Tubes: help!

[Whoopysnorp]

Well, I am now a tube amp user. I have had an Ampeg SVT-II head for about a year now, and I just got a Marshall TSL601 for guitar. Now I think it's time I learn something about retubing. I bought the SVT-II from a friend of mine who owned it for years (I'm not sure exactly how long; probably at least since the mid '90s). He said he has never changed the tubes in it, so I think it's definitely past time to do that. I'm aware that I'll have to get into rebiasing, and I intend to learn how to do that because I'm a cheapass. However, for now I'm just wondering about tube brands. I see a lot of brands out there, from Sovtek on the low end all the way up to incredibly expensive Cryovalve pieces. My SVT uses 4 12AX7s, 2 12AU7s, and 6 6550s, so I'm looking at a lot of dough here. Do I need to shell out for the expensive tubes? Am I best off avoiding the Sovteks and spending as much more money as I can spend? What brands do you like?

 

[mshilarious]

A tube should last a couple thousand hours; is there something in the tone of the amp that makes you think they need changing? How heavily was the amp used in the past?

 

[Whoopysnorp]

He used to gig with it on a pretty regular basis (haha, bassis). The tone seems on the dull side. On July 4th, the former owner (who is still in a band with me) played a gig with us with the amp running somebody else's 8x10 cab, which is just like the one he used to own. He remarked that the amp seemed weaker than he was used to.

 

[Scottgman]

Generally, if your tubes need to be replaced you should be able detect a significant change in tone. If this amp is new to you, you might have to rely on the previous owner's opinion. If any of the metal stuff inside any of the tubes is glowing orange, they definately need to be replaced.

I haven’t used a plethora of different brand tubes. My experience lies in Groove Tubes (Sovteks) and Svetlana. There are only a few companies that make tubes anymore. For instance, Groove Tubes doesn’t “make” tubes-- they buy Sovtek tubes, test and match them, and then re-label them as Groove Tubes. Same with companies like Mesa Boogie.

I wouldn’t get too caught up in the tube hype. I replaced some Groove Tubes with Svetlanas several years ago and the Svetlanas maybe sounded better. But I think tubes in general sound sweet so I’m not worried about the nuances. So I usually stick with Groove Tubes. They are reasonably priced and they are consistent and reliable. Next time I re-tube my amp, I know what it will sound like if I get Groove Tubes.

Oh yeah, I wouldn’t mess with biasing your amp unless you are a real electronics-savvy kind of guy. It’s not that expensive anyway, I used to use a local guy who charged $20 to re-bias my amp. Also, some amps don’t need to be re-biased if you are using the same style of tubes (e.g., EL-84) and some amps are self-biasing.

Good Luck!

 

[Imaduck]

Yeah, I'm with Scott. Tubes, for the most part, are tubes. Unless you're a super-clean tone-freak I really wouldn't worry about the cheaper tubes. As far as biasing, it's pretty hard to do yourself, and I wouldn't suggest it, however, the good news is that you really shouldn't need to. As long as you're not using drastically different tubes (different power ratings, etc.) it really shouldn't matter.

 

[M.Brane]

Biasing an amp with an adjustable bias is not that difficult if you have a scope, and are reasonably familiar with basic electronics. Just remember that an amp like the SVT runs very high voltages, and can give you quite a jolt (read: possibly fatal) if you screw up. Be careful.

There is no such thing as a "self biasing" amp (with the exception of EL84/6BQ5). Some are just more tolerant than others. Some are adjustable (potentiometer) and some are fixed (resistors).

As for tubes, any name brand should be fine. I wouldn't worry about using 'boutique" or NOS tubes in an instrument amp unless you have money to burn.

I've run Telefunkens, Groove Tubes, and Mesas in my MKIII head. The Telefunkens sounded great, but for what they cost vs. the Mesas I'll be re-tubing with Mesas again myself. The Groove Tubes were a close 3rd.

The Telefunkens are now in my Marshall JCM800, and sound pretty good still. They became too microphonic for the MKIII.

I have some old Sylvania USA made Groove Tubes (STR415) in my Super Reverb. I don't use it much for that reason. The clean tone is stunning.

A friend of mine has a JMP 100 watt head with some old Mullards in it. It sounds awesome, but I doubt that's just due to the tubes. He's scared to change 'em though!

 

[Whoopysnorp]

Biasing an amp with an adjustable bias is not that difficult if you have a scope, and are reasonably familiar with basic electronics. Just remember that an amp like the SVT runs very high voltages, and can give you quite a jolt (read: possibly fatal) if you screw up. Be careful.

You mean an oscilliscope, right? I don't have one right now, but I think there's one kicking around in my parents' house. If not I'm sure I could pick up a cheap one easily.

 

[deafen]

Nah, you don't need a scope. In fact, there are those that feel that "visually biasing" using a scope and tone generator tends to overbias an amp, shortening tube life.

For an excellent overview of rebiasing by the hobbyist, check out http://www.duncanamps.com/technical/lvbias.html -- this method has worked for me for years.

 

[Thatupstateguy]

The only reason you would need to re-bias your amp is if you are replacing the power tubes, and then only if you feel that it does not sound right after you re tube,... as for the Preamp tubes you can change them as often as you like with no effect on the amps bias,.... you can even try other than the 12AX7s, anywhere you see an AX7, you can use any of the following,..... 7025,(low noise) 5751 (less gain, military version), 12AT7,12AU7,12AV7,12AY7,12AZ7, 12DT7,ECC83, and a few more,.... the differences in all the 12--7s are mainly the gain,.... an AT, and an AZ are about 60% of the AX7,... the AU, and AV are about 40%, and the AY is about 45% .... all the others vary with brand, and function,... usually the military versions are less gain, and low noise, but they do have some desirable qualities,... and are sought after by some who crave that tone thing,..... Phillips JAN 12AX7WXA are one such version,.......(JAN= joint Army Navy) The power tubes,... are a little tougher to call, some amps will tolerate the changing without too much trouble at all,... as my Univox head, two 6L6s,... and as stated above the amps using EL84s have very little problems with re tubing,.... but others are VERY sensitive about the power tube section,... and I think the Ampegs are one of them,... I have never owned one so cannot say for sure,...... but anything based on the 6550 is fairly strong, as is the tube,.... and there can be an amazing difference between brands,...... Groove Tube IS making tubes again, and in this country,.... re opening an old plant in California,.... they are making several types of tubes, and I am not absolutely certain just which ones,... I know that they are using some of the old Mullard designs,.. and tooling,...and that the 6L6 is one of the 'new' tubes they are producing,... I do believe that they have recently released a new 12AX7 version also based on the old Mullard designs,....

Of course I personally prefer the NOS tubes, but that is a matter of taste, and opinion,..... some prefer the svetlanas,... and yet others swear by EIs or JJs,.....

I have heard that NOS, or old GE 6550s are the absolute best ever made,.... but then there are the Genelacs,.... they can go for as much as $300 a pair,...... Audiophiles swear they are the best,... sweeter sounding ......

I do know you must try out some if you can to help you decide,..... if you make it to the fest,... bring that head,... and we can throw a few preamp tubes in to try,.... but since I do not own an amp that requires 6550s, I never really bought too many,.... I do have 1 pair....

lots of pre tubes tho,....

I hope you can get at least a little bit outta this post,....


Steve