Replacement Tubes for Ampeg SVT CL

[Wasnex]

Ok, I'm noticing there are KT-88 being offered as well as the 6550's for power tubes. It's saying the KT-88's are compatible, is there a difference? My amp is spec'd with 6550's, I don't want to mess it up.

Opinions vary, but I would run KT88s in an SVT. I don't think you would notice much difference unless you push the output tubes into overdrive.

Here's a relevant thread: Are 6550's and KT88's a Direct Swap in an SVT Head?

 

[JGbassman]

Opinions vary, but I would run KT88s in an SVT. I don't think you would notice much difference unless you push the output tubes into overdrive.

Here's a relevant thread: Are 6550's and KT88's a Direct Swap in an SVT Head?

Thanks my friend, sorry for all the questions, I had no idea I knew so little about something I knew nothing about....

Do the power tubes have that much of an impact on sound, or is that primarily the preamp tubes? I'm looking hard at the JJ power tubes, but It seems the KT88's are cleaner, and more available. I'm more interested in getting an even matched sextet that's burned in though. Ugh, another rabbit hole...

Seems it would be easier to get a good solid set of power tubes, then do a little rolling on the preamp tubes to get the sound dialed in. Am I heading in the right direction, or is this overkill? This amp will be used for live shows, where I will run a direct line and a mic on the cab. I know a lot of subtle nuances will be lost, but we all know we play better if we are enjoying the sound of our rig.

 

[Smooth_bass88]

I'm partial to Sovtek tubes. They seem to be very consistent. I've had problems with Tung-Sols and Electro-Harmonix tubes.

 

[Wasnex]

Thanks my friend, sorry for all the questions, I had no idea I knew so little about something I knew nothing about....

Do the power tubes have that much of an impact on sound, or is that primarily the preamp tubes? I'm looking hard at the JJ power tubes, but It seems the KT88's are cleaner, and more available. I'm more interested in getting an even matched sextet that's burned in though. Ugh, another rabbit hole...

Seems it would be easier to get a good solid set of power tubes, then do a little rolling on the preamp tubes to get the sound dialed in. Am I heading in the right direction, or is this overkill? This amp will be used for live shows, where I will run a direct line and a mic on the cab. I know a lot of subtle nuances will be lost, but we all know we play better if we are enjoying the sound of our rig.

The only amp I have rolled 6550 and KT88 in is my Aguilar DB359. It's running the original Winged C 6550s which are excellent but no longer made. Just for fun I put in a set of JJ KT88s and reset the bias. I couldn't tell any difference in the sound. Unfortunately the JJs are bit too tall to fit in the amp. I think when I have to retube I will probably have to go with Sovtek 6550WE due to the height restrictions. With any luck the Winged Cs will outlast me.

Now in other amps I have run various brands of KT88s and noticed a difference. For example in one amp, I recently pulled out a good set off JJs and installed some Ruby KT88V-STR and thought they sounded significantly different than the JJs. To my ears the JJs are bit more harmonically complex and lively sounding.

FYI the KT88V-STR is supposed to be an upgraded tube made by Shuguang that has a 50W plate rating. I bought them specifically for an amp that is hard on the tubes. You can recognize it by the solid plate structure. Other KT88s have holes in the plate. This model has also be sold as Tube Store Preferred Series KT88, Shuguang GEKT88, and Penta KT88SC. The run of the mill Shuguang (KT88-98) is also a good tube and is sold as Valve Art, Sino, TAD, Ruby, etc.


I am actually a big fan of JJ KT88s and have had really good luck running them in several amps. Others will tell you they have had repeated infant failures with JJ KT88s.

Here an image of Shuguang GEKT88 so you can see the solid plate structure:

And here is a Ruby KT88STR (same as Shuguang KT88-98) with the holes in the plate structure:

 

[Wasnex]

I'm partial to Sovtek tubes. They seem to be very consistent. I've had problems with Tung-Sols and Electro-Harmonix tubes.

I have had the most problems with EHX tubes. I have not bought any new ones, but every used amp I have bought with EHX KT88 or 6550 was malfunctioning when I got it, or started soon after. All of them failed with very few hours of play time. The Sovtek 6550WE seems to have a fairly good reputation for reliability. If I eventually buy a set, I will give TC Tubes my business.

 

[JohnnyChatter]

I vote for JJ. I also vote you change your preamp tubes and try a tungsol in V1. The Tube Store and Eurotubes have been recommended but I also have had great experiences with Viva Tubes.

 

[Wasnex]

Thanks my friend, sorry for all the questions, I had no idea I knew so little about something I knew nothing about....

Do the power tubes have that much of an impact on sound, or is that primarily the preamp tubes? I'm looking hard at the JJ power tubes, but It seems the KT88's are cleaner, and more available. I'm more interested in getting an even matched sextet that's burned in though. Ugh, another rabbit hole...

Seems it would be easier to get a good solid set of power tubes, then do a little rolling on the preamp tubes to get the sound dialed in. Am I heading in the right direction, or is this overkill? This amp will be used for live shows, where I will run a direct line and a mic on the cab. I know a lot of subtle nuances will be lost, but we all know we play better if we are enjoying the sound of our rig.

I can't say how responsive the CL is to rolling preamp tubes. Some amps do change noticeably when you swamp preamp tubes, and with others, it's really hard to hear any change other than slightly different amounts of gain.

@JimmyM says he prefers JJs in the preamp because it sounds more like his 69. JJ makes two 12AX7 variants, ECC83S (short plate) and ECC803S (long plate). I assume JimmyM is referring to the ECC83S.

I've tried the JJ ECC83S in a couple of bass amps and I felt it had the narrowest frequency response of any tube I have rolled. Lot's of mids, with very little highs or lows. I also found that it seemed to be fairly low gain, but have a tendency to break into distortion fairly easy. In fact it never really seems to sound clean; like its always on the edge of breaking up. I haven't liked this tube in any bass amps, but I haven't tried it in a CL...also I think my tonal goals are a lot different than JimmyM's.

The ECC803 has a bit wider frequency response to my ears. The lows are fairly lean and overall I would describe the tube as tight, muscular and relatively neutral. It does seem to have a bit of shimmer in the upper mids that I like. It's one of my favorite tubes with bass amps, but I have never chose it as my favorite for V1. I put it pretty much everywhere, but V1. It's usually my 2nd or 3rd choice for V1.

The Tung Sol 12AX7 is probably the highest rated current production 12AX7 you can buy. I think it has a wider frequency response than the other tubes I have discussed. It has a lot of character with big lows and hard upper mids. It's one of higher gain tubes you can buy, but it does not tend to compress or break into distortion very easily. Instead it tends to remain very hard and punchy. The upper mids are a bit too hard for my taste. I like the highs to be sort of smooth, glassy, and a bit compressed instead of super hard and punchy like the Tung Sol.

The tube I have been most likely to put in V1 in a bass amp is the Mullard ECC83. It has big lows, but in my amps this tube has really seemed to tighten, focus, and extend the low end. It also has a lot of high end extension, but the upper mids are soft and compressed. I think the mids and highs of the Sovtek 12AX7LPS sounds very similar, but the lows are woollier.

If I want a tube that emphasizes the mids but also has wider frequency response than a JJ ECC83S, I go for one of the Gold Lions. So far I have preferred the Russian ECC83/B759 if the circuit is always played clean. If the circuit is used for OD, I tend to think the Chinese Gold Lion ECC83 standard is better. Great touch sensitivity and the distortion is a bit darker and more organic, as opposed to bright and fizzy. I have had almost identical results with Sino 12AX7B.

I think you probably get the idea that you can really go down the rabbit hole here. You might want to try rolling a couple of different tubes to see how much difference they make before you get too far in.

If your interested, here's a sampler pack Invalid Link Removed

 

[JGbassman]

I can't say how responsive the CL is to rolling preamp tubes. Some amps do change noticeably when you swamp preamp tubes, and with others, it's really hard to hear any change other than slightly different amounts of gain.

@JimmyM says he prefers JJs in the preamp because it sounds more like his 69. JJ makes two 12AX7 variants, ECC83S (short plate) and ECC803S (long plate). I assume JimmyM is referring to the ECC83S.

I've tried the JJ ECC83S in a couple of bass amps and I felt it had the narrowest frequency response of any tube I have rolled. Lot's of mids, with very little highs or lows. I also found that it seemed to be fairly low gain, but have a tendency to break into distortion fairly easy. In fact it never really seems to sound clean; like its always on the edge of breaking up. I haven't liked this tube in any bass amps, but I haven't tried it in a CL...also I think my tonal goals are a lot different than JimmyM's.

The ECC803 has a bit wider frequency response to my ears. The lows are fairly lean and overall I would describe the tube as tight, muscular and relatively neutral. It does seem to have a bit of shimmer in the upper mids that I like. It's one of my favorite tubes with bass amps, but I have never chose it as my favorite for V1. I put it pretty much everywhere, but V1. It's usually my 2nd or 3rd choice for V1.

The Tung Sol 12AX7 is probably the highest rated current production 12AX7 you can buy. I think it has a wider frequency response than the other tubes I have discussed. It has a lot of character with big lows and hard upper mids. It's one of higher gain tubes you can buy, but it does not tend to compress or break into distortion very easily. Instead it tends to remain very hard and punchy. The upper mids are a bit too hard for my taste. I like the highs to be sort of smooth, glassy, and a bit compressed instead of super hard and punchy like the Tung Sol.

The tube I have been most likely to put in V1 in a bass amp is the Mullard ECC83. It has big lows, but in my amps this tube has really seemed to tighten, focus, and extend the low end. It also has a lot of high end extension, but the upper mids are soft and compressed. I think the mids and highs of the Sovtek 12AX7LPS sounds very similar, but the lows are woollier.

If I want a tube that emphasizes the mids but also has wider frequency response than a JJ ECC83S, I go for one of the Gold Lions. So far I have preferred the Russian ECC83/B759 if the circuit is always played clean. If the circuit is used for OD, I tend to think the Chinese Gold Lion ECC83 standard is better. Great touch sensitivity and the distortion is a bit darker and more organic, as opposed to bright and fizzy. I have had almost identical results with Sino 12AX7B.

I think you probably get the idea that you can really go down the rabbit hole here. You might want to try rolling a couple of different tubes to see how much difference they make before you get too far in.

If your interested, here's a sampler pack Invalid Link Removed

Wow, just amazing stuff. This was what I was hoping for. Thank you so much for chiming in.

I definitely feel a little better educated now regarding this topic. This was an amazing read.

 

[ultra60]

I'm partial to Sovtek tubes. They seem to be very consistent. I've had problems with Tung-Sols and Electro-Harmonix tubes.

I had an issue with Tung-Sol 6550's. Put 6 matched 6550's in the SVT. One shorted within a year. Kind of a bummer but I chalked it up to Sh*t happens.

 

[u2brothr]

Thanks for this thread. I have an SVT-CL and I bought it used. It was a demo model and I got it at a good price. I've been using it since 2016 and recently noticed it acting strange. After researching on Talk Bass and looking at all the tube talk, I decided to look at the bias lights. The amp was able to bias, but the right side control seemed to be harder to stay green. The red would often show.

I took a look at the Power tubes. They are Sovtek Tubes. Numbers on them say 1110, 1110. 1201 on the left side. Numbers on the right side say 1110, 1110, 1203. So I'm guessing four of these tubes are balanced... and the two that aren't balanced are on opposite sides. They glow and they work.

I decided to leave those and replace the 3 x 12AX7 and the 2 x 12AU7. I was hoping to make those all the same brand, but my music store in Toronto didn't have all the same brand in stock. So the 12AX7's are Electro-Harmonix and the 12AU7's are Tung-Sol (is that ok? Different brands?). The tubes taken out were all JJ's.

So I put them in.... and boom. The amp is a different beast. Bias sets without issue.

So I shouldn't bother touching the Sovtek Tubes...right?
I play through a 410 HLF.

 

[Wasnex]

Thanks for this thread. I have an SVT-CL and I bought it used. It was a demo model and I got it at a good price. I've been using it since 2016 and recently noticed it acting strange. After researching on Talk Bass and looking at all the tube talk, I decided to look at the bias lights. The amp was able to bias, but the right side control seemed to be harder to stay green. The red would often show.

I took a look at the Power tubes. They are Sovtek Tubes. Numbers on them say 1110, 1110. 1201 on the left side. Numbers on the right side say 1110, 1110, 1203. So I'm guessing four of these tubes are balanced... and the two that aren't balanced are on opposite sides. They glow and they work.

I decided to leave those and replace the 3 x 12AX7 and the 2 x 12AU7. I was hoping to make those all the same brand, but my music store in Toronto didn't have all the same brand in stock. So the 12AX7's are Electro-Harmonix and the 12AU7's are Electro-Tung-Sol (is that ok? Different brands?). The tubes taken out were all JJ's.

So I put them in.... and boom. The amp is a different beast. Bias sets without issue.

So I shouldn't bother touching the Sovtek Tubes...right?
I play through a 410 HLF.

The output tubes in SVTs are organized in two groupings of three tubes. Ideally you would have six tubes with the same rating, but if this is not possible, you can use two matched trios, because each trio has it's own bias adjustment.

This image shows how the tubes are grouped:

Obviously you don't have two matched trios, but if they are close enough for the bias lights to work properly and the amp sounds good, I would not worry about it.

As far as having all of your preamp tubes the same brand, I think that is silly, but YMMV. I have rolled tubes in a bunch of my bass amps, and one of my favorite combinations is a current production Mullard ECC83 in V1 and a JJ ECC803S pretty much everywhere else.

As far as why new preamp tubes fixed your problem. Technically it was probably not the preamp tubes. The two 12AU7 tubes are drivers. The driver tubes in the SVT are a bit unusual in that they control the bias of the output tubes. So if the 12AU7s are bad, it may cause problems with the bias.

However, usually a weak 12AU7 will make it hard to get the output tubes to conduct hard enough for the red LED to come on. A weak driver tube will let the bias rise to a higher negative value, which lowers current in the output tubes. You need a nice strong driver tube to pull the bias voltage down in order to get the output tube current up into the proper range.

I suspect what may have happened, is you cleaned a bit of crud/corrosion off the tube sockets by removing and replacing the tubes. If the tubes sockets are a bit loose, they can arc and cause a carbon build up. This carbon build up will increase the impedance of the connection. If there is a carbon deposit on the control grid contact, it can cause the tubes to pull too much current (red LED). The solution is to clean and retension the tube sockets with something like a dental pick. Before this is attempted, the power supply capacitors should be discharged so you don't get shocked.

The way the LEDs work is a bit confusing. Here's my understanding of how the circuit works. The Green LEDs have an AND logic function. When all three tubes assigned to the green LED conduct at least 15mA, the Green LED turns on.

The Red LEDs have an OR function, so if the current for one of the tubes exceeds 30mA, the Red LED turns on.

So if the Red LED turns on and the Green LED does not, it could mean one or two of the tubes is running hot, or one of the tubes is dead. If you have a trio with the following ratings, 1201, 1203, 1110, this is a likely outcome.

 

[u2brothr]

understood.... but they are trio'd properly.... with the 1201 on one side.....(left) and the 1203 on the right....

so...1110 back left/1201 beside it/ 1110 in front - that's one triangle

other side 1110 back right /1110 and 1203 in front of it

But yes... I'm thinking 12au7 connections might be the cause. The biases did go green and red before.... but I couldn't get the one on the right to have a static green without the red showing.
I guess I will monitor further...

 

[Wasnex]

understood.... but they are trio'd properly.... with the 1201 on one side.....(left) and the 1203 on the right....

so...1110 back left/1201 beside it/ 1110 in front - that's one triangle

other side 1110 back right /1110 and 1203 in front of it

But yes... I'm thinking 12au7 connections might be the cause. The biases did go green and red before.... but I couldn't get the one on the right to have a static green without the red showing.
I guess I will monitor further...

It's possible whoever set the amp up sorted the tubes in that order for a particular reason. IMHO, I would leave it alone as long as the amp is biasing properly. If the amp starts having problems again, you could try combining three of the 1110 tube in one circuit and either finding a better match for the 1201 and 1203, or buying a new matched trio a saving the remaining tubes for spares.

It's really hard to know what going on without some way to actually measure the current passing through each tube. I have a set of bias probes that I use to shuffle to tubes to get the best current match. It's possible whoever originally installed the tubes in the amp did this, but over time the tubes can drift apart so one tube pulls a lot of current and another barely turns on. Sometimes you can reshuffle the tubes to get a better current match, and sometimes you need to buy some new tubes.

 

[u2brothr]

It's possible whoever set the amp up sorted the tubes in that order for a particular reason. IMHO, I would leave it alone as long as the amp is biasing properly. If the amp starts having problems again, you could try combining three of the 1110 tube in one circuit and either finding a better match for the 1201 and 1203, or buying a new matched trio a saving the remaining tubes for spares.

It's really hard to know what going on without some way to actually measure the current passing through each tube. I have a set of bias probes that I use to shuffle to tubes to get the best current match. It's possible whoever originally installed the tubes in the amp did this, but over time the tubes can drift apart so one tube pulls a lot of current and another barely turns on. Sometimes you can reshuffle the tubes to get a better current match, and sometimes you need to buy some new tubes.

Man. A wealth of knowledge here. I am going to leave it alone for now.... and perhaps passively look for a matching sextet somewhere. Again, if it weren't for reading on talkbass about all this stuff, I would never know about the triad grouping of tubes, how to take the amp apart, how to bias and how to troubleshoot.

Finding a matching sextet has proven difficult living in Toronto. I may have to go with a respectable online dealer.

Thank you!

 

[coreyfyfe]

I took a look at the Power tubes. They are Sovtek Tubes. Numbers on them say 1110, 1110. 1201 on the left side. Numbers on the right side say 1110, 1110, 1203. So I'm guessing four of these tubes are balanced... and the two that aren't balanced are on opposite sides. They glow and they work.

Those sound like the date codes (for some examples look at the date codes on these sovtek tubes - Invalid Link Removed, Invalid Link Removed, Invalid Link Removed) used on the tubes which tells you nothing about matching. Matching refers to the electrical characteristics as described above.

Finding a matching sextet has proven difficult living in Toronto. I may have to go with a respectable online dealer.

These guys are in Hamilton, ON. www.thetubestore.com - Your online source for audio vacuum tubes.

 

[u2brothr]

Those sound like the date codes (for some examples look at the date codes on these sovtek tubes - Invalid Link Removed, Invalid Link Removed, Invalid Link Removed) used on the tubes which tells you nothing about matching. Matching refers to the electrical characteristics as described above.



These guys are in Hamilton, ON. www.thetubestore.com - Your online source for audio vacuum tubes.

Muther Trucker..... THEY ARE the date codes. I thought they were the electrical characteristics.

I've taken a look at that Hamilton site.

 

[P A U L]

Has anybody tried Psvane?

Next set I get, I'm thinking about getting some of those. They have 2 types though, one says KT88, while the other says KT88/6550...

KT88/6550:

KT88:
[Invalid or Expired Link Removed]

I know they are Chinese, from a group that left Shuguang, that ran the "Treasure" line of higher end tubes.

Invalid Link Removed

They claim that the carbon on the bottle (bottom tube image) image helps performance, etc. I know that the cryo treatment claims that, & to make the tubes last longer. (I know, there are nay-sayers, as well as zealots) I know a guy who used to sell/deal in tubes & he was always a nay-sayer, until he tried the new Telefunken tubes (by JJ).

[Invalid or Expired Link Removed]

He thought they (cryo-treatments) were snake-oil, but said that he thought they sounded a lot better than typical JJ power tubes. He wasn't so sold on their pre-amp tubes though...

I see that, Ampeg just released a 50th anniversary amp. In the amp, it shows Ampeg branded OEM tubes. I wonder if those are available?

now I'm lusting after that amp again...

Ok, looking at the manual, now I'm wondering where you can get the tubes, they claim they are Ampeg Super Valve 6550 tubes...

 

[Wasnex]

Muther Trucker..... THEY ARE the date codes. I thought they were the electrical characteristics.

I've taken a look at that Hamilton site.

The test data is usually put on a sticker on the base instead of stenciled on the glass.

Sometimes you have just one number, but usually you have two, plate current (PC) and transconductance (TC).

 

[u2brothr]

@coreyfyfe @Wasnex - Man.... it feels good to learn thanks for all this.

Update. So the amp is biased.... and biases quite easily.... and despite no markings, the tubes must be matched.

I decided to take the 6 Sovtek tubes out....mix them up and put them back in to see if I would need to do a re-bias. (in my head that would indicate that the tubes weren't matched right?) I put them back in, in random, and the green lights came on at the back without me touching a thing.

Good sign right?

 

[Wasnex]

Has anybody tried Psvane?

Next set I get, I'm thinking about getting some of those. They have 2 types though, one says KT88, while the other says KT88/6550...

KT88/6550:


KT88:


I know they are Chinese, from a group that left Shuguang, that ran the "Treasure" line of higher end tubes.

Invalid Link Removed


They claim that the carbon on the bottle (bottom tube image) image helps performance, etc. I know that the cryo treatment claims that, & to make the tubes last longer. (I know, there are nay-sayers, as well as zealots) I know a guy who used to sell/deal in tubes & he was always a nay-sayer, until he tried the new Telefunken tubes (by JJ).

[Invalid or Expired Link Removed]


He thought they (cryo-treatments) were snake-oil, but said that he thought they sounded a lot better than typical JJ power tubes. He wasn't so sold on their pre-amp tubes though...

I see that, Ampeg just released a 50th anniversary amp. In the amp, it shows Ampeg branded OEM tubes. I wonder if those are available?


now I'm lusting after that amp again...

Ok, looking at the manual, now I'm wondering where you can get the tubes, they claim they are Ampeg Super Valve 6550 tubes...

A lot of the tubes you mention are premium tubes sold primarily to the HiFi crowd. Some of them are considerably more expensive than "regular" tubes. I would suggest a bit of caution because there is a lot of graft and relabeling in the tube market. You might order a set of high end Psvanes at a premium price, and get run of the mill Shuguang tubes with special silk screening.

The only special production tube I have tried is the Ruby KT88V-STR. This tube has been sold as Shuguang GEKT88, Penta KT88SC, and Tube Store Preferred Series KT88. It's easy to distinguish from a Shuguang KT88-98 because it has a solid plate structure, whereas the KT88-98 has three holes.

I bought the KT88V-STRs for a particular amp that likes to eat tubes. It has a higher plate and screen dissipation rating than any other KT88 on the market. It's also highly rated for sound quality and some people say they sound better than the Treasures.

The amp I bought the tubes for has too much resistance in the bias and grid network so the tubes go into thermal runway after about 45 minutes off operation. I added some small fans to keep the tubes cool and the amp stabilized. I was hoping the higher plate and screen rating of the tube would allow me to run the amp without the fans.

Unfortunately, the KT88V-STRs did not fix the problem and actually seemed more prone to running away. If I switched the fans off, the current would start to creep up within minutes. Also the matching was really horrible and the tubes drifted like crazy for about two weeks, which suggests they were a bit gassy. I had to shuffle the order of the tubes a couple of times, but eventually they settled down and I got a match that was barely within 15%. The tube that was supposed to be the coldest per the test results wound up being the hottest. The tubes sound decent, but I think the JJs they replaced were better in every respect.

This is the first set of tubes I have run in the amp from beginning to end with the fans installed. They seem to be holding up well so far.