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Post subject: Tube Question
Posted: Mon Sep 01, 2014 2:14 pm
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My Egnator Renegade has 2 6L6 and 2 EL34 power tubes with a blend knob. When I turn the blend knob towards the EL34 side the volume drops off to almost nothing. This happens on both channels. I assume that the EL34 tubes have given up already even though I've only had the amp about 6 months and haven't put very many hours on it. Is this a pretty good assumption. Everything else works fine and there's plenty of power when the blend knob is at the center or over on the 6L6 side.
Any suggestions on replacing the EL34's? What's the difference of EL34L's? Should I buy matched tubes.
This is my first tube crisis, so I want to handle it properly. Thanks.

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Post subject: Re: Tube Question
Posted: Mon Sep 01, 2014 3:52 pm
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Yes you should buy matched tubes.

Tube Store chart

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Post subject: Re: Tube Question
Posted: Mon Sep 01, 2014 5:05 pm
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Thanks for that chart BMW. It looks like I'm going to learn how to set bias also. Will a better quality tube last longer than cheaper ones? I can't believe how short the life span was for the stock tubes.

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Post subject: Re: Tube Question
Posted: Mon Sep 01, 2014 8:33 pm
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That's not the only chart out there. Go to the standard tube suppliers and poke around their web sites. Are you following the tried and true routine for powering up and down your amp(s)?

Power up:
60 - 90 seconds main power on but in standby mode. Then switch out of standby to play.

Power down:
Switch into standby mode 60-90 seconds before main power off.

Amp has no standby mode? Not much you can really do about it.

Following that routine can increase power tube life by allowing the tubes to warm up and cool off more gradually. Tubes can last anywhere from 2 years to 20 years. There are lots of variables. The routine helps. Keeping the amp biased for a more neutral tone helps too. Trying to bias for as much overdrive as possible will shorten tube life. Our forum amp gurus could undoubtedly have more to add.

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Post subject: Re: Tube Question
Posted: Tue Sep 02, 2014 2:51 am
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Standby switches do more harm than good. Look at a modern tube hifi amp, you won't see many with standby switches.

http://www.valvewizard.co.uk/standby.html

Applying high voltage (i.e. throwing the standby switch) to a hot tube makes it conduct a surge of current. That's not good for the tubes, filter caps or choke.

If you throw the standby then switch the amp on (i.e. "do it wrong") you avoid this surge as the tube heats up gradually and slowly begins to conduct current up to its idle current.

Some types of tube have to be warmed up before use to avoid damaging the electrodes but those aren't the types used in guitar amps.

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Post subject: Re: Tube Question
Posted: Tue Sep 02, 2014 11:51 am
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Thank for the article, Frank. Interesting reading. I will have to read it again before assimilating it as gospel truth.

I believe my Rivera is likely designed with a soft-start standby but I will look into it to be sure. I say that because of the way it behaves, not because I have as yet any knowledge of it. When I flip the amp into standby while the guitar is still ringing it takes about 3 or 4 seconds for the amp to ramp down to silence and vise versa ramping up. I hadn't paid much thought to that until I read the article and recognised it as the way my Fandango behaves.

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Post subject: Re: Tube Question
Posted: Tue Sep 02, 2014 12:38 pm
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A lot of amps go into standby that way. The standby switch disconnects the transformer but there's still enough charge in the filter capacitors to power the tubes for a few seconds.

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Post subject: Re: Tube Question
Posted: Tue Sep 02, 2014 2:31 pm
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My amp has a fast blow fuse for each set of power tubes. The manual says that if the fuse is blown, you most likely need to change out that set of power tubes. My fuse is blown, so I'm going to order some EL84's.
The amp is also set up to adjust the bias on each set of power tubes, right from the rear panel. Looks like this will be a fairly painless fix.

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Post subject: Re: Tube Question
Posted: Tue Sep 02, 2014 3:06 pm
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Drew365 wrote:
My amp has a fast blow fuse for each set of power tubes. The manual says that if the fuse is blown, you most likely need to change out that set of power tubes. My fuse is blown, so I'm going to order some EL84's.
The amp is also set up to adjust the bias on each set of power tubes, right from the rear panel. Looks like this will be a fairly painless fix.


Drew...not familiar with your amp, but does it have EL34's or EL84's you mention both in your posts for your amp. There is a HUGE difference in those two tubes. Just want to make sure you get the right tubes.

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Post subject: Re: Tube Question
Posted: Tue Sep 02, 2014 3:35 pm
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Sorry, they are EL34's. I was reading about EL84's and must have had a brain fart on that last post. I ordered 4 EL34's and 2 6L6's so I have a complete set as spares. I went with Tung Sols for both.
The original sets are Ruby's.

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Post subject: Re: Tube Question
Posted: Tue Sep 02, 2014 6:12 pm
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BMW-KTM wrote:
...Power up:
60 - 90 seconds main power on but in standby mode. Then switch out of standby to play.

Power down:
Switch into standby mode 60-90 seconds before main power off.

Amp has no standby mode? Not much you can really do about it.

Following that routine can increase power tube life by allowing the tubes to warm up and cool off more gradually. Tubes can last anywhere from 2 years to 20 years. There are lots of variables. The routine helps. Keeping the amp biased for a more neutral tone helps too. Trying to bias for as much overdrive as possible will shorten tube life. Our forum amp gurus could undoubtedly have more to add.


+1

You said it as good as anybody. Anybody that knows what they are talking about, that is. Guitar amps are not hi-fi..... :wink:

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Post subject: Re: Tube Question
Posted: Sun Sep 07, 2014 10:20 am
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I have an Egnater Rebel. 20. Egnater amps are easy to bias. Bruce usually spells it out in the manual or on the forum. I have the dual power tube setup also. I you all buy matched quads when I get power tubes. It saves you from biasing if you're in a hurry to get back up and running as long as the tubes don't short and cause other problems.

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Post subject: Re: Tube Question
Posted: Sun Sep 07, 2014 10:40 am
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shimmilou wrote:
You said it as good as anybody. Anybody that knows what they are talking about, that is. Guitar amps are not hi-fi..... :wink:


Why exactly? Because that's what the manual says?

Other than having lower-quality output transformers, how is a tube guitar amp different from a tube hifi amp?

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Post subject: Re: Tube Question
Posted: Sun Sep 07, 2014 3:35 pm
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GilgaFrank wrote:
Other than having lower-quality output transformers, how is a tube guitar amp different from a tube hifi amp?


Old DIN HiFi = 50-12500 Hz +- 3 dB <1% THD
New HiFi = 20-20000 Hz +- 6 dB <0.5% THD
Guitar amp = 75-5500 Hz, wildly non-linear and up to hundreds %THD - even adible harmonic distortion on no signal!

Also keep in mind that most "Class A" guitar tube amps are not Class A at all. It's a big fat lie. You simply cannot get the umph and breakup many guitar players are looking for with a Class A.

A HiFi tube amp is a quite different kind of animal. Controlled, made for fidelity and not volume, and where any kind of overdrive is considered bad, bad, bad.


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Post subject: Re: Tube Question
Posted: Sun Sep 07, 2014 4:24 pm
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Sure, the distortion figures are way different but the basic design and operation is identical in hifi and guitar tube amps.

My point is that with similar plate voltages and PSU filter designs a hifi tube amp needs no standby switch. Guitar amps are really no different in that regard, we've just grown accustomed to having a standby as a mute switch. Leo Fender installed one, Jim Marshall copied Leo and every single guitar amp manufacturer ever since has copied them. But electrically speaking, there's no need for a standby and there are some very good arguments against using them at all.

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