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Which tubes in my system are most critical to sound quality?

post #1 of 18
4/2/04 at 2:59am
Thread Starter 
Just curious if anyone would have a rough idea of how to rank the importance of the tubes used in my system.

My preamp is an MG-Head OTL32 with 2 x 12au7 (RCA clear tops), 4 x EL84 (JJ), and a 5Y3 (some random old Silvertone)

My Rogue 88 power amp has 4 x 12au7 (JAN philips 5814a), 2 x 12ax7 (RCA 7025) and 4 x KT88 (Electro Harmonix)

I'm guessing that the 12au7 in my preamp probably influence the sound the most and the 5Y3 has the least effect. But for the ranks of everything in between I'm not entirely for sure.

Any ideas?
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post #2 of 18
4/2/04 at 5:43pm
Do you have circuit diagrams of your gear?
My guess is any tube in the circuit path.
(as opposed to those used for power rectification for example)
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post #3 of 18
4/2/04 at 6:10pm
When you're not sure, replace them all
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post #4 of 18
4/2/04 at 6:37pm
The two RCA cleartops (12AU7) will affect the sound the most on your OTL32.
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post #5 of 18
4/2/04 at 6:39pm
Thread Starter 
Quote:
Originally posted by bootman
Do you have circuit diagrams of your gear?
My guess is any tube in the circuit path.
(as opposed to those used for power rectification for example)
i'm pretty sure they're all in the signal path, except for the 5Y3 rectifier. if i have time, i'll see if i can find circuit diagrams later.
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post #6 of 18
4/2/04 at 6:41pm
I would think switching the amp's output tube would result in the largest change, especially for something like 6550 instead of the kt88.
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post #7 of 18
4/2/04 at 6:48pm
1. Input tubes first.
2. Output tubes second.
3. Anything else after these two.


This means replace the 12AU7 first, then the EL84, then whatever else you decide to change. Ray Samuels and many others have stated unequivocally here that input tubes make the biggest change, not output tubes.
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post #8 of 18
4/2/04 at 6:51pm
Thread Starter 
thanks for all the thoughts so far guys. the complicating thing here is that i'm trying to figure out with regards to the amp and the preamp working together, which tubes make bigger differences.

for example, should rolling tubes in the preamp make more of a difference than in the power amp?

or should i just forget about trying to quantify effect and just focus on synergy?
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post #9 of 18
4/2/04 at 7:15pm
You should figure out what you think you're missing now, or what you want to add or change. Then you can decide on which tubes to try.
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post #10 of 18
4/2/04 at 7:24pm
Thread Starter 
well i think i've reached a pretty good combo for the moment. i do have plenty of tubes with which to experiment.

except for the kt88s. no spares yet for those. they're pretty pricey to get though.
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post #11 of 18
4/2/04 at 7:33pm
Yeah, those kt88 and there substitutes can get expensive, depending on how many you need. In my case, I need 12 of them. I'd like to get 12 matched 6550 but man, that's gonna hurt!
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post #12 of 18
4/2/04 at 7:44pm
Quote:
Originally posted by usc goose
for example, should rolling tubes in the preamp make more of a difference than in the power amp?

or should i just forget about trying to quantify effect and just focus on synergy?
Goose,

Take one set of the input tubes and swap them on the preamp first, then remove then and try them in the amp. Lastly, try using a swap of the input tubes on both amps to see how it sounds. The general rule of swapping tubes is just that, a general rule. Each case is different, as each system is different, therefore tyr doing things a little differently and see what the results. are.
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post #13 of 18
4/2/04 at 7:50pm
Thread Starter 
Quote:
Originally posted by ServinginEcuador
Take one set of the input tubes and swap them on the preamp first, then remove then and try them in the amp. Lastly, try using a swap of the input tubes on both amps to see how it sounds...
sounds good. i just haven't had the patience. what i've noticed is that 12au7s on my preamp change the sound the most. i'm not really sure about whether the 12ax7s or 12au7s in the power amp have more effect though. i usually swap those around at the same time. if i get a chance i'll try seperately and report back.
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post #14 of 18
4/2/04 at 8:04pm
Quote:
Originally posted by usc goose
sounds good. i just haven't had the patience.
You're not alone there. I know that tuberolling requires more patience than most have, and I count myself among those without enough. I have about eight different sets of tubes to roll into the new CDP, and I have a pretty good idea on which ones will sound the best. Will I make it thru more than one other pair before rolling in the better tubes? I hope so. I really want to get a sense of what works best to my ears, and as such I need patience to give the proper time to each set fo evaluate them.
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post #15 of 18
4/2/04 at 8:13pm
Keyword: upstream

I've always found input/gain tubes make the biggest difference, followed by drivers then the outputs. Well, sometimes I find the outputs matter more then the drivers, but gain tubes always makes the biggest difference IME.
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