Anyone Tube Rolling with the Ultravalve??

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trackball02

Re: Anyone Tube Rolling with the Ultravalve??
« Reply #40 on: 11 Oct 2011, 01:51 pm »
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?

avahifi

Re: Anyone Tube Rolling with the Ultravalve??
« Reply #41 on: 11 Oct 2011, 01:57 pm »
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

trackball02

Re: Anyone Tube Rolling with the Ultravalve??
« Reply #42 on: 11 Oct 2011, 02:26 pm »
Frank, Have you ever tried the JJ 6CA7s?

avahifi

Re: Anyone Tube Rolling with the Ultravalve??
« Reply #43 on: 11 Oct 2011, 03:52 pm »
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


trackball02

Re: Anyone Tube Rolling with the Ultravalve??
« Reply #44 on: 12 Oct 2011, 01:05 am »
I ordered a quad set of JJ 6CA7s today from Eurotubes, I'll report back on how they compare.

rlee8394

Re: Anyone Tube Rolling with the Ultravalve??
« Reply #45 on: 12 Oct 2011, 01:10 am »
Quote
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

Opus Flatus

Re: Anyone Tube Rolling with the Ultravalve??
« Reply #46 on: 13 Oct 2011, 02:53 am »
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.

trackball02

Re: Anyone Tube Rolling with the Ultravalve??
« Reply #47 on: 15 Oct 2011, 05:56 pm »
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? 

Tom Alverson

Re: Anyone Tube Rolling with the Ultravalve??
« Reply #48 on: 15 Oct 2011, 06:59 pm »
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.

rlee8394

Re: Anyone Tube Rolling with the Ultravalve??
« Reply #49 on: 16 Oct 2011, 04:19 am »
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

trackball02

Re: Anyone Tube Rolling with the Ultravalve??
« Reply #50 on: 16 Oct 2011, 03:55 pm »
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

rlee8394

Re: Anyone Tube Rolling with the Ultravalve??
« Reply #51 on: 16 Oct 2011, 04:53 pm »
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

trackball02

Re: Anyone Tube Rolling with the Ultravalve??
« Reply #52 on: 16 Oct 2011, 05:08 pm »
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

rlee8394

Re: Anyone Tube Rolling with the Ultravalve??
« Reply #53 on: 16 Oct 2011, 05:18 pm »
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

trackball02

Re: Anyone Tube Rolling with the Ultravalve??
« Reply #54 on: 16 Oct 2011, 05:35 pm »
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.

trackball02

Re: Anyone Tube Rolling with the Ultravalve??
« Reply #55 on: 7 Dec 2011, 11:09 pm »
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

listentothemusic

  • Newbie
  • Posts: 2
Re: Anyone Tube Rolling with the Ultravalve??
« Reply #56 on: 31 Jan 2017, 04:23 am »
Hi,

Are the GE 6GH8A tubes you guys are speaking of here the ones made by Tungsram for GE?

ohenry

Re: Anyone Tube Rolling with the Ultravalve??
« Reply #57 on: 29 Jul 2017, 04:15 pm »
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.

RPM123

  • Full Member
  • Posts: 371
Re: Anyone Tube Rolling with the Ultravalve??
« Reply #58 on: 29 Jul 2017, 05:09 pm »
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.

ohenry

Re: Anyone Tube Rolling with the Ultravalve??
« Reply #59 on: 6 Aug 2017, 07:09 am »
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