This circuit ok? - diyAudio
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 February 2008, 01:02 AM   #1
diyAudio Member
 
Join Date: Aug 2006
Default This circuit ok?

Aside from the reliability of the 6C33C, can someone with more knowledge than I comment on the viability of the following circuit? I'm on a quest for a low-powered circlotron..

http://img165.imageshack.us/img165/3...clotronjb9.gif

I have some particular questions, but if the circuit isn't sound (sorry) I won't bother.
  Reply With Quote
Old 25th February 2008, 04:49 AM   #2
diyAudio Member
 
Miles Prower's Avatar
 
Join Date: May 2005
Location: USA
Blog Entries: 6
Default Re: This circuit ok?

Quote:
Originally posted by CarlyBoy
Aside from the reliability of the 6C33C
They're terrible, either avoid 'em or use 'em for what they were intended: series pass regulator.

Quote:
I have some particular questions, but if the circuit isn't sound (sorry) I won't bother.
How low powered? You can definitely use 6AS7s instead. How many, that depends on both Po and Zl.

Cirucit looks OK except that the DC offset pot would be better in the cathode circuit, as opposed to the plate. The cathode has more control than the plate, and you would neither need such a big pot, nor expose yourself to dangerous voltages.

I would also like to see a DC offset servo on the finals. It doesn't take much DC offset to poof your speeks.

Another thing: this must run from a Lo-Z source, otherwise, your gNFB is going to become badly imbalanced, and that won't help the sonics a bit.
__________________
There are no foxes in atheistholes
www.dolphin-hsl.com
  Reply With Quote
Old 25th February 2008, 05:04 PM   #3
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
I designed and built a somewhat more complex circlotron based on 6C33 about 10yrs ago. The key thing with 6C33 is to burn them in for about 24 hours at moderate plate current to stabilize their characteristics before use. The filaments should be allowed to warm up fully before B+ is applied, this will go a long way to preventing arcing and other problems.

There are a lot of people who use 6C33 successfully here on diyaudio and would vehemently disagree with Miles although my experience with them should make me very sympathetic to the viewpoint expressed.

Selection and burn in is one key to success with the 6C33, another is to make sure that the filament current does not cause contact failure.
The cheap Chinese sockets won't cut it, some surplus Russian mil-spec stuff works fine. One common approach is to use the European style terminal blocks removed from their plastic bodies to make strong physical connections to the filament pins - obviously if you do this you won't be able to just unplug them, but you won't have fireworks from failing filament pin contacts either. (I used forced air cooling around the sockets which kept them cool enough to avoid contact problems, and used good sockets. The chassis was basically a sealed plenum pressurized by a fan which blew air out around the sockets which were slightly recessed - this worked very well - this monoblock amplifier had 6 x 6C33 per channel.)

The 6C33 can sound very good indeed, I was unsuccessful partly because I was distracted by the allure of SE toward the end of the project. I gave the amps away and the fellow who inherited them has been able to get them to work.

Check out my site for the sordid tale of the 6C33 otl..
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 26th February 2008, 02:46 AM   #4
diyAudio Member
 
Join Date: Aug 2006
Miles, how low powered you ask? Say 30W. Anything that won't fry the Quad 57 - impedance curve on Sheldon Stokes site:

www.quadesl.com/quad_main.html

I've no experience with the 6C33C. Have done enough reading to be tentative, but also trying to keep an open mind. I'd rather stay with the 6AS7...

Interesting insights on your site, Kevin. Thank you.
  Reply With Quote
Old 26th February 2008, 03:20 AM   #5
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Don't assume the 6AS7 is all that great either, just a different set of problems.

Many USA and Canadian made 6AS7G do not perform well or last long in OTL service. The current hot tip is to use Russian surplus. (I have some and they seem more consistent in section to section match than the US ones I had.)

The 6C33 is a practical choice if you are careful, a number of Dutch and German members of this forum are running circlotrons with these and have reported very good long term reliability. (up to 6yrs on the same set of outputs.)

Search here for otl, 6C33, etc. Make up your own mind.. Other potential choices are 6336, some tv sweep tubes are suitable, (ask George of tubelab fame) etc.

I ran mine with no feedback and it sounded very good driving 4 ohm maggies despite the relatively high output impedance. I didn't find dc drift on the output to be a problem - my issue was with arcing during warm up, excessive hum, and a very inadequate driver design. (No spice in those days.. )
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 26th February 2008, 03:22 AM   #6
diyAudio Member
 
Miles Prower's Avatar
 
Join Date: May 2005
Location: USA
Blog Entries: 6
Quote:
Originally posted by CarlyBoy
Miles, how low powered you ask? Say 30W.

I've no experience with the 6C33C. Have done enough reading to be tentative, but also trying to keep an open mind. I'd rather stay with the 6AS7...
I've done some very preliminary design work on this since I'd like to do a OTL some day. 6AS7s are a good choice, and you can get 30W with eight sections per phase, and stick to the conservative side of the ratings. Here's a loadline for this.
Attached Images
File Type: png 6as7ga-loadline.png (77.4 KB, 237 views)
__________________
There are no foxes in atheistholes
www.dolphin-hsl.com
  Reply With Quote
Old 26th February 2008, 03:28 AM   #7
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
I should think with the Quad 57 you wouldn't need more than 15 - 20 watts total.. ( A single pair of 6C33 will do that for you.) I apparently have a bee in my bonnet tonight... Probably should just ignore me..

Confession, I think I am going to revisit the 6C33 issue in a more modest form at some point. Maybe a pp cathode follower amp...
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  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
Circuit help jetbat Tubes / Valves 16 11th May 2009 04:23 AM
6c4 pre-amp circuit dito Tubes / Valves 2 2nd January 2007 07:42 PM
amp circuit help scott3292 Solid State 10 11th July 2005 11:16 PM
Trouble with speaker protection circuit (Randy Slone's circuit) whalefat Solid State 3 13th April 2005 10:13 AM
What circuit? palesha Solid State 1 24th November 2002 10:18 PM


New To Site? Need Help?

All times are GMT. The time now is 07:51 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