small and cheap OTL schematic needed - 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 16th June 2010, 12:34 PM   #1
neazoi is offline neazoi  Greece
diyAudio Member
 
Join Date: Aug 2007
Default small and cheap OTL schematic needed

hello,
I was wondering if there are any OTL amplifiers using small tubes. I have found one which I attatch but I wonder if there are any other out there.
thanks
Attached Images
File Type: gif se_otl.gif (25.2 KB, 837 views)
__________________
Great DIY site: http://www.neazoi.com
  Reply With Quote
Old 16th June 2010, 01:03 PM   #2
TheGimp is offline TheGimp  United States
diyAudio Member
 
TheGimp's Avatar
 
Join Date: Aug 2009
Location: Johnson City, TN
Grid and plate are swapped in the output of that schematic.

You also have a strong possibility of dc bias thorugh the speaker.

The only other OTL i've seen discussed lately was based on 6AS7, which while a dual triode does not qualify as a small tube.

Actually, there are several errors in the schematic. bias reisstors for one tube not ten in the output stage. 700V supply for triodes designed for 250V max, -213 V on the grid (currently shown as plate) of output with -13 on the cathode ....

Hopefully someone else can point you to a schematic of an amp that meets your requirements, and works.

Last edited by TheGimp; 16th June 2010 at 01:14 PM.
  Reply With Quote
Old 16th June 2010, 01:39 PM   #3
cnpope is offline cnpope  United States
diyAudio Member
 
Join Date: Aug 2009
Location: College Station, TX
Default Looks bizarre, but it's right...

The circuit looks quite strange, but actually it is what is intended. The design, by Steve Bench, runs the output tubes in "inverted triode" mode. More details can be found at Inverted Tube Operation, and other articles by Steve Bench at Steve's Tube Pages. I think this is a mirror of his original, now defunct, website. He seems to like exploring slightly unusual circuit designs!

Chris
  Reply With Quote
Old 16th June 2010, 01:40 PM   #4
diyAudio Member
 
Join Date: Apr 2002
Location: Cayman Islands
12B4 Amps12B4 Amps
__________________
None of us are leaving this world alive. Enjoy it responsibly as you may.
  Reply With Quote
Old 16th June 2010, 01:41 PM   #5
diyAudio Member
 
Sch3mat1c's Avatar
 
Join Date: Jan 2003
Location: Milwaukee, WI
Send a message via ICQ to Sch3mat1c Send a message via AIM to Sch3mat1c
Simple answer: either use a metric sh**load of tubes in parallel, or forget it. OTL is a fundamentally flawed concept around vacuum tubes. The impedances just aren't right.

If you insist, I recall there are some Russian types with very low plate resistance, analogous to 1/2 6AS7 in a 9-pin bottle. I don't remember the number.

Tim
__________________
Seven Transistor Labs
Projects and Resources
  Reply With Quote
Old 16th June 2010, 01:56 PM   #6
danzup is offline danzup  Romania
diyAudio Member
 
danzup's Avatar
 
Join Date: Oct 2007
Location: Bucuresti
Quote:
Originally Posted by Sch3mat1c View Post
Simple answer: either use a metric sh**load of tubes in parallel, or forget it. OTL is a fundamentally flawed concept around vacuum tubes. The impedances just aren't right.

If you insist, I recall there are some Russian types with very low plate resistance, analogous to 1/2 6AS7 in a 9-pin bottle. I don't remember the number.

Tim
6H13C ( with europeen letter is 6N13S ) but this is in 8 pins socket
direct equivalent of 6AS7G
of course , but you need a power plant to lite up 10 pieces of that tube for a decent low output impedance !
__________________
There are not better tube than 6P3S and 6N2P for my ears !

Last edited by danzup; 16th June 2010 at 02:11 PM.
  Reply With Quote
Old 16th June 2010, 02:01 PM   #7
danzup is offline danzup  Romania
diyAudio Member
 
danzup's Avatar
 
Join Date: Oct 2007
Location: Bucuresti
Quote:
Originally Posted by TheGimp View Post
Grid and plate are swapped in the output of that schematic.

You also have a strong possibility of dc bias thorugh the speaker.

The only other OTL i've seen discussed lately was based on 6AS7, which while a dual triode does not qualify as a small tube.

Actually, there are several errors in the schematic. bias reisstors for one tube not ten in the output stage. 700V supply for triodes designed for 250V max, -213 V on the grid (currently shown as plate) of output with -13 on the cathode ....

Hopefully someone else can point you to a schematic of an amp that meets your requirements, and works.
As posted by fellow user that schematics really work !
But no need to say that are lot of other OTL schematics better that that :
- circlotron OTL
- futterman OTL
- technics OTL variant of futterman
- ciufolli OTL variant with 6C33C
- atmasphere variant (Nice AT M60 schematics will you find on this forum !) with 6H13C
- and of course old Philips OTL with capacitor on output (like an SRPP but with pentode )
__________________
There are not better tube than 6P3S and 6N2P for my ears !

Last edited by danzup; 16th June 2010 at 02:06 PM.
  Reply With Quote
Old 16th June 2010, 02:05 PM   #8
diyAudio Member
 
Join Date: Apr 2002
Location: Cayman Islands
Quote:
if you insist, i recall there are some russian types with very low plate resistance, analogous to 1/2 6as7 in a 9-pin bottle. I don't remember the number.

6c19
__________________
None of us are leaving this world alive. Enjoy it responsibly as you may.
  Reply With Quote
Old 16th June 2010, 02:10 PM   #9
danzup is offline danzup  Romania
diyAudio Member
 
danzup's Avatar
 
Join Date: Oct 2007
Location: Bucuresti
Quote:
Originally Posted by Andrewbee View Post
6c19
Yes that is in 9pin glass bottle .
__________________
There are not better tube than 6P3S and 6N2P for my ears !
  Reply With Quote
Old 16th June 2010, 02:22 PM   #10
cnpope is offline cnpope  United States
diyAudio Member
 
Join Date: Aug 2009
Location: College Station, TX
An example of a more conventional simple OTL is the design by Tim Mellow, which appeared in the February issue of Audio Express. It's 25W per channel. Admittedly the output tubes (a pair of 6C33C's per channel) could hardly be called "small" (unless you compare them to transmitting tubes or something like that!), but the design is about as simple as they get. I have built one, and it sounds great. Another nice design, which I've also built, is the one by Hans Beijner, again using 6C33C's. Both of these are essentially modified Futterman designs. I've built a circlotron too, using a design by Alan Kimmel, using EL509S tubes in the output. This one is a bit more complicated, because of the need for two separate floating output power supplies per channel.

Interestingly enough, it is really rather easy to get a low output impedance with an OTL, particularly with the use of negative feedback. A fraction of an ohm output impedance is quite routine for such amps.

Chris
  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
Can this schematic work? 6N6P driver with 6C33C-B OTL Koifarm Tubes / Valves 13 13th April 2010 03:28 AM
Recomendation needed, small cheap full range. internecine Full Range 26 27th May 2009 08:36 AM
help! T16 OTL schematic foboleyns Tubes / Valves 1 21st June 2006 04:26 PM
PC-speakers + small amp (key words: small, cheap) rho Multi-Way 8 18th May 2006 01:19 PM
design for 6336A OTL amp needed icarex69 Tubes / Valves 7 5th April 2006 04:46 PM


New To Site? Need Help?

All times are GMT. The time now is 08:32 AM.


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