GU-50, GM70 and KT88 - Page 5 - 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 24th September 2012, 02:53 PM   #41
palmas is offline palmas  Portugal
diyAudio Member
 
Join Date: Jun 2007
Quote:
Originally Posted by Wavebourn View Post
450V B+, 510 Ohm 10W cathode bias resistor shunted by 50 uF 100V capacitor; 2K 100 MA OT; 100 Ohm screen grid stopper connected to anode; G3 connected to cathode; 220K grid leak resistor to the ground (may be higher due to autobias).

That's it.

Can you draw it now?
Thanks, for the suggestion, it'll be a good starting point for tryal of my PSE.
Will also try 480V and 45mA per tube.

You prefer the GU50 with self bias over fixed bias?
  Reply With Quote
Old 24th September 2012, 04:43 PM   #42
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
Quote:
Originally Posted by palmas View Post
You prefer the GU50 with self bias over fixed bias?
I mean single ended. Self bias means negative feedback by DC current, so you don't need to measure and adjust bias. The tube will do it for you. However, for parallel SE it would be better to have the way to adjust bias for each tube, but anyway it is better to select tubes for parallel operation.
__________________
"Our youth [...] have bad manners, contempt for authority; they show disrespect for their elders, contradict their parents, [...] and tyrannize their teachers. -- Plato, 447-367 BCE
  Reply With Quote
Old 25th September 2012, 01:26 PM   #43
palmas is offline palmas  Portugal
diyAudio Member
 
Join Date: Jun 2007
Quote:
Originally Posted by Wavebourn View Post
I mean single ended. Self bias means negative feedback by DC current, so you don't need to measure and adjust bias. The tube will do it for you. However, for parallel SE it would be better to have the way to adjust bias for each tube, but anyway it is better to select tubes for parallel operation.
I'm aware of what it is, but having to decide and as in my experience most tubes sound better with fixed bias, I was wondering about your suggestion.

Even with fixed bias I always add a bit of "self bias", even if it is just to measure current and stabilise the DC part.
When in parallel it is usefull to be able to adjust bias independent for each tube, as it gives more latitude on pairing the tubes.

If you have some experience on using the GU50, I'd like to profit from it, as I'm building a PSE with 2xGU50 into a LL1620/90.
PSU is about 480V (I can reduce it replacing the rectifier tube or using some stabilising circuit). I think 480V is too much for triode GU50 and to little for pentode, but as I will only be using each tube at 45mA, the grid current will not aproach the limit of 5mA. Can you help me on this?
  Reply With Quote
Old 26th September 2012, 04:06 PM   #44
diyAudio Member
 
torrence's Avatar
 
Join Date: Feb 2008
Location: Oregon
Quote:
Originally Posted by Wavebourn View Post
450V B+, 510 Ohm 10W cathode bias resistor shunted by 50 uF 100V capacitor; 2K 100 MA OT; 100 Ohm screen grid stopper connected to anode; G3 connected to cathode; 220K grid leak resistor to the ground (may be higher due to autobias).
Hi Wavebourn,

I have been playing with GU50 Triode curves for a while now, and it really looks like a 3.5k-5k transformer gives better power output with lower distortion, especially sitting at a quiescent point around 80mA at 400V. I have noticed in these forums that you typically advocate for something lower, more like 2k. What is pushing you in this direction?

A good example is attached (not my work, swiped from here).

Thanks
Attached Images
File Type: jpg GU50 350v100ma.jpg (77.6 KB, 232 views)
  Reply With Quote
Old 27th September 2012, 05:14 PM   #45
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
I don't remember when I pushed toward 2k. Probably 2k5 for 300V B+ and 45W dissipation Anode+G2?

Edit: also if you add positive voltage on G2 curves shift left. I used +12V that I had from filament rectifier.
Attached Images
File Type: gif gu-50_penintriod_g3.gif (21.1 KB, 201 views)
__________________
"Our youth [...] have bad manners, contempt for authority; they show disrespect for their elders, contradict their parents, [...] and tyrannize their teachers. -- Plato, 447-367 BCE

Last edited by Wavebourn; 27th September 2012 at 05:37 PM.
  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
want to do PP-GM70 day Tubes / Valves 79 10th October 2011 06:30 PM
GM70 sockets? otto88 Tubes / Valves 41 7th September 2009 09:08 AM
GM70/GM70 parafeed SET? louischia Tubes / Valves 10 4th December 2008 03:12 PM
any example of SE designs using GM70? jarthel Tubes / Valves 3 31st May 2007 08:10 AM
Another Gm70 amp !! HFGuy Tubes / Valves 4 8th July 2005 08:41 PM


New To Site? Need Help?

All times are GMT. The time now is 08:14 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