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TUBE HELP?


rugby1970

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 No, I'm not getting my tubes tied. And yes, my fat ass does have some difficulty fitting into a floating tube in the pool.

The real issue is my Sock Monkey amp (thanks @gtrdaddy) took a dump. It started producing horrific sounds whenever I powered it on; couldn't play it. So I took off the back panel, turned it on that one of the EL84 tubes was producing a great light show. So that one is dead.

The real question is all of the tubes are a matched set. Can I just replace the defective tube and call it a day? Should I get a new matched set of (2) EL 84s and (3) AX7s?

Thanks.

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Only power tubes require matching. Preamp tubes are cathode self-biasing and don't need to be matched at all. The preamp tubes also are subjected to far less wear and tear, and need replacement far less often.

What kind of power tubes are in it now? If you don't know the rating of the tubes, it won't be possible to get a good match unfortunately.

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So Dave, you're recommending a new set of matched power tubes? I don't know too much about this, that's why I'm asking.

The existing set are JJ Ruby EL84CZ, IMG matched #135, PC: 24, TC: 6050. That's all I know. Thanks for the help.

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JJs should not be expensive for a matched set. Under $30 at Euro Tubes, IIRC. I would get a matched set (check, as they have more than one EL84 spec depending upon your amp and sound desire) and keep the existing good one as an emergency backup.

You might also consider the tube damper rings that may help extend the life of the tubes., esp in a combo amp.

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If the amp is rated at 18 watts with two EL84s in the power section, wouldn't that probably/likely make it cathode biased?  The reissue Marshall 18 watt amps use two EL84s and are cathode biased, which means (from what I've been told, correct me if I'm wrong, I use a couple of  18-watt Marshall clones/semi-clones myself) no need to bias?  Of course, if in doubt, check with the manufacturer or a experienced amp tech/repair person for their recommendations first.

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Most el84 amps are cathode biased, sometimes erroneousLy referred to as class A . Tubes should be matched and depending where the bias is set ,will break up sooner or later In the output range. Hopefully you didn’t blow any resistors when the tubes red plated. If you buy a set of tubes rated in the mid-range, you shouldn’t have a problem. It will either breakup a little sooner or later than the old set.

arniez

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As a rule, I always change the phase inverter with the power tubes. It's usually the last 12AX7, closest to the power tubes. Might not be necessary with your amp, but is a good idea with a fixed-bias amp, like a Bassman.

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On 2/23/2021 at 9:26 PM, ArnieZ said:

Most el84 amps are cathode biased, sometimes erroneousLy referred to as class A . Tubes should be matched and depending where the bias is set ,will break up sooner or later In the output range. Hopefully you didn’t blow any resistors when the tubes red plated. If you buy a set of tubes rated in the mid-range, you shouldn’t have a problem. It will either breakup a little sooner or later than the old set.

arniez

Per the 3 Monkeys website, the Sock Monkey is definitely cathode biased.  So the main question is what brand of tubes to go for.

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I would find some used old Brit/Euro/USA el84s that test great. But that’s me. I find the old stuff, as a rule, will way outlast current production.

That said, I have done very well with JJ in cathode biased 18 watt el84 circuits.  My Mesa TA15 LOVES the Mesa el84 tubes which are Sovtek, I believe. I bought a fancy set of Genelex Gold Lion Chinese reissue el84 and one died in a month. 
 

Go with JJs.

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22 minutes ago, Jakeboy said:

I would find some used old Brit/Euro/USA el84s that test great. But that’s me. I find the old stuff, as a rule, will way outlast current production.

That said, I have done very well with JJ in cathode biased 18 watt el84 circuits.  My Mesa TA15 LOVES the Mesa el84 tubes which are Sovtek, I believe. I bought a fancy set of Genelex Gold Lion Chinese reissue el84 and one died in a month. 
 

Go with JJs.

I think the Genalex Gold Lion tubes are all Russian made, not Chinese. But yes, the Genalex EL84s are known for being unable to stand up to high currents, and are recommended to not be used in Cathode Biased amplifiers. If only they had known that before everyone started buying them.

The Sovtek tubes, made at the same plant, are pretty invincible, but more popular for hi fi applications because they are really clean.

Tube Depot has some NOS tubes available. They have U.S. NOS tubes for $100 a pair, and say they have enough brands and bias points to match them. They also have RFT Germany tubes at $120 a pair.

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5 hours ago, Jakeboy said:

I would find some used old Brit/Euro/USA el84s that test great. But that’s me. I find the old stuff, as a rule, will way outlast current production.

 

In the past I've stayed away from NOS or vintage stuff because I didn't trust what's out there except from reputable businesses and I didn't think the extra $$$ was worth any perceived tonal upgrades,,,, one thing I have found though is that they have a much longer life span. It's worth factoring in and the few times I've ventured out for moderately priced NOS glass (from reputable dealers) I've actually been quite pleased with the results...

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3 hours ago, 0054 said:

Stoli Tubes! Long live the cold war!

Da tovarich, Da!

The only reason I mention them is the references above to longer life.  The 6π14π (aka 6P14P, also incorrectly cited as 6N14N, I suppose because the π on the side kind of looks like a lower case n) is a ruggedized Soviet military version of the EL84 and is supposed to be longer lasting.  According to Dr. Z they also sound better. 

Personally, I've paid big bucks for EL84 variants (well, EL84 big bucks - they aren't very expensive) and I've bought JJs and personally I can't tell a worthwhile difference.  I have, but have not installed, a set of 6π14π I bought on the board from @santellavision, so I'm looking forward to the comparison (if and when I actually get my tube amp out and plug it in again).

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19 hours ago, velorush said:

Da tovarich, Da!

The only reason I mention them is the references above to longer life.  The 6π14π (aka 6P14P, also incorrectly cited as 6N14N, I suppose because the π on the side kind of looks like a lower case n) is a ruggedized Soviet military version of the EL84 and is supposed to be longer lasting.  According to Dr. Z they also sound better.

Did Sovtek make many changes to their tubes when they started selling them over hear? They still sell an EL84 and EL84M. The 5881WXT and 6L6WXT tubes that they still make, which are used by Mesa Boogie, are re-labeled 6P3C and 6P3C-E tubes. You can find the actual data sheets and see where they just used a rubber stamp right over the original soviet designation.

http://www.jayskyler.com/guitar-gear-guide/sovtek-5881-wxt-6l6-wgc-tube-guide.html

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@rugby1970, I asked Greg Howard @ 3 Monkeys about the need to bias my Orangutan Jr. when it comes time to replace its two cathode-biased JJ 6V6S power tubes. He said "Always good to check the bias when changing tubes, but most current production tubes are similar in spec."

Contact Greg directly at [email protected]. He's responsive and helpful.

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