~ VALVES for SALE ~ March 2021 ~

Valve box images you will see elsewhere as they are stolen from this site

For years this section of my web site listed thermionic valves for sale and I still have many 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 NOS or lightly used but may have logos rubbed due to handling and are not in manufacturers original boxes but they are all good quality items

Valve box images you will see elsewhere as they are stolen from this site

Refreshing the listings and trying to keep them in line with ebay and other 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

~ I sometimes buy Valves and can test Valves for you ~

When measured using the correct method and reference data valves should not be described as testing STRONG or more than 100% ~ This suggests that the valve is conducting more anode current Ia than it should for the specified negative control grid voltage Vg1 and indicates that the static gain may be out of specification

At a higher Ia than specified the gm will also be higher but this greater than 100% mutual condition may not be achieved in practice with auto–bias or even desirable for some designs ~ Valves sold by others as testing more than 130% should be considered out of spec but according to most manufacturers and valve meters a correctly measured gm of –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 when the valve is fully hot and are often overlooked so when purchasing from places like ebay you should check that they have been measured

The AVO 163 Valve Characteristic Meter provides for measuring the screen grid current Ig2 and 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 gm are almost non existent due to bad alignment between g1 and g2 which prevents these and similar copy KT66 valves from performing correctly in circuits like the QUAD II and some 'Ultra Linear" designs but they are often okay when triode connected

When testing valves like a CV5112 that have high gm >10 it is often difficult to get meaningful readings with many valve testers and some give over optimistic results ~ For high gm valves and also other valves the most meaningful test is the gm measured at a particular Ia ~ When the specified Ia is achieved at very low Vg1 for a high gm valve then Vg1 value is not important and in practice these valves should be run with constant anode current

For an explaination of the codes used by some valve manufacturers see here

Dynamic testing and comparison of valves using a TEK 576 curve–tracer

This level of testing will often show differences in valves that are not obvious from the single point Ia and gm testing available with a valve tester — It also shows that many modern equivalent valves DO NOT exactly follow the characteristics of the original items which may explain reported differences between good NOS valves and some modern replacements

Testing valves for Beard Audio repair service        Beard Audio repairs schematics plot

See also

QUAD Hi-Fi Valve data Sheets Valve Audio Articles Component Colour Codes

"Got a case of dynamite ~ I could hold out here all night"