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Tr00 Kvlt
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I think I already know the answer, I googled it, but to no avail on anything remotely related. I want to put something different in my Mesa, possibly some KT77s or 5881s, however my Single Rectifier has a fixed bias. Is it possible to use these tubes without having a bias mod done to the amp? I'm piss poor so I can't currently afford mods, and if I can't do it, I will still be content with the current Mullard EL34s i've got in it now.
 

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Reverend Secret Flower
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11,836 Posts
I'm not sure how different kt-66's are from kt-77's, but when i bought my rectoverb it came with the 66's. My impression of them was way too bassy for the amp. They didnt seem to have much dynamics, it was just too much juice on the tone. Kinda like it had a boost on it all the time, but not in a positive way. More like in the way bass can over power the rest of the tone.

Again, these may have been old, but i didnt care for them.
 

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Premium Member
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8,188 Posts
Yes. You will need to bias the amp.

FWIW, a friend of mine got a Triple Rect fitted with KT88s. It is no longer an amp. It is a fucking bad ass sounding space-heater! :lol:
 

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Uses more gain than you.
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But..can I use them without biasing my amp?....since it's a fixed bias amp?
They bias the same as a set of EL34s. Now, I dunno how Mesa's are biased, "Fixed Bias" is a bit confusing, as that type of set-up is supposed to have a bias pot.

Now if you have no adjustment what-so-ever, I dunno how well they'll work in your amp.
 

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Guiterrorizer
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15,696 Posts
Mesa makes KT77's (so I was told) - so those should work in it.

I'm dropping KT77's in my roadster when I can. I Loved them in my Peavey.
 

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Registered
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I have never heard of Mesa making kt77's, I am pretty sure that you will have to take your head in to be biased. That being said it shouldn't be expensive, I have never heard of anyone charging more than $50 to do so.
 

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Premium Member
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I have never heard of Mesa making kt77's, I am pretty sure that you will have to take your head in to be biased. That being said it shouldn't be expensive, I have never heard of anyone charging more than $50 to do so.
Mesas are fixed bias, though - it's not a matter of tweaking a trim pot as much as it is installing one.
 

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Premium Member
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2,232 Posts
I ran KT-77's in my Rectoverb with zero problems. I loved them for more of a 'versatile" sound, but for straight out heavy I preferred 6L6's.
Just make sure the Bias switch is on the El-34 setting and you'll be all set.
 

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...
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I believe someone explained it to me as: Mesas are biased really cold, which is why you can swap in a wider variety of tubes safely, despite their own rules of only using Mesa tubes. This is also why a bias mod on a Mesa can really open them up, as you can set the bias as hot or cold as you like.
 

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Slow Money
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eleven59 said:
I believe someone explained it to me as: Mesas are biased really cold, which is why you can swap in a wider variety of tubes safely, despite their own rules of only using Mesa tubes. This is also why a bias mod on a Mesa can really open them up, as you can set the bias as hot or cold as you like.
No, Mesa rebadges other tubes (currently jj pre ruby power) and they pick ones that need to have the same bias. Also, Mesa does not make their own toobz

in short, let's kill 3 rumors that have come up in this thread
1) Mesa does not make and have not made kt77s (Or any other tubes for that matter, at least not in a long time)

2) mesas have a completely 100% fixed bias. This can be modified while maintaining warrantee by an authorized Mesa tech

3) mesas are not "biased so cold" you can use whatever tubes. They are biased cooler rather than hotter on an average tube, but that's all relative. You bias cold to specific tubes, there's no such thing as biasing cold as a general thing to do. Mesa tubes are chosen to need the same voltage, so you can retube without biasing. This is not why you can put in other tubes with few issues. You can do this cause you can do it in any amp, provided it hasn't been biased hot relative to a set of tubes with a high draw.

I'm assuming the kt77s you'll be using are JJs since that's just about your only option other than gold lions which are 2.5 times the cost, or NOS bottles. You can swap them in without biasing and they will work fine. Get the amp modded and biased and they will simply perform better (potentially a lot so)
 

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Guiterrorizer
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15,696 Posts
I guess I should have said "mesa re-brands KT77's" - but I didn't see them on the online store.

I was told that I think it was -C-' KT77's that are safe to run in the rectos, might have been Svetlana.. I'd have to dig up a thread or two.
 

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crying in your beer
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3,782 Posts
afaik, you can run KT77s in the newer Mesas that have the 6L6/EL34 switch, and you still need a tube-reseller with some knowledge because you need a set with the correct rating. The brand doesnt really matter. You cant buy a random set of KT77s and put them in.

FWIW: as the 5881 were mentioned in the first post - these are actually 6L6WGB so the sound wouldnt be much different to the stock Mesa tubes , you cant use all of them, as most 5881 have a maximum plate rating of 360V if i recall correctly...the common 6L6GC-designed power-stages have a much higher plate voltage and would propably melt the tubes. However, i know there are Sovtek 5881 which can be used, but these are also the ones Mesa buys and relabels as Mesa tubes, so these wont make a real difference.
 
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