can you get by without rebiasing the amp....

pchorman

pchorman

New member
after swapping tubes (preamp and power amp sections)?

has anyone ever done this without any real problems? I want to swap tubes in an old practice amp but don't want to bring it in - don't know where to bring it nearby in the first place and don't trust places like GC, assuming they even have techs to do that kind of thing.

thanks for any advise
 
Preamp tubes don't require biasing. Change at will.

Power tubes do but you might get lucky. A few things you want to be aware of:

If the plates ( the large grey or black metal pieces inside) begin to glow do not continue to run those tubes without an adjustment. This is due to an "under-biased" condition.

If the amp can't seem to get a good clean tone and the distortion is nasty sounding the amp is "over-biased". This won't hurt anything except your tone.

Unless you drive the preamp hard for distortion, preamp tubes can last for years. I've got some old Telefunkens that became too microphonic for my Boogie head but sound great in my JCM800.

Power tubes wear out faster if you play the amp at full volume. My Super Reverb was retired from gig duty because it has some of the last american made 6L6's.

I wouldn't trust GC to work on any of my babies either.;)
 
My Super Reverb was retired from gig duty because it has some of the last american made 6L6's.

Try www.tubesandmore.com they are part of Antique Electronics Supply, they recently had a big buy of new, old stock military tubes, they also have a regular supply of US made tubes.

Clive
 
hey there - no shortage of tubes here - I have new ones (spares). I just don't know whether I should swap them without taking the amp somewhere for rebiasing.
 
Try www.tubesandmore.com they are part of Antique Electronics Supply, they recently had a big buy of new, old stock military tubes, they also have a regular supply of US made tubes.
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Thanks for the heads-up Clive. I'll have to check 'em out. The tubes in my Super are Sylvania STR415's. I have found some but they're real pricey ( like $200 each from reputable sources:eek: )

hey there - no shortage of tubes here - I have new ones (spares). I just don't know whether I should swap them without taking the amp somewhere for rebiasing.
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What amp/tubes do you have?
 
what amp/tubes do you have?
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I'm embarrassed to say, and when I do say, the responses will be something like "with that pig it won't matter". This is an old practice amp, nothing more.

Peavey Bravo
12AX7A's front, and EL-84's rear stage I believe
 
"with that pig it won't matter"
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That's funny you would say that because it's true!:D

EL84 output tubes don't require biasing. :)

At least it's an all-tube amp instead of one of those not-so-incredible simulations. As long as you put good quality tubes in it, it should sound fine.

Edit: I just downloaded the manual. I see it's a single 12" combo. Looks like a cool little amp. If you really want to make it sound good consider swapping the stock speaker for a Celestion. A "Greenback" would rock in that thing. Or you could just plug it into another cabinet. Just make sure if you do that the ohm load is properly matched.
 
I've considered it. Loads of people who rated the amp at Harmony Central have gone that route (speaker replacement), and it may be something I'd consider but it's hard to imagine this little pig ever sounding real good.

so EL-84s don't need biasing like other tubes? pentodes? Maybe I'll swap them and see. still running stock chinese tubes circa 1994.
 
pchorman said:
[Bstill running stock chinese tubes circa 1994. [/B]
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1994?!! You're in for a world of difference.

Just a note, I took my amp in to a local guy who builds tube amps - http://www.krank.itgo.com/ - and does a lot of mods. For biasing he uses a voltmeter to get it close to the recommended voltage then just tweaks it and listens to the amp and looks at the tubes for that nice blue glow - definitely something to be said for an experienced tech as opposed to some kid with a book and a voltmeter. He also did a bunch of other cool stuff like changing caps and put a high value resistor on the negative feedback - my amp sounds awesome now. You can bring this guy CDs with your favorite guitar sounds and he'll do mods while you sit there and watch and you tell him which ones you want to keep.
 
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gnarled:

That krank.itgo guy sounds cool.


pchorman:

I personally wouldn't knock the Bravo (especially becuause I own one). It won awards when it was first introduced in the early 90's. The preamp section is similar to the Peavey RockMaster and it can hold its own for certain tones when compared to my Mesa/Boogie Triaxis and Quad.

The main problem was that it came from the early 90's and it is close to a one trick pony. In particular, you can get a great 90's saturated crunch from it, but it's not extremely versatile.

I have also used an external cab with it and it sounds great. More particularly, a celestion-equipped 4x12 with it when playing live. I would keep my 5150 head on it to look cool and hide the Bravo behind it. IMHO, it sounded much better for my style than the 5150.

Another great aspect of the amp is that you can get good preamp tube saturation at low volumes for practicing.

I definitely wouldn't call the Bravo a pig and would not be embarrased to admit I have one.


Matt
 
thanks of the backing Lopp. When I first bought it I loved it, but over the years, perhaps as the tubes gradually lost their electron emission from the cathode or whatever makes them age, the tone suffered - clean and dirty channels. I hope retubing will help. Have you done this and did you have them properly biased?

One thing that bothers me about the Bravo which disqualifies it from gigging with me is the drop-out after channel switching. Too much delay. Is that the case with yours?
 
Since you asked,

I haven't used mine that extensively. I couldn't use it during band practice because it didn't have enough power in a 2 guitarist band. However, I would sometimes use it for gigging because my amp was mic'ed. I sometimes still use it for practicing. Thus, it probably doesn't need retubing yet because it doesn't have many hours on it. IMHO it still sounds great (aside from that fact that I blew the clean channel... don't ask). :rolleyes:

I don't recall the channel prob, probably because I didn't need to switch channels often. Of course, I haven't switched much recently because of the blown clean channel.

Hmmm. Maybe I blew more than the clean channel and that's why I think the dirty channel sounds so good. ;)
 
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