Triode Mode; Tube Substitution - Mapletree Stealth Max User Manual

Max . Lowest distortion is obtained using a matched pair to achieve identical bias currents
in both tubes. The 6SJ7 metal small signal pentode was designed for audio use, offering
low noise and high gain. The glass 6SJ7GT can be substituted without change in
performance. The special red series 5693 can also be directly substituted and offers the
potential for very long life (10,000+ hrs). No currently manufactured versions are
available but NOS tubes are readily available from large tube suppliers and on ebay. The
6SN7GT is a dual high mu triode. It is currently manufactured in Russia and available
under the Electro Harmonix brand and others. NOS versions are not hard to find but the
supply is limited. The special red equivalent is the 5691. The rectifier tube can be any
GZ34/5AR4 type.
You may be told that the 6550 power tube can be substituted for the KT88. With its lower
screen grid voltage rating, the 6550 is not recommended for the Stealth Max with its 500
V screen potential operating in either ultra-linear or triode mode.
Triode Mode – The toggle switch located next to the
KT88 tubes permits changing the output tube
configuration from ultra-linear to triode mode. You
can switch "on the fly" and determine which mode
suits your sonic preferences. The maximum power
output in triode mode is around 20 W.

Tube substitution____

Any vintage or currently manufactured pair of KT88
beam tetrode power tubes can be used in the Stealth
5