#1
From what I've read, it seems like 12TU7 preamp tubes/valves put out a cleaner tone than 12AX7s. Is this true? I'd like to get a lil more clean headroom outta my amp. The amp is around 25 years old and still has the stock tubes (stock everything actually) so maybe a general tube replacement will help but I was thinking of going with 12TU7s specificly for the clean headroom boost. Good idea? bad idea?
#2
JAN Phillips 5751 FTW. I use them in every preamp position with very nice results.
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#3
^ +1 Great tube.

12AT7 will be in the middle of a 12AX7 and a 12TU7.

Otherwise TS, you are on track. What amp do you have? Contact Doug at www.dougstubes.com

It won't be a 'clean headroom boost' as much but more like less gain basically. Same thing I guess
#4
Thanks, I just looked up the 5751 and found a helpful "gain factor" page. I think I might try those but it says it cuts the volume by about 30% too and I'm already trying to keep up with drums with a 15w amp. Does it cut the volume that much? I'm worried I really just need a bigger amp
#5
i've never noticed a volume drop

where did you read that?

not sure I'd get all 5751s but we can help a bit further. Cathbard is the real preamp tube expert here.

What amp? What tubes does it have now? What do you like about the tone of your amp now? What do you dislike about the tone of your amp now? Do you like bright? Darker? etc
#6
Please answer 311's questions, we need more information. A 12AU7 isn't always better or worse than a 12AX7 and it really depends on what you want to do with the amp.

When people say 'volume' a lot of the time they might mean 'gain'. It's more helpful to say preamp gain or power amp gain.

Since the 12AU7 is a preamp tube, it will cut your preamp gain and clean up your amp, but it might also drop the overall volume as a result.
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#7
Its an Electar Tube 30R, not 30w, cathbard said probly 12-18w and I think that sounds about right, 2x 12ax7 sovtek, 2x el84 EH, 8 ohm 10" speaker(I play it thru a 1x12 cab though). Call me crazy but I like Epiphone amps (while simultaneously hating they're modern guitars). To my ears it sounds like thick, creamy, fuzzy goodness, I love that about this amp. I don't like that its just barely not clean enough for drums with a few of our songs. I dig the amp, just want a lil bit more clean when needed.
#8
so this is a 'play with drummer' thing? I don't think preamp tube changes are going to make the differences you are looking for. You may still need/want new tubes. The JAN 5751 are still great tubes. Try one.

I would get some new power tubes first. Not a fan of the EH but that is irrelevant. I think you'd get more mileage out of that swap. Then, maybe grab a few different preamp tubes and experiment. Maybe consider getting a better cab. A 2x12 stood up on end for example might give everyone's ears a bit more of an audible hit.
#9
I had planned on changing the power tubes, I posted this thread to see if maybe it'd be worth changing preamp tubes too, esp if it'll give me a lil more clean. Thanks for the insight, think I'm gonna give the 5751s a try just to see what happens.
#10
12AU7's are not always a drop in replacement for a 12AX7. They will often just blow up.
Now here's the thing. From what you are saying this is a simple 18W type amp with an extra couple of EL84's? If so precious little distortion is coming from the preamp anyway so you probably won't gain a lot in the way of headroom regardless.
The second preamp tube isn't a preamp tube, it's the phase inverter. You can try a 5751 or a 12AT7 in there but I doubt it will do a lot. If it does run the topology of an 18W'er, V1 will be running the triodes in parallel, that won't be driving the PI into clipping really either. If it isn't actually an 18W circuit with extra power tubes and actually has the two triodes in series then you may get some benefit. Show me a schematic.
You can give it a go but don't expect a lot, any improvement will be about the same as just backing off the volume a little. You'll mainly just notice a difference in tone.
The distortion on an 18W arrangement is coming from the power valves so your best bet is to drop better EL84's in there. EHX are pretty meh. Grab a set of JJ's. As for the preamp tube, JJ ECC83S tubes sound phenomenal in an 18W circuit. I find in my 18W'ers that they can compete very well toe to toe with top flight NOS tubes like Amperex and British Mullards. Replace your power tubes before experimenting with the preamp/PI tubes.
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#11
^ You're the man Cathbard! I can see clearly now, haha. I'd put a link for the Electar Tube 30R schematics here but I can't even figure out how to reduce pic size to post pics.
I can happily play the amp as is. I can see how with a smaller amp the preamp isn't gonna affect the gain too much. I'm gonna get jj el84s, and probly jj12ax7s but maybe 5751s (think it would hurt to use one of each?) if my fav guitar shop has them.
I would think a simple tubes replacement after 20+ years may give me that extra lil oomph of clean I want. Thanks guys, I'm learning.
#13
You may want to look into filter caps also if its all original. That can have a big impact also, but its a tech job... Not for us amateurs.
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#14
Grab a few different ones. JJ ECC83S, JJ ECC803, Phillips 5751, maybe a British Mullard and just try them in different positions. There will be a combination that you'll particularly like but you won't know until you try it. Just experiment.
Just post the link to the schematic, you don't need to embed it as an image.
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Last edited by Cathbard at Oct 27, 2011,
#16
That's quite a bit different to an 18W'er. Like, nothing like it, not even close. It uses a single triode for the phase inverter and the other three in series. I bet it gets pretty savage with the gain knob turned up, huh?
A 18W'er uses two triodes for the phase inverter and two triode in parallel in the high input. In the low input it's a single triode straight into the phase inverter.
So what does that mean for you? Basically everything I said was a load of bs.
5751's in both positions would tame it without killing it. You could try a 12AT7 in the phase inverter if you want but I think that may suck all the life out of it.
The JJ ECC803 has a tiny bit less gain than an ECC83S and they are pretty noiseless (prone to microphonics in combos). 'Twer I you I'd grab two 5751's, two ECC803's, one ECC83S and a pair of JJ EL84's. Then play mix and match. You'll have a ball.

btw, that's a 20W amp thereabouts.

Edit. It has a SS rectifier too. About the only resemblance it has to an 18W'er is the fact that it has two EL84's and two 12AX7's. It would be hard to design an amp with those tubes that was further from an 18W'er if you purposely sat down to do just that.

Funny though huh? Even though it was for a totally different situation that required different logic, I ended up recommending the same tubes for different reasons. Gotta love that. I love tube amps.
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Last edited by Cathbard at Oct 28, 2011,
#17
20w!!! Holy suit!! Sometimes I think my 5w epi valve jr is louder than the Electar. I have the day off so I'm getting new tubes today, damn guitar shop doesn't open til noon though, haha.

BTW, Is it safe to put the amp on its side and put a (1x12) cab on it? That way I can get the speaker higher but still use the top mounted amp controls?
#18
Yeah. It'll be fine.
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#19
Okay it was a weekend long fight to find tubes. Now I finally got them but I'm stuck at home and my amps at the practice room I got my jj power tubes. The preamp tubes were hell. Couldn't find any 5751 or ecc803 yet, might have to order those. I did find and buy tung sol 12ax7 and jj802s(12au7?) so I'm gonna give those a try. Couldn't quite convince myself to splurge for the $150 NOS mullards. Though I was close. Maybe next year. Thanks all, I've learned a ton bout the lil bulbs behind my amp recently
#20
Cool man. Well I guess we did not make it clear that you will probably not find the best tubes or best choice of tubes at a retail type place. On-line is where it is at.

www.dougstubes.com
www.thevalvequeen.com
www.tubedepot.com
www.thetubestore.com
www.eurotubes.com (not in europe)
www.hotroxuk.com (in europe)
Last edited by 311ZOSOVHJH at Oct 31, 2011,
#21
Personaly after someone mentioned them I looked up the JJ's and they sound really good, I found this site

https://ssl.eurotubes.com/

the guy seems really helpful and the reviews I found on him seem justified. I told him the amp I have and asked about the options and he told me my amp to a T, totally spot on, he also explained about the revalve (retube) kits that he stocks and how they differ from the likes of the standard electro harmonix etc.
#23
They also have those EL844 things too. They are supposed to break up at lower volumes so that's not what you want. Some claim that they are simply sub-par EL84's that break up early just because they are crap. ie. relabelled tubes that failed QC and passed off as something special - it's a feature not a fault. Eurotubes deny that emphatically. The controversy over it is quite an entertaining read. There's a button called EL844 info on their front page.
If you want that thing to sound more like a Marshall I'd stick ECC83S's everywhere. No question. Sticking an ECC803 in V2 may tame it a bit but it should still sound a bit Marshally. The more I think about it I'd try every combination of ECC83S and/or ECC803 until you find what you like. It's not like they are expensive. If already paying for shipping you may as well get a couple of extras chucked in. They'd make good spares anyway.
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Last edited by Cathbard at Nov 1, 2011,
#24
He reckons you can get them for more break up sooner or more head room, they grade them somehow and select certain ones for certain jobs. Interesting idea on getting extras though. I was also decided till you chimed in so now I'll have to do MORE reading Lol oh well google here I come.
#25
Always good to have spares. This is part of my collection of 12AX7's:

Can't have too many. Trying different tubes is fun.
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#26
u know cath, why is the cathode resistor on the EL84's 120k? that would ruin the whole el84 scheme. why? and R7/R8 voltage divider. heavy loading on the second tube. and first tube doesn't have cathode bypassed. a lot of what the ****s. this amp is screaming to be modified.
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Last edited by ECistheBest at Nov 1, 2011,
#27
Quote by ECistheBest
u know cath, why is the cathode resistor on the EL84's 120k? that would ruin the whole el84 scheme. why? and R7/R8 voltage divider. heavy loading on the second tube. and first tube doesn't have cathode bypassed. a lot of what the ****s. this amp is screaming to be modified.

Well I guess B+ is higher so it needs a bigger cathode resistor there. Either that or it's running damn cold.
Yeah, I'd be in there with a soldering iron within the hour of it arriving at my door. R7 seems crazy, why isn't it 1M? Putting a 50uF cap across R5 would be high on my mods to test too, especially if you bumped R7 up. It's all a bit odd. It certainly bears little resemblance to a 1974X. The LDR setup on V1b is odd too.
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#28
i think the amp has to be biased warmer with a lower cathode resistor on the EL84's.
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#29
What amp are you guys talking about? Or is this standard practice with EL84's?
#30
for a cathode biased push-pull pair of EL84's, it's quite standard to put a 5w 120R~330R resistor on the cathode. this biases the EL84's at an optimal working condition in most cases. however, the schematic he gave us has a 120k (1000 times the "standard") resistor at the cathode, which drives the cathodes waaaaaay at the cutoff that it gives no headroom.
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#31
I use a 125 ohm resistor on my 18W'ers. It's just all sorts of weird. Look at what's hanging off the grids of V3 and V4.
We are talking about this:
http://www.freeinfosociety.com/media/pdf/3346.pdf

It has to be a typo. 120R instead of 120K. i bet if you actually looked inside it's 120 ohm.
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Last edited by Cathbard at Nov 1, 2011,
#32
grids look like 47k grid stoppers and a 470k grid reference resistor which would work. not typical but ya. if you're talking about the diodes on the plate, that actually helps low power push pull circuits. it kills all the awkward negative bounce on the plates so each tube gives clean upward waves, and no downward waves.
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#33
Oh hang on, I'm a bit sleep deprived. That's how mine are actually except my grid stoppers are 8K2, not 47K. For some reason it looked weird to me but on closer inspection it's pretty normal 1974X fare.
It'd be an interesting amp to mod. Lots of scope for a bit of cutting and hacking.
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#34
Is it easier to mod than an epi vj? I was gonna try my hand at modding one of them. I didn't pay much for either so it isn't too much of a risk and I've always wanted to mod my own stuff.
#35
How easy it is to actually mod is more about physical access and quality of PCB. There is a lot of scope to mod it but how easy or hard to actually do it is down to physical construction.
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Telecasters
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#36
If it was 30 years old, it would be quite difficult working with the old solder or the gunk build up over the years.
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#37
Just thought I'd let you know, my Electar is now sportin' 2 jj el84s, 1 sovtek 12ax7 and 1 jj 12au7(in the first spot) and I frickin' crapped my pants when I first heard it! Well worth the new underwear! Now my clean chimes beautifully and LOUD! I can 11-ize it and it stays clean enough and LOUD while sounding pants crapping warm and creamy and clear! I'm glad I walked outta the shop with the Electar and not a fender bj, I would take this amp over a blues jr any day