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Attn. Gear Geeks: Tube Amp Questions

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Attn. Gear Geeks: Tube Amp Questions

Postby auntgoodness » Wed Mar 04, 2009 1:19 pm

OK. So I managed to bust a tube in my Hot Rod DeVille 212. It's one of the big tubes, so it's a power tube, right? The glass is broken and the amp squeals like crazy when I take it off standby. Time for repairs.

I'm not afraid of replacing tubes myself, but every online source I look at seems to say I should retube the whole amp. Why? What is the purpose of retubing the whole dealio when only one goes bad? And what's with the matched pair stuff?

I'm not necessarily against retubing the whole thing, I mean, it's been sounding more like Rice Krispies than rawk lately, but full sets are pricey. And will it really make that much of a difference anyway?

Thx,
Gdnss
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Re: Attn. Gear Geeks: Tube Amp Questions

Postby Kyle Motor » Wed Mar 04, 2009 1:22 pm

You'll probably have to re-tube all of the power tubes (I'm guessing there are 2 or 4 in yours....most likely 2). You'll need a matched pair that should be properly biased. You shouldn't have to replace the preamp and rectifier tubes, unless there is something wrong with them, or they are terrible. Also, if I'm not mistaken, you don't need matched preamp tubes, but I could be way off on that assumption.
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Re: Attn. Gear Geeks: Tube Amp Questions

Postby minicat » Wed Mar 04, 2009 1:51 pm

Yeah, you should be able to just replace the two big ones. The ones in your amp were probably due to be replaced relatively soon, anyway.
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Re: Attn. Gear Geeks: Tube Amp Questions

Postby lil bunny fufu » Wed Mar 04, 2009 2:24 pm

In my experience, different make & model tubes really do sound different from one another. It may be worth a call to a tube dealer or a tube-savvy repair tech to discuss how tube selection can help you get more of what you want from your amp. There's also lots of review information and opinions on a wide variety of tubes on the interwebs that may help identify a flavor that would work for you.

Making sure your tubes are properly biased by a competent repair tech is an important step in tube amp maintenance, and a good tech will also give your amp a once-over when they adjust the bias and look for any failing solder joints, dodgy components, etc that might help avoid an unscheduled headache down the road.
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Re: Attn. Gear Geeks: Tube Amp Questions

Postby dave esmond » Wed Mar 04, 2009 3:52 pm

If your amp only has two output tubes think about buying a matched quad. That way you can replace just one down the road if you break just one and not worry about them matching.

Rice crispies might be preamp tubes, or worse. So you might want to replace those too. Or at least tap on 'em (gently) with a chopstick or something while it's on to figure out which one it is. Preamp tubes go pretty quickly and they're not always the best quality these days to start with.

Good luck.
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Re: Attn. Gear Geeks: Tube Amp Questions

Postby chainsawcurtis » Wed Mar 04, 2009 5:30 pm

Old tubes can get "microphonic" meaning that when the cabinet vibrates when you're rockin' it can adversely affect the tone. Sometimes that shows up as rice crispies, sometimes as (unwanted) feedback. !2ax7s are pretty cheap on the web go for it. Good ones will last quite awhile. The problem is that different tubes contribute to different types of tone and experimenting can run up some dough.

Most amp geeks will tell you that when you replace the power tubes - in your case they are 6L6s (I had the same model amp a while back)- you should re-bias the output (it has something to do with how hot or cool the tubes run). This is something that needs to be done by a guy who knows what he's doing and will cost you whatever the bench charge is now for the work but power tubes last for quite a while if you're a weekend warrior and it will probably be worth the $$.
I have used and would recommend edtronics if Ed's working now.

If you haven't already found it the Fender discussion pages are a pretty good fount of info - http://www.fenderforum.com/
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Re: Attn. Gear Geeks: Tube Amp Questions

Postby ArturoBandini » Wed Mar 04, 2009 6:07 pm

I like http://www.tubedepot.com/. I don't know any tube dealers around town, but I'm fairly new here. I like JJ 6L6GC's for cheapness and quality.

I've built 5-6 amps from scratch using both new and NOS parts. Old NOS 6L6GC tubes are nice, but you'll probably get better tone for your dollar by buying some dependable Chinese or Russian output tubes (like the OEM tubes in your Fender) and then investing some dough instead in a NOS USA-made 12ax7 to go in the V1 position on the amp. This depends on what type of playing you do - if you are driving the output tubes hard, then it might pay off to buy a pair of high-dollar 6L6GC's too. If you use mainly preamp distortion, then 12ax7 is where all your tone is coming from anyway.

I like the idea of buying a matched quad to have spares, but I'm not sure how "matched" the quad will remain when 2 of the tubes have 200 hours and 2 have 0 hours... I've never done a quantitative test of this.

The Hot Rod amps are fixed-bias (a poor choice of words, because bias voltage is adjustable), and therefore need to be re-biased with a new set of tubes. Biasing is really not difficult if you have a multimeter and can read a circuit diagram. http://studentweb.eku.edu/justin_holton/bias_print.html

You can certainly play on your new set of tubes using the previous bias setting (from the old set of tubes) but you won't be optimized for either tone or tube longevity.

Kyle Motor is right, matched preamp tubes are not important, if it's even possible to buy them in matched sets. Preamp tubes work in series, power amp tubes work in parallel, where balance is much more important.
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Re: Attn. Gear Geeks: Tube Amp Questions

Postby auntgoodness » Wed Mar 04, 2009 6:19 pm

Sweet. Thanks, folks! This is great info.
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Re: Attn. Gear Geeks: Tube Amp Questions

Postby ArturoBandini » Wed Mar 04, 2009 6:39 pm

I forgot to mention - the Hot Rod series of amps commonly have problems with the plate load resistors, typically in the phase inverter section. (82k resistor that sees high voltage). I had intermittent pops and crackles in my HRDlx (now sold) that were caused by a bad resistor in this spot. I replaced all the plate load resistors with new, higher-tolerance resistors and the popping stopped!

Tutorial: http://studentweb.eku.edu/justin_holton/plateloads.html
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Re: Attn. Gear Geeks: Tube Amp Questions

Postby chainsawcurtis » Thu Mar 05, 2009 9:22 am

the Hot Rod series of amps commonly have problems with the plate load resistors, typically in the phase inverter section


Yup, this happened to my Hot Rod Deluxe. Just died one gig. Ed fixed it (thanks, Ed!) and it's been a great amp. The Deville was also a great amp but got too heavy to lift and to loud for most rooms.
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Re: Attn. Gear Geeks: Tube Amp Questions

Postby eriedasch » Thu Mar 05, 2009 11:06 am

chainsawcurtis wrote:I have used and would recommend edtronics if Ed's working now.

I would also mention / recommend Ginter's Guitar Shop on Atwood next to the Harmony Bar.
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Re: Attn. Gear Geeks: Tube Amp Questions

Postby Spooky_Noodle » Fri Mar 06, 2009 12:46 pm

I would be more than happy to help out with your amp Goodness. I have worked on many amps in this series. please feel free to contact me at repairs at ed-tronics.com
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Re: Attn. Gear Geeks: Tube Amp Questions

Postby droidsattack » Sun Mar 08, 2009 5:59 pm

Something tells me you're going to need more then a mere re-tubing if the tube melted/shattered instead of just burned out. I'd take it to Ed for sure.
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Re: Attn. Gear Geeks: Tube Amp Questions

Postby lil bunny fufu » Sun Mar 08, 2009 10:08 pm

I dig the "placeholder" page, Ed.
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