AudioCircle
Industry Circles => Audio by Van Alstine => Topic started by: schw06 on 10 Apr 2010, 03:19 pm
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I've been enjoying the Ultravalve amp with the stock tubes but I am curious to hear opinions on tube changes in the amp. More specifically, I'm wondering which of the tubes has the biggest impact on sound when changed, and what changes people have found with swapping tubes (positive or negative).
David
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I have an Ultimate 70, and I thought that replacing the rectifier tube made the most difference. The sound just seemed to open up. The bass seemed more defined.
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Henry,
Which rectifier tube/brand did you like?
Wayner :D
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Henry,
Which rectifier tube/brand did you like?
Wayner :D
Wayner:
I am using a NOS Philips ECG 5AR4 rectifier tube that Jim McShane recommended. There was a substantial improvement in sound.
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Anyone have any updates on their experience with Ultravalve tube rolling?
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Anyone have any updates on their experience with Ultravalve tube rolling?
On the power tube front, I compared a set of the Genalex reissues with the EH and could not say there was much of a difference. Testing conditions were not strictly a/b testing of course, due to having to wait about an hour between listening sessions, re-biasing, etc.
Same problem with testing conditions of rectifiers, so I gave up and kept using the Mullard in there. I even bought a fat-base NOS Mullard from Bill Thomas, and never plugged it in... ended up putting it in the reserve tube cabinet. Had these rectifiers tested along with the Matsushita that the amp shipped with, and the guy testing them (Dr. Cilantro here) was very impressed with all three of them. So I left it at that.
Don't get me wrong, I'm not saying all tubes sound alike--I think I heard an improvement in my Avastar preamp when I switched the 6cg7's from the EH that it ships with to a NOS RCA pair (and, in fact, the first RCA pair had a noise issue, so there the tube rolling was bloody obvious). I'm just saying that the impossibility of balanced test conditions is to be kept in mind. However, if you have two Ultravalves to play with, it may be a different matter...
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I built my Ultravalve with a Triode power transformer and Magnaquest output transformers. The triode puts out a few more volts and can stress the rectifier tube. (The stock setup gets about 35 watts per channel . My amp measured 40 watts per channel.) I went through 2 stock rectifiers before buying a nos mullard. I haven't had any trouble since.
When it became time to buy new output tubes, I sprang for a matched quad of Genelex Gold Lion KT-77s. I have been very happy with them. The bias is rock stable between channels and only varies with the line voltage.
I loved the amp before I did any tube rolling and nothing has changed my opinion. I think the amp is better with these changes but that is my opinion. My only comparison has been with worn out power tubes versus new power tubes not exactly a fair test.
Tube rolling allows one to optimize his/her amp to their system and ears. In my opinion the results can be too subjective to claim real sonic improvements.
Regards,
Dean
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What change will give the most dramatic difference in sound? A rectifier swap or a power tube swap? How about the two small signal tubes?
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What change will give the most dramatic difference in sound? A rectifier swap or a power tube swap? How about the two small signal tubes?
I did it with the U70. Power tubes made a moderately big difference (EH 6ca7 was the most neutral, Mullards were very "warm" but they were also very old). Small signal tubes made a tiny bit of difference but I couldn't tell which was most accurate. Aside from the frequency of blowing up, I could tell no difference at all with the rectifier tubes, none, zero. I checked the rectified voltage and it changed the voltage a bit depending on which rectifier you used, but it was in the 1-2 volt range so it's essentially negligible compared to the wall power variation.
That was before I put in the series diodes, but I would expect that it would still make no difference, particularly since with the diodes in there, the rectifier tube is pretty much only there as a soft-start circuit.
JJ Rectifiers died the quickest, Sovtek close behind. I never got to blowing up a Mullard since it wasn't in there for more than about an afternoon. The Japanese/RCA that was in there when the amp was first built in 1962-3 still works but it well down on output voltage.
After the diodes went in, there have been no rectifier failures in use, and everybody has managed to remember not to power cycle it, which I expect would still cause a blown fuse and then failed rectifier, diodes notwithstanding.
Brett
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Brett:
please explain the "series diodes"
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Brett:
please explain the "series diodes"
See this thread:
http://www.audiocircle.com/index.php?topic=83843.0 (http://www.audiocircle.com/index.php?topic=83843.0)
Ron
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Most people use the term "tube rolling" as a way to identify different sound characteristics from different tube, actually it is simpler than what most people make it.
If tube "A" sound better than tube "B", then tube "B" is not the right tube for the circuit, and it should be thrown in the trash.
I don't do "tube rolling" as a ritual, other word, I don't purposely spend th extra money for different sets of tubes so I can tube roll. The ones than come with the unit from the factory should be good enough.
I occasionally "try" other tubes if I can find them cheap just to see if they are the right one for the circuit.
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If tube "A" sound better than tube "B", then tube "B" is not the right tube for the circuit, and it should be thrown in the trash.
... ones than come with the unit from the factory should be good enough.
I occasionally "try" other tubes if I can find them cheap just to see if they are the right one for the circuit.
:scratch:
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Getting back on the topic....Anyone else with first hand experience in trying different tubes in their Ultravalve?
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Getting back on the topic....Anyone else with first hand experience in trying different tubes in their Ultravalve?
No, I don't. I don't have a reason to. I only use my tube tester to test the tubes periodically to make sure they have good conductance. In Frank's old catalog, he mentioned that the tubes that he selected sound better than the German made tubes. That's good enough for me.
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If my "old catalog" you refered to is really old, the info could be obsolete now.
Tube types, brands, and versions are changing and becoming more available so what I may have recommended as the "best tubes" some time ago is not necessarily correct now.
One interesting thing, as we are finding good tube availability to be increasing, the opposite is true for solid state devices. One after another, discrete transistors are going obsolete, and even the long standard heat fins for them. Mainstream solid state is way down the road to integrated circuits and smaller and smaller devices and designs.
And, unfortunately, there seems not to be any vocal group of "transistor lovers" out there demanding for production of new versions of their favorite old semiconductors. :(
Best regards,
Frank Van Alstine
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The catalog I was referring to was the 1993 issue. I am assuming the West German original tube mentioned in there were the Telefunken (no specific brand was mentioned), that came with some of the old Dyna units.
Anyway, tube rolling fans tend to use the same tube type but different brands as a tone control. They document and label the sound characteristics of the tubes made by different makers, so they can listen to certain tube on certain date in certain season at certain part of the country. That is crazy. They may call a weak tube sound relaxing.
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there seems not to be any vocal group of "transistor lovers" out there demanding for production of new versions of their favorite old semiconductors.
Not yet, I have not heard of "transistor rolling", but there certainly are "op amp rolling", just ask that guy at Upscale Audio, a few years back, he imported this CD player from Netherlands with the DAC section that would accept three types of opamp. He called it "changing the flavor of the sound" for crying out loud. We all know that there are "capacitor rolling", swapping out the capacitor and replace them with ultra expensive oil in paper cap with grounding copper foil. Why don't they just put a tone control in their preamps.
http://www.primaluna-usa.com/index.php?option=com_content&view=article&id=119&Itemid=44&tmpl=component
Here, all of a sudden tube has become so magical and quiet that they use it in the oscillator of a DAC, I've always thought that tubes are inheritally noisy, unstable and drift.
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Frank himself offered up op-amp rolling (http://www.audiocircle.com/index.php?topic=65476.0) a couple of years ago.
Mighty fine upgrade, indeed. :thumb:
Have fun,
Jerry
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Wow, so basically, if your transistor count is under a zillion (and growing), then Silicon Valley will not return your phone calls? Surely the Bay Area audiophools must be able to do something about this?!
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Frank himself offered up op-amp rolling a couple of years ago.
I doubt that Frank found this by just rolling some op amps, he probably studied the spec sheet of the device, and determined the compatibility and result of the biasing ckt. Same with his tube upgrade, he probably studied the operating point and characteristic curves and all that stuff, instead of just pluging in tubes. Also I suspect a little tone control action would have accomplished the same thing.
What "rolling" mean is blindly plug in and unplug something into the exsiting socket just because it fits, without knowing what the hell he's doing. Then justify the result of the sound (if it didn't blow up) by using terms from the Stereophile magazine, calling it liquid, relaxing, tube like, buttery, syrupy and so on. Furthermore, have a log book going, and document the result of sound of the device that they have "rolled.
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We all know that there are "capacitor rolling", swapping out the capacitor and replace them with ultra expensive oil in paper cap with grounding copper foil.
I can supply almost as many of those as they want. I remove them in old radios by the bucketful. Occasionally I will test them and so far not a single one of them was within a country mile of the marked value. Frequently they will initially test 5x the supposed value which seems odd until you check the DC resistance - which is most definitely not infinity. A goodly number of them on the power supply side have blown up and spewed their little guts all over the place like confetti.
At one time I was keeping the old ones in a box on my workbench, I probably had something like 5 pounds of them before I tossed it.
It's actually pretty amazing that a lot of these old radios still actually work, after a fashion, with dozens of leaky and grossly out-of-tolerance wax/paper capacitors in them. But to get almost any of them working "right", you have to get rid of them.
I also note that NOS Sprague "black beauties" or "bumblebee" caps (paper/foil caps in molded bakelite) are favored for "good sound" by some guitar players. That is probably a legitimate use since they are shooting to generate a sound they like. But I guarantee whatever you like about it today, it won't be sounding the same 6 months from now.
Brett
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Wow, so basically, if your transistor count is under a zillion (and growing), then Silicon Valley will not return your phone calls? Surely the Bay Area audiophools must be able to do something about this?!
Audiophiles generally don't like to compare sound by de-solder, and resolder transistors, it may be too hard, or too time consuming for them. Also their general believes are tube sound better than transistor, so they don't bother with rolling the transistors.
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With the EL34 tube it seems that the "bubble" of sound is projected out into the room. Very nice. with the KT77 it seems that the bubble is inverted and one looks "into" it.
Both perspectives are nice, depends upon what you like. I seem to prefer the EL34 sound but when the tubes finally blow up (i have been running them for a while now) I think I will be perfectly happy with the KT77.
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I tried some matched old stock Mullard El34's and the sound was ok but not great, East German El34's were horrible. The big bottle Cryo EH's sounded much better. The Mullard rectifier tube was the most solid sounding compared to a Japan made tube or Russian. The most difference for the better was the use of GE 6GH8A's. They seemed much more alive in their sound. Almost brought the Ultravalve up to the level of the Ultra350 I have hooked up to use in the same system. Then I got the Cryo Genalex Gold Lion 12AT7's for the Ultra350 and I now listen to the Ultra350 about 75% of the time. The Ultravalve has more natural vocals but the Ultra350 does everything else better. At least in my system. I am running them through a set of DIY Elsinore speakers and both amps are quite seductive.
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Hi all,
There are not many tube rolling choices for the 6GH8A
tube except one which I found and tried recently. This is the
7687 tube which was used in a number of Scott amplifier as
an upgrade replacement for the 6U8 and/or 6GH8A. Same 9AE
pinout as the 6GH8A......Expect to pay upwards of $50 per tube
if you can find them. Quite rare...Most are Sylvania branded.
Kevin @ Dynakit
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I swapped out the stock rectifier with a NOS Mullard. Wow, huge difference. I like the direction of the change. More body, three dimensional and velvety (not sure the best way to describe). I'll let this burn in. This is my first tube rolling experience, and a lot of fun. :lol:
I may try the GE 6GH8As, do you have a good source for purchase?
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I swapped out the stock rectifier with a NOS Mullard. Wow, huge difference. I like the direction of the change. More body, three dimensional and velvety (not sure the best way to describe). I'll let this burn in. This is my first tube rolling experience, and a lot of fun. :lol:
I may try the GE 6GH8As, do you have a good source for purchase?
If it starts to sound crappy, or fatiguing, ride it out. Somtimes, that's break in. :thumb:
Have fun,
Jerry
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Trackball02, I got mine on the Bay. I also bought a spare pair since they were so "reasonable", about $10 each if I remember right. The GE's made more of a difference than the Rectifier. If you want to try out my spare pair you are welcome to, but I think you will end up getting some of your own. I did some tweeking on my crossover and raised the impeadence a little over the entire spectrum and the Ultravalve now sounds as good or better than the Ultra350. These amps really need to be matched with the speakers they drive to sound their best. Cheers TPate
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Hydro,
How did you choose the GE's? Did you try several brands?
I'm curious how you tweaked the crossover and impedance, was that through your preamp?
I'm running 16 ohm Zu Soul Superflys with my Ultravalve, and it seems that is is a great match.
Jay
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From what I can tell, only three manufactures made this tube in the US. GE, Sylvania and Tung Sol. I haven't found a Tung Sol to try but did try the Sylvania's. The Sylvania's were better than the "stock" tubes, but not much. The sound with the GE's fit my taste so I quit looking.
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Jay, Concerning tweeking the crossovers, the Elsinores are a DIY speaker that is really made to be run by a tube amp. Very flat impeadence and very little phase shift. I have a friend in the speaker business and we ran tests on the speakers parameters. He suggested some changes in the published crossover that made them an easier load for the amps. I don't run a preamp, CD based system only, no phono. I use a DIY 100k stepped attenuator from Glassware.
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I swapped out the stock rectifier with a NOS Mullard. Wow, huge difference. I like the direction of the change. More body, three dimensional and velvety (not sure the best way to describe). I'll let this burn in. This is my first tube rolling experience, and a lot of fun. :lol:
I may try the GE 6GH8As, do you have a good source for purchase?
Did you put in the diodes? I am thinking they make the rectifier tube less critical.
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I believe that my speakers do not have crossovers due to the full range driver so any crossover adjustments would not apply to my system.
No, I did not put in any diodes. My Ultravalve was built this January. Can I assume that no diode modifications are needed, since this is a newer version?
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Your Ultravalve has the diodes.
Regards,
Dean
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I've been using these and like 'em!! :thumb:
http://www.vacuumtubes.com/6BG6.html (http://www.vacuumtubes.com/6BG6.html)
At $48/quad you can't go wrong.
Ron
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Ron,
Interesting. Are you running this conversion on the Ultravalve?
How did this change the sound?
Are there any bias issues or changes in the power output?
Thanks, Jay
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I'm using these in my two Ultimate 70's that I built from Frank's kit. They bias up just fine, have a greater plate dissipation than el34s, and sound great. I am using them with the adapter sockets right now. You can see them on my gallery. I want to try some Shuguang KT-66's for comparison. If I think it's too close to call, I'm going to rewire the sockets to use the 6BG6GAs. I've written instructions on rewiring the sockets. If anyone is interested I'll post them.
I think that the sound is much more immediate if you know what I mean. Plenty of bass, great separation, etc. I don't notice any power differences, but then again no one would unless measured on a o'scope. Of course only your ears can decide for you. If cost of the tubes are of any concern, then I don't see how you can beat these.
Ron
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Ron,
Sounds like a cost effective upgrade.
Right now, I have a pair of GE NOS 6GH8As on order, I'm going to try them out first, see how it sounds, then play around with the power tubes. I was thinking of trying the JJ 6CA7s which seem to have some nice reviews. Not that expensive. Might be fun to compare with your suggested 6BG6GAs. Aren't tubes fun?
Jay
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Yeah, that's a new tube that they just released. I would like to know how they compare to the EH 6CA7s. Since Frank uses JJ tubes for some of his products, I wonder if he'll get some in to try and report back. Would be nice. But you gotta love the look of the KT-66s!! :thumb:
Ron
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I'm going to order the JJs and I'll report back how they sound compare to the EHs.
Doesn't the Ultravalve use KT-77 instead of the KT-66s?
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Correct, the JJ KT77s are fine for the Ultravalve, I am not so sure about KT-66s.
I would note that when we tried JJ KT77s a year or go or so, we noticed that they had smaller than spec pins and made only marginal contact in some tube sockets. I understand this is an old report and that the issue may be fixed now, but make sure any JJ EL34 or KT77 tubes you try fit firmly into their sockets.
Regards,
Frank Van Alstine
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Frank, Have you ever tried the JJ 6CA7s?
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No, we have not tired JJ 6CA7 tubes. We are having good results with EH 6CA7 tubes with our Ultravalve amplifier.
If any of you have tried JJ 6CA7 tubes with our amp, we would like a report back on how well they work for you.
Thanks,
Frank Van Alstine
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I ordered a quad set of JJ 6CA7s today from Eurotubes, I'll report back on how they compare.
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I would note that when we tried JJ KT77s a year or go or so, we noticed that they had smaller than spec pins and made only marginal contact in some tube sockets. I understand this is an old report and that the issue may be fixed now, but make sure any JJ EL34 or KT77 tubes you try fit firmly into their sockets.
Yes that issue has been corrected for several years now. Unfortunately, the stigma still persists.
Ron
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I'm using the JJ EL34's and the pins fit fine into my U70. The tubes have been very reliable and sound sweet, which I credit to Frank's circuits not the tubes. I have used other brands of EL34's and I don't hear a difference (Shuguang and Winged "C"). I have not tried other flavors of tubes. I would like to try 6L6's as per RLee's suggestion. A good new old stock rectifier tube makes a difference in reliability and maybe bass authority - the quality and durability is apparent. I pulled a good old stock 5AR4 out of an old EEG. No markings on it, can't tell what brand.
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I got my JJ 6CA7s but am having trouble setting the bias on the right channel. After running the amp for at least an hour and rechecking the bias, the max I can get the voltage on the right channel is 1.50, by turning the know completely clockwise. I have no trouble setting the left channel correctly.
Switching the power tubes to the other side with out without switching the signal tubes does not correct the right channel. The left channel remains fine.
Also, when I replace JJ 6CA7s with the original EH6CA7s, I have no problems in getting the correct bias in both channels.
This is strange. Should I just keep both channels at 1.50v? Do the JJs need to be broken in?
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I got my JJ 6CA7s but am having trouble setting the bias on the right channel. After running the amp for at least an hour and rechecking the bias, the max I can get the voltage on the right channel is 1.50, by turning the know completely clockwise. I have no trouble setting the left channel correctly.
Switching the power tubes to the other side with out without switching the signal tubes does not correct the right channel. The left channel remains fine.
Also, when I replace JJ 6CA7s with the original EH6CA7s, I have no problems in getting the correct bias in both channels.
This is strange. Should I just keep both channels at 1.50v? Do the JJs need to be broken in?
I would check each new JJ tubes individually in circuit for bias levels. To do this, put two other tubes in one channel to keep a load on the power supply. Then put the JJ tubes in the other channel one at a time (leaving one socket empty) and measure the test point voltage. It will be around half the voltage you see when both tube are in that channel. Turn the amp off between each tube change. All four tubes should have about the same voltage reading. If one is way different I would not use it. I would match them in pairs and then put them back with the closest matching tubes in the same channel. If you can only get 1.50 from one channel I wouldn't worry about it but I would set the other channel to the same reading.
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Trackball02,
There is interaction between the channels when you bias the amp. As you bring one channel up, the other drops. You need to go back and forth until they are alike. If the left channel biases up to the proper voltage, and is higher than the right channel which seems to top out at 1.50 volts, then back off of the left channel bias. The right channel should come up a bit. You can probably get an even bias setting between the two channels, maybe around 1.53 volts.
I would try the following:
1 ) Turn off amp
2 ) Rotate the bias pots in both directions until full stop. This can help clean the pots. If you have some Cramolin or other quality potentiometer lubricant/cleaner, try that as well.
3 ) Rotate post fully counter clockwise.
4 ) Power amp on and let stabilize for 15 or 20 minutes.
5 ) Note the bias voltage for each channel.
6 ) Adjust the bias for the channel with the lowest initial voltage first.
7 ) Adjust the other channel to proper bias voltage.
8 ) Go back and forth between the channels to get a balance close to the desired bias voltage.
Once the two channel are balanced, operate that way for several hours/days, keeping an eye on the bias for both channels. It's possible that the weaker tube may bounce back after significant use.
I've run the U70 biased from 1.2 vdc to 2.0 vdc with no trouble. The bias voltage isn't the absolute setting to consider. The whole idea is to bias the tube to a certain level of its maximum plate dissipation. The rule of thumb is around 70%. The JJ 6CA7 has a 25 W plate dissipation, so 70% would be around 17.5 watts at idle. This translates to a bias current of about 42 milliamps per tube, or 84 milliamps for the pair based on 415 vdc on the plates of the tube. If you have accurate 15.6 bias resistors in the amp, then the bias voltage to set the tubes at 84 milliamps would be 1.32 vdc. See if you can get the bias voltage at least to that value and run for a while. Running the tubes a bit on the low side won't hurt and will give longer tube life. If this works out, you can go more towards the 1.56 if you like.
Hope this helps,
Ron
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Thanks for the last 2 replies.
Tom, I checked the voltages for the 4 JJ tubes, here are the values: 0.65, 0.65, 0.60 and 0.575 volts. These are lower then the stock EH tubes. I tested 2 of the EH tubes and got 1.00 and 0.95 volts.
I paired the jj tubes to the closest values, and I am running them at 1.4 to 1.5 v without a problem.
Ron, it seems that the optimal bias for the JJ tubes are lower than the EH tubes. Do you know off hand the specs for the EH tubes.
So far, I like the JJs but it is way too early to tell until I put some hours on them
Jay
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Jay,
I don't have the specs for the EH 6CA7, but I doubt that they would clue you into what you're seeing. If you want to reach the stock bias level, you could replace R17 (20 Kohms) for each channel to a slightly lower value like 18 Kohms. That will allow the bias adjust to a bit lower voltage in order to reach the proper bias current. If you need more adjustment range, try a 16 Kohm value resistor. I would also measure the voltage at the anode of D2 and make sure it is close to -43 vdc. If it is too far off, like -48 or -50 vdc, then it is most likely bad and should be replaced.
Did you build the U70 yourself? If so, this shouldn't be difficult for you. If you need more assistance, let me know.
Ron
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Ron,
I have a production Ultravalve, built Feb this year. I'm all thumbs, when it comes to electronics. I'll leave it up to the experts.
Given your calculations, I'm listening to the Ultravalve at 1.45 volts bias both channels, and it sounds fine. I'm not worried that it is not at 1.6 v. I'll take your advice and let it run and check often.
Thanks, Jay
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Jay,
Probably best. So the tubes are idling at 45 ma each instead of 50 ma. No big deal. Don't think anyone could walk into the room and detect the difference.
Have fun with the UV. I'm using two U70s in bridged mode for great separation, imaging, and drive.
What are you using to drive the UV?
Ron
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I have an Avastar. I'm really interested in the new FET Valve, and would love to hear if anyone at RMAF has any comments on the new preamp.
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Just a follow-up with tube rolling on the Ultravalve. I replaced the stock EH with the JJ 6CA7s and biased to 1.45 volts. I really liked the sound. One tube completely stopped working after one month, and Eurotubes immediately replaced the tube within a few days (great customer service by the way). I put the EH tubes back in the mean time and my impression was that the sound was quite similar to the JJs. I have now swapped back to the JJs.
Overall, I like the JJs better but the differences are not that dramatic, and to my ears either of the two brands are fine. On the other hand, I have found that replacing the rectifier tube with a Mullard NOS and the signal tubes with GE NOS made the most dramatic improvements
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Hi,
Are the GE 6GH8A tubes you guys are speaking of here the ones made by Tungsram for GE?
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I had a vintage Mullard GZ34 rectifier tube on hand and tried it out. That really seemed to wake things up a bit, a very nice change. Mainly the mids and highs gained a little smoothness, space and definition.
Would I spend the relatively big money on another? Maybe, we'll see. :| I have a reissue Mullard GZ34 coming soon to see if it can come close to the vintage tube. Meanwhile, I'll enjoy the golden oldie. I've yet to try the TAD and JJ GZ34's in this amp. That's for another day.
Also, after reading this thread I ordered some vintage GE6GH8A's to see how they behave. I'm sticking with the supplied EH 6CA7 output tubes for now. I have a feeling they are plenty good enough... just a hunch. :?
I'm using the Ultravalve to run a pair of updated Bozak Concert Grands and they sound great with Frank's beautiful amp. The little Ultravalve pushes the massive Bozaks around extremely well. Thanks Frank for the great product that makes me smile, even when it's turned off.
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I am using an Amperex Bugle Boy GZ34 (if nothing else, it looks cool!) and Sophia Electric "coke-bottle long life" EL34 tubes that have really elevated the sound of the Ultravalve. They do take at least 100 hours to break-in though, plus because of their shape and size, they are a bit tricky to bias if you have large fingers/hands. They are quite a bit larger than the stock tubes and you may burn your fingers, if not careful, during biasing.
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A short follow up to my limited tube rolling exercise.
The GE 6GH8A tubes made an improvement IMO. Certainly worth a try since a guy on epay still has some nice NOS stock for peanuts.
Also, it seems that the Mullard reissue rectifier is a good fit for me.
Happy listening... :D
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A short follow up to my limited tube rolling exercise.
The GE 6GH8A tubes made an improvement IMO. Certainly worth a try since a guy on epay still has some nice NOS stock for peanuts.
Also, it seems that the Mullard reissue rectifier is a good fit for me.
Happy listening... :D
So... a follow up to the follow up. :roll: I can't stand it, I still brag on the awesome little Ultravalve. I continue to be amazed with the smooth highs and great bass extension. It sounds like a hybrid amp.
Anyway, I added a matched quartet of reissue Genelex KT-77's and they sound crazy good after some hours logged. I'd love to have a set of those renown blue bottle EL-34's, but I couldn't pull the $500 trigger. I'm content with the KT-77's and have no desire to screw with anything. I don't even want to turn a screw to see what lurks in that shiny chassis. I could make it sound different, but not better.
Mr. Frank steered me perfectly when I asked about what to do with powering the big Bozaks. I'll be trying it with another system that uses more efficient speakers. Regardless of that outcome, the Ultravalve is staying with the Bozaks. The worst that could happen is that I'll be forced to buy another one. :green:
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I've had a number of AVA products over the years. All have been reliable and not at all finicky or difficult to maintain. I found a used ultravalve on AC and it's now the center of my son's system. Original tubes, bulletproof build and exquisite sound.
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Thanks for the info. I should of found this thread before I purchased 2 new 6CA7, thinking that one or two where bad.
The funniest thing is that when all 4 JJ 6CA7 where new (about one year ago), I'm one hundred percent sure that I was able to adjust the bias to 1.6v. When I double checked the bias one week later, it was off. I will try to adjust to 1.45
Ron,
I have a production Ultravalve, built Feb this year. I'm all thumbs, when it comes to electronics. I'll leave it up to the experts.
Given your calculations, I'm listening to the Ultravalve at 1.45 volts bias both channels, and it sounds fine. I'm not worried that it is not at 1.6 v. I'll take your advice and let it run and check often.
Thanks, Jay