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For years this section of my website listed thermionic valves for sale and I still have hundreds for Sale ~ They are mainly British or US made Vintage parts which are tested to the Manufacturers or AVO 163 specification before shipping ~ They are either New Old Stock or lightly used and may have logos rubbed due to handling and may not be in the manufacturers original boxes but they are all good quality items |
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Refreshing the listings and trying to keep them in line with ebay and other crazy prices was a thankless task so I now ask ~ If you need a particular valve please contact me and I will check what I have and may be able to match the type and style of the one you need to replace if you send clear pictures of the valves you want to match ~ When Correctly Tested ~ VALVES DO NOT TEST STRONG ~
At higher anode current Ia than specified the gain gm will also be higher but this greater than 100% mutual conduction may not be achieved in practice with autobias or even desirable for some designs ~ Valves sold as testing more than 130% should be considered out of spec especially if Ia >100% with gm <100% According to most manufacturer and valve meter data a correctly measured gm of as low as 50% is still considered GOOD There are valve test conditions other than Ia and gm that also need to be tested which include cathode to heater insulation CH and positive grid current due to GAS or an imperfect vacuum ~ These measurements need to be made after some time when the valve is fully hot and are often overlooked so when purchasing from places like ebay you should check that they have been correctly measured The AVO 163 Valve Characteristic Meter provides for measuring the screen grid current Ig2 and its gain gmg2 ~ This measurement often proves very useful and can highlight problems with modern copies of classic valves like the PM Components retro look KT66 where the g2 current and gmg2 are almost non existent due to bad alignment between grids g1 and g2 which prevents these and some other tetrodes KT66 from performing correctly ~ especially in circuits like the QUAD II and some 'Ultra Linear' designs but they are often okay when triode connected
For an explaination of the codes used by some valve manufacturers see here Dynamic testing and comparison of valves using a TEK 576 curvetracerTesting with a Tektronix 576 or similar will often show differences in valves that are not obvious from the single point Ia and gm testing available with a standard valve tester It may also show that many modern equivalent valves do not follow the characteristics of the original items which may explain reported differences between NOS valves and some modern replacements |
"Got a case of dynamite ~ I could hold out here all night"