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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment. |
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28th Jan 2014, 3:01 pm | #1 |
Retired Dormant Member
Join Date: Mar 2012
Location: Greece ,Athens
Posts: 16
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Help!How to replace an Electromagnetic speaker with a Pm one?
Hello ,
I recently owned a Rca radio in bad condition and without a speaker. I have recapped it but the electromagnetic speaker and the output transformer is missing.I have read about changing the transformer with a filter choke or a resistor but I am a little bit confused about the real values I must put on or how to connect them. The radio is RCA Q122 as you can see in the schematic. It has two 6f6 output tubes with a 10Kohm plate to plate load resistance. I also have a spare output transistor that has primary resistance of 450 ohms and secondary 1.5 ohm. Can I use it somehow? Any suggestions will be appreciated! Thank you in advance |
28th Jan 2014, 3:26 pm | #2 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,953
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Re: Help!How to replace an Electromagnetic speaker with a Pm one?
For the output transformer - you need a standard "Push-pull" valve output transformer - have a look here: http://www.hammondmfg.com/1608A.htm I'm thinking the 1609A would do just fine.
The original speaker's field-coil is also the smoothing choke - the item marked as "FIELD" connected to the right of the 5Y3-GT rectifier tube. For this you need a 10-Henry choke - I'd suggest one rated at 100 milliamps or so. Have a look at http://www.hammondmfg.com/153.htm where the "158M" looks like it would serve the purpose admirably. Alternatively you can not use the choke [the circuit in the bottom right corner of the diagram shows how to use a non-field-coil speaker] |
30th Jan 2014, 5:44 pm | #3 |
Retired Dormant Member
Join Date: Mar 2012
Location: Greece ,Athens
Posts: 16
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Re: Help!How to replace an Electromagnetic speaker with a Pm one?
Thank you for your suggestions.
I will put a 5.6 K 10 watt ceramic resistor in the field place! As for the output transformer I will search here in Greece a suitable substitute. As you proposed me I should search for a Push Pull 10 Watt output transformer? But at the tube manual for the 6F6 the maximum power output goes up to 10 watt! |