Low voltage tubes - 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 23rd March 2005, 04:55 PM   #1
cozza is offline cozza  Italy
diyAudio Member
 
Join Date: Mar 2005
Location: italy
Default Low voltage tubes

Someone have practical experience in using ECC88, 12AX7 or similar tubes with low cathode voltage (40-50V) ?.

Thanks
  Reply With Quote
Old 23rd March 2005, 05:38 PM   #2
diyAudio Member
 
Shoog's Avatar
 
Join Date: Aug 2002
Location: Eire
Hi there,
The ECC81 works really well at very low voltages in the Musical Fidelity X10D valve buffer. There are copies of the circuit on the net somewhere. The wall socket supply is just 12VAC. Must use some sort of voltage doubling.

Joe Rasmussens Valve buffer for the Gainclones works reasonably well at +/-35V. My experience is that it improves with increased voltages. I personnal am running the ECC85 at 85V and am quite satisfied with the results.
  Reply With Quote
Old 24th March 2005, 08:23 PM   #3
diyAudio Member
 
Shoog's Avatar
 
Join Date: Aug 2002
Location: Eire
Correction to the above, the X10D uses ECC88's, as does my own preamp with 85V rails.
Sorry for the mistake, my brain must have been on low voltage.


Shoog
  Reply With Quote
Old 27th March 2005, 07:00 AM   #4
PRR is offline PRR  United States
diyAudio Member
 
PRR's Avatar
 
Join Date: Jun 2003
Location: USA
> tubes with low cathode voltage (40-50V)?

Surely you mean low anode voltage?

To a rough approximation, a tube is a resistor. If you can work it at 100V 1mA, you can work it at 10V 0.1mA. The problem is that tubes are all high resistance so the available power gets very small at low voltages.

To a better approximation, many tubes have a "bend" at around 50V on the plate, and at lower voltages the plate resistance doubles. So 10V might only allow 0.05mA.

At very low voltages, 1 or 2 volts, you get into "contact potential" effects. But in any practical audio use, you just can't get any useful output at such low voltages.

To run 35V-50V, just try it. Be prepared to increase the plate resistor, and accept that the output will be weak. If self-biased with a cathode resistor, you probably won't have to change the cathode resistor much or at all. If fixed-biased, change the grid voltage in proportion to anode voltage.

For best results, look for tubes with high current at low anode voltage. Many of the "TV Tuner" tubes are very good, since they had to run VERY high current for high gain and low noise, yet could not waste a lot of heat so they were worked with low anode voltage. Such tubes were often run 100V 10mA, and will often run 50V 4mA or 30V 2mA.

> My experience is that it improves with increased voltages.

This is my experience too. While any tube "can" be run at low voltage, and might be "OK", they almost always "sound" better if you crank them up almost to melting. Both voltage and current (being sure you have plenty of swing as well as bias). I don't understand the fashion for starving tubes. You may as well use a 741 chip for sound and an underpowered light bulb for glow.
  Reply With Quote
Old 27th March 2005, 07:31 AM   #5
Giaime is offline Giaime  Italy
diyAudio Member
 
Giaime's Avatar
 
Join Date: Oct 2004
Send a message via MSN to Giaime
Quote:
Originally posted by PRR
You may as well use a 741 chip for sound and an underpowered light bulb for glow.
Ah! That would make sense... At least you don't have to search for NOS or military-grade bulbs!

At what about fluorescent lights? I read somewere that they give a brighter tone...
  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
Cathode stripping in low voltage tubes engels Tubes / Valves 1 26th March 2008 04:05 PM
A use for those old voltage regulator tubes zigzagflux Car Audio 0 22nd July 2007 09:01 PM
Voltage Regulator Tubes dsavitsk Tubes / Valves 5 27th March 2007 10:01 PM
mid voltage tubes? theChris Tubes / Valves 2 18th November 2003 09:52 AM
low voltage tubes (6GM8 and 12DL8) needtubes Tubes / Valves 28 17th July 2003 09:09 PM


New To Site? Need Help?

All times are GMT. The time now is 12:36 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