp tubes are actually groove tubes, just re labeled for fender and they cost 10 bucks. that's what i have right now.

i bought my amp used and when i decided that i should replace the tubes just so that i know when the last time they were replaced was i found out they had never been replaced. still the original tubes from the manufacturer. the amp was made in 97, so they were freaking 5 or 6 years old. needless to say i had already fallen in love with my amp, but when i changed the tubes i really loved it.