|
|
Post by DHockey on Jul 11, 2023 21:15:09 GMT 12
I found this shortwave converter in the back of a Philco 91E I purchased some time ago. It looks to be NZ made as there is a coil stamped T&J (I presume Turnbull and Jones) inside. The valve is a 6A7. Unlike other shortwave converters I have seen, this one appears to lack any way to tune it, so there may be a part missing. The only control is a switch the that turns it on/off. There are two trimmers, accessed through the side, one was sealed with wax.
There are 5 wires coming from the unit, a aerial, two heater wires, and HT wire and a screened cable that was connected to the aerial terminal of the Philco when I purchased it.
Has anyone seen one before? Or have any knowledge of how it might work?
|
|
|
|
Post by davidballantynezl1tfg on Jul 12, 2023 9:05:19 GMT 12
My guess is that is has a fixed frequency oscillator which can be adjusted by the trimmer cap. The tuning would be done by whatever it is fed into on an unknown frequency. The converter would be broad band untuned. It may suffer from spurious signals? Needs good shielding between the converter & receiver. David
|
|
|
|
Post by Peter Walsham on Jul 12, 2023 9:46:53 GMT 12
I would be thinking the same as David. The radio that it's connected to would be used as a 'tuneable IF' - almost like a double conversion receiver
|
|
|
|
Post by DHockey on Jul 20, 2023 11:18:11 GMT 12
Thanks for the replies. I have replaced the paper caps in the converter and checked for any out of spec resistors. Powering it up on my bench supply with the output connected to my 'scope revealed it oscillates at around 10Mhz. This can be varied by adjusting the trimmers.
With the unit connected up to the radio I can't pick up any shortwave stations, but I do get static and can pick up signals injected via signal generator around 11-12MHz with the radio tuned to the lower portion of the broadcast band. The static fades out as I tune the radio higher.
I have found one mention made in the 1939 Excelrad catalogue of a "Coil Type 116 S.W. Converter" which may be the type used in this unit.
|
|
