Klausmobile Tube Tester Files
Reflector (Saratov), 12/1972 - Closed box plate type. Referred to as ECC88 clone. There are two designs of this tube that I know: one has box-shaped plate, consisting of two Pi-shaped halves, closed on all four sides. These tubes were marked with Reflector logo, dated 1970. The other type (Voskhod Kaluga logo, dated 1980-s) has a Pi-profile plate, missing one side so the grid/cathode assemblies are visible. Today, I checked 8 unused tubes of both varieties, dated 1971 to 1985, and 7 of them measured surprisingly close to each other and the tubes' halves were also close. Unfortunately, one was emitting weakly, just opening at zero grid level. So what, at 1/4 dollar a piece it's not a great loss.
However, none of the tubes ever came close to the operating point's Ug, that is, specified Ua/Ia is achieved at -4 .. -3V grid level not ar -9V specified. Even more confusing are Vade Mecum numbers for ECC88 (Ug=-1.2V for 90V/15mA through plate).
|Standard specifications per each triode|
|Parameter||Maximum||Operating Point||Measured - 12/1972 tube|
|Ua, V||+300 open -470 closed||100||100|
|Ia, mA||20 continuous 200 pulse||15 (10..20)||15|
|Gm, mA/V||-||10 .. 12.7||10.6|
|Rp, kOhm||-||(2.0 .. 4.6)||3.3|
|Mu, V/V||-||34 (25..43)||33|
Looking at the curves, you see that standard 15mA/100V (Ug=1V) is too close to where grid begins conducting - why not shift it to lower Ug?
1. Curve at normal Uheater, full operating power
2. Same at Uheater=5V. S,Mu,Rp are identical, only grid levels shift by 1/4V.
3. Closer look at specified operating point (normal Uheater)
4. 8mA closeup
5. As the hybrid amp first published
6. Gm/Mu/Rp measurements. Very consistent for all 7 tubes I checked, despite different plate designs.
Legend: White curves: Ig<5uA Yellow: 5<Ig<20uA Red: 20<Ig<300uA. Measurements terminate at Ig>300uA
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