Box of old tubes - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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 13th October 2015, 10:42 AM   #1
diyAudio Member
 
gmonno's Avatar
 
Join Date: Jul 2004
Location: Madrid
Default Box of old tubes

Hi all, for a chain of coincidences (the father of a friend who was cleaning in his old house..) I have received a box full of old tubes, there were a number of them…so all the weekend was devoted to cleaning and classifying all of them.
A lot had no name, erased by age and dust, but most were classified.

Attach a photo of the box as I received and a txt with a list of names, seem that are from old TV.

Now I have the following questions that surely the expert will be able to answer :

1) Which of them are useful? Which are worthless?
2) I don’t owe a tube tester nor an oscilloscope, only a multimeter, are there some checks to differentiate between the good and the bad ones? For example I understand that checking for continuity of the filament can be done, but what more?


Thanks a lot, hope to give these tubes a new life
Attached Images
File Type: jpg Tubes.jpg (507.9 KB, 260 views)
Attached Files
File Type: txt Tubes list.txt (968 Bytes, 104 views)
__________________
giuseppe (madrid)
  Reply With Quote
Old 13th October 2015, 10:56 AM   #2
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Cleaning may have removed much of the marking, as this was often fragile even on new valves. Best to identify them before cleaning. Some may have a code near the base which can still be used to identify them.

Most of them look like they have done long service in a TV receiver, so may have little life left. You can check for heater continuity, but to do much more with just a multimeter would require reading of datasheets to set up a temporary test circuit.

For the European valves you can learn something about their purpose from the name. For example, C means a small signal triode, F means a small signal pentode, L means a power pentode. Lists are available online.
  Reply With Quote
Old 13th October 2015, 11:45 AM   #3
Tesla88 is offline Tesla88  Italy
diyAudio Member
 
Tesla88's Avatar
 
Join Date: Dec 2011
Location: Italy
Quote:
Which of them are useful? Which are worthless?
It depends on your goals, receivers , transmitters , Instrument amplifier , HiFi...

You have quite a good list, problem is tubes are not tested and you need a tube tester or a test circuit , otherwise you can only check for filaments...

I would buy them for cheap, since i enjoy this kind of things but if you want to start a project maybe is better to start with new / tested parts, expecially if you're a beginner !

Regards
  Reply With Quote
Old 13th October 2015, 11:52 AM   #4
diyAudio Member
 
Join Date: Feb 2010
Location: Helsinki
There's a bunch of types that are very good, like the 6DQ6; the problem is you only have one or two of most of those types. Not enough for a stereo amp.

The triode-pentode tubes at the bottom of the list are good for audio amps and you have plenty of them. Four PCF80 will make a nice balanced amp.
  Reply With Quote
Old 13th October 2015, 12:33 PM   #5
diyAudio Member
 
gmonno's Avatar
 
Join Date: Jul 2004
Location: Madrid
Quote:
Originally Posted by MrCurwen View Post
There's a bunch of types that are very good, like the 6DQ6; the problem is you only have one or two of most of those types. Not enough for a stereo amp.

The triode-pentode tubes at the bottom of the list are good for audio amps and you have plenty of them. Four PCF80 will make a nice balanced amp.

Thanks Mr Curwen
About testing tubes, is there a way apart from buying a tube tester?
__________________
giuseppe (madrid)
  Reply With Quote
Old 13th October 2015, 01:16 PM   #6
diyAudio Member
 
Join Date: Feb 2010
Location: Helsinki
gmonno, well what I do is I set up a testing circuit; a gyrator plate load (which sets the plate voltage) and variable negative grid bias. Cathode grounded via 1 ohm resistor.

Look up datasheets and check recommended typical operation values. Set the plate voltage via the gyrator, and grid bias voltage. Then using the millivolt meter over the 1 ohm resistor write down the current. It should be close to datasheet specs. Then test a bunch of the same type tubes, and see how they compare. If some are off a lot, they might not be so good.

While doing this remember that datasheet values were very conservative. I've found many NOS tubes have lower plate resistance than spec'd, hence a bit more (maybe +10%) current than they should doing this kind of test.
  Reply With Quote
Old 13th October 2015, 01:41 PM   #7
diyAudio Member
 
gmonno's Avatar
 
Join Date: Jul 2004
Location: Madrid
Quote:
Originally Posted by MrCurwen View Post
gmonno, well what I do is I set up a testing circuit; a gyrator plate load (which sets the plate voltage) and variable negative grid bias. Cathode grounded via 1 ohm resistor.

Look up datasheets and check recommended typical operation values. Set the plate voltage via the gyrator, and grid bias voltage. Then using the millivolt meter over the 1 ohm resistor write down the current. It should be close to datasheet specs. Then test a bunch of the same type tubes, and see how they compare. If some are off a lot, they might not be so good.

While doing this remember that datasheet values were very conservative. I've found many NOS tubes have lower plate resistance than spec'd, hence a bit more (maybe +10%) current than they should doing this kind of test.

Sorry...a gyrator plate load is a variac or variable transformer?
__________________
giuseppe (madrid)
  Reply With Quote
Old 13th October 2015, 02:07 PM   #8
diyAudio Member
 
Join Date: Feb 2010
Location: Helsinki
No. Example schematic attached.

R3 is a trimmer pot, and R10 is connected to the pots wiper. R10 value is not critical, anything above 1M is fine. C2 value is not critical, anything above 100nF is fine. R7 can be 470 ... 1k ohms.

When setting up the test;

1) tube not yet in socket, power on; set the bias voltage "too high", so tube will be initially cut off

2) power off, put tube in socket

3) power on, set plate voltage with the trimmer, about 5 to 10 volts higher than specs

4) then adjust bias to spec

5) check and readjust plate voltage

6) when bias and plate are just about spec, check the voltage over 1 ohm cathode resistor. Write down and compare to specs.

7) leave the bias and plate voltages where they are, and test a bunch of other tubes of the same type. Compare results, find deviant ones.

This is a crude test, but will give you a pretty good idea which tubes might be bad and which ok. Also rudimentary matching can be attempted.
Attached Images
File Type: png gyrator.png (5.7 KB, 212 views)
  Reply With Quote
Old 13th October 2015, 02:40 PM   #9
diyAudio Member
 
Tom Bavis's Avatar
 
Join Date: Jun 2002
Location: Macedon NY
You can build a small stereo amp using just two ECL86 or PCL86 - about 2-3 watts per channel. Same tube except for heater voltage. ECL uses 6.3V for the heater, PCL is 14, but should be fine on 12.6V. This tube has a high gain triode plus a power pentode in one bottle. The American number for ECL86 is 6GW8, so you could Google for "(ecl86, PCL86,6gw8) amplifier" and find numerous circuits.
  Reply With Quote
Old 13th October 2015, 03:11 PM   #10
diyAudio Member
 
gmonno's Avatar
 
Join Date: Jul 2004
Location: Madrid
Thanks Tom
__________________
giuseppe (madrid)
  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
Picked up a box of tubes for $5.. What tubes are usable? timkoh Tubes / Valves 5 2nd February 2015 01:36 PM
Box of tubes john65b Swap Meet 17 18th June 2013 06:26 PM
Box of tubes mworks Swap Meet 9 4th December 2012 04:24 PM
Triad New in Box NOS Tubes pwdiya12 Swap Meet 4 28th September 2012 07:57 PM
Big Box O' Tubes bigjppop Tubes / Valves 5 30th September 2009 04:47 PM


New To Site? Need Help?

All times are GMT. The time now is 12:09 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2016 DragonByte Technologies Ltd.
Copyright ©1999-2016 diyAudio

Content Relevant URLs by vBSEO 3.3.2
Wiki