Hallicrafters SX-100

[n8fvj]

A few questions. I read the 6BZ6 is an improved RF amp tube replacing the older 6CB6. Why does the SX-100 use 6AU6 and 6BA6 mixers vs the common 6BE6. I cannot find theory of operation on the SX-100.

I am getting back into AM and found this Hallicrafter Guy rebuilt SX-100 (rebuilt in 2007). Looking for a Johnson Ranger or Ranger II.

[n8fvj]

No one knows a 6CB6 vs a 6BZ6?

[Pete, WA2CWA]

No one knows a 6CB6 vs a 6BZ6?

In your first post, you said: "I read the 6BZ6 is an improved RF amp tube replacing the older 6CB6."
It's a statement, not a question. I suspect if you review the specs for each tube, you can determine the differences.
Good place to get tube specs: https://frank.pocnet.net/

[n8fvj]

Meant to be a question.

[DMOD]

Why does the SX-100 use 6AU6 and 6BA6 mixers vs the common 6BE6...

It is not absolutely necessary to use a 6BE6 or similar mixer tube for mixing.

Looking at the schematic the V2 6AU6 is receiving amplified RF at its control grid from V1 while the cathode is being given oscillator injection generated by the V3 6C4. The plate current is a mixture of signals but the tuned plate circuit is only passing 1.650MHz.

At V6 the oscillator signal from V12 is injected at the cathode AND the suppressor grid. 1.650MHz 1st IF appears on V6's control grid. The plate current is a mixture of signals but the tuned plate circuit only passes 2nd IF 50.5kHz. V12 generates either 1600kHz or 1700kHz, depending on which sideband is selected.

A 6CB6 has an internal 280k plate resistance while a 6BZ6 has a 260k internal plate resistance. As an exercise for you look at the gain equations for a Pentode and determine why the 6BZ6 has a slight edge in gain over the 6CB6.


RL (external plate resistance) Assume 50 ohms
Rp (internal plate resistance) From Data sheet
gm From Data sheet

mu = gm * Rp = ?

Voltage gain = Av = (mu * RL) / (RL + Rp)

[n8fvj]

Thanks DMOD.