Tung-Sol 5881 Reissue - PAIR-

It's hard to escape the sound of the G12H, just listen to any Hendrix recording and chances are you'll be hearing a whole raft of them powering the guitar out of the mix.

These faithful re-creations capture the unmistakeable mojo of late 60s rock guitar tones. Unsurpassed in a 4x12 for cranking out towering, huge power chords, the Heritage Series G12H (55) features the 55c/s 'bass' cone. This model is famous for its thick syrupy tones, with a deep growling back end, densely complex mid-range and a finely detailed top end.

General Specifications

• Nominal diameter: 12", 305mm
• Power rating: 30Wrms
• Nominal impedance: Available 8Ω or 15Ω
• Sensitivity: 100dB
• Chassis type: Pressed steel
• Voice coil diameter: 1.75", 44.5mm
• Magnet type: Ceramic
• Magnet weight:50oz, 1.42kg
• Frequency range: 55-5000Hz
• Resonance frequency, Fs: 55Hz
• DC resistance, Re: 6.53Ω and 12.11Ω

• Cut-out diameter: 11.1", 283mm
• Diameter: 12.2", 309mm
• Magnet structure diameter: 6.6", 168mm
• Mounting slot PCD: 11.7", 297mm
• Number of mounting slots: 4
• Overall depth: 5.3", 135mm
• Unit weight: 10.4lb, 4.7kg

Kit of a bias probe for indirect measurement of the quiescent bias current of a tube. The adapter is placed between the tube and the socket and is connected to a standard voltmeter (not included). Pay attention to the quality of the meter and to sufficiently charged batteries!

The quiescent current is measured indirectly via a precision resistor built into the adapter. The advantages of this measuring method are harmless voltages in the mV range at the measuring plugs as well as short ways for the current, since it does not have to be led through the measuring device (common practice with many measuring adapters of Far Eastern production). As a result, there is no risk of oscillation of the amplifier, which could damage the tubes or the amplifier itself.

Note: This adapter cannot be used when additional tube brackets are installed. These must be removed before using the measurement adapter and reattached after the measurement is complete.

Measurement procedure
Determine the resistance of the adapter, including the test leads. Connect the adapter to the meter, but do not connect it between the tubes and the amplifier. Select the ohms range on the meter and note the reading, e.g. 1.1 ohms.
For the final measurement, insert the adapter between the tube and the de-energized amplifier, connect it to the meter, select the mV range and switch on the amplifier. When the amplifier has reached a stable operating condition, read the value in mV from the meter and calculate the quiescent current using Ohm's law.

Example
Measured voltage = 47 mV, adapter resistance = 1.1 ohms.
Formula (I = V / R) or in this case
Bias Current (in A) = Measured Value (Voltage in V) / Measured Value (Resistance in Ohm)
0.047V / 1.1 Ohm = 0.042A or 42mA

For the calculation of the correct bias current as well as further information on bias measurement please refer to further documents or the bias setting instructions in the info section as well as the manual of the amplifier itself.
This adapter is suitable for all EL34, 6L6, 6550, KT88, 6V6, 6CA7 and other tubes with the same pinout.

Attention HIGH VOLTAGE ! Measurements and work on tube amplifiers should only be done by qualified personnel.

Files:

• Datasheet