Mike Kropotkin of KCA N.O.S. Tubes and Amplifier Repair has a large selection of high quality New Old Stock tubes. Everything from the coveted Mullard GZ34 rectifier tubes to Tung Sol 5881’s. Current production tubes are also on the stock list. All tubes are burned in for 48 hours and output tubes are digitally matched for both mutual conductance (within 5%) and current draw (within 3mA but usually closer @ Vplate ~= 400Volts) on a Maxi-Matcher. Closer matching is available on request. All output tubes are tested in a guitar amp for matching, noise and microphonics. Preamp tubes are tested for gain, noise and microphonics on a VTV Triode Characteriser. Balanced triodes on preamp tubes are available upon request. KCA also specilaizes in repair and modification of Fender amps from the 1950’s-1970’s, Marshall amps from the 1960’s-1970’s, Traynor, Gibson, Ampeg and Dynaco ST-70 amplifiers. They are located in Sterling, Virginia and their website has many useful resources for tube guitar amp enthusiasts. Credit: KCA N.O.S. Tubes.