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Post subject: should new tubes.....
Posted: Mon Aug 23, 2010 1:48 pm
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Make a "popping" sound as they heat?
just got my tubes in, tweaked the bias pot till every one had the same cheery glow,(hot plating occurred on initial warm up).
Now.... as I was test driving the 135(BEAST, even at low volume)
I got a popping noise, I understand expansion and contraction but this was worrisome enough that I powered her down, is this normal?
4 new Tung sol 5881's
2 jj 12ax7's
1 jj 12at7

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Post subject: Re: should new tubes.....
Posted: Mon Aug 23, 2010 2:10 pm
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xsinner13x wrote:
tweaked the bias pot till every one had the same cheery glow


:!: :!: :!:

Do the words "digital volt meter" ring any bells?

That's what a competent amp tech uses to set the power tube bias.

(and 5881's are not recommended for use in a 135-watt ultra-linear chassis).

Rotsa ruck!

Arjay

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Posted: Tue Aug 24, 2010 1:54 pm
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+1 Retroverbial.

Your tubes are biased too hot


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Posted: Tue Aug 24, 2010 3:25 pm
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The bias does not matter in this case.

The max plate voltage design center value for a 5881 is 400 volts (either in a triode or a pentode configuration). The ultra-linear amps are running close to 490 volts......nearly a 20% increase. Only the hardiest of 6L6GC's should be used in these amps. If not mil-spec NOS then JJ's, Sov-Teks, or the Tung-Sol re-issues. And forget about the Winged C's -- their elements vaporize at around 450 volts.

Arjay

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Posted: Tue Aug 24, 2010 3:51 pm
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+1 Retroverbial

I thought 5881 was more tough than 6L6GC


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Posted: Tue Aug 24, 2010 3:55 pm
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Yeah, I agree with Arjay about the power tubes needing to be capable of working with a 500-600 plate voltage. But I know the new generation of 5881's are only distant relatives to the older ones. So first, I would find out what the plate volt specs are for your tubes, second, I'd get a meter on the those tubes, PRONTO ! And no "popping" is not normal. Art

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Posted: Sat Sep 04, 2010 8:25 am
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Retroverbial, I've had the same set of Winged C's in my UL Twin for almost 2 years. No problems so far. I have kept the original Fender output tubes, they are labelled 6L6GC. The Winged C's are also labelled 6L6GC, whats the difference?

As for the "popping" no its not normal. Get it checked out by a tech.


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Posted: Sat Sep 04, 2010 8:37 am
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There are many tubes builders but 6L6GC is almost the same but could have little difference in tone or breakup


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Posted: Sat Sep 04, 2010 10:48 pm
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Hey Minoan, it's been a while ! I think what Arjay was getting at, is that the more recent Winged-C 6L6GC tubes have had quite a few QC problems. Low vacuum is one that I am aware of. Over the past year, I've had to return 3 matched sets because of different current draw. For years, I relied on the St. Petersburg Svetlana 6L6GC (now Winged-C) without any problems. Don't know what happened. I'm guessing that your original power tubes are the last of the great Sylvania tubes that were produced. Very robust 6L6GC tubes. Most of these were gobbled up by Fender and Peavey, but Mesa Boogie seems to have gotten a good share of them too. I've seen mid 80's Peaveys and Boogies with these tubes. Hang on to those, unless they had some kind of problem. Art

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Posted: Sun Sep 05, 2010 9:46 am
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You are correct, Art. There was a time when the winged C's were some of the best bottles being made, and they still are to an extent. I'd have no qualms about using them in tweeds, browns, blackfaces, even some of the early silverfaces. But recent examples of these tubes have demonstrated some abnormally high failure rates (sometimes catastrophically) when pushed to the edge of the envelope, which the ultra-linear platforms surely do when driven to design limits. Minoan isn't the first person to tell me I'm full of crap and he certainly won't be the last -- the line is long and distinguished. But many of those apostates would later plead for redemption and salvation when my advice went unheeded and they learned how the words "China" and "Syndrome" could be applied to a guitar-amp meltdown situation.

Thus......I stand by my assertion.

Arjay

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Posted: Tue Sep 07, 2010 5:30 am
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I wonder if the original poster meant "cherry glow" instead of "cheery glow".... :D
he's probably out buying new tubes....


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Posted: Tue Sep 07, 2010 9:19 am
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Rebelsoul wrote:
I wonder if the original poster meant "cherry glow" instead of "cheery glow".... :D
he's probably out buying new tubes....


Hard to determine, RS.

I only hope the amp itself suffered no lasting ill effects. Most of the components in that chassis are common parts but those UL trannies are both scarce and pricey.

Arjay

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Posted: Tue Sep 07, 2010 10:19 am
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No word back from the OP in two weeks. Must be still cleaning up after the tubes exploded on the first power chord. :shock:

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Posted: Tue Sep 21, 2010 2:52 pm
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I think you'd be better off not messing with the bias unless you know what your doing.


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Posted: Tue Sep 21, 2010 3:37 pm
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Johnny Z wrote:
I think you'd be better off not messing with the bias unless you know what your doing.


Indeed!

I've seen a lot of amps damaged over the years by FNG's who read something in a book or saw something on the internet that made them think they were "egg-spurts".

Arjay

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