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Post subject: Champ 25SE 6L6 tubes
Posted: Mon May 27, 2019 4:41 am
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I've got 90' Fender Champ 25SE with Fender 6L6GC P/N 023556 tubes. Can I replace them with Fender GT6L6C P/N 073314 tubes? I've been thinking to buy those and not sure about compatibility.


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Post subject: Re: Champ 25SE 6L6 tubes
Posted: Wed May 29, 2019 1:25 am
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You can put any 6L6GC you want.

Do you mean with no need to do bias ?
I don't know, I always do bias.

If your amp' original tubes are Groove Tube, you have to buy the same one and no need to do bias. Read here;

https://support.fender.com/hc/en-us/art ... ng-System-

Schematic here ;

http://ampwares.com/schematics/champ_25_se.pdf


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Post subject: Re: Champ 25SE 6L6 tubes
Posted: Wed May 29, 2019 4:46 am
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My buddy has a 1990 Champ 25 SE

It is designed for the tubes to be plug n' play.

Good clean channel on that amp.
Decent dirty channel at lower gain settings.
It becomes less impressive the more you crank the gain.
Solid state preamp section.
Under-rated and under-appreciated amps in my opinion.
Easily better sounding than a Hot Rod Deluxe and much sturdier to boot.
Except for a tube swap a couple of years ago, my friend has done nothing to his amp.
He bought it brand new back in the day.
It just keeps going.

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Post subject: Re: Champ 25SE 6L6 tubes
Posted: Wed May 29, 2019 5:29 am
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BMW-KTM wrote:
My buddy has a 1990 Champ 25 SE

It is designed for the tubes to be plug n' play.

.


Explain me how ?

It is a "normal" fixed grid bias and need a bias check with new power tubes.

Schematic here;

http://ampwares.com/amplifiers/fender-champ-25-25se/


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Post subject: Re: Champ 25SE 6L6 tubes
Posted: Wed May 29, 2019 8:12 pm
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I'm not an amp tech.
I have never pretended to be.
I'm just going by what the authorized Fender depot told my friend.
Told him in my presence.
I am a witness to what the guy said.
I was there.
My friend plugged in a set of GrooveTubes at the direction of the dude and put the amp back to work.
That was several years ago.
The amp has played well and sounds good and has been reliable.
Feel free to disagree with the directions he gave us.
I'm just telling you what I saw and heard the guy say and do and then later what I saw and heard the amp do.

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Post subject: Re: Champ 25SE 6L6 tubes
Posted: Thu May 30, 2019 1:47 am
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If you install exactly the same Groove tube as it was originally it should work. This is probably the only exception.
Any other tubes installed without doing bias is playing the lottery.

In your case your friend would have won. But it is not certain, the bias is perhaps not at its best nor the sound of the amp.

In any case we should never pretend that it is a "plug and play" it would be a disservice to people who read the forum. Because in the worst case the tubes can be destroyed

I'm surprised that you who is very present on the forum says something like this . The importance of bias is so much discussed


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Post subject: Re: Champ 25SE 6L6 tubes
Posted: Thu May 30, 2019 4:45 am
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They were the OEM tubes.
They had not been changed before.

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Post subject: Re: Champ 25SE 6L6 tubes
Posted: Thu May 30, 2019 9:50 am
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Why didn't we care about bias back in the '60s and '70s? Because tubes were very consistant, and would almost always be in the safe range.

Why did we start caring in the late '80s? Because early Sino-Soviet tubes were wacky. '80s and '90s Svetlanas and Teslas sounded great, but they drew crazy amounts of current. Sometimes redplated with the bias pot set as cold as it would go, and required changing/adding resistors to change the pot's range.

And a lot if the Sino-Soviet tubes weren't actually what they were labeled to be. They were servo tubes for Soviet jet fighters that were coincidentally close enough to audio tubes to function in amps.

Some of those tubes could kill marginal power transformers if you just slapped them in without checking/adjusting bias. A few even required rewiring the sockets on some amps (something about whether unused pins are tied together).

Along the way, people began to notice that some amps and/or tubes have "bias sweet spots", and that might be an argument for always checking/adjusting fixed bias.
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But this is 2019, not 1989. The tube industry is no longer in disarray after the shut down of Western tube production. The Chinese and former Soviet factories have been catering to audio needs for decades now. The improvised, close-enough, pressed-into-audio-service designs have been weeded out, or modified. They've got a secure, sorted product niche that's allowed enough investment to produce tubes that meet specs.

It's pretty much unheard of for a modern tube to be so out of spec that the current draw could damage the amp. Or even light redplating is rare. Maybe a little hot or a little cold, possibly not in the "sweetest sweet spot", but the reality is that you can almost always plug'n'play safely.
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Fender's tech reps, sales reps, and even some of their amp manuals say all sorts of stuff that's incorrect. Fixed bias is fixed bias -- it doesn't self-adjust like cathode bias.

But again, modern tubes are reasonably consistent -- especially sorted/rated/matched tubes.

And 25 watts from a pair of 6L6's is pretty light-duty. Fairly low voltages, not pushing the tubes anywhere near their maximum output.
--------------------
The best practice is to always check bias. But modern tubes are unlikely to damage an amp. They may wear out a bit prematurely because they're a little hot, or they may sound anemic because they're a little cold, but they won't smoke the amp.


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Post subject: Re: Champ 25SE 6L6 tubes
Posted: Fri May 31, 2019 9:42 am
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Whilst plug-n-play may be possible with tubes of the same brand, my experience has been that there is a huge difference between brands.

I had Tungsol 6V6GT tubes in my DRRI biased at about 20mA. I thought I would try some TAD 6V6GT-STR tubes and without touching the bias pot the current was 35mA. I also tried the stock GT (JJ) 6V6S tubes that came with the amp and the current was just under 26mA.

After re-biasing the amp for the TADs to about 20mA I re-installed the Tungsols and the reading was about 14mA.

Based on that experience it wouldn't be possible to swap tubes without biasing and expect the amp to perform similarly.

Incidentally, it is impossible to bias my amp hotter than about 22mA with the Tungsol tubes as that is at the extreme of the adjustment.


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