Source for least expensive 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
Thread Tools Search this Thread
Old 15th September 2014, 04:33 PM   #1
cmerdan is offline cmerdan  United States
diyAudio Member
Join Date: Sep 2014
Location: Avon, MN USA
Default Source for least expensive tubes.

Where can I find a 12SL7 tube for my Heathkit A7 amp?
  Reply With Quote
Old 15th September 2014, 05:17 PM   #2
diyAudio Member
smoking-amp's Avatar
Join Date: Dec 2001
Location: Hickory, NC
$4 here:

Electron Tube List range 12A - 12Z5 @
Without MS, how would we live without all those hackers?
  Reply With Quote
Old 15th September 2014, 05:27 PM   #3
diyAudio Member
KatieandDad's Avatar
Join Date: Nov 2011
Location: UK
cmerdam - where are you living ?
  Reply With Quote
Old 15th September 2014, 05:44 PM   #4
tomchr is offline tomchr  United States
diyAudio Member
tomchr's Avatar
Join Date: Feb 2009
Location: Greater Seattle Area is another good source. There's always that auction site...
Modulus-86: Composite amp achieving 0.00018 % THD. Damn Good 300B, Novar Spud, 21st Century Maida Reg., Filament Reg., etc.
Neurochrome : : Audio - - Engineering : : Done : : Right
  Reply With Quote
Old 16th September 2014, 01:14 AM   #5
diyAudio Member
Join Date: Feb 2010
Location: Helsinki
Cheapest solution: get a NOS russian 6N8 tube, and put two 10 ohm 2W resistors in series with it's heater. =)
  Reply With Quote
Old 16th September 2014, 02:36 AM   #6
RTF671 is offline RTF671  United States
diyAudio Member
Join Date: May 2008
Location: North Carolina, USA
If you were brave you could rectify it for just that tube and use a zener to drop the voltage across the heater. You'd get the benefit of a quieter tube too.

Just a random passing thought! ;D
Otherwise the resistor will drop your voltage for the heater just as well.
  Reply With Quote
Old 16th September 2014, 04:02 AM   #7
kevinkr is offline kevinkr  United States
diyAudio Moderator
kevinkr's Avatar
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
I'm fairly familiar with the A-7, and running a 6SL7 with a dropping resistor given the increased filament current is probably not a good idea - the stock power transformer is hanging on by a thread.. The 12SL7 is very cheap here, it has not attained collector status because of the filament voltage. The OP appears to be located in the U.S.
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 16th September 2014, 04:37 PM   #8
diyAudio Member
Palustris's Avatar
Join Date: Aug 2006
Location: Cape Cod
Antique Electronic Supply
  Reply With Quote
Old 16th September 2014, 05:46 PM   #9
GoatGuy is offline GoatGuy  United States
diyAudio Member
Join Date: Dec 2012
Location: SF Bay Area
You know, the "cheap solution" for using 6 volt tubes as substitutes for 12 volt tubes is to do 2 things:

Full-wave bridge rectify the 12.6 VAC winding (this drops the 1.414 12.6 = 17.8 peak voltage by 20.7 = -1.4 volts. 16.4 volts - if you use a 2,200 F 25 V electrolytic to smooth things out. Now, string downwind of that 5 or 6 of the standard 3 amp 100 PIV silicon diodes in series. That'll drop the DC to 12 volts, for all the 12-volt tube filaments. Now another string of 8 diodes, to get the 6 volt needed for the 6-volt substitution tubes.

Sounds like a lot of diodes? Nah... they're less than 3 cents each. Further, having a bunch of 'em in series takes care of the power-dissipation problem. Each is capable of about 2 watts (0.75 volts times 3 amps = 2.25 watts). So, having 8 in series is like having a 18 watt resistor up there.

Sometimes the "old, simple solutions" are warranted. Oh, sure, you could put in a fixed-value regulator, and a heat sink, and ... and ... and ... but why? Its just a heater circuit, dude!


PS: if you go this route, say, "on the test-bench" ... don't forget to LOAD the 6-volt output with a nice resistor between 5 and 25 ohms. It is only under load that the diodes have a voltage-drop of nearly-constant 0.75 volts, nominal. If you leave it open, the voltage will drift up to near-12 volts! A life of dealing with quixotic semiconductors uncovered this truth some 45 years ago, to me.

Five things matter in audio LED underlit tubes, gold connectors bearing bright plastic ID bands, speaker cable thicker than your thumb, a hundred pounds of granite under the turntable, and those little spikey-things under the speakers.

Last edited by GoatGuy; 16th September 2014 at 05:49 PM. Reason: caveats, quixotic semiconductors, loads, etc.
  Reply With Quote


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
Source for SED "winged C" tubes? dgta Tubes / Valves 5 29th October 2011 06:32 PM
Just WHY are DHT tubes SO Expensive....? Alastair E Tubes / Valves 17 8th March 2011 06:03 PM
Good Source for NOS tubes for guitar Daveis Instruments and Amps 1 29th May 2007 03:09 PM
Source of tubes & associated stuff in Sydney? ray_moth Tubes / Valves 9 6th February 2006 11:04 PM

New To Site? Need Help?

All times are GMT. The time now is 02:35 PM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2015 DragonByte Technologies Ltd.
Copyright 1999-2015 diyAudio

Content Relevant URLs by vBSEO 3.3.2