Topic on tubes

Schematics, layouts & other technical mumbo jumbo.

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Doc Holliday
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Re: Topic on tubes

Post by Doc Holliday »

Is it unhealthy to pull power tubes from one amp and put them in another?
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jerms
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Re: Topic on tubes

Post by jerms »

It depends..... If you're putting them in a cathode biased amp you'll be fine...... Not so with a fixed bias amp, you'd need to make sure the bias is set right.... Don't want the plates glowing red!
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HorseyBoy
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Re: Topic on tubes

Post by HorseyBoy »

^ Yeah, the whole "fixed bias" actually meaning "not really fixed, needs adjusting" always used to confuse the shit out of me. But, as Jim says, if it's a cathode biased amp you can swap tubes in and out to see how they sound.
I'm always terrified of electricity (I can tell you from youthful experience that playing a guitar through an overloaded solid state amp standing barefoot in a garage on a concrete floor covered with water during an electrical storm is a really bad idea) so I always turn off the amp first and keep one hand behind my back, but I've seen old amp guys swap tubes in and out without even doing that. On a kind of related topic, I always giggle when I read about people wearing gloves to change tubes so the glass doesn't smeared by greasy fingers. I've NEVER seen an amp repair guy wear gloves.
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Doc Holliday
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Re: Topic on tubes

Post by Doc Holliday »

Haha gloves... that's crazy.
Cheers guys yeah I wouldn't mess with a fixed bias.
I've just bought a Tayden Ace 25 alnico which is a British Celestion blue copy. 25 watts instead of 15w and has a little more bass for closed back cabs.
My Jensen P12R sounds great and after replacing that microphonic 6SL7 the cone rub I thought I was hearing... well I can't. Still I haven't cranked it up. It made me realise though that I didn't want to ruin the speaker so I'll swap it out and store it. Might look into getting some Mazda or brimar tubes and get this thing roaring!
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Radiotron
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Re: Topic on tubes

Post by Radiotron »

Whenever possible I try to pull them out by the base, but that’s not for fear of smearing the glass.

The wires (coming from inside the tube) that are soldered to the pins are somewhat fragile and the glue fixing the glass envelope to the base often has become brittle over time.
When that bond breaks it allows the tube to flex/twist a little making it prone to rattling and increasing the risk of breaking those wires when removing the tubes.

On the topic of fixed bias, you can easily do that yourself, get a nice DMM and take caution when working inside the live chassis.
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Doc Holliday
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Re: Topic on tubes

Post by Doc Holliday »

Cheers Robert! I'll replace EL84's and 6V6's quite regularly over the years with amps. Wasn't sure if pulling these 1940s/50s Tungsol out and sticking them in my Fender Excelsior would cause any damage? Didn't know whether over time with a faulty amp one might burn out quicker than the other? My amp guy said they checked out ok so hopefully shouldn't be a problem :) just check the transformer on that Jensen as it's been attatched ( like they all were in the 50's I believe) . But worried about drilling into the frame of the Tayden incase I hit the cone...
Didn't really want to do anything to the amp thar can't be put back to stock with an easy fix
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