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 24th May 2004, 10:23 AM   #1
cwteoh is offline cwteoh  Malaysia
diyAudio Member
 
Join Date: Sep 2003
Location: Penang, Malaysia
Default Dynaco ST70

Hi, if you are build your own Dynaco, I wish I can get some info from you, because I am thinking of build 1 for my own. I need some experience expert for guides.

I got the original Dynaco ST70 schematic with me (shown below). With the following tube I could able to start my construction.

4 x E34L quad matched
2 x 7199
1 x GZ34
Attached Images
File Type: jpg dynaco_st70.jpg (43.7 KB, 624 views)
__________________
Regards,
C.W. Teoh
  Reply With Quote
Old 24th May 2004, 11:27 AM   #2
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
7199s were difficult to source last time I checked. Have you located some? What transformers are you planning to use?
__________________
"It is difficult to get a man to understand something, when his salary depends upon his not understanding it." Upton Sinclair
  Reply With Quote
Old 24th May 2004, 11:29 AM   #3
diyAudio Member
 
Frank Berry's Avatar
 
Join Date: Sep 2003
Location: Midland, Michigan
Replace the 7199 tubes with 6U8's. Performance will be the same. Be aware that the pinout is slightly different.
__________________
Frank
  Reply With Quote
Old 25th May 2004, 06:19 AM   #4
cwteoh is offline cwteoh  Malaysia
diyAudio Member
 
Join Date: Sep 2003
Location: Penang, Malaysia
what do you think about the following schematic. It has been modified by one of my local DIY guy. Please advise, thanks
Attached Images
File Type: jpg custom_el34.jpg (49.6 KB, 537 views)
__________________
Regards,
C.W. Teoh
  Reply With Quote
Old 25th May 2004, 08:02 AM   #5
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
In the 2nd circuit, I'm somewhat dubious about a 12AU7, with it's mu of 20 having enough gain, especially since there is degeneration in the O/P stage due to the unbypassed cathode resistor.

In general, I LIKE the 2nd circuit. I would quibble with the details. The reality of tubes not being TIGHTLY matched can't be ignored. "Fixed" bias with individual adj. pots. for each tube allows exact setting of idle currents, which compensates for mediocre matching. I would use a tube with more gain than the 12AU7, say the 12AT7 and instead of grounding the non-inverting triode's grid, use it as the point of application of negative feedback picked up from the O/P transformer's secondary.
__________________
Eli D.
  Reply With Quote
Old 25th May 2004, 10:41 AM   #6
Jax is offline Jax  Sweden
diyAudio Member
 
Join Date: Nov 2003
Location: South Sweden
Something like this?

Click the image to open in full size.

Still subject to tweaks but a prototype is up and running just fine.
__________________
Jan
  Reply With Quote
Old 25th May 2004, 08:25 PM   #7
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
Jax,

That's impressive! There's very little I would change. Use the less expensive, but EQUIVALENT Locktal 7N7 instead of the 6SN7. Change the EL34 cathode resistors to 100 Ohms, for a "dose" of Dennis Boyle's combination bias.

FWIW, I had a 2 stage circuit with a 12AT7 as the phase splitter in mind using a less sophisticated CCS (an enhancement MOSFET).
__________________
Eli D.
  Reply With Quote
Old 25th May 2004, 08:44 PM   #8
frugal-phile(tm)
diyAudio Moderator
 
planet10's Avatar
 
Join Date: Oct 2001
Location: Victoria, BC, NA, Sol III
Blog Entries: 5
Quote:
Originally posted by Frank Berry
7199 tubes with 6U8's.
I've a whack of used 7199s -- even a couple cryoed new ones i'll never use... even more 6U8s.

This is the direction i'm going with my ST70 (compliments of Allen Wright):

Click the image to open in full size.

I may well use 6H30Pi or ECC99 (althou with 6H23Pis on hand...)

dave
__________________
community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi
p10-hifi forum here at diyA
  Reply With Quote
Old 25th May 2004, 08:52 PM   #9
Jax is offline Jax  Sweden
diyAudio Member
 
Join Date: Nov 2003
Location: South Sweden
Thanks, Eli.

One of my goals in the design was to reduce the number of low frequency poles within the loop to a reasonable minimum. There are only two left, the coupling caps and the transformer. Differential stages is a good way to avoid decoupling caps combined with the DC-coupling.

I have been thinking of stabilizing the output stage bias with higher cathode resistors but 100 ohms? Should they be decoupled? You made me curious now
__________________
Jan
  Reply With Quote
Old 25th May 2004, 09:09 PM   #10
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
p10- all you need is a Jensen JT11-P1 on the input...
__________________
"It is difficult to get a man to understand something, when his salary depends upon his not understanding it." Upton Sinclair
  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
DIY Dynaco ST70 wingking3000 Tubes / Valves 2 25th July 2008 10:20 PM
Bias adjustment on Dynaco ST70 ghisdal Tubes / Valves 1 12th March 2007 08:05 PM
DIY Preamp for use with Dynaco ST70 liggs17 Tubes / Valves 3 7th December 2006 06:46 PM
Dynaco ST70 clone Tekko Tubes / Valves 8 9th April 2005 02:02 PM
SDS power supply board for Dynaco ST70 Mikelo Swap Meet 0 17th January 2005 09:58 PM


New To Site? Need Help?

All times are GMT. The time now is 02:46 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