Which is what I sold my Eden WT-300v and opted for a Mesa WD-800.
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how to replace preamp tubes ampeg svt classic
- Thread starter justbass4
- Start date
Which is what I sold my Eden WT-300v and opted for a Mesa WD-800.
@justbass4
A different cab will make a lot more difference than changing out the preamp tubes.
Tung Sol 12AX7 will probably be slightly brighter than the stock tubes. I have not rolled the tube in an SVT, but I have rolled it in some other amps. If you like gank and fret rattle, this could be a good choice as the tube seems to be really hard and punchy in the high-mids.
A lot of people don't hear enough difference to justify the hassle of rolling tubes (I am not one of them). The results vary from circuit to circuit and range from slight to imperceivable, but sometimes a subtle change can be really nice IMHO.
As has been mentioned, rolling tubes carries some degree of risk, especially if you have not done it before. Don't use too much force and make sure the pins line up with the tube socket during installation.
A different cab will make a lot more difference than changing out the preamp tubes.
Tung Sol 12AX7 will probably be slightly brighter than the stock tubes. I have not rolled the tube in an SVT, but I have rolled it in some other amps. If you like gank and fret rattle, this could be a good choice as the tube seems to be really hard and punchy in the high-mids.
A lot of people don't hear enough difference to justify the hassle of rolling tubes (I am not one of them). The results vary from circuit to circuit and range from slight to imperceivable, but sometimes a subtle change can be really nice IMHO.
As has been mentioned, rolling tubes carries some degree of risk, especially if you have not done it before. Don't use too much force and make sure the pins line up with the tube socket during installation.
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Big question: Why? Unless they're crackling or microphonic, preamp tubes seldom need replacing. They run at low currents and don't "burn out". As previously stated, the bank of 6550's is another story, along with the 12AU7s or 12BH7s which control the bias. Power handling tubes do wear out, but if not well versed in measuring and setting bias PER AMPEG'S PROCEDURES leave that to a pro.
Cost?? $400?? For the tubes plus other associated maintenance issues. Setting bias, inspecting resistors, and other electrical components. You don't want to have anything else that might fail crash a $400 dollars worth of tubes.
This could mean you have one or more dead 6550s on that side of the amp.
The tubes are organized into two triplets. Each triplet has a bias adjust and bias indicator.
For the indicator circuit in a CL to show green, all three tubes must pull at least 15mA. If any one tube in the circuit pulls more than 30mA, you get red.
So the circuit does not expect very tight matching. As long as all three tubes in a circuit are between 15mA and 30mA you get green.
If a tube in a circuit is dead or has super low emissions, you get red before green. I.E. one tube pulls more than 30mA before all three pull more than 15mA.
If a fresh trio of tubes does not fix the problem, the bias indicator circuit maybe ganked or there may be a problem in one of the individual tube circuits. The screen resistors on SVTs are designed to act as fuses. So if an output tube goes bad it will sometimes blow the screen resistor. This is to protect the amp from more serious damage.
The bias for the 6550s flows through the driver tubes. So a weak driver tube could cause the problem as well. If you replace the driver tubes, I suggest adjusting the bias for minimum tube current in the 6550s before pulling the old drivers out. If you put a strong driver in without doing this, it may pull the bias down causing the 6550s to pull too much current.
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And, I should have added, changing a good preamp tube for a different good preamp tube of the same type will make as much difference as replacing the perfectly working HDMI cable on your TV with a super-duper-paratrooper kevlar jacketed 100% oxygen free copper with titanium ends $500 cable. Zero. The difference is in your head.
This may or may not be true. Some circuits do respond noticeably to tube rolling, but I agree changes tend to be subtle.
Perceivable differences may involve modified tone and changes in how the circuit transitions from clean into overload. Also the tonal quality of drive in the circuit can be impacted. If a tube produces three subtle, but desirable changes to the sound and feel, it's totally worth it IMHO. But YMMV.
JeezyMcNuggles
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- Feb 23, 2018
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Over $500 for tungsols
The three ax7 tungsols for the pre amp are 80.
Bout the same for the two au7 drivers.
Total of $700 to go Russian in an SVT.
But, that's really not bad. Seeing as how amps today have a hard time making it half the standard tube life, don't sound as good, and cost more than the 500 for a full set of power tubes. You really only save weight. Not money.
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- Feb 12, 2006
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- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
How do “amps today having a hard time making only 1/2 the standard tube life and don’t sound as good”?
Could be I just have "bad one." Hope not. Had one before and I played it through the same cab's as now. I just can't get an "grrrrrrit" from it. It just sounds boring. It doesn't do that SVT mid range thing at all. I was told that is the preamp tubes. The other tubes, the power tubes, they bias. So I was told if you get a "green" bias light, then they're ok
Gotta tell you - it's not the amp or the bass, it's the fingers.
Ignore the tubes as long as they work. Try different strings, a pedal or other alternatives. You can make nuch more difference that way.
Could be I just have "bad one." Hope not. Had one before and I played it through the same cab's as now. I just can't get an "grrrrrrit" from it. It just sounds boring. It doesn't do that SVT mid range thing at all. I was told that is the preamp tubes. The other tubes, the power tubes, they bias. So I was told if you get a "green" bias light, then they're ok
Could be I just have "bad one." Hope not. Had one before and I played it through the same cab's as now. I just can't get an "grrrrrrit" from it. It just sounds boring. It doesn't do that SVT mid range thing at all. I was told that is the preamp tubes. The other tubes, the power tubes, they bias. So I was told if you get a "green" bias light, then they're ok
Maybe your not cranking the gain high enough or playing loud enough. Also, to me the grind comes out easier if you select 800hz mid and crank the Mid rotary a bit. Hitting the string fairly hard helps as well.
For me the Tung Sol 12AX7 seems to fight to stay clean. It could help get more grit if you place the Tung Sol before the tube stage you are trying to push into OD. So you might get different results depending on if you put it in V1 or V2.
For driven circuits I have had good luck with Shuguang 12AX7B or Gold Lion ECC83 standard. So you might like a combination like a Tung Sol in V1 and a Gold Lion ECC83 standard in V2...or vice versa.
Unfortunately Shuguang has been shut down for awhile so 12AX7B are probably hard to find. The standard Gold Lion is still available and it has been my favorite tube for drive...maybe I should grab a few more before they are gone as well.
Ultimately it depends a lot on your particular taste. AFAIK the Tung Sol 12AX7 is one of the top rated tubes, and I can understand why people like it...but it takes the sound in the opposite direction from what I typically want with bass. It may be exactly what you are looking for though.
So replacing preamp tubes is easy and I have noticed a difference in tone for sure depending on the curcuit. I honestly find SVTs dull but that’s just my experience and tone is subjective. I will tell ya though your strings make a much more noticeable difference than preamp tubes. Also what are your amp setting's? I personally bought hundreds of different 12AX7 tubes and did a shoot out with a few bass amps and a few Marshall guitar amps. First it’s more noticeable in guitar amps. Next a tube that sounds amazing in one amp may not in the next. My Mesa Walkabout has an EHX tube in it. I typically hate that tubes tone but it makes that amp sound great. Cabs can also make a big difference. I have had several Ampeg 810’s and can tell ya now that they all don’t sound the same in that line. They have been around for ever and they have had speaker changes and different owners and different woods. I had an Ampeg 610 that to my ears sounded dull dull dull. My friend had a newer one that blew mine out of the water. This is long winded but when your chasing tone it’s best to start with settings, strings, cab, pickup position, bass and than preamp tubes. Changing them tubes is not going to change your tone drastically enough that you will notice it in a mix. Changing tubes is more like putting sprinkles on a already delicious cake. Yeah. It makes it better but you wouldn’t notice if they weren’t there.
1. Locate preamp tubes.
2. Unplug old preamp tube.
3. Plug in new preamp tube.
4. Test amp function.
5. Repeat step 2, 3, & 4 for each preamp tube, reversing the process for any tube replaced that causes malfunction of the amp.
2. Unplug old preamp tube.
3. Plug in new preamp tube.
4. Test amp function.
5. Repeat step 2, 3, & 4 for each preamp tube, reversing the process for any tube replaced that causes malfunction of the amp.
This is my personal opinion, but if you have a CL, you DO have a bad one. I build amps, fix amps, and examining the circuit it's a FrankenSVT compared to the original. I played one in a provided backline and it sounded like dogshht compared to the '69 I used to have. When the CL was developed, it was built around tubes in production. 6C4's? 12BH7's? 12DW7s? Unobtanium. A 6C4 is half of a 12AU7. A 12DW7 is half a 12AX7 and half a 12AU7. Do the arithmetic, the preamp would have to have 2 12AU7s and 1 1/2 12AX7s with the other half unused (ignoring the second channel) to use the same circuit. The CL uses 2 tubes. It uses 12AU7s as drivers instead of the beefier 12BH7s to push the 6550s. It's an SVT in name only. Dump it and get a used original from the 70's (the '69 needed a modification to keep from eating power tubes like candy) if you're looking for that Ampeg grit. There are pedals that do the SVT grind better than the CL does.
