Radio with no IF transformers

[Les Dickson]

I have an Emerson model BM-215 that’s unlike any previous radio I’ve worked on. It has no IF transformers as you can see in the attached schematics. I have it working – recapped and a new rectifier tube and ballast resistors. So to get it aligned the schematic says:

• an oscillator with a frequency of 1400 kc is required
• set the radio to 1400 kc
• feed the signal into the antenna through a 0.0001 cap
• adjust the two trimmer capacitors for maximum output

So my questions:

1. is the oscillator that is required different than a signal generator putting out 1400 kc of RF?
2. has anyone worked on a similar setup and if so, what advise do you have?

(The photos are before restoration.)

Attachments:

1. 

   chassis-Model-BM-schematic.pdf
   

2. 

   M0004881-2b.pdf
   

3. 

   IMG_20160211_201840.jpg
   

4. 

   IMG_20160211_201918.jpg
   

[Alistair Thomson]

This is a tuned radio frequency (TRF) receiver, so it has no local oscillator to convert the tuned frequency into an IF. A signal generator is simply a variable frequency oscillator, so injecting the sig gen into the antenna connector at 1400KHz is the same as receiving a radio signal at that frequency.

The radio is very simple: a signal is amplified in the first two valves, then the audio is extracted by rectification and filtering out the RF. Be aware of course that the chassis is live to mains, so great care needs to be taken if working on the set while it is powered up.

By the way, I had difficulty reading the diagrams you sent, and had to get the originals from RMOrg: you should use a higher resolution in your pictures! 🙂

[Les Dickson]

Thanks for the information Alistair. I haven’t worked on a TRF before so it’s a learning adventure.By the way, I always use an isolation transformer.

[Dan Walker]

Les” I am trying to get some alignment information about a radio you recapped a couple of years ago . It is a
DeForest Crosley model 851 with two speakers.
I have the radio up and running but I can’t find any information about aligning the radio.
It is a York / Mayfair.
I have a real hard time to navigate this forum,, I can’t find anywhere to PM you or email you.
My email is .
Please email me
Thanks Dan Walker in Calgary

[Dan Walker]

Thanks Les. I have the radio playing good now. If you need information when you get to yours , ley me know.
Dan in Calgary

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