Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 31st May 2005, 06:39 AM   #1
diyAudio Moderator Emeritus
 
ray_moth's Avatar
 
Join Date: Jan 2004
Location: Jakarta
Default More crappy Russian EL34s - Svetlana this time

I posted a few weeks ago about a bad Sovtek El34 that virtually stopped conducting. That left me with a still-working matched pair plus an orphan.

Well, I bought a so-clalled "matched quad" of Svetlana EL34s in Singapore and used those to replace the Sovteks. I swear I can hear no difference in quality between the Svetlanas and Sovteks, despite popular rumours to the contrary. However, the transconductance of the Svetlanas is very low, perhaps around 8 mA/volt instead of 11 mA/volt it should be. Consequently, the bias point of the Svetlanas was very different from that of the Sovteks (which were about normal).

I'm running the EL34s in triode mode, with 360v plate voltage and fixed bias set to give quiescent cathode current of 60mA. I have found that, while one pair of the Svetlanas behaves OK, the other pair is ill-matched and is inclined to drift, so I had to readjust the fixed grid bias for one or both of the tubes in that pair. In the end, I gave up with them and replaced them with the working pair of Sovteks (and readjusted the bias drastically!)

So now I've got the good pair of Svetlanas in one channel and the good pair of Sovteks in the other, albeit with widely different grid bias. It all sounds OK but what a bl**dy state of affairs!

I feel angry about the junk I've managed to collect, acquired from (Indonesian and Singaporean) traders; not that I really blame them, I realize they don't have the education or experience to understand what they're selling. The only advantages of buying in Singapore seem to be cheapness and availability. I can and do blame the Russian manufacturers, though. Don't those bums give a sh*t about the products they let loose on the world?
  Reply With Quote
Old 31st May 2005, 11:32 AM   #2
diyAudio Moderator Emeritus
 
Bas Horneman's Avatar
 
Join Date: Apr 2002
Location: The Netherlands
Blog Entries: 18
Quote:
I can and do blame the Russian manufacturers
Quite a blanket statement! The real Svetlana's i.e. winged C's are great tubes.

Svetlana=Sovtek and Sovtek=Svetlana due to Svetlana USA's buying the rights to the Svetlana name. Conning people into thinking they've got Svetlana's. Well they do...but eh..they don't.

There is no substitute for buying from a good dealer. WHATEVER tube you buy. Whether its Russian, Chinese, European or American.
  Reply With Quote
Old 31st May 2005, 02:54 PM   #3
diyAudio Moderator Emeritus
 
ray_moth's Avatar
 
Join Date: Jan 2004
Location: Jakarta
Quote:
Quite a blanket statement!
You're right, Bas, I should have said that I blame the maker(s) of the particular tubes that I bought, not all Russian makers. These are not the "winged C" Svetlanas, by the way. If I'd known more about it when I bought them, I would have chosen differently.
The Singapore dealer seems to have others to choose from, although he didn't say much when I was in his shop. However, I've since been looking at his web site http://www.wellaudiolab.com/
  Reply With Quote
Old 31st May 2005, 03:19 PM   #4
diyAudio Moderator Emeritus
 
Bas Horneman's Avatar
 
Join Date: Apr 2002
Location: The Netherlands
Blog Entries: 18
Quote:
The Singapore dealer seems to have others to choose from, although he didn't say much when I was in his shop.
Hi Ray,

That is quit a luxury, being able to walk into a tube shop! LOL.

Good luck..make sure he knows what he is doing. (Ask him how he matches tubes to test his knowledge.

And try to get the winged C's...at least in the States and Europe they look are excellent value for money tubes....

Regards,
Bas
  Reply With Quote
Old 31st May 2005, 11:17 PM   #5
EC8010 is offline EC8010  United Kingdom
diyAudio Moderator Emeritus
 
EC8010's Avatar
 
Join Date: Jan 2003
Location: Near London. UK
Default Re: More crappy Russian EL34s - Svetlana this time

Quote:
Originally posted by ray_moth
I'm running the EL34s in triode mode, with 360v plate voltage and fixed bias set to give quiescent cathode current of 60mA.
So you're running them at a slightly unusual voltage and with fixed bias - I'm not surprised they're not matched. Valves have quite large variations (although not as bad as hfe for bipolar transistors or Vgs for FETs). I'm afraid that once you stray off the beaten path of "normal" operation, you can expect this sort of problem. If you have a really kind valve vendor he might be prepared to match for your precise operating conditions, but be prepared to pay the price - it takes time.
__________________
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
  Reply With Quote
Old 1st June 2005, 04:00 PM   #6
hacknet is offline hacknet  Singapore
diyAudio Member
 
Join Date: Nov 2002
Location: sg
i was talking to the owner of well audio labs today and it seems rare for one to get a pair of faulty tubes since he tests every tube before it gets on the shelves. he labels the transconductance and the current on the boxes too.. so you shouldn`t encounter such problems of instability.

i`ve personally got a quad of svet el34`s from him and they are working perfectly.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
IRFBC20 as source follower drivers for EL34s in AB1 PP ray_moth Tubes / Valves 21 21st March 2008 05:43 PM
Svetlana Svetlana EL509-II: Please disregard all my statements about this tube! Morgan L Tubes / Valves 2 30th January 2004 06:15 PM
Boo!!!Crappy scams!!! seangoesbonk Everything Else 12 2nd February 2002 07:28 PM


New To Site? Need Help?

All times are GMT. The time now is 05:03 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2