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 25th March 2012, 06:15 PM   #21
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
Andy,

The 6BGs from the Siberian Shop rate to be Soviet NOS and lack the toughness of current production Sovtek 6B4Gs. AFAIK, New Sensor uses the same anode stamping for 6B4Gs and 300Bs, for economy of scale. It's no wonder that their 6B4Gs are tough.
__________________
Eli D.
  Reply With Quote
Old 25th March 2012, 07:13 PM   #22
diyAudio Member
 
Join Date: Sep 2003
Location: London
Hi Eli,

I may be interested in some of these Siberian '70s Svetlanas. Do you have any experience or reports of their sound quality?

andy
  Reply With Quote
Old 25th March 2012, 07:58 PM   #23
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
Quote:
Originally Posted by andyjevans View Post
Hi Eli,

I may be interested in some of these Siberian '70s Svetlanas. Do you have any experience or reports of their sound quality?

andy

I can't comment.
__________________
Eli D.
  Reply With Quote
Old 26th March 2012, 12:39 AM   #24
rhone is offline rhone  Australia
diyAudio Member
 
Join Date: Dec 2005
Location: Melbourne
I used these 6B4Gs recently. They were a reasonably well matched quad at about half the price of Sovteks, and not much more than Russian NOS. Good value, I reckon.
  Reply With Quote
Old 15th February 2013, 10:27 AM   #25
diyAudio Member
 
mr2racer's Avatar
 
Join Date: Jul 2009
Hey All,
I have a question about the EL34 musical machine. On the input there is a 100k pot and beyond it the voltage .785. does this mean the voltage should max out at .785 or be set at .785?

I'm using HK output transformers and a Fisher power transformer. I happened on to a matched quad of Siemans EL34's and some, what were sold to me as Mullard 6GK5's. The 6gk5's came in purple Pro/Comm boxes and are labeled made in Great Britain. Are they actually Mullards?
  Reply With Quote
Old 15th February 2013, 02:30 PM   #26
diyAudio Member
 
boywonder's Avatar
 
Join Date: Jan 2008
Location: So.Cal.
I'm guessing at bit here, but the .785V ac may be an indication of the input sensitivity of the MM.

One other thing (after looking at the schemo) Poinz' is not showing any grid stopper R's on the 6GK5's, but SY and a few other folks here recommended adding them. Use carbon comp R's.

The 6GK5's in the ProComm boxes sound like the ones that Stan sells at ESRC in Orlando. I have about 20 of these, see pic. The ones I have have 2 seams on the top of the glass and say "gt. britain" next to the 6GK5 ink. These are Mullards.
Attached Images
File Type: jpg 6GK5.JPG (704.5 KB, 273 views)

Last edited by boywonder; 15th February 2013 at 02:42 PM.
  Reply With Quote
Old 16th February 2013, 12:16 AM   #27
diyAudio Member
 
mr2racer's Avatar
 
Join Date: Jul 2009
Thanks boywonder,

It seems logical that the .785 is a maximum input. Yes they are the same Mullards that you have. Woo Hoo! I also have 8 NOS Hitachi 6GK5's to try as well.

I think this design could be modified to use 6550's couldn't it?

I've heard others mention that carbon composition make good grid stoppers, (and nothing else). Does 1k sound right?
What about carbon film?

Kevin
  Reply With Quote
Old 16th February 2013, 12:32 PM   #28
diyAudio Member
 
mr2racer's Avatar
 
Join Date: Jul 2009
By my calculations, (which are always suspect) Rdrop in the heater supply is about .015 ohms?
  Reply With Quote
Old 16th February 2013, 01:35 PM   #29
diyAudio Member
 
boywonder's Avatar
 
Join Date: Jan 2008
Location: So.Cal.
Quote:
Originally Posted by mr2racer View Post
I think this design could be modified to use 6550's couldn't it?
Kevin
I don't think that the 6GK5 has the voltage swing to fully drive 6550's/KT88's. The miller C is higher with those tubes as well, requiring a fair bit of gm. IIRC, I popped some KT88's in my MM when I had it on the bench, and got similar power out as the EL34's. That was a few years ago.

One other minor mod you may want to consider is the bias circuit. The way it's shown in the schemo, if the pot wiper lifts the bias goes away, leading to red plates. One project that comes to mind for a safer bias arrangement is the mullard KT88 project thread started by Tubemack; there are lots of other projects with similar bias arrangements around as well.
Attached Files
File Type: pdf KT88 UL Mullard EF86 draft8b.pdf (126.0 KB, 81 views)

Last edited by boywonder; 16th February 2013 at 01:48 PM.
  Reply With Quote
Old 17th February 2013, 03:54 PM   #30
diyAudio Member
 
mr2racer's Avatar
 
Join Date: Jul 2009
BoyWonder.

I see what you mean. If you use the 27k / 22k voltage divider and then use the pot to adjust the voltage within the divider if the wiper fails you still have minimum bias not zero bias. I've attached a schematic to show my change. I hope/ think its correct?
Attached Images
File Type: gif bias 1.GIF (4.8 KB, 208 views)
  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
EL34 Musical Machine Output XFMR suggestions greyhorse Tubes / Valves 4 10th June 2011 01:32 AM
EL34 PP triode mode hums slideman82 Tubes / Valves 5 11th March 2011 03:51 AM
FS: parts for Musical Machine PP 6V6 amp jrebman Swap Meet 5 28th October 2009 08:27 PM
Which do you prefer - EL84 UL PP or EL34 Triode PP - and why? ray_moth Tubes / Valves 4 23rd February 2007 12:22 PM


New To Site? Need Help?

All times are GMT. The time now is 11:44 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