Kevin Deal Talks Vacuum Tubes, Testing, and Testers

[@JA-en5xc]

Kevin seems like a great guy! Very honest about how things really are. I liked that he discussed how there are a lot of grey areas in tubes, rather than just giving "black or white" answers.

[@willwill5595]

Good show!

[@frankgeeraerts6243]

All "classic amplifiers" of MAC do NOT have an adjustable bias , you are correct ! Maybe they are only checking tubes are still OK ? ( or trying to sell you new tubes )

[@frankgeeraerts6243]

Difference between 300A and B is a different wiring of the heaters ......and indeed the price !

[@frankgeeraerts6243]

HIGH gain tubes in a PHONO input stage ........ECC808 ( very low noise , version of the 83 but different pinout, the symetrical pinout of this tube also means a better slound stage )..........ECC803s TFK.......E83CC TESLA ( original , not JJ )= same construction (span gitter ) as the 803 from TFK! Some NOS 7025 tubes ( not current;production 7025 ) All tubes in that.position should be tested in circuit , The tube socket should be dampend ! Lay out of the heater wires is critical.........as well as the noise floor of the HV..( under dynamic conditions ! ) A NOS triple mica / black plates 5751 command series of RCA ( or a Gold Brand 5751 Sylvania ) may also be a good choice... High gain is the standard choice for a tube in that position but notthe best sounding ..........the proof of the pudding is always in its eating .

[@frankgeeraerts6243]

INDEED.............dropping the heater voltage.........that's how I do it for decades. Many tubes sold as testing new or falsly sold and announced as nos wil fail this test ! The truth is what in you say .............using your ears and use/ listening to the tube in your amp.......I have some tubes into ( pre)- amplifiers that still sound fine after thirty years of duty........current production tubes mostly do not have the life expectancy of " good" nos tubes due to ecological restrictions on the use of what are considerd dangerous/poisonous /or radioactive chemicals ... ( or the loss of the ( inhouse secret chemical ) knowhow of certain brands of that era . . In lack of owning a tube tester , often the amplifier itsef can be used as a kind of tube tester ......... Just like diesel engines ...Tubes are prone and vulnerable to degradation/ mainly during their warming up time (1-2 minutes for power tubes/same after shut down - HV should be shut down before the heaters to drain the capacitors)....or when heaters are shut down while the PS has still high voltage/energy in the capacitors ( modern huge values )....( The BBC never shut their amplifiers down )... Tube life CAN be very long and extended when taken some precautions....... At WEsome tubes were operated under lab conditions for 12 years .........they were still within specification ...ex WE403 etc......some Telefunken on old radios that xere never shut down for whole days .....up to 100;000 hours ........211 stillperfect after 20.000 H.....and some tubes will fail as nothing is perfect. In my MAC 240 ( 1062) the original power tubes ( 7027A US made by -SYLV ) were replaced in 1993. In some ( mostly modern ) amplifiers the tubes will only last for ..............MONTHS.........