Replacement Tubes for Ampeg SVT CL

[JimmyM]

@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?

Good sign, right.

 

[Wasnex]

@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?

The bias circuit in the amp does not require tight matching of the tubes. When only the Green LEDs are lit, I believe it means all tubes are conducting between 15 and 29 mA. If the current level of one of the tubes rises to 30mA, the associated Red LED will light. So, the worst case acceptable match the circuit will accept is 15/29= ~0.52 which which means the mismatch could be as bad as ~48%. Here's the math: 29x(1-0.48)=~15.

Ideally you want the current between tubes to be matched within +/- 15%. So the bias sense circuit will accept tubes that are far from optimally matched.

 

[P A U L]

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.

aren't the Ruby STR just Shuguang "made for" tubes?, like the TAD STR one you posted above... (post #38)

I understand that people say "audiophile", "hi-fi", etc., but, in reality, all tubes were for hi-fi & audiophile purposes. You can say that some tubes have less color, & more headroom, but, we all know, that when you push a tube to it's threshold, it starts to color the audio. That ends up where it's either magical/musical, or a turd...

I know, it would suck to pay twice as much for a tube that is designed to be a turd, (relatively) when functioning properly. I have seen the Psvanes on sale for less than TAD, Ruby & anything by New Sensor. 6550 tubes can get expensive quick. My last set, I found a sextet of Fender branded GrooveTubes for $125 in LA.

I was told they were New Sensor, not sure which ones, maybe Svetlana?

I took a snapshot of 1 (I had to hunt down a pic):

I figured if they were sturdy enough for Fender OEM, then I'd probably fare well w/ them in the SVT...

 

[Wasnex]

aren't the Ruby STR just Shuguang "made for" tubes?, like the TAD STR one you posted above... (post #38)

Ruby Sells a KT88-STR which I believe is the same as Shuguang KT88-98. This is the common Chinese KT88 sold under a bunch of different brands.

The Ruby KT88V-STR is a different tube, but yes it's also made by Shuguang.

I believe the TAD 6550A in post #38 is also made by Shuguang, but it's a third tube.

I understand that people say "audiophile", "hi-fi", etc., but, in reality, all tubes were for hi-fi & audiophile purposes. You can say that some tubes have less color, & more headroom, but, we all know, that when you push a tube to it's threshold, it starts to color the audio. That ends up where it's either magical/musical, or a turd...

I know, it would suck to pay twice as much for a tube that is designed to be a turd, (relatively) when functioning properly. I have seen the Psvanes on sale for less than TAD, Ruby & anything by New Sensor. 6550 tubes can get expensive quick. My last set, I found a sextet of Fender branded GrooveTubes for $125 in LA.

My point is you don't always have certainty in what you are getting. Psvanes are generally expensive when sold through reputable dealers. So when you see them cheap, are they genuine Psvanes or are they knockoffs? Also since the glass envelope on many Psavanes is opague and the tube guts are concealed, do we have any certainty that Psvanes are unique and special to begin with? Perhaps the are just regular tubes, with opague treatment on the glass. I don't know and I am not willing to pay premium prices to find out.

Most of my amps run KT88s, and so far I prefer JJs and have had good luck with them. The only special output tubes I have bought is the Ruby KT88V-STR and preferred regular JJ KT88s which are $16 cheaper per tube.

I generally try to buy tubes from vendors who have a good reputation rather than random vendors on Amazon, Ebay, or Reverb. I think it's important to use a vendor that provides burn in, testing and matching services, because the QC in tube production is pretty awful. I don't worry about QC and testing so much with small signal tubes, because the are relatively cheap and if one fails you just put another tube in. QC is more important with output tubes because the are more expensive and matching is important. If one tube fails, the matching of the whole set is degraded.

 

[P A U L]

Ruby Sells a KT88-STR which I believe is the same as Shuguang KT88-98. This is the common Chinese KT88 sold under a bunch of different brands.

The Ruby KT88V-STR is a different tube, but yes it's also made by Shuguang.

I believe the TAD 6550A in post #38 is also made by Shuguang, but it's a third tube.



My point is you don't always have certainty in what you are getting. Psvanes are generally expensive when sold through reputable dealers. So when you see them cheap, are they genuine Psvanes or are they knockoffs? Also since the glass envelope on many Psavanes is opague and the tube guts are concealed, do we have any certainty that Psvanes are unique and special to begin with? Perhaps the are just regular tubes, with opague treatment on the glass. I don't know and I am not willing to pay premium prices to find out.

Most of my amps run KT88s, and so far I prefer JJs and have had good luck with them. The only special output tubes I have bought is the Ruby KT88V-STR and preferred regular JJ KT88s which are $16 cheaper per tube.

I generally try to buy tubes from vendors who have a good reputation rather than random vendors on Amazon, Ebay, or Reverb. I think it's important to use a vendor that provides burn in, testing and matching services, because the QC in tube production is pretty awful. I don't worry about QC and testing so much with small signal tubes, because the are relatively cheap and if one fails you just put another tube in. QC is more important with output tubes because the are more expensive and matching is important. If one tube fails, the matching of the whole set is degraded.

the amazon tubes I bought above were from these guys:

Penta Laboratories > Home

in LA.

The Psvanes that I've seen on sale are from Viva Tubes...

VIVA TUBES | Thousands of vacuum tubes always tested, matched, and guaranteed

Pentalabs were part of Raytheon, during the '70s....

I'm kind of a tube nerd. I've also got my eye on the resurgance of Brimar UK, as they are trying to revive great British tubes again...

I haven't checked in the last few months, but, they started farming out production, but are working on mfgr'ing their own...

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look up the "valve project" in the about me section. Oh, they've moved things around, go here:

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There's also PM Components, that have a US distributor (running out of his house) a few miles from me. Not sure who makes their PM brand though.

PM Components Ltd - World Leaders in Vacuum Tube Distribution - PM Guitar Tubes - Golden Dragon Tubes - SED Tubes

 

[HOOLIGAN]

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?

View attachment 3521404

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...

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?

View attachment 3521404

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...

View attachment 3521366

Judging from Ampeg's "suggestion" in the manual for the new amp, I'd say they'll have plenty of these new tubes available in the near future!

Replace a set of power tubes every 4 months?!?!?!
Looks like they're planning on selling lots of tubes, or scaring people away from tube amps!

 

[Wasnex]

Replace a set of power tubes every 4 months?!?!?!
Looks like they're planning on selling lots of tubes, or scaring people away from tube amps!

There have been threads over the last year or so, where some users are struggling to keep tubes in their SVTs for much longer than 3 months, so I think this is pretty realistic. I get the impression those users are using the amps daily and pushing them hard. However, a casual user who doesn't push the amp hard might use the same set of tubes for 20+ years.

 

[JimmyM]

There have been threads over the last year or so, where some users are struggling to keep tubes in their SVTs for much longer than 3 months, so I think this is pretty realistic. I get the impression those users are using the amps daily and pushing them hard. However, a casual user who doesn't push the amp hard might use the same set of tubes for 20+ years.

Yes, note the key words "If you play long and hard every day." Only one place I play long and hard and it ain't onstage

 

[LeGaston]

I'm totally happy with the JJ's in my HSVT-CL. Have tried a few different ones in the preamp, like a new Tung Sol and a handful of NOS tubes that I still have, but they're all too bright for my tastes while the JJ's make it sound like my 69 with all NOS tubes.

Hi JimmyM, do you have a link for the JJ valves you recommend for the Ampeg Heritage SVT-CL?

 

[JimmyM]

Hi JimmyM, do you have a link for the JJ valves you recommend for the Ampeg Heritage SVT-CL?

Not really. They're just your run of the mill JJ 12ax7's, or whatever their EU equivalent is.

 

[Wasnex]

Hi JimmyM, do you have a link for the JJ valves you recommend for the Ampeg Heritage SVT-CL?

AFAIK he likes the JJ ECC83S which their shortplate 12AX7 offering. The ECC803S is a long plate.

 

[LeGaston]

Do you know what the original valves are in the Heritage SVT-CL, ECC83S or ECC803S?

 

[Wasnex]

Do you know what the original valves are in the Heritage SVT-CL, ECC83S or ECC803S?

I am about 99.99% sure the original tubes for the Heritage SVT-CL were 3 JJ ECC83S, 2 JJ ECC82, and 6 JJ 6550. Since the ECC803S is a long plate, it would be a bit unusual to put that tube in V1 of an amp. It's actually my favorite tube for other tube slots. But if you want OEM parts I think you want ECC83S.

Usually you don't need to replace every tube in the amp. What is in your amp currently and why do you want to replace them? If the preamp tubes are working fine, I suggest buying one spare ECC83S and two spare ECC82s. If one of the ECC83Ss goes bad you can roll the spare through all ECC83S positions.

The ECC82 tubes work in pairs and they control the bias for the output tubes. Before pulling these tubes from the amp the bias should be set for minimum current. After you put the new tubes in the amp, follow the bias procedure in the manual. I recommend this to prevent the new 12AU7s from causing the output tubes from pulling excessive current and potentially causing damage.

Some people recommend replacing the 12AU7s whenever a new set of 6550s is installed.

 

[JimmyM]

Do you know what the original valves are in the Heritage SVT-CL, ECC83S or ECC803S?

83S.

 

[Jim C]

The ECC82 tubes work in pairs and they control the bias for the output tubes. Before pulling these tubes from the amp the bias should be set for minimum current. After you put the new tubes in the amp, follow the bias procedure in the manual. I recommend this to prevent the new 12AU7s from causing the output tubes from pulling excessive current and potentially causing damage.
.

Oh the irony.
It seems the post office has finally found my NOS GE 12AU7's from an eBay sale from a month ago.
The first set from a different vendor have never been found. Not a good time for vacuum tubes and the Postal Service.

The tubes in the amp were only marked with CHINA on a decal and 12AUX7 on the glass which must be replacements.
Looking at the bias adjust trim pots; which direction is minimum current draw?

 

[Wasnex]

Oh the irony.
It seems the post office has finally found my NOS GE 12AU7's from an eBay sale from a month ago.
The first set from a different vendor have never been found. Not a good time for vacuum tubes and the Postal Service.

The tubes in the amp were only marked with CHINA on a decal and 12AUX7 on the glass which must be replacements.
Looking at the bias adjust trim pots; which direction is minimum current draw?

Go to 2:19.

Looks like CCW decreases tube current.

 

[coreyfyfe]

Oh the irony.
It seems the post office has finally found my NOS GE 12AU7's from an eBay sale from a month ago.
The first set from a different vendor have never been found. Not a good time for vacuum tubes and the Postal Service.

The tubes in the amp were only marked with CHINA on a decal and 12AUX7 on the glass which must be replacements.
Looking at the bias adjust trim pots; which direction is minimum current draw?

I just got a set of 5670Ws I ordered a month ago, a day after a second order shipped via fedex had arrived. The USPS set enjoyed a few weeks of no tracking updates followed by a week apparently sitting at a post office a town over after being misdelivered. A lot of staffing/covid issues on their end.

 

[Count_Le_Pew]

Just replaced all my preamp tubes to IEC mullard and all my power tubes to GE 6550.

Wow, maybe its copium, but the sound is definately an improvement.