BELL & HOWELL: Model 601 amplifier

Picked up another Bell & Howell Gaumont today, with the speaker cab - a Model 601 from 1950 (based on the capacitor dates).  Nice to see the original speaker still in the cab - I gave a quick test, sounds fine.  

The 601 is the same amp as the 621 (full details here).  The 601 and 621 amplifiers share the same part number (202000); I believe the model relates to the projector more so than the amp in some cases.

It came as the complete package with the projector and what appears to be a really exciting Australian training film about bandages from 1975.

Not sure where I will go with a conversion just yet.  I did quite like the last one that I did using an early Gibson circuit - so that's probably top of the list at the moment.  

BELL & HOWELL PROJECTOR AMPLIFIER - MODEL 601

A few minor differences with this one - transformer ends are painted, and there are a couple of large wirewound resistors that I've not seen in these before - quite good quality by the look of them.  

OUTPUT TRANSFORMER MEASUREMENTS

~8.4K with 16 and 8 ohm loads

Primary DCR 470 Ω 

10.35 VAC across the primary and measured two secondary taps:

• Tap A: 0.454 VAC

  • Turns ratio (Vp/Vs): 22.80:1

  • Impedance ratio (N²): 519.7

  • 0.454 V with 16Ω → 8.32 kΩ p-p

• Tap B: 0.319 VAC

  • Turns ratio (Vp/Vs): 32.45:1

  • Impedance ratio (N²): 1052.7

  • 0.319 V with 8Ω → 8.42 kΩ p-p

So far, on all of these that I've had, the plastic on the fuse holder breaks when I try to check the fuse.  Not great, as this leaves an uninsulated 110v conductor sticking out the back.  Bit of a death trap, but it will be replaced with a new one.  

I like that, back in the day, someone clearly thought about protecting the speaker, adding this tea-cosy-style cover.   These are normally branded as B.A.F Type 60 (British Acoustic Film) - which look just like a Goodmans Axiom from the same time period. 

The valves mostly tested OK - one of the 6V6 is a bit average, but not from the output pair, so that's good.  There is a mix of English Mullards, Australian Miniwatts.

Bell & Howell Part Number 202000