If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated recently. Green bold denotes those who have recently donated to keep the server carbon neutral.
Special Thanks To:
Aaron Holmes
Aaron Wheeler
Adam Horden
Alan Scrimgeour
Andre
Andrew Haynes
Anonymous000
asabase
Austin Weil
barney
Barry
Bert Hickman
Bill Kukowski
Blitzorn
Brandon Paradelas
Bruce Bowling
BubeeMike
Byong Park
Cesiumsponge
Chris F.
Chris Hooper
Corey Worthington
Derek Woodroffe
Dalus
Dan Strother
Daniel Davis
Daniel Uhrenholt
datasheetarchive
Dave Billington
Dave Marshall
David F.
Dennis Rogers
drelectrix
Dr. John Gudenas
Dr. Spark
E.TexasTesla
eastvoltresearch
Eirik Taylor
Erik Dyakov
Erlend^SE
Finn Hammer
Firebug24k
GalliumMan
Gary Peterson
George Slade
GhostNull
Gordon Mcknight
Graham Armitage
Grant
GreySoul
Henry H
IamSmooth
In memory of Leo Powning
Jacob Cash
James Howells
James Pawson
Jeff Greenfield
Jeff Thomas
Jesse Frost
Jim Mitchell
jlr134
Joe Mastroianni
John Forcina
John Oberg
John Willcutt
Jon Newcomb
klugesmith
Leslie Wright
Lutz Hoffman
Mads Barnkob
Martin King
Mats Karlsson
Matt Gibson
Matthew Guidry
mbd
Michael D'Angelo
Mikkel
mileswaldron
mister_rf
Neil Foster
Nick de Smith
Nick Soroka
nicklenorp
Nik
Norman Stanley
Patrick Coleman
Paul Brodie
Paul Jordan
Paul Montgomery
Ped
Peter Krogen
Peter Terren
PhilGood
Richard Feldman
Robert Bush
Royce Bailey
Scott Fusare
Scott Newman
smiffy
Stella
Steven Busic
Steve Conner
Steve Jones
Steve Ward
Sulaiman
Thomas Coyle
Thomas A. Wallace
Thomas W
Timo
Torch
Ulf Jonsson
vasil
Vaxian
vladi mazzilli
wastehl
Weston
William Kim
William N.
William Stehl
Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
Registered Member #2628
Joined: Fri Jan 15 2010, 12:23AM
Location:
Posts: 627
Ive got this small tube, and after finding out a little bit about the pinout (found the heater, which I belive to be directly heated) however, this tube has no part number, no markings at all, at one point they where probably there, but now they are gone from age, I had an idea to try to follow the anode connection and apply variable voltage from a limited supply up to 200VDC, but before I risk it, Id like to hear some of your opinions and inputs, to either a better method of figuring out the voltage, or if anyone knows the range of the voltage ratings for a tube like this. (if I helps, it came from a 220V furnace control unit)
EDIT: nevermind everyone, Ive figured this out a little bit after I post this, turns out that on the underside of the frame, the part number of the tube was scratched, this thing is a dual triode part number 12AX7 and it is also indirectly heated
Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
Normally you can tell what sort of tube you have by looking at the internal structure. If the tube's indirectly heated, you will see the cathode on top and if it's directly heated, you will see the filament or the lack of cathode connection. It's a triode if there is only one pair of grid posts (the things surrounding the cathode supporting the grid). It's a tetrode if there are two pairs. It's a pentode if there are two pairs and two metal tabs or just three pairs of grid supports. Sometimes you can find the pinout of the tube by following the element connections down to the base. The 12AX7 is a very common dual triode (as you have found).
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
The data sheet for General Electric's take on 12AX7 even has a pre-calculated component value table and a recommended circuit diagram, so you don't even have to do any calculation to use it as a resistance-capacitor coupled voltage amplifier if you don't want to.
A peek at the characteristic curves in the data sheet shows that useful, fairly linear, operation for 12AX7 begins at about 50V anode voltage, though 100V is the recommended minimum. You could get it to perform after a fashion with as little as 25V, and maybe less, on the anode.
Be sure to put it in a screening can if you use it as a high gain amplifier - which means a voltage gain of 50 or so in this case - or it will pick up EMI, directly demodulate strong local signals, start to oscillate as a protest against sloppy wiring, and other mischief.
Think of it as two completely separate triodes in the same envelope, rather than the very common double triode with common kathode, which has far more limited options. You can have a lot of fun with a versatile little valve like this.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
The -A suffix denotes a special heater warm up feature to integrate the valve into the series heater chains almost universally used in domestic televisions, except for the very early years. The idea was to delay the operation of the valve by a few seconds, so that it didn't start doing its thing until all the other valves were ready.
Its main role seems to have been as a vertical deflection amplifier, so you could get some big swings in the anode voltage if you wanted to.
In Tung-Sol's 12BH7 data sheet, they even throw in their recommended vertical deflection amplifier circuit, and you'll see that you could wire both triodes in parallel and substitiute a step-up transformer for the step-down transformer in the anode circuit if you wanted to, without having to make many other circuit changes.
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
Interesting relay on that controller; also the contacts on the sequencer are rated to switch the primary of the ignition transformer and the fan motor.
Tou have enough parts on the board to make a preamp for a guitar.
What do you think would happen to the furnace if the 12BH7 tube and 12AX7 were exchanged by mistake?
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.
Determining anode voltage of unknown tube
