Ampeg SVT-VR Tube Rolling thread...

blastjv · #1 10-03-2010, 06:17 AM

This has been mentioned in several threads along the way, but only in bits and pieces. I was thinking we could use a thread for more comprehensive info.

For my own purposes, I'm looking to tighten up the bottom end focus and add a little smooth top end clarity at higher volume.

I like aggression and grind when I'm really playing hard, but I'm not looking to make the amp any more 'high gain' than it is. I understand that the differences are usually subtle, but it's fun to experiment and to be honest, in my opinion, MOST of the things we discuss on TB amount to subtle differences.....that's what we're all about here!!!

But for others this could be a thread to centralize what preamp tubes worked for what purposes.

I'm mostly interested in readily available and not terribly expensive tubes. I've considered grabbing a Telefunken off of ebay (somewhat risky I understand), but I'm not looking to spend $100 on a tube.

-John

bluestarbass · #2 10-03-2010, 06:21 AM

The type of tone your going after sounds more like a power tube thing. What kind of power tubes are in that bad boy?

blastjv · #3 10-03-2010, 06:36 AM

I'm pretty sure the factory tubes are Soveteks. Have to check.

I'm getting all the OD/grind I'm looking for. Just trying to tighten things up a bit.

Son of Bovril · #4 10-03-2010, 12:33 PM

Tim1 · #5 10-03-2010, 01:46 PM

The guy who seems to have the most experience of tube rolling with the VR is Johnk - search his threads and you should come up with some good advice.

blastjv · #6 10-03-2010, 02:10 PM

I've seen his. And his findings are very useful, but also very specific using a number of vintage tubes he had available and toward the goal of getting it to sound identical to his vintage SVT. These are great goals and means, but not exactly the same as mine, so I thought I'd ask more general advice...

But, yeah, JohnK really seems to know his stuff and seems happy to share and help.

-John

Tim1 · #7 10-03-2010, 05:21 PM

Fair comment, and I must admit that I am watching this thread with interest as, like you, I am more interested in easily obtainable tubes for my VR.

beans-on-toast · #8 10-03-2010, 06:37 PM

One possibility is to play with the bias. You can over bias or under bias an amp to some extent to have different break up characteristics. The SVT is designed to operate with a very conservative bias setting. This helps if one power tube blows as the other two will not be forced to draw more current than they can take. The conservative bias also ensures long tube life when the amp is operating to spec.

You might find this info interesting, especially the bit at the end. People always talk about getting matched sets of tubes but you also have to consider what plate current level the tubes are matched to.

Tubes are often matched for transconductance and plate current at the working voltage. You can buy sets of tubes whose plate current levels are matched at high, low, or any level in-between. The headroom and breakup will vary depending on the plate current level. So you need to get a matched set, but if you want early breakup or more clean headroom, you also need to specify a plate current. A good tube seller, who has checked out the tubes that they stock, can help you select what plate current to specify to best meet the type of performance that you want from your SVT.

JimmyM · #9 10-03-2010, 10:58 PM

i've got mostly rca's in mine, i believe...might have a ge in there somewhere, too. i've tried sylvanias and jj's in there, too. and believe it or not, i honestly can't tell much of a difference with any of them. i would try a tele or a mullard in v1, but i'm like you...can't bring myself to drop $100 on one.

i should also mention mine is a 69, not a vr, so it uses 12dw7's mostly. but ampeg is using jj's in their heritage series svt-cl, so i think they would be a good place to start.

blastjv · #10 10-04-2010, 02:58 AM

I'd be interested, also, to hear people's input on the sonic differences between power tubes, though I'm less inclined to drop $300-something on retubing an amp with perfectly functional tubes...though if it makes a very noticable difference I can keep the stock tubes as a complete spare set.

Here's a question - I haven't touched the bias on mine as it came from the factory. I wouldn't want to intentional over or under bias it, but am I correct in assuming that withing 'normal' parameters there is a little but of range so that it could be favoring a LITTLE over or under? Also, which direction is which when adjusting the pots?

beans-on-toast · #11 10-04-2010, 08:08 AM

Quote:

Originally Posted by blastjv

Here's a question - I haven't touched the bias on mine as it came from the factory. I wouldn't want to intentional over or under bias it, but am I correct in assuming that withing 'normal' parameters there is a little but of range so that it could be favoring a LITTLE over or under?

Yes. Some people prefer the sound of an amp that is slightly under or slightly over biased. It does affect the sound and might allow you to squeeze out a little more headroom so that's why I threw it out as a possibility.

Something important to note is that the optimal bias setting for a tube can change as it burns in. It is a good idea to recheck the bias periodically as the power tubes age. When to do this depends on how many hours are on the tubes. I like to check the bias a few months after installing new tubes and then maybe once a year after that. So since you haven't changed the bias since you got your amp, you might want to consider having it checked. Maybe all you need is a tune-up.

Also, I believe that the best way to check the bias is to open the amp and measure the currents with a meter. The older SVT's made it a lot easier with test points installed on the chassis. I like the idea of the LED based bias circuit that is used in the SVT-VR and other Ampeg amps but sometimes it isn't as accurate as it should be.

With experience you can set the bias with a meter and then tune the bias by ear for maximal headroom or optimal tone, then recheck the final setting with a meter to ensure that it is with the tube's spec. This is how a good tech can make an amp sing. If you take it to a tech they can show you how to safely experiment with different pot settings.

jackcheez · #12 10-04-2010, 08:32 AM

Quote:

Originally Posted by blastjv

For my own purposes, I'm looking to tighten up the bottom end focus and add a little smooth top end clarity at higher volume.

What I and some techs in my area are using.

Quote from...

http://thetubestore.com/6550c.html

Quote:

From our 6550 tube type listening test:
"The Winged "C" 6550C has very controlled sound - nothing offensive can be found in any part of the frequency response. Also very consistent in detail and separation, with clean highs and exceptional balance throughout." This 6550 tube is a popular choice in Audio Research amps...

beans-on-toast · #13 10-04-2010, 08:39 AM

+1 I really like this tube.

eyeballkid · #14 10-04-2010, 08:54 AM

Winged C are in every tube amp i can put them in and dem tubes sound MM-MM-GOOOD!

blastjv · #15 10-04-2010, 09:15 AM

Is there any sonic benefit at all to changing just some of the tubes to Winged C's? They ain't cheap to do all at once...

So I guess the long story short is, either Winged C's and JJ's, or experiment with various NOS tubes...???

jackcheez · #16 10-04-2010, 09:44 AM

Quote:

Originally Posted by blastjv

They ain't cheap to do all at once...

True, and the odds that you will get what you want even with a complete new set are slim. If I were going to experiment, I'd start with the preamp tubes. Cheaper that way. Still slim odds that you will get what you want. Any difference is likely to be subtle. If everything in your amp is working well, that's pretty much what it's going to sound like.

eyeballkid · #17 10-04-2010, 09:54 AM

uh... not so much...
when i got my fender 300pro, i cant remember what tubes were in it, but it just sounded.. well... kinda yucky..... i decided to put Winged C's in it, and DAYUM!!! a whole new amp!

if you dont hear much of a difference with different tubes, then you either bought a brand/model very similar to the previous ones, or you running thru a cabinet that makes everything sound like that cabinet no matter what you put thru it IME.

MAMMOTHvolume · #18 10-04-2010, 11:33 AM

Quote:

Originally Posted by Son of Bovril

JJ

used to be my favorite but the quality seems to have slipped.

New favorite are the shuguang GEC kt88's which are made on the same machine as the original. Either those or the kt100's since they're cheaper and still do the goods.

blastjv · #19 10-20-2010, 01:17 PM

Regarding upgrading to JJ preamp tubes, for what it's worth, after some guidance from Eddie at Eurotubes (who was EXTREMELY helpful and thorough) I went with these for my SVT-VR:

(2) Matched and Balanced ECC82
(2) Standard ECC82
(1) Matched and Balanced ECC83S
(3) High Gain ECC83S

We'll see what that does when they get here...

I am also about to pull the trigger on some Winged C's for the power tubes. I'll try the new preamp tubes first.

-JV

jackcheez · #20 10-20-2010, 02:08 PM

Quote:

Originally Posted by beans-on-toast

Yes. Some people prefer the sound of an amp that is slightly under or slightly over biased. It does affect the sound and might allow you to squeeze out a little more headroom so that's why I threw it out as a possibility.

While we're on the subject...

When I re-tubed my SVT-CL, I noticed that there was a range of "green light" when adjusting the bias. You could move back and forth a little and still be in the green. The thing is, there was a hum that would increase in volume the farther from center I got in either direction.