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Tube rolling question on phono preamp

73.34.149.187

Posted on October 23, 2020 at 18:46:18
dandaroy
Audiophile

Posts: 421
Location: Denver, CO
Joined: June 24, 2003
I am trying out a Pro-ject tube box DS2 phono preamp. I do not know what the pair of 12AX7 stock tubes are as there are tube coolers around them (looks corrugated) which are adhered to the tube and will not come off. I read somewhere that it might tung-sol reissue 12AX7s. The unit is pretty quiet at my listening level.

Anyhow, the question is what current production 12AX7s do you recommend that is low in microphonics and quiet enough to be in a phono stage? I can entertain a NOS pair if the cost is less than $100/pair. I was thinking of GL 12AX7s.

Also since the stock ones have the tube coolers around them, do I need to get pair of tube coolers as well since the existing ones do not come off? Where should I look for it? Does the tube cooler help with microphonics as well?

TIA.

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I. Dandaroy

 

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RE: Tube rolling question on phono preamp, posted on October 23, 2020 at 19:22:55
Eli Duttman
Audiophile

Posts: 10356
Location: Monroe Township, NJ
Joined: March 31, 2000
Discuss your needs with AA sponsor Jim McShane. If he has a nice pair of phono grade Sovtek 12AX7LPS tubes in the "stash", look no further.

In any event, Jim will fix you up with a nice, quiet, set of tubes.


Eli D.

 

Sovtek 12AX7LPS, posted on October 23, 2020 at 19:27:13
dandaroy
Audiophile

Posts: 421
Location: Denver, CO
Joined: June 24, 2003
They do not seem to be that expensive. Are they better than the Gold Lions? Also should get tube coolers?

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I. Dandaroy

 

RE: Sovtek 12AX7LPS, posted on October 23, 2020 at 19:44:01
Eli Duttman
Audiophile

Posts: 10356
Location: Monroe Township, NJ
Joined: March 31, 2000
Define better, please. Properly culled specimens of the 'LPS are clean, quiet, and reasonably priced. What's not to like?

As 12AX7s run at plate currents in the 900 μA. to 1 mA. range, heat is, most definitely, a non-issue. Refer to TFK "smoothplates" with over 20 years of use still testing good. Tube coolers combined with 12AX7s strikes me as bullshit.


Eli D.

 

JJ e83cc frame grid tube., posted on October 23, 2020 at 19:53:40
viridian
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Posts: 6226
Location: Portland, Oregon
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Contributor
  Since:
February 1, 2012
The other JJ 12ax7s are good, and quiet, but the frame grid is the bees knees.

 

+1 ~nt~, posted on October 23, 2020 at 20:27:42
Sondek
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Posts: 6100
Location: Fort Worth
Joined: May 17, 2000
Contributor
  Since:
April 5, 2002

 

RE: Sovtek 12AX7LPS, posted on October 23, 2020 at 20:46:37
Sondek
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Location: Fort Worth
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Contributor
  Since:
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Eli's right. Skip the coolers.

 

RE: Sovtek 12AX7LPS, posted on October 23, 2020 at 22:52:10
dandaroy
Audiophile

Posts: 421
Location: Denver, CO
Joined: June 24, 2003
Hmm.. not sure why project would put them on stock tubes.

Anyway, when I meant better I was talking of a smoother most natural tone. Everyone seems to rave about GLs. I am just saying what I have read and heard. I have no personal experience except the Mullard RI 12AX7s. If the Sovtek LPS is really good for a fraction of the price of GLs, then I do not need to spend extra cash.

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I. Dandaroy

 

RE: Sovtek 12AX7LPS, posted on October 24, 2020 at 03:34:57
Story
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Posts: 4005
Location: NJ
Joined: December 11, 2000
Contributor
  Since:
February 21, 2019
they probably put them on as some kind of selling point, which is technically stupid. Even if used for damping or heat dissipation it's a stupid waste. Maybe it's a way to get owners to go back to Project for tubes which some owners will bend over to do.

I've seen a few people on AA who are wrongly critical of Russian tubes. We all can only approve what works for us. Obtain different samples, sit back and listen over time, and YOU decide which sound best in your house.

!...!


 

I put in an order with Jim McShane a few months ago, posted on October 24, 2020 at 05:49:31
1973shovel
Audiophile

Posts: 9245
Location: Greenville SC
Joined: February 25, 2007
...And I asked him the same question about his best recommendation for 12AX7s for phono duty. I too was interested in the Gold Lions, but Jim said that for phono, the Sovtek 12AX7LPS were his best (AX7) tube. I ordered some from him, and they sound great. I'm very happy with them.

Keep in mind that Jim does extensive testing to his tubes prior to shipping. I might not have gotten such good results (low noise, etc) had I tried to save a few bucks buy buying the Sovteks from ebay, or the like.

 

Tube coolers?, posted on October 24, 2020 at 06:13:10
1973shovel
Audiophile

Posts: 9245
Location: Greenville SC
Joined: February 25, 2007



I'm not familiar with your phono stage (other than hearing the name), so I did a search. Are you talking about the protective discs in the above picture, or do the tubes actually have Pearl type heatsink coolers on them, as shown in the picture below?

Another possibility is damping rings. I tried some Audioquest sorbothane tube rings on a pair of Telefunken smooth plate 12AX7s years ago. While they were removable, they left a mess, and the rings certainly weren't reusable. Beyond the mess, they didn't make a damn bit of difference. I've never had a problem with microphonic 12AX7s.





A picture would be helpful.

 

RE: Tube coolers?, posted on October 24, 2020 at 06:40:53
Byrd69
Audiophile

Posts: 2452
Location: East Syracuse, New York
Joined: August 23, 2004
I've sold 12AX7s for years. I've never had one person, or myself say....Hey, this 12AX7 is microphonic.

Screw the dampers, rings, etc. Save your pennies.


Your interest may vary but the results are the same (Byrd 2020)

I can't compete with the dead. (Buck W. 2010)

Cowards can't be heroes. (Byrd 2017)

 

(+1) Tube Coolers? "Save your pennies" (nt), posted on October 24, 2020 at 09:13:39
Jonesy
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  Since:
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nt


"I know just enough to get into trouble. But not enough to get out of it."




 

RE: Tube coolers?, posted on October 24, 2020 at 09:17:21
dandaroy
Audiophile

Posts: 421
Location: Denver, CO
Joined: June 24, 2003
Those discs are just cosmetic. The tube have those pearl tube coolers like stuff around them.

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I. Dandaroy

 

RE: I put in an order with Jim McShane a few months ago, posted on October 24, 2020 at 14:06:13
Eli Duttman
Audiophile

Posts: 10356
Location: Monroe Township, NJ
Joined: March 31, 2000
Yes, sir! Noise factor is critical in tubes doing phono duty. Pay a reliable dealer his money and get properly culled specimens.


Eli D.

 

RE: Tube coolers?, posted on October 24, 2020 at 14:18:46
Eli Duttman
Audiophile

Posts: 10356
Location: Monroe Township, NJ
Joined: March 31, 2000
If a mildly microphonic tube is encountered, silicone rubber "O" rings, available from McMaster-Carr, mounted on the bottle at the level of the mica wafers can be beneficial.

Silicone can take the heat, unlike the sorbothane previously mentioned, and there's absolutely no reason to pay audiophool prices, when industrial stuff is quite adequate.


Eli D.

 

RE: Tube rolling question on phono preamp, posted on October 26, 2020 at 00:49:58
Akolegov88
Audiophile

Posts: 246
Joined: January 7, 2014
I have the same phono preamp. It appears that the stock tubes are JJ ECC 803S, which are not bad.

However, when I tried to open it in order to try various NOS ECC83 tubes, I could not open the cover because the screws wouldn't go (and I couldn't find the proper tool). I could open the circular covers on top, but still could not get access to the tubes. Even if one manages to open the cover and get access to the tubes, he would have to break the corrugated heat dampers (or whatever they are), so I gave up the idea.

 

Jim inspires confidence, posted on October 26, 2020 at 09:05:32
1973shovel
Audiophile

Posts: 9245
Location: Greenville SC
Joined: February 25, 2007
...in his tube matching as well as his noise testing. I wanted a back-up matched quad of Gold Lion EL-84 (a great tube, by the way) and would never trust the "factory matching" some vendors offer.

Some forget (or simply don't know) that Jim also sells parts, ones which he can personally recommend through experience. While placing my last tube order, I asked Jim if he had any 0.47 uF Russian K40-9-Y PIO caps in stock. He didn't, but he did have one remaining pair of NOS Pyramid PIO caps in the value I needed for my 12AX7 based phono.

An Asylum search revealed a few posts by Mike Samra, stating that the Pyramids were even better than than the K40s, and Mike was the K40s biggest cheerleader. I asked Jim to include them with my tube order.

Without trying to be too melodramatic, these caps took a bland phono stage I rarely used, to a musical, pleasurable circuit I now spend many hours listening to. To say I'm pleased is an understatement. The only drawback is now I'm frequently thinking about what else I can do to further improve it. RIAA caps and resistors are next on my list.



 

"Those discs are just cosmetic", posted on October 26, 2020 at 09:26:38
1973shovel
Audiophile

Posts: 9245
Location: Greenville SC
Joined: February 25, 2007



As has been discussed previously on the Asylum, the 12AX7s themselves may be largely cosmetic as well.

How does Pro-Ject properly run 12AX7s, which generally use a plate voltage >200 VDC with but 18 VDC fed in?

Someone I trust told me that it sounds good, but he couldn't explain the voltage mystery either.

 

RE: "Those discs are just cosmetic", posted on October 26, 2020 at 09:35:28
Tre'
Industry Professional

Posts: 14581
Location: So. Cal.
Joined: February 9, 2002
You can run signal tubes on low voltages in a phono circuit where the signal is very small.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: Tube rolling question on phono preamp, posted on October 26, 2020 at 19:55:17
dandaroy
Audiophile

Posts: 421
Location: Denver, CO
Joined: June 24, 2003
How did you figure that they were JJs. I heard they were Tungsols. If you take top cover off, you should be take the tube off the sockets, but the tube coolers are fixed to the stock tubes, so you have replace the tube without any coolers on them or buy new coolers. The general consensus is that coolers are BS. I just got the unit, so when I tube roll I will just replace the tubes without any coolers.

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I. Dandaroy

 

RE: "Those discs are just cosmetic", posted on October 26, 2020 at 20:02:46
dandaroy
Audiophile

Posts: 421
Location: Denver, CO
Joined: June 24, 2003
Depends on your definition of cosmetic. I think they are just buffers to add some tube warmth which is typical of products in this range.

However, it certainly does not sound tubey in the old fashioned way. Bass is tight, well defined and overall the sound is crispy. Sound has enough detail for my ears. Users have reported that it does respond to tube rolling.

I have a Parks Audio Puffin phono and this is almost twice the price. I am letting it break in while I decide if the audible improvements are worth keeping it over the Puffin.

-------
I. Dandaroy

 

RE: "Those discs are just cosmetic", posted on October 26, 2020 at 21:15:34
Eli Duttman
Audiophile

Posts: 10356
Location: Monroe Township, NJ
Joined: March 31, 2000
I have no idea if the circuit in question is truly tubed. However, it's easy enough to get the 250 VDC or so needed for B+. Voltage multiply that 18 VAC.

The attached 1/2 wave parallel setup would certainly take care of the few mA. 4X 12AX7 sections draw. Even the less efficient Cockcroft-Walton configuration might be good enough.






Eli D.

 

RE: "Those discs are just cosmetic", posted on October 26, 2020 at 21:22:49
Eli Duttman
Audiophile

Posts: 10356
Location: Monroe Township, NJ
Joined: March 31, 2000
It's hard to think of a worse type for buffer duty than the 12AX7. The triodes in that type "can't fight their way out of a wet paper bag".

My hunch is triode voltage amplification and SS buffers. FWIW, I did that in the tweaked RCA setup.






Eli D.

 

RE: "Those discs are just cosmetic", posted on October 26, 2020 at 21:35:00
dandaroy
Audiophile

Posts: 421
Location: Denver, CO
Joined: June 24, 2003
I claim total ignorance on tubes or their use in a audio circuitry. Here is a snippet from a magazine review of the unit. May be you can translate in layman's English:

"The Pro-Ject Tube Box DS2 phono preamplifier has two 12AX7 dual triodes. It is designed with the first triode as the input stage and is cascaded with a 2SK170 J-FET transistor. The gain of this stage is about 70. The second triode is used as a classic gain stage biased into pure class A."

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I. Dandaroy

 

RE: "Those discs are just cosmetic", posted on October 26, 2020 at 22:52:44
Eli Duttman
Audiophile

Posts: 10356
Location: Monroe Township, NJ
Joined: March 31, 2000
I need to see an accurate, honest, schematic.

Frankly, I don't trust the magazine. Of course, the 2nd gain stage is Class "A". All Class "A" means is that the device conducts 100% of the time. That sort of operation is mandatory for single ended audio work. The "aroma" of marketing BULLSHIT is intense.

The late Allen Wright is known for advocating SS/triode cascodes at the input of phono preamps. However, cascode topology and 12AX7 sections are not what I expect. The 'X7 triode exhibits very low transconductance (gm) and that's opposite of what's desirable in a cascode.

Yes, there's a HUGE difference between cascade and cascode. That tweaked RCA setup I previously provided employs cascaded triode gain stages, with passive RIAA equalization between those 2 gain stages. The output is buffered by a MOSFET voltage follower.

I want to know how the vendor meets the requirement of driving the 10 Kohm IHF "standard" load. Commercially sold items must (IMO) comport with the IHF standards, as well as complying with local legal standards (FTC, etc. in the U.S.)


Eli D.

 

RE: Tube rolling question on phono preamp, posted on October 27, 2020 at 01:45:39
Akolegov88
Audiophile

Posts: 246
Joined: January 7, 2014
Re JJ 803 tubes: I was mistaken, but I thought that I'd read it somewhere...
I will figure out how I can (and whether I should) remove the top cover to replace the tubes.

 

RE: Tube rolling question on phono preamp, posted on October 27, 2020 at 06:10:05
dandaroy
Audiophile

Posts: 421
Location: Denver, CO
Joined: June 24, 2003
you need a hex wrench to take the screws off.

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I. Dandaroy

 

RE: Tube rolling question on phono preamp, posted on October 27, 2020 at 23:43:16
Akolegov88
Audiophile

Posts: 246
Joined: January 7, 2014
Thanks, I will look for it.

 

RE: "Those discs are just cosmetic", posted on October 28, 2020 at 02:21:58
Akolegov88
Audiophile

Posts: 246
Joined: January 7, 2014
Yes, it sounds good, but I also suspected that the 12AX7 tubes are just cosmetic, so I decided not to do any tube rolling here.






 

RE: "Those discs are just cosmetic", posted on October 28, 2020 at 02:24:06
Akolegov88
Audiophile

Posts: 246
Joined: January 7, 2014
This phono preamp doesn't show any tube warmth - it is neutral and dynamic, but musical at the same time.

 

RE: "Those discs are just cosmetic", posted on October 28, 2020 at 02:26:14
Akolegov88
Audiophile

Posts: 246
Joined: January 7, 2014
Before buying the ProJect Tube Box DS2, I had (and still have) a Budgie phono preamp. In my opinion, the ProJect is better.

 

Thanks Tre', posted on October 28, 2020 at 04:34:53
1973shovel
Audiophile

Posts: 9245
Location: Greenville SC
Joined: February 25, 2007
The last time this topic came up nobody had any answers (even speculative ones), so we were left scratching our collective heads.

 

Thanks Eli, posted on October 28, 2020 at 04:40:29
1973shovel
Audiophile

Posts: 9245
Location: Greenville SC
Joined: February 25, 2007
As I just responded to Tre', the last time this issue came up no one had any suggestions, so I was left wondering if the low voltage might do nothing more than light the heaters for listening room tube glow.

 

RE: "Those discs are just cosmetic", posted on October 29, 2020 at 15:43:38
Tre'
Industry Professional

Posts: 14581
Location: So. Cal.
Joined: February 9, 2002
The PS input to the unit is 18vdc

My guess, they're just running the 12ax7 at super low plate voltages like a lot of guitar effects boxes do.


Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: Thanks Tre', posted on October 29, 2020 at 15:45:43
Tre'
Industry Professional

Posts: 14581
Location: So. Cal.
Joined: February 9, 2002
I know a lot of the tubed guitar pedal effects boxes run their tubes super low voltage.


Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

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