Sovtek 12AX7LPS versus JJ ECC803S

[Mark]

This is a horse for course sort of thing. That is to say in my Bluesmaster 50 watt clone (Mesa Boogie SOB as a platform) the LPS has more bass and lower mids, while the JJ has nice presence.

I find I like the bass and mids from the LPS in my amp, but an amp that was very bass heavy might work better with the JJ tube.

As far as construction goes, both tubes have a similar appearance to the untrained eye.

I had been using Groove Tube 12AX7M valves in all positions. I found the JJ 83S tubes were vastly better in the BM amp. Basically I heard more output and better harmonics from the JJ's. I did try NOS tubes in the amp, and I thought the JJ 83S compared very well to the NOS valves I have. (G.E. Brimar, Mullards, RFT's).

I hope this overs some assistance to those who were told "use this tube".

[boldaslove6789]

I prefer the Mullard reissue Ecc83's (New Sensor rebranded Sovtek's ) in my BM

[talbany]

Sovtek WA, WB, WC have very low transconductance, around 1250 instead of 1600. WC's mu is standard (95-105) WB's mu is slightly lower (95-100), while WB's mu is higher 100-115. The transconductance is so low that it cannot be tolerated if you need a real 12AX7.
On the other hand, Sovtek LPS tubes have higher then standard transconductance, around 1800. The mu is around 100-110.
The third isolated group contains the JJ and TT Blackplate (7025) tubes. They have standard gm but low mu (85-95)
All the other tubes are distributed around the standard values, with slightly higher mu (100-110)

http://www.knzaudio.com/tubeampsecrets/tubetest/

Not sure of this source!!

Tony

[Mark]

Thanks for the input and the chart Tony.

The whole MU and transconductance thing can be difficult to understand as one would assume gain and transconductance operating hand in hand.

I dare say a document explaining this and labelled sticky would be beneficial.

I usually have to read up and refresh the memory on this sort of thing.

http://en.wikipedia.org/wiki/Transconductance

I didn't see anything on MU.

[talbany]

The whole MU and transconductance thing can be difficult to understand as one would assume gain and transconductance operating hand in hand.

mu= The amplification factor (or gain) of a tube, expressed by the greek letter "u". It is a unitless quantity expressing the ratio of the change in plate voltage to the change in grid voltage, with the plate current held constant. It can also be expressed as: u = gm * rp, where gm is the transconductance of the tube, and rp is the plate resistance.

Tony

[Mark]

Well done Tony.

I think I have it in a book somewhere, though I thought there would have been a site somewhere for those wanting read up on such matters.

Looks a lot like E=I*R, change in current by resistance. Thus high transconductance with a low U value must mean a low plate resistance. Is this bad thing?

The Valve Wizard site has some good info as done the Aiken amplification site.

[David Root]

+1 Tony, I had not seen that study before.

He didn't by any chance do that with some NOS tubes did he?

[talbany]

Dave
Hope you are well!!

Not that I know of on the NOS stuff.. The experiment was only done on a handful of tubes and we all know of the quality control and consistency of some of the newer stuff out there..I take these findings with a big grain of salt..It would be cool to see the same results with a larger testing of the NOS though..If I find a good one in the future I will no doubt post it..
BTW..I remember reading of the problems of the LPS having trouble in cathode follower drivers..FWIW I've had no trouble with them so far..

FWIW.. I prefer LPS in PI and 803's in V2.. Long plates a more prone to micro phonics so it never ends..

Enjoy the weekend.

Tony

[Mark]

Dear Tony

Why do you prefer the 803 in the V2 position?

How does it differ in tone from the short plate ECC83S?
(I ask as I don't want to disturb [annoy] the family with loud guitars on the weekend.)

The 12AX7LPS is definitely the tube for the PI. It just sounds bigger as described above.

The weekend is proving to be damp, especially as I have BBQ on today. It is teeming down with rain in Sydney, the backyard is semi flooded which is unusual as the rain has been so light all week. Still I happy to be at home with the troops.

[stelligan]

FWIW.. I prefer LPS in PI and 803's in V2.. Long plates a more prone to micro phonics so it never ends..

This has worked for me well also.
I have tried JJ branded 803 at the PI with mixed results, some very good and some bad. The cheaper ones always did better than the "gold pin" fancy version for me. JJs in general have been extremely variable for me - when they are great, they're great. Sovtek LPS has never failed at the PI.

[Mark]

I've tried the JJ 803S in the V2 position, my mate and I thought the 803 sounded a bit thicker than the 83S. Once again horses for course, and I dare say it's nothing that couldn't be adjusted with the HRM.

I will have to look at the HRM pots again and see what works best with the 803S tube. The amp sounded impressive today and it worked well with my three guitars, but his three pickup SG sounded a bit bass heavy through the amp. (Master volume, master tone, pickup configuration is set via a chicken head knob.)

We could get good sounds out of the amp with this guitar, the high gain stuff was bass heavy as the tone controls were within the amp.

All food for thought.

Back to the topic, either the 83S or the 803S are good.

[Drumslinger]

WOW! This was very informative. Thanks for the info and the chart Tony.

[talbany]

FWIW..My opinion on the 803 was mainly directed at the Non HRM's.. The larger plates no doubt contribute to the slightly thicker tone so if you have a Non HRM and want a bit thicker/punch OD tone the long plates will help...w/ HRM's you can kind of dial in that thickness of coarse.. The reason I like the 803's a bit better is they have that pronounced midrange liveliness the JJ's are known for which is always nice vs the LPS which have a bit flatter mid spank!!
IMO.. The the 803's are kind of all over the place so you may want to try a few there if you have them on hand..

This is of coarse pretty subjective stuff..

WOW! This was very informative. Thanks for the info and the chart Tony.

Drum..Your welcome!!... So glad you found this helpful...

Tony