First tubeamp, dont laugh too hard - 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 26th November 2006, 06:41 AM   #1
diyAudio Member
 
jerluwoo's Avatar
 
Join Date: Feb 2006
Location: Ashland,Ky U.S
Default First tubeamp, dont laugh too hard

This is my first attemp at building with tubes. The results were much better than I had hoped so its definitely not a failure to say the the least. Great sound out of this little beasty, better than any of the ss amps I've been listening to. I'm still a little iffy on working with high voltage so I shot for something simple.
I'm well aware that I'm running the 50C5's above rating but they seem happy enough, no glowing plates or grids with the lights out. All and all a fun a rewarding little project.
Attached Images
File Type: jpg tubeamp.jpg (91.8 KB, 767 views)
  Reply With Quote
Old 26th November 2006, 10:13 AM   #2
diyAudio Moderator Emeritus
 
ray_moth's Avatar
 
Join Date: Jan 2004
Location: Jakarta
Looks OK to me, except for:

(a) lack of bias on the first stage. The 270k grid resistor R8 should not go to ground but should go to the bottom end of an extra cathode bias resistor (perhaps ~2k but that's a guess - you need to calculate it) that should be placed between the tube's cathode and the 50k cathode load resistor R7. There is no need to change the value of R7.

(b) the 2k pot R1 in the tail of the 6J6 differential amp driver. If you reduce the value of that pot too far, you'll damage the 6J6 because it will have no bias and its current will run away.

(c) the value of the driver's grid resistors R9 and R10. These seem a bit low and may place an undue load on the first stage. Increasing them to 470k and decreasing the decoupling capacitors C4 and C5 to 0.1uf might give less distortion.

(d) running in pentode mode without any negative feedback. This would cause damping to be very low (giving imprecise, woolly and boomy bass) but, hey, if it sounds good in your speaker, then OK. It would not be easy to add global negative feedback to this design but some local feedback could be added.
  Reply With Quote
Old 26th November 2006, 02:31 PM   #3
Klimon is offline Klimon  Belgium
diyAudio Member
 
Join Date: Apr 2005
Location: Leuven
Quote:
so I shot for something simple
Ever heard of single-ended?

Looks nice!

Simon
  Reply With Quote
Old 26th November 2006, 06:42 PM   #4
diyAudio Member
 
jerluwoo's Avatar
 
Join Date: Feb 2006
Location: Ashland,Ky U.S
Tried single-ended but not enough output for my taste.
Definitley overlooked the bias issue on the input tube. Was looking at basic splitter circuits on the net to determine which I was going to use, they all seem to ommit this resistor as a way to simplify things I guess. Changing grid resistors and decoupling caps on the driver inputs seemed to make the sound less full so I swapped them back. The 2k pot is adjusted for 1.5v at the cathode (or cathodes, 6j6 datasheet shows both triodes sharing a single cathode). Was unsure about how to run the 50C5's as the only schematics I could find were the dreadful ac/dc aa5 setups, so I ran it basically how those showed it with less voltage on the screens since I'm running the plates above rating.
Attached Images
File Type: jpg tube schema.jpg (90.1 KB, 381 views)
  Reply With Quote
Old 26th November 2006, 07:05 PM   #5
diyAudio Member
 
Miles Prower's Avatar
 
Join Date: May 2005
Location: USA
Blog Entries: 6
Default Re: First tubeamp, dont laugh too hard

Quote:
Originally posted by jerluwoo
This is my first attemp at building with tubes. The results were much better than I had hoped so its definitely not a failure to say the the least. Great sound out of this little beasty, better than any of the ss amps I've been listening to.
Amazing just how horrible those SS amps sound, isn't it?

Quote:

I'm well aware that I'm running the 50C5's above rating but they seem happy enough, no glowing plates or grids with the lights out. All and all a fun a rewarding little project.
Hell yeah. That's almost the ideal way to run 50C5s (or the comparable 6.3 volt version: 6CU5) get that plate voltage up, and the screen voltage down. (Vsgsg= 90Vdc so you're close enough) and they linear up nicely. VTs are tougher than transistors, so busting the specs a bit won't do any harm.

I have a tenative 50C5 design as well, however, it looks like I'm gonna have to learn to wind my own OPT since the stock OPT for 50C5 amps SUX, and I can't seem to be able to locate a really good one.

Oh well.
Attached Images
File Type: jpg 50c5-amp.jpg (33.5 KB, 401 views)
__________________
There are no foxes in atheistholes
www.dolphin-hsl.com
  Reply With Quote
Old 27th November 2006, 01:29 PM   #6
diyAudio Member
 
Geek's Avatar
 
Join Date: Sep 2004
Default Re: Re: First tubeamp, dont laugh too hard

Hi Miles,

Quote:
Originally posted by Miles Prower
I have a tenative 50C5 design as well, however, it looks like I'm gonna have to learn to wind my own OPT since the stock OPT for 50C5 amps SUX, and I can't seem to be able to locate a really good one.
Contact Planet10.... he might have a few goodies for those little gems
  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
New tubeamp Tekko Tubes / Valves 14 2nd May 2010 04:54 PM
se tubeamp with px4 sonix Tubes / Valves 1 10th July 2004 09:14 PM
you gotta laugh theChris Everything Else 1 11th March 2004 06:13 AM
More on IP: check this out and have a laugh! grataku Everything Else 1 7th March 2004 08:44 PM
Please dont laugh Scribble Pass Labs 1 14th January 2003 07:21 AM


New To Site? Need Help?

All times are GMT. The time now is 03:59 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