Testing tubes before send

freq sniffer tube

 The 2-01C was the old probe diode, going all the way back to the first (1948) HP 410A high frequency VTVM. It was original equipment on the 410B's until the early 1960s. However, it apparently became unavailable about that time, and HP switched to the EA53. The EA53 was used on the later 410B's and all 410C's, and was sold in a retrofit kit if somebody ordered a replacement for the earlier tube. The EA53 is nearly a direct replacement for the 2-01C except for two things:

The EA53 is physically shorter, so when used as a replacement for a 2-01C, the aluminum extension contact and spring seen on your tube (which came in the retrofit kit) had to be installed. Later probes originally equipped with the EA53 don't use the contact or spring.

Both tubes are available  

 The 12BY7, 12BY7A, 12BV7 and 12DQ7 are all the same. They are a miniature type used as a video amplifier in TV receivers. They are used in Harmonic Distortion Meters, Oscilloscopes and Monitorscopes. They are also used quite extensively in Short Wave radios. They require a miniature 9-contact socket.

 7788 is a high transconductance pentode which should in theory be able to give higher audio resolution than say 12AX7, 6072 tubes in tube mic pre designs.

The 6DJ8 is a frame grid sharp cut-off twin (dual) triode with separate cathodes originally intended for use 
as a cascode circuits, RF and IF amplifiers, mixer and phase inverter stages.  Originally the 6DJ8 had
popular applications in:  tuners in television receivers, front ends of VHF radio receivers.  One triode acted
as the local oscillator and the other as the mixer (frequency changer).  Tektronix test equipment.
Although not designed for the purpose the ECC88 has found favour with builders of high performance audio 
equipment.  The tube features high transconductance, low plate resistance and low noise properties.

PCC88=7DJ8 can be substituted for the 6DJ8/ECC88
6N23P=Russian made 6DJ8/ECC88
6N1P subs are 6922 and 6DJ8

Heater voltage 6.3V 
Heater current 365mA 
Max plate voltage (Ia=0) 550V 
Max operating plate voltage 130V *
Max plate dissipation 1.8W 
Max plate current 25mA 
Max grid voltage -50V 

Heater = 6.3
Heater Current = 365ma
Vplate = 90V
Vgrid = -1.2V
Iplate = 15ma
Rplate = 2650 ohms
Gm = 12500 
Mu = 33

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