|First R.F. Amp.||6BA6|
|Second R.F. Amp.||6BA6|
|First I.F. Amp.||6BA6|
|Second I.F. Amp.||6BA6|
|Third I.F. Amp.||6BA6|
|Second Detector - A.V.C.||6AL5|
CIRCUIT: The double conversion circuit of the NC-183D achieves a very advantageous condition wherein the high I.F. provides a high order of image rejection and the low I.F. gives a sharper selectivity so necessary in a communication receiver. The incoming signal on bands, A, B and C is first converted to a high intermediate frequency of 1720 kcs. and then to the low intermediate frequency of 455 kcs. An new type sliding switch is ganged with the band switch for a efficient and automatic insertion of the double conversion stage when either the A, B or C band is in use. Selection of the D and E bands results in a single conversion to an I.F. frequency of 455 kcs.
NOISE LIMITER: The noise limiter in the NC-183D receiver uses an automatic type double-action circuit resulting in the limiting of noise pulses on both positive and negative peaks. A threshold control on the front panel permits adjustment of the level at which limiting action starts.
CRYSTAL FILTER: The selectivity characteristics of the NC-183D are made adjustable by means of a crystal filter. A six-position Selectivity switch and a crystal phasing control are mounted on the front panel for the adjustment of this filter.
SIGNAL STRENGTH METER: An S-meter for signal strength readings is associated with the A.V.C circuit. The S-meter scale is calibrated is S units from 1 to 9 with approximately 5 db per S unit, and in db above S9 from 0 to 40 db. An adjustment is provided to enable the operator to change the above calibration if he so desires.
ACCESSORY CONNECTOR SOCKET: A standard octal socket, is mounted on the receiver chassis and wired in a manner to permit connection of various accessories such as a National Model SOJ-3 Select-O-Ject unit or a National type NFM-83-50 Narrow-Band-FM adaptor.
TONE CONTROL: The tonal output of the NC-183D receiver may be varied to suit the listener by means of the Tone Control. In the extreme clockwise position the greatest degree of high audio frequency response is obtained and, as the control is rotated counterclockwise from 10 to 0, a comparatively flat response is obtained over the entire usable audio frequency range.
PHONO INPUT JACK:
A phono input jack is mounted at the rear of the receiver and can be used to connect auxiliary apparatus, such as a record player, to the audio system of the receiver. This input circuit is high impedance and feeds into the 6SJ7 first audio amp. stage. The Radio-Phono switch on the front panel must be at the Phono position when the phono input jack is used.
NC-183DT Receiver, table mounting gray finish, complete with tubes, crystal filter, noise limiter, 115 and 230 volt, 50/60 cycle built-in power supply.
NC-183DTS 10" PM Loudspeaker in matching cabinet for the above receiver.
NC-183DR Receiver , same as table model but mounted on 1/8 inch aluminum standard rack panel, 10 1/2" high, gray finish.
NC-183DRS 10" PM Loudspeaker mounted on 1/8" aluminum standard rack panel, 10 1/2" high, gray finish.
NFM-83-50 Narrow-Band F.M. Adaptor.
Source: The National NC-183D instruction manual
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