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Trace V-Type Tube Rolling

Discussion in 'Amps and Cabs [BG]' started by Wasnex, Apr 6, 2018.


  1. Wasnex

    Wasnex

    Dec 25, 2011
    I recently added a little tolex covered V-Type to my collection. I installed a set of perfectly matched JJ KT88s from Eurotubes. I have put several hours on the tubes and the bias is holding solid just under 70%. Every time I turn the amp on, it stabilizes with 1.66 amps on my variac with the line adjusted to 120V.

    The amp had all the original TE preamp tubes. It sounded decent but the bass was a bit too heavy and uncontrolled at high volume for my taste. (I think a lot of people would love the way it sounded. It was thick rather than woolly, but it had a bit more bloom than I like. I rolled my favorite 12AX7s through the amp and got a few surprises.

    Other Equipment
    Speakers are Electro Voice TL405 cabinets that are ported around 27 hz. Bass is Series 1 Yamaha TRB6P.

    In V1 I tried Gold Lion ECC83/B759, Mullard ECC83, and Mullard CV4004 (All Russian New Sensor products). None of the tubes really seemed to make much of a difference to the amps treble response. The biggest change seemed to be in the bass, low mids, and mids. Even after playing the amp for an extended time, the preamp tubes are barely warm, so maybe it's no surprise that changing tubes makes very little difference.

    The Mullard ECC83 is my normal "go to" for V1, but I finally found a home for one of my expensive Gold Lions. With the Gold Lion, the bass is reduced and a bit tighter and the mids take on kind of a vocal quality that is really cool.

    The TE tube I pulled from V1 wound up going in V3 and making a slight improvement.

    I put a JJ ECC803S in V2 and the gain control became noisy, as if it had too much DC voltage on the wiper. Perhaps this tube pulls too much grid current for the circuit? I put the TE tube back in and the gain control function returned to normal.

    I also tried a Mesa branded tube (Slovak) in V3 and a Ruby branded tube (Sino) in V4. These tubes didn't seem to make much difference, so I reinstalled the TE tubes. Both of these tubes are good pulls that have been very bright and punchy in other amps.

    I actually did this experiment about a week ago and decided to leave the original TE tubes in place. I was confident the Gold Lion was the best V1, but I thought the difference was pretty subtle. But over the week I felt dissatisfied with the sound, so yesterday I moved V1 to V3 and put the Gold Lion back in. After playing the amp for two days, I feel that it is more musical and expressive with the Gold Lion. The low end is more even with less bloom, and notes are more focused, distinct, and articulate.

    The Gold Lion ECC83/B759 has been my #2 choice a couple of times for V1 in various amps. It may be a good choice if you need stronger mids and tight controlled lows.

    The difference in sound in the V-Type is subtle, but IMHO nice. It's a long plate tube, so it will plink a little if you tap it. The original TE tubes have short plates and don't make any sound if you tap them. The V-Type has a relatively low gain preamp so I don't expect any problems.

    Here is a link to a review if your interested in giving this version of the Gold Lion a spin. Review - Gold Lion ECC83 / B759 - thetubestore Blog
     
  2. Bigbri

    Bigbri

    Aug 4, 2015
    Thanks for that ! That was a good read. What power tubes were in it when you got it? Did you notice much change when you put in the JJ's? I have a V6 with all original TE's and was going to just change them all to Gold Lion's. The Gold Lion KT88 here work out to 100 bucks each. I hear alot of people putting in jj's. I figured the tubes were all in there for over 20 years now so the amp might sound a lot better than it does now. When I got it one of the power tubes had a violet glow in the bottom half at power on and before playing. It's gone now. I've seen glowing violet power tubes working but this was only the 1 power tube. I'm really getting the feeling this amp could sound better than it does now.
    When I got my 78 stingray I couldn't plug it into the V6 fast enough and put it in the normal input. After realizing that, I put it in the active input but don't think it sounds as good. Maybe it's all the years I used an SVT.
     
  3. Wasnex

    Wasnex

    Dec 25, 2011
    My V-Type had what appears to be relatively new EH6550s. The amp came to me with a blown HT fuse. Two of the tubes were still working and two of them would quickly runaway and blow the fuse when I increased my variac to about 110 volts even with the tubes biased as low as I could set them.

    I replaced the two bad tubes with a couple of old spares I keep laying around and it biased up fine and sounded really good, except one of the tubes was a bit noisy (hiss). I didn't compare the old tubes with the JJs so I can't comment on the differences. I have a V6 running Sovtek KT88s and it also sounds great, but I think the Sovteks may have been discontinued.

    I would be careful running the Gold Lions KT88s. I have read they sound excellent, but don't like high plate voltage. I have personally had really bad luck with Electro Harmonix KT88s. I have bought three amps with these tubes and over 80% have failed.

    I have had really good luck running JJ KT88s but several people have swore them off after repeated early failures. Eurotubes does a 24 hour burn-in before matching. The current match on the set I received is perfect and they have not drifted any over several hours of playing.

    My second choice after JJs would be Shuguang KT88-98. These tubes are also marketed as Sino KT88-98, Valve Art KT88, TAD KT88-STR, and Ruby KT88-STR. With any tube, grading and culling is essential. TAD and Ruby have their own proprietary selection process. Use trusted suppliers with good testing practices if you buy brands other than TAD or Ruby.

    Shuguang also makes an uprated 50 watt tube sold here in the states by the Tube Store as Preferred Series KT88. For bias purposes I think KT88s are normally treated as 35 watt tubes, although most spec sheets seem to list them at 42 watts. I have also seen this tube sold as Penta KT88-SC and Ruby KT88V-STR. The cost for the 50 watt tubes is about 50% higher, so I would only use these in an amp that is really hard on tubes...although the reviews say they sound excellent!

    I think the lesson of my tube rolling experiment is the model of tube you use in V1 makes just enough difference where it might be worth your while to experiment if you think the amp has too much bass. With the original tube in V1, I had the bass set around 9 o'clock. With the Gold Lion, i run the bass control up to about 11 o'clock. I believe this shifts the contour of the low end so there is a bit more mid bass.

    V2, V3, V4 probably just needs a good healthy run of the mill 12AX7.

    Do you still have an SVT? Which plays louder clean? If the answer is SVT, your V6 probably needs to be serviced. The V6 should have a very deep but controlled low end and it should remain clean sounding until extremely loud. I can't say which one sounds better SVT or V6...IMHO they are both awesome!

    I normally use the passive input on all of my V-Types with my Yamaha TRB6P. It's only necessary to use the active input if the output of your bass is so hot that your causing V1 to distort. The input jacks are connected to V1a. V1a drives the effects loop which is returned to V1b. V1b drives the tone controls and gain control, which is connected to V2a.
     
  4. Jim C

    Jim C Is that what you meant to play or is this jazz? Supporting Member

    Nov 29, 2008
    Bethesda, MD
    Just as a point of reference, I've collected a few original Telefunken, Mullard, and Amperex 12AX7's.
    I haven't been that impressed with modern manufacturing no matter what the platform.

    I have tried rolling a number of tubes through SWR, Ampeg 3 and 7 Pro, Walkabout, GB and some stereo gear.
    Out of the above MI amps, most had a very minor change with the exception of the WA which was more sensitive and sounded incredible. As I recall, I had a similar good situation with an Ampeg pre-amp and V4B.
    Sounds like the V series respond very well.
     
  5. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    Why not try bias rolling. If 70% max plate dissipation is not sounding right, try 65% or 75%. Bias by ear to optimize the sound and performance of the amp while ensuring the the tubes are operating within a safe region.

    Some power tubes/ amp designs sound better if you tweak the bias rather than adhere to a written in stone 70%.
     
  6. Wasnex

    Wasnex

    Dec 25, 2011
    Unfortunately those NOS 12AX7 gems are way out of my price range. The only NOS 12AX7s I have splurged on are Jan GE and Jan Philips 12AX7WA and I haven't had a chance or need to roll those yet.

    My V8 was definitely more responsive to tube rolling than the little V-Type. The circuitry around V1 is almost identical, but the V8 has a different tonal profile. I believe it's natural voice is a bit more aggressive in the upper mids and leaner in the bottom. I wound up choosing totally different tubes for the V8 and I could hear an improvement everytime I switched out each of 7 preamp tubes. Maybe the old Sovtek 12AX7WAs that I pulled out of the amp were just done.

    IMHO the changes are always subtle, but given the limited EQ capabilities of most tube amps, a slight reshaping of the tone profile can make a pretty significant difference in the way an amp feels when you play it. The difference with the Gold Lion in V1 of the V-Type is very subtle, and I plan to swap the original tube back into the amp and play it for a few day to make sure I not deluding myself.
     
  7. Wasnex

    Wasnex

    Dec 25, 2011
    I think this is valid. I normally set my amps up just shy of 70% dissipation using current figures taken from here Tube Bias Calc 70% is what most of the manufacturers recommend so I usually go just a bit under to be conservative. The one exception is the AD200B. I believe factory setup is under 50% if the plate voltages I found are right. I haven't opened my amp up, so I don't know how it is set up...it sounds really nice.

    The only amp I have used my ear to bias is a Matchless Thunderchief. Factory spec is -52V with no respect to current, but I have done a fair bit of Googling to deduce 117% dissipation as my best guess. I also believe the model was discontinued because it was eating tubes. After going through the original tubes and new set of JJs in under 30 hours with the amp biased to spec, I bought an inline bias meter and started doing research. The inline bias meter is required because the Thunderchief's output tubes do not have bias sense resistors and I prefer to avoid making connections to high voltage sources when possible...so the shunt measurement method is out.

    I found a thread where a guy who used to provide factory authorized service recommended setting up the Superchief at 97% dissipation. The Superchief is very similar but uses EL34s and has a slightly different preamp. Also, I have corresponded with a couple of techs who have worked on Thunderchiefs who set them up at around 70-75%. By ear, I think mine sounds best around 90% with JJ KT88. If your curious, bias for 90% dissipation is -60.8V (-58.6V on the tube socket), so no wonder the amp was killing tubes with only -52V of bias. Next time I retube the amp, I am gonna try out the 50 watt Shuguangs...a buddy of mine is running KT120s in his (factory approved) and says it sounds great.

    My impression is the Thunderchief makes maximum power when biased around 90% and becomes hazy and unfocused when biased hotter.

    What is your experience varying bias levels.
     
  8. Bertr

    Bertr

    May 6, 2013
    The tube bias calculator does not take the screen current out.
    For accurate plate dissipation calculation, I use excel with the actual resistor values around the valve (1R cathode and/or cathode and/or OT primary res, screen res...) as explained by the Father of homebrewers:
    What Is Biasing?
    Idle Current Biasing - Why 70 percent?
    The Last Word On Biasing
    As said above 70% is not written in stone. As long as it does not smell funny....
     
  9. Wasnex

    Wasnex

    Dec 25, 2011
    In general, you could assume that 5% or 5.5% of the measured cathode current is screen current but I simply disregard this. I realize the set up I am doing is a bit imprecise...however, it is imprecise in the conservative direction. If I was more concerned about precision I would measure the plate current instead of the cathode current.(Note. Estimated screen current would likely vary by tube type).

    My setup is focused somewhat on protecting the amp and extending tube life. I set the current a few milliamps below 70% dissipation and also disregard the screen current. The idea is to give the tubes some range in case the line voltage goes too high. Perhaps I am missing the opportunity to set the dissipation lower and sound even better. That is a possibility.

    I do not have an interest in running higher than 70% dissipation unless the amp is "class A" such as my Vox AC 30 or Superchief. Of course we all know these amps are not truly class A but they probably do sound better biased close to 100%. I have both of my class A beasts sitting at 90% dissipation but I have to use a variac set to 110 volts with the Vox because it's English. Some of my other vintage English amps like 115 volts best. (Edit. I guess if you factor in the screen current, these amps are setup up for about 85% dissipation.)

    FYI if you scroll down to the bottom of the Tube Bias Calculator link I provided you will find the recommendation to play around with various levels of dissipation to find the level that sounds best.
     
    Last edited: Apr 10, 2018
  10. Bertr

    Bertr

    May 6, 2013
    Yes correct, the mains tolerance usually puts the myth of absolute accuracy to rest.
    Jim Marshall used to say (a bit tongue in the cheek) that his amps loved the UK's imperial 240V (as opposed to the dreaded continental 220V). Those were the days... now we're all 230.
     
    Wasnex likes this.
  11. Wasnex

    Wasnex

    Dec 25, 2011
    I guess I have probably played around with line voltage more than bias with my amps, especially the amps that are early 70s or older. I have a large laboratory grade variac with a built in ammeter, so I document the current each amp typically idles at when fully warm. With the vintage amps I document current at 110V, 115V, and 120V and put an asterisk next to the voltage I think sounds best. All of the newer amps I have experimented with on the variac seem to sound best at 120V. I haven't gotten around to the entire collection yet.
     
  12. Cool thread and puts my mind at ease as it doesn't seem necessary to get into the tube rolling game again...

    I got my V4 with the original valves, first gig it blew 2 tubes and burnt out a few components... I refuelled with a full set of matched JJ's based on reviews here and also felt like they would get me closer to a dirtier tone.

    Replaced V1/2 in the preamp with a new JJ and a spare JJ. This was over 10 years ago! I replaced all the preamp valves last year as there were a few issues that were potentially tube related. I started down the rabbit hole of the tube rolling and just decided 4 JJ ECC83S would do the trick! Everything going strong and sounds great to me.

    I'll definitely be sticking to JJ KT88's!

    Now what I am a little confused about is you're talking about the biasing... I was under the impression the V4(MK1 at least)/V6's were self biased? EDIT I is a stupid :banghead:. How are you changing the bias?
     
    Last edited: Apr 10, 2018
  13. Bertr

    Bertr

    May 6, 2013
    > I was under the impression the V4(MK1 at least)/V6's were self biased?
    Not according to the schemos I found. Bias is not adjustable (no pots in the bias circuit, just fixed resistors, a bit like in the old Boogies). See Biasing an Ampeg V4?
    for more detail.
     
  14. Apologies, yes, I meant they had no variable bias! My bad. Morning coffee hasn't kicked in yet...
     
  15. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    I find that the V4B sounds just as good with 62-65% bias and tube life is extended. So it depends on the amp. People that run their AB amps with higher than 70%are usually seeking more power and distortion. They are willing to pay the price of shorter tube life to get the crunch that they want.

    Normally V4B bias is changed by substituting a resistor. Tubes were fairly matches and consistent back then and you really didn’t need to rebias when changing tubes. A common mod these days is to add a potentiometer. This makes rebiasing a lot easier as you don’t have unsolder and resolder resistors to change the bias.


    BTW, Tung-Sol has reissued a good 7027A tube:
    www.thetubestore.com - Tung-Sol 7027A Audio Tubes

    There is also the Tung-Sol 7581A which is the one that I currently use in my V4B:
    www.thetubestore.com - Tung-Sol 7581A Audio Tubes
     
  16. Wasnex

    Wasnex

    Dec 25, 2011

    The amps I am discussing are Trace Elliot V-Types. All have adjustable fixed bias. The V8 has 10 ohm resistors on the cathodes. You simply measure the voltage across the resistors to determine how much current is passing through the tubes and adjust the bias control as required to get the necessary/desired level of current.

    The V-Type (V4) and V6 have their cathodes connected directly to ground so I use an inline bias meter with them. The bias meter has four tube bases that breaks the connection with the cathode and wires an ammeter inline with the tube so you can measure the current directly. I could also measure the plate current using a transformer shunt technique. Although this method is more accurate, it involves poking around with high voltage more than I like.

    When output tubes are self biased, it is commonly called cathode bias. The cathode of all tubes are connected to a large cathode resistor that is connected to ground. As current passes through the cathode resistor it drops voltage which causes the cathode to go positive with respect to ground. The control grids are also referenced to ground. As very little current flows through the control grids they only have a small positive voltage. However, with respect to the cathode, the control grids are negative. If the tubes are not conducting the proper amount of current, you can change the size of the cathode resistor. Or you might put it tubes with a different bias point.
     
  17. Tim1

    Tim1

    Sep 9, 2005
    New Zealand
    So just to clarify....if I want to change the power tubes on my Trace Elliott V4 I do need to take it to a tech to have the bias adjusted??
     
  18. It would probably be worth it on the assumption the amp won’t have been serviced in some time?

    If like me you keep the same brand of valve you should be ok and are replacing with a matched quad
     
  19. Wasnex

    Wasnex

    Dec 25, 2011
    IMHO, any time you change the output tubes it is a good practice to check the bias. YMMV

    If you don't have the knowledge and equipment to do it yourself, I would suggest taking the amp to a technician. Without a basic understanding of tube electronics you could easily damage the amp or expose yourself to lethal voltages if you decide to work inside the chassis.

    Some people might buy a matched quad of tubes with the idea that they can replace the first set with the second set at some time in the future without checking the bias. I think this is a good strategy to cover to possibility of a tube failure on a gig. But personally, I would check the bias of the amp at the first chance after installing the tubes. Electronic components change values over time and tube matching is not an exact science.

    If you install a set off tubes that is not matched to the original tubes, the amp definitely needs to be biased.
     
    Last edited: Apr 10, 2018
    Jim C likes this.
  20. Wasnex

    Wasnex

    Dec 25, 2011
    I wanted to give a few updates and address a few questions and comments regarding my Trace Elliot V-Type (V4) that came up earlier in the thread.

    The amp has a little bit of noise from the power supply or tubes heaters. I tried clipping in extra capacitance at various stages of the power supply and messed around with lead dress a bit and didn't make much progress. I also rolled in a Tung Sol 12AX7 into V3. The New Sensor tubes with the spiral wound heaters are supposed to reject heater hum. The Tung Sol did seem to quiet the amp down a little, but also seemed to give it a bit of a smiley face EQ which worked against the Gold Lion I have in V1. A pretty minor improvement in S/N ratio offset by a minor unwanted change in EQ, so the TE tube went back in.

    Note. I think the noise might be normal as my V6 has a similar level and type of noise. Before I looked at the schematic, I thought the noise might be from the fan operation...but the fan is AC driven off the primary of the power transformer and the fan supply wires do not come close to any signal wires. If you have any ideas on solving the riddle, please let me know.

    I also had an opportunity to compare the JJ KT88s to the crap tubes I pulled out of the amp and also try different bias levels with the JJs. First the reason this occured. I had been playing the amp on my bench for about two weeks because I was waiting for a new handle to come in for the case. Of course it operated flawlessly on the bench. I finally put the whole thing back together and decided to give the amp a torture test sitting on top of my Greenboy Dually. The Dually is exceptionally light weight for a 215, so it really vibrates at high volume, especially when it's sitting on a wood floor. I played for about 10 minutes at high volume then decided to try the amp through one of my other speakers. When I switched the amp back to operate, I noticed a little crackle. I played for another 10 minutes then switched back to the Dually. About 15 seconds after I put the amp in operate, while playing a low volume, the amp crackled again, and the HT fuse opened up.

    So I pulled the amp apart and rechecked all voltages and everything looked good. Put the tubes back in and everything worked fine. Chop stick test...no problem or noise. So, I put the chassis back on the Dually, and after about 10 minutes at medium volume there was a bright flash of light, a loud crack, and another blown fuse. I called Eurotubes and they seemed pretty confident in the tubes, but said send them back and they would be happy to test them and honor their 6 month warranty if they found manufacturing defects.

    Before sending the tubes back, I wanted to eliminate the possibility of an intermittent fault in the amp. I rechecked voltages, installed the old tubes, and played the amp well into clipping for about 30 minutes sitting on top of the Dually. The old set consisted of two EH6550s (current match but one unstable), one EH KT88 (microphonic), and one Ruby KT88 (noisy)...all of my serviceable spares have been used and these probably should be thrown in the trash. For those who asked. The JJs are much louder and have a stronger bass response than the old tubes. The older tubes have that "creamy" upper mid range thing.

    I looked closely at the pins on the JJs and they are scratched up pretty good and I didn't see any evidence of arcing, but I wanted to eliminate lose contacts as a source of the problem. Luckily my local hardware store had a cheap Chinese pick that allowed me to retension the tube sockets. My normal tool wouldn't fit. I checked the JJs with a DVM and found no obvious shorts. Installed them in the inline bias meter (in the amp) and brought the amp up slowly on a variac. Despite taking a hard hit and putting on a spectacular light show the tubes are still perfectly matched.

    Different Bias levels. I tried with the cathode current set as high as 35ma and as low as 25ma. The best way I can describe the difference is the sound is softer/looser at lower current levels and harder/tighter at higher current levels. Given proper test equipment, I would probably consider what minimum level of bias provides max power while providing a safety margin for variation in line voltage. After the experiment I reset the bias as I originally had to 32ma of cathode current.

    I beat the amp at high volume for about 20 minutes on the bench last night. Today, I reluctantly took it upstairs for a third round of Dually torture testing. I played it for a good 20 minutes on the verge of clipping with no crackles, flashes of light, or blown fuses. I guess/hope the problem was loose contacts in the tube sockets. Fingers crossed.
     
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