Vacuum Tube OTL power amp!! - Page 14 - 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 6th July 2011, 10:42 PM   #131
M Gregg is offline M Gregg  United Kingdom
diyAudio Member
 
M Gregg's Avatar
 
Join Date: Jun 2010
Location: UK
Quote:
Originally Posted by Alastair E View Post
12AU7 was used in the schematic as I havent a 6SN7 'part' in the library, and didnt update its reference....
6SN7 used in real-life though, just check its pinout when you come to wire it up--Not the same as a 12AU7!....

C3 and C4, Should be 0.47 or 470N. The 'default' on my Proteus schematic capture is 220N, ...
Alastair,

Your help is very much appreciated...I think it's great that you have overcome the feedback issue.

Just me checking that I use the correct parts!

Regards
M. Gregg
__________________
What is the sound of one hand clapping?

Last edited by M Gregg; 6th July 2011 at 10:53 PM.
  Reply With Quote
Old 6th July 2011, 11:57 PM   #132
diyAudio Member
 
Alastair E's Avatar
 
Join Date: Feb 2004
Location: South Wales
Quote:
Originally Posted by M Gregg View Post
Alastair,

Your help is very much appreciated...I think it's great that you have overcome the feedback issue.

Just me checking that I use the correct parts!

Regards
M. Gregg
Not at all--

You've invested your dosh on parts and time on a design I put forward, Its only right that I / we all work get it as good as we can make it....
__________________
Das Beste Oder Nichts
  Reply With Quote
Old 8th July 2011, 09:57 AM   #133
M Gregg is offline M Gregg  United Kingdom
diyAudio Member
 
M Gregg's Avatar
 
Join Date: Jun 2010
Location: UK
Alastair,

Couple of questions linked to schematic (is this what we have now?)

Is the coupling cap C2 also a 470N ?

Also is the 470K resistor still in the FB loop as shown?



Regards
M. Gregg
Attached Images
File Type: jpg OTL feedback modsmall.jpg (33.5 KB, 624 views)
__________________
What is the sound of one hand clapping?
  Reply With Quote
Old 9th July 2011, 12:30 PM   #134
diyAudio Member
 
Alastair E's Avatar
 
Join Date: Feb 2004
Location: South Wales
Ah--OK here we go....

No 470K in the FB loop. Its joined directly, so that the 18K on bottom end of phase-splitter sits on the O/P line....

C2 is 0.22 or 220N I'm using and works well....
If you wanted to pull up the LF pole, you could reduce its value to 0.1 or even 0.047....
__________________
Das Beste Oder Nichts
  Reply With Quote
Old 9th July 2011, 05:17 PM   #135
M Gregg is offline M Gregg  United Kingdom
diyAudio Member
 
M Gregg's Avatar
 
Join Date: Jun 2010
Location: UK
Quote:
Originally Posted by Alastair E View Post
Ah--OK here we go....

No 470K in the FB loop. Its joined directly, so that the 18K on bottom end of phase-splitter sits on the O/P line....

C2 is 0.22 or 220N I'm using and works well....
If you wanted to pull up the LF pole, you could reduce its value to 0.1 or even 0.047....
Ok thank's,

Just short out the 470K..OK

Have you used any special type of fuse on the OP (Quick blow?)

Started building the chassis..<<<< always takes a while!

Looking at components I'll use the IRF710

Should be interesting

Regards
M. Gregg
__________________
What is the sound of one hand clapping?
  Reply With Quote
Old 9th July 2011, 05:28 PM   #136
diyAudio Member
 
Alastair E's Avatar
 
Join Date: Feb 2004
Location: South Wales
I'm using a standard, Anti-Surge fuse inline with the speaker, its possible with a QB type a powerful transient could pop it....

Chassis work is always a time consuming process!
__________________
Das Beste Oder Nichts
  Reply With Quote
Old 19th July 2011, 05:25 PM   #137
M Gregg is offline M Gregg  United Kingdom
diyAudio Member
 
M Gregg's Avatar
 
Join Date: Jun 2010
Location: UK
Just some progress

For interest, this was just to try the components for fit.
Some more work required..and ideas to try.



Regards
M. Gregg
Attached Images
File Type: jpg DSCN3547.JPG (27.5 KB, 523 views)
File Type: jpg OTL case.jpg (13.7 KB, 513 views)
__________________
What is the sound of one hand clapping?
  Reply With Quote
Old 19th July 2011, 06:27 PM   #138
diyAudio Member
 
Alastair E's Avatar
 
Join Date: Feb 2004
Location: South Wales
Hey--Thats coming along really nicely!

Wont be long now till you have it done!
__________________
Das Beste Oder Nichts
  Reply With Quote
Old 24th July 2011, 04:29 PM   #139
diyAudio Member
 
Join Date: Jan 2002
Location: Tyrone Ga. U.S.A.
How much current are the 6c33c's drawing. I was wondering if I could use 100 ohm
cathode resistors and reduce the voltage to 120 + and - for a 10W amp?
  Reply With Quote
Old 24th July 2011, 08:35 PM   #140
diyAudio Member
 
Alastair E's Avatar
 
Join Date: Feb 2004
Location: South Wales
Quote:
Originally Posted by woody View Post
How much current are the 6c33c's drawing. I was wondering if I could use 100 ohm
cathode resistors and reduce the voltage to 120 + and - for a 10W amp?
Yup--Dont see why not....

Ive run the same scheme at 100V, and 100 ohm, get around 160-180 through
the tubes, depending on whether Ive got 6C33, 6C41C or single heater 6C33C rigged up....
At 100V we get around 5-8 W depending on what tube/dual/single heater, into 8ohm

At 120V and 100ohm, you'll prob be puling about 200-220mA through each 6C33C tube (Both heaters) with around 100V across the actual tube itself....

Just make sure that you burn the tube heaters for a good couple of hours first-(Pref a day or so), then you can plug 'em into the amp, with dummy load across speaker-term --10 ohm WW will do--and run the amp for around 3 hours before trying to match up the valves, and shooting some sound through.

--This above, applies obviously only to New, Unused 'green' valves that have never been used....
-If you have some with some time under their belts, just fire 'em up and check the DC Offset....

Matching the valves for min DC Offset--

There's NO need to buy 'matched' valves--Which are difficult to find in 6C33 and always drift a little anyway.

You can measure the DC Offset across the 10 ohm WW and switch round the 6C33c until you get below 100mV offset.--(Best Ive ever achieved, was 15mV with a couple of pretty old 6C33, running single-cathode operation.)

--Normally this is pretty easy, you're sure to find a combo of tubes that give you below 100mV for both channels, if you have say, 6 tubes, just chop/change 'em round and test the offset....

You can quite happily pull the valves while the amp is still on and switch them round for the offset matching process, but I wouldnt recommend doing this if its attached to a speaker--Although thats the way I actually do it....

--Take Care, Oven-Glove time, they get HOT!

Even though 6C33C take 20 mins to stabilise, the 'offset test' can be checked as soon as the valves have fully hot cathodes, They seem to 'track' reasonably well over time in hours and time as in weeks, it varies very little, as they seem to age together.
__________________
Das Beste Oder Nichts
  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
FS: Vacuum Tube Monoblock Power Amp Kit cuibono Swap Meet 13 7th May 2011 01:49 AM
Vacuum tube VCO Bitrex Tubes / Valves 1 15th March 2011 01:07 PM
HLLY MK III 3 Vacuum Tube Headphone Amplifier Pre Amp hllyelec Vendor's Bazaar 2 19th July 2009 06:54 AM
S3E Vacuum Tube angsuman Tubes / Valves 12 15th March 2008 06:12 AM
DIY Vacuum tube amp turbo_h4 Tubes / Valves 2 1st July 2004 02:48 AM


New To Site? Need Help?

All times are GMT. The time now is 03:06 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