Pre amp Tube Replacement Advice

Pre amp Tube Replacement Advice

Postby Cmnaround » Wed Oct 26, 2011 6:38 pm

Hey All, I am going to replace the tubes in my Mesa V-twin rack preamp - currently two Mesa 12AX7 tubes. Any recomendations on options other than getting the same direct from Mesa? I realize it's not a fender preamp, but looking to see if there is anything I can drop in that may get in that direction.

Also replacing tubes in the 20/20 power amp, planning on getting matched pairs of EL84 and individual 12AX7s from the factory - but are there other options to consider for my power amp that may get me a better tone?
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Re: Pre amp Tube Replacement Advice

Postby jeager » Wed Oct 26, 2011 7:07 pm

I would recommend the Eurotubes web site at least for the information. They offer a variety re-tubing sets for mesa amps that are tested to run well in them. I'm no expert but the info is really good and I know Brad and others have recommended the JJ tubes (which Eurotubes is real big on as well). There is a nice section of FAQs and a list of tube descriptions.
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Re: Pre amp Tube Replacement Advice

Postby Cmnaround » Thu Oct 27, 2011 12:42 pm

Thanks for the advice on the EuroTubes website - helpful in that it has led me to more questions:

What is the differnce between low, medium and high rated tubes? I'm assuming gain, but I can't quite put that into terms that I can grasp - what is going to give me the closest thing to what Jerry was getting with his clean tone, even when he was using his mesa amps?

Do I want low rated so that I can get break up early on the clean channel or high rated?

Any additional advice or insight is apprciated - although I have learned this is an easy swap and no apparent need to give my amp up for 2-3 weeks to a tech who will charge a lot to do it - no offense to any amp techs on this board, but its not like I'm swapping out the transformer.

Thanks!
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Re: Pre amp Tube Replacement Advice

Postby jeager » Fri Oct 28, 2011 12:14 pm

You might try calling Eurotubes with your questions...some of the amp building modification guys on this site could certainly help too.
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Re: Pre amp Tube Replacement Advice

Postby dancingrizz » Fri Oct 28, 2011 2:50 pm

I hate to be negative but I got barley good non matched 12ax7a’s from there, and I paid for matched sections. In his defense I did not tell him I had a problem (or give him a chance to make it right) and just ordered more from thetubestoredotcom. I gave the euroglass to a tech friend for free.
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Re: Pre amp Tube Replacement Advice

Postby strumminsix » Fri Oct 28, 2011 3:01 pm

dancingrizz wrote:I hate to be negative but I got barley good non matched 12ax7a’s from there, and I paid for matched sections. In his defense I did not tell him I had a problem (or give him a chance to make it right) and just ordered more from thetubestoredotcom. I gave the euroglass to a tech friend for free.

I've never heard of non matched 12ax7s. The reason for matched output tubes, as I understand, is that the signal is split parallel then joined so if they are too far off things sound off. Preamp tubes, by contrast, are series and flow one to the next so it's a non issue.
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Re: Pre amp Tube Replacement Advice

Postby dancingrizz » Fri Oct 28, 2011 3:20 pm

strumminsix wrote:
dancingrizz wrote:I hate to be negative but I got barley good non matched 12ax7a’s from there, and I paid for matched sections. In his defense I did not tell him I had a problem (or give him a chance to make it right) and just ordered more from thetubestoredotcom. I gave the euroglass to a tech friend for free.

I've never heard of non matched 12ax7s. The reason for matched output tubes, as I understand, is that the signal is split parallel then joined so if they are too far off things sound off. Preamp tubes, by contrast, are series and flow one to the next so it's a non issue.



Are we talking about preamp glass or power glass? Because 12ax7, 12au7 and 12at7 ect… are really two tubes in one glass. Perhaps I should’ve said balanced not matched.
After all one would test two sections with any decent tube tester. And get two different readings for one preamp tube. But I suspect you know this.
From Etubes own website:
ECC83S High Gain and Balanced
Price: $16.00
Description: Both triodes graded for high gain and current balance. Because of the extremely high demand for these tubes and the fact that we only get a certain percentage that test out to be high gain these are more expensive as singles than when ordered in a retube kit.
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Re: Pre amp Tube Replacement Advice

Postby FretfulDave » Fri Oct 28, 2011 9:29 pm

Tossing in another $0.02...

I did a lot of research on the tube stuff a couple years ago when trying to improve the sound of my Peavey Classic 30, to my ears anyway. I wanted much clearer and unstaturated sound on the clean channel.

Preamp tubes are pretty simple as noted, plug and play. The main factor in these tubes are the models... 12AU7, 12AY7, 12AT7, 5751, 12AX7. They all are preamp tubes and are basically rated against the 12AX7 model which is classed at 100%. 12AX7s have the most gain. Others have less gain, but perhaps other characteristics and uses. For example, 12AT7s are often used in reverb circuits, sometimes 12AYs. The 5751, not a 12AX but has 70% of the gain of a 12AX and is bell-like and clear (to my ears). I used this preamp tube in the V1 position of the Peavey.

The previous poster, dancingrizz, was talking about the two tubes in one. The 12A series of preamp tubes are two part tubes w/ two separate gain stages. An amp schematic will show how the signal flows through these devices. It seems that with balanced preamp tubes, each gain stage has similar characteristics as measured. The closer they are to the measurements and within a given tolerance, the 12A series twin tube can be "balanced". I figure a good place for this type of tube is specifically in the drive/phase inverter section of the amp where the signal is prepared for the power amp section. In this spot of the amp, I used a 12AT7 balanced to reduce the drive into the power section but maintain a even signal from tube stages.

So within a category, say 12AX7, different tubes will have different values, ultimately determining gain versus noise. There is stuff like differing plate designs to try to produce different characteristics or more desirable characteristics.

All good fun. I would take a look at www.thetubestore.com. They have the tubes and a little synopsis of the tube and its characteristics as viewed by musician testers. I have ordered from them with no issues in the past. Just gotta try your best to pick out what you may want, try it and see and be prepared to try again if you selection doesn't work the way you hoped it would.

Good luck and enjoy.

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Re: Pre amp Tube Replacement Advice

Postby Cmnaround » Fri Oct 28, 2011 10:55 pm

Dave this is exactly what I was looking for - thanks man!

I see what you are saying about the different options for other 12AX7 type tubes to go in the phase inverter spot and impact the sound.

What exactly do you mean by noise and gain? Is it simply that low noise is a really quiet signal and low gain is minimal saturation even at high volumes? So low noise and low gain = super clean tone?
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Re: Pre amp Tube Replacement Advice

Postby barefootdave » Sat Oct 29, 2011 4:52 am

You might also try talking to Groove Tubes. They don't make the tubes, from what I understand, they source them, rate them, match them, then put their logo on them. Expect to pay a little more for their time and expertise.
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Re: Pre amp Tube Replacement Advice

Postby SarnoMusicSolutions » Sat Oct 29, 2011 10:22 am

I see no reason at all to try and get a 12AX7 with matched sections unless you're a hardcore audiophile where each section drives the left and right channels of audio and you want the balance to be precise. In our guitar preamps, there's simply no need at all to match these sections since they cascade on after another. Matching sections means nothing.

Not a bad idea to get a matched 12AT7 for the phase inverter, but really the 12AT7 spec already calls for pretty well matched sections by nature. So, overall, I'd say try to buy preamp tubes tested for low microphonics, but other than that, don't waste your time or money.

NOS GE, RCA, Mullard, Telefunken, Tung-Sol, etc. are great tubes. Sovtek's are pretty crappy sounding preamp tubes, dull and veiled. Chinese Shuguangs are quite good for a new tube and are sold under a number of brand names (GT, Ruby, TAD, etc.). Reissue Tung-Sol and Mullard are decent. JJ's sound pretty good too. EH's aren't bad.

Power tubes should be purchased in matched pairs or quartets.


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Re: Pre amp Tube Replacement Advice

Postby tigerstrat » Sat Oct 29, 2011 12:10 pm

GE and RCA 7025's from the 60's in particular seem to have fantastic tone even at 40+ years old. I just blew one of my old GE's though! In my Super Champ. Catastrophic for the tube but it had served me for an amazingly long time. i should post a pic...
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Re: Pre amp Tube Replacement Advice

Postby dancingrizz » Sat Oct 29, 2011 2:05 pm

SarnoMusicSolutions wrote:I see no reason at all to try and get a 12AX7 with matched sections unless you're a hardcore audiophile where each section drives the left and right channels of audio and you want the balance to be precise. In our guitar preamps, there's simply no need at all to match these sections since they cascade on after another. Matching sections means nothing.

Not a bad idea to get a matched 12AT7 for the phase inverter, but really the 12AT7 spec already calls for pretty well matched sections by nature. So, overall, I'd say try to buy preamp tubes tested for low microphonics, but other than that, don't waste your time or money.

NOS GE, RCA, Mullard, Telefunken, Tung-Sol, etc. are great tubes. Sovtek's are pretty crappy sounding preamp tubes, dull and veiled. Chinese Shuguangs are quite good for a new tube and are sold under a number of brand names (GT, Ruby, TAD, etc.). Reissue Tung-Sol and Mullard are decent. JJ's sound pretty good too. EH's aren't bad.

Power tubes should be purchased in matched pairs or quartets.




You could be right. =]B?)>>

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Re: Pre amp Tube Replacement Advice

Postby strumminsix » Mon Oct 31, 2011 7:30 am

dancingrizz wrote:
strumminsix wrote:
dancingrizz wrote:I hate to be negative but I got barley good non matched 12ax7a’s from there, and I paid for matched sections. In his defense I did not tell him I had a problem (or give him a chance to make it right) and just ordered more from thetubestoredotcom. I gave the euroglass to a tech friend for free.

I've never heard of non matched 12ax7s. The reason for matched output tubes, as I understand, is that the signal is split parallel then joined so if they are too far off things sound off. Preamp tubes, by contrast, are series and flow one to the next so it's a non issue.



Are we talking about preamp glass or power glass? Because 12ax7, 12au7 and 12at7 ect… are really two tubes in one glass. Perhaps I should’ve said balanced not matched.

Just mild confusion. You used a poweramp tube term when talking about preamp tubes so I gave a mixed reply :-)
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Re: Pre amp Tube Replacement Advice

Postby Cmnaround » Mon Oct 31, 2011 1:00 pm

Well it turns out that replacing tubes makes a HUGE difference. I need to play more to get a good feel for the changes, but after plugging and playing, was a very simple switch out, things sounded much louder at the same volume setting I previously used, and a lot cleaner, crisper and more sparkly. A very very noticeable difference, and the humm in my right channel is now gone.

I'll post a youtube clip this week so you can hear how it sounds in this rig. Some pics below of inside the preamp and the new vs. old tubes. Can you tell anything from looking at a tube that it is good/bad/on the way out? I know if they are white-capped they lost vaccuum - but am curous about other physical characteristics. Two 12AX7s in the preamp, three 12AX7s and four matched EL84s in the 20/20 power amp.

Ended up going with Mesa new stock as Mesa amps are fixed bias (from what I have read) and they match specifically to work in their amps. Apparently most are made somewhere in Russia, Eastern Europe otr China, and it is teh Q and selection/matchig process that is what is important.

Thanks again for all of the advice - way much appreciated.

Inside the Mesa V-twin preamp
Image
EL84s
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12AX7s
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