powertubes............does it matter?

ivan H said:
Yes, that's it. Just as running the 4 ohm (amp) output into an 8 ohm cab will limit output tube plate current, running the 8 ohm (amp) output into a 4 ohm cab will allow too much output tube plate current to flow, possibly frying the output tubes &/or more. Cheers
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no no no fried tubes taste like a$$ ----bacon -- we fry B-A-C-o-N ;)
 
ivan H said:
Yes, that's it. Just as running the 4 ohm (amp) output into an 8 ohm cab will limit output tube plate current, running the 8 ohm (amp) output into a 4 ohm cab will allow too much output tube plate current to flow, possibly frying the output tubes &/or more. Cheers
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Hey sir. I run my Mesa Rectoverb out the 8 ohm jack into 1960bx cab wired at 16 ohms. Am i running the amp a lil cooler or hotter? Is my bias pr something goin or changing by any chance with the mismatch versus the 8 ohm into 8 ohm? thanks
 
BFT Gibson said:
Hey sir. I run my Mesa Rectoverb out the 8 ohm jack into 1960bx cab wired at 16 ohms. Am i running the amp a lil cooler or hotter? Is my bias pr something goin or changing by any chance with the mismatch versus the 8 ohm into 8 ohm? thanks
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Running the amps 8 ohm output into your 16 ohm cab is mismatching within acceptable limits. This is a 100% mismatch "up".
To explain what is happening, suppose that with the normal 8 ohm cabinet connected to the 8 ohm output that your OT has a 3,500 ohm (plate to plate) load impedance (about right for two EL34's).
If we instead use a 16 ohm cabinet connected to the amp's 8 ohm output, the output tubes now "see" a 7,000 ohm (plate to plate) load impedance.
The 7,000 ohm load "impedes" the flow of current more than a 3,500 ohm load does (though the voltage swings across 7,000 ohms will be greater than across 3,500 ohms).
Hope I made that understandable. Cheers
 
ivan H said:
Running the amps 8 ohm output into your 16 ohm cab is mismatching within acceptable limits. This is a 100% mismatch "up".
To explain what is happening, suppose that with the normal 8 ohm cabinet connected to the 8 ohm output that your OT has a 3,500 ohm (plate to plate) load impedance (about right for two EL34's).
If we instead use a 16 ohm cabinet connected to the amp's 8 ohm output, the output tubes now "see" a 7,000 ohm (plate to plate) load impedance.
The 7,000 ohm load "impedes" the flow of current more than a 3,500 ohm load does (though the voltage swings across 7,000 ohms will be greater than across 3,500 ohms).
Hope I made that understandable. Cheers
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Thanks, it seems the amp is more aggressive in the mids & upper mids running into 16 ohms

Why do you think Marshall chose 16 ohms...Fender 4 & mesa 8? just curious as to how they land on their selection.
 
BFT Gibson said:
Why do you think Marshall chose 16 ohms...Fender 4 & mesa 8? just curious as to how they land on their selection.
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I imagine that in the early days it may have been as simple as what the available speaker impedance were.
I can tell you that in the early days, the British speaker manufacturers "had also" used lower impedances (2 ohms, 4 ohms). The change to 15 ohms (common in England, Australia etc) came about because people were hooking the speakers to audio amps by using long runs of thin speaker wire, so that they could have speakers in different rooms than the amp. These long runs of thin wire added series resistance.
Imagine a 2 ohm speaker with an added say, 1.5 ohm series resistance from the long thin speaker wire, adding up to a total of 3.5 ohms.
By changing the speaker impedance to 15 ohms, the added series resistance from the long thin speaker wire made a LOT LESS of a difference, 15 ohms plus 1.5 ohms = 16.5 ohms.
Notice that early Celestion Greenbacks, bulldogs etc have a nominal 15 ohm impedance, not 16 ohm.
Cheers
 
ivan H said:
I imagine that in the early days it may have been as simple as what the available speaker impedance were.
I can tell you that in the early days, the British speaker manufacturers "had also" used lower impedances (2 ohms, 4 ohms). The change to 15 ohms (common in England, Australia etc) came about because people were hooking the speakers to audio amps by using long runs of thin speaker wire, so that they could have speakers in different rooms than the amp. These long runs of thin wire added series resistance.
Imagine a 2 ohm speaker with an added say, 1.5 ohm series resistance from the long thin speaker wire, adding up to a total of 3.5 ohms.
By changing the speaker impedance to 15 ohms, the added series resistance from the long thin speaker wire made a LOT LESS of a difference, 15 ohms plus 1.5 ohms = 16.5 ohms.
Notice that early Celestion Greenbacks, bulldogs etc have a nominal 15 ohm impedance, not 16 ohm.
Cheers
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Every time I find a post like this, or info specs, reviews of components, amp builds or repairs in progress by members such as Sg John's, Ivan's, 67's, Sysco's, Amp mad Scientist, Bastarddon, etc, I am blown away at the level of teaching each has experienced in their electronics lives, and just how lucky I am and we are for the assemblage of all of these guys here. I know personally from Ivan, how he gained his knowledge from his " boss" and mentor. When Ivan first helped me diagnose and fix my 4 hole JMP 50 watt head and told me how he got his beginnings @ learning amps. All I could say was that man is incredibly smart if amp servicing was like a kid riding a bike to him. Then with Ivan showing him how much he learned from the book and then demonstrated his understanding to the point where he got hired and this made the mentor/boss able to pass on the "trivial" servicing of amps to Ivan, so he could then devote his time to even more involved and challenging projects.

Much like Ivan, I do believe that all the members I mentioned above, plus a few I missed, sure do have quite remarkable computers up on top of their shoulders. I sure do aspire to somehow stow away enough of what you guys know and share so that I too can know electronics from the basics to the advanced nature of circuit designing, tweaking, and troubleshooting when I set out to build or service ones I own or that wind up on my bench in the years to come.

Thank you Ivan and all you other guys.
 
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I also have a bit and this is just a wee bit of ( Tube experience)

I am the farthest from LearnED on these matters. BUT my own personal experience to date involves only 1 amp "tech" known here in Baltimore.
In my own attempts to arrive at dependable valve amps from ones I own or purchased, were requested to fix that needed work, I only had 2 that turned out truly NEEDING power tubes.

First amp I needed to fix was my JMP 50 watt 4 holer. Despite putting new tubes in it, and a cap job, I still wound up needing other things AND eventually the main reason for failures, fuses blowing etc, was not related to tubes or caps, but bad connections at the Ohms selector.

2nd was a friend's Marshall Vintage Modified amp. This amp was working fine then as my friend said, it stopped making a sound. This has added meaning, because he is blind and stuff like an indicator light is basically useless to him. As I learned though, this amp has a propensity for blowing the indicator light and it even causes issues if this happens. ( Sort of foggy memory here) BUT what I learned is pretty clear. Marshall had a design glitch and some simple fixes help such as increasing value of a resistor at R72 ...AmpMadscientist knows of this as he was in on some conversations with other VM owners elsewhere on the web.
This particular VM needed new tubes to fix it for the owner, Once I told him they were shot, he tells me he left the amp on for something like 3 straight days with the cover on it, before realizing it was still on. ( Obviously being blind ) it is easy to understand how this could have happened.

3rd is my Laney that needs some mouse chewed wires fixed and can benefit from new caps.

4th is my Orange Tolexed, Superlead 100 watt head, It DID need new Power tubes for sure. Instant blown fuses from bad tubes arcing inside and red plate issue.

SO, it is due to the 4th amp, where I learned or was told by a tube seller, he alluded to the fact that we guitar players focus on our Power tubes and the resulting effect they have on sound. BUT he was saying his point is, where one gets most coloring ( differences) in how audio really sounds, essentially is more affected by Preamp tubes than power amp ones. He said his background was 40+ years in owning and running a car audio and home audio business. He had thousands of tubes at his house, and testers, amps he built for stereo use, and so I leave hsi comment to you guys.
 
All I know is this.
Whilst gigging my PRS H 1x12 combo a tube blew. Luckily I limped through the last 20 mins.
The tubes in there were Winged C 6L6. I replaced them with Groove tubes and didn't like it. Big change even after bias adjust.
Spoke to PRS support and they recommended Ruby. Got a set of Ruby 6L6 and bam! Right back to the tone I loved!
So... answer is yes for me.
 
Not keep up with Flips, keep up with your keepers of the good stuff or stuff I never have even tried yet like Oranges, Mesa's, Blackstars, Kempers, etc.
 
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