Another FM tuner: Eagle FMT640.

[Geordie McBoyne]

This FM tuner was imported from Japan by Eagle Products.
Seven Hitachi valves are employed, two 6AQ8, two 6BA6, two 6AU6 and one 6AL5.
Note the solid state multiplex decoder.

It would be interesting to determine the original manufacture. The fact it employs Hitachi valves doesn't mean that the tuner was made by that firm.

in the 1960s Eagle imported many good things from Japan.

Geordie McBoyne.

[Synchrodyne]

The Eagle FMT640 was listed in the Hi Fi Year Books (HFYB) 1964 through 1968/69 inclusive.  This is from HFYB 1967/68:

   

It looks to have been quite highly specified, with particularly a four-stage IF strip, two amplifiers (6BA6) and two limiters (6AU6)  plus a wide-band discriminator.

With a pair of 6AQ8 (ECC85), we may only speculate as to how the front end was configured.  Possibly one 6AQ8 as RF amplifier and mixer, the other as oscillator and AFC reactance valve.  But by the 1960s, the use of a varicap diode for AFC was quite common.  So perhaps one half of a 6AQ8 was used as an AF cathode follower.  Or maybe it had a single-valve front end using one 6AQ8, with the second used entirely form AF purposes, amplifier and cathode follower.  With a wideband demodulator and its concomitant lower output (as compared with a conventional demodulator), some AF gain may have been desirable.  In that case, one might ask why not use say a 12AX7 (ECC83) for the AF job.  But valve commonality could have been a factor.  For example, Armstrong used the ECC85 for AF purposes in some of its equipment that also deployed an ECC85 FM front end.

I recall Eagle audio equipment advertising from the 1970s.  This referred to the Japanese origin of its equipment, but I am not sure if the OEM was mentioned.  Featured was the fact that Eagle’s principal, Gerry Adler, had learned Japanese in order to better engage with the supplier.  By then I think that Eagle was working at the lower-middle end of the audio market, though.

Cheers,

Steve

[Geordie McBoyne]

The attachments show the component layout of the Eagle FMT640.
One on the 6AQ8 double-triodes is employed as the grounded grid RF amplifier with the other section functioning as the mixer.   The other 6AQ8 is the local oscillator and the AFC control valve.

Geordie McBoyne.

[Geordie McBoyne]

Circuit diagram of the local oscillator and AFC.

Geordie McBoyne.

[Synchrodyne]

An interesting point is that this Eagle FM tuner had a three-gang tuning capacitor.  Typically, where a grounded grid RF amplifier was used, two-gang tuning was employed.  Given the low input impedance presented by a grounded grid stage, it was easier to use a wideband, untuned input, and that might have been slightly better from the noise perspective, as well.  Conceivably though, the third gang was used to provide a bandpass interstage, rather than to tune the input.

Cheers,

Steve