Back when I was a young ham, I was given an ARC-5 receiver, with power supply, that covered the 80-meter ham band.
That receiver provided hours of listening enjoyment, and it, along with its power supply, were small enough that I could take them on family vacations for listening during the evenings.
Somewhere along the way the receiver went one way and I another. But I've always had fond memories of it.
In more recent years I've picked up a few ARC-5 receivers at various swap-meets, and I've finally decided to see if I could get any of them back on the air (some are more heavily modified by previous owners than others, and those might not be worth the trouble).
My ARC-5 receiver stable currently consists of the following six radios:
- CCT-46129 (0.19 - 0.55 MHz). One of the ARA series of receivers.
- CCT-46104 (1.5 - 3 MHz). One of the ARA series of receivers.
- BC-454-B (3 - 6 MHz). One of the SCR-274-N series of receivers.
- R-26 (3-6 MHz). One of the AN/ARC-5 series of receivers.
- CBY-46106 (6 - 9.1 MHz). One of the ARA series of receivers.
- R-27 (6-9.1 MHz). One of the AN/ARC-5 series of receivers. (Somehow this one wound up with a cover from an R-23 receiver).
In this blog post I will:
- Introduce the three receiver series that comprise the ARC-5 receiver family.
- Discuss the differences in design between these three series.
- Describe how to recognize which series a receiver belongs to.
- Describe how to power receiver.
- Describe the receiver's connectors and their signals.
- Describe controlling the receiver.
- Describe how to interface with an 8-ohm speaker.
- List the steps to take when first checking out a receiver.
- And finally, describe of my efforts in bringing my BC-454-B back to life.
Introduction, the ARC-5 Receiver Series:
Per Wikipedia, the term ARC-5 is used to describe three similar (yet different) series of receivers deployed during World War Two. Of these three series, only one series has the "official" ARC-5 nomenclature (the AN/ARC-5series), which was actually the last of the three series to be introduced (in 1943).
The other two series, unofficially, are also referred to as "ARC-5" receivers. The first series, developed for the Navy prior to World War Two, was the "ARA" series. This series was followed in 1941 by the "SCR-274-N" series, which was initially adopted for the US Army Air Corps.
The table below (from the AN/ARC-5 Wikipedia entry) lists the receivers of each of the three series that cover the medium through high-frequency range of 0.19 to 9.1 MHz. This frequency span is typically divided between five different receivers (note that the SCR-274-N series does not have a receiver covering 1.5-3.0 MHz).
| MHz | ARA-ATA | SCR-274-N | AN/ARC-5 | |
|---|---|---|---|---|
| Navigation Receiver (Beacon Band) | 0.19 - 0.55 | CBY-46129 | BC-453-(*) | R-23(#)/ARC-5 |
| Navigation Receiver (Broadcast Band) | 0.52 - 1.5 | CBY-46145 | BC-946-(*) | R-24/ARC-5 |
| Communication Receiver | 1.5 - 3.0 | CBY-46104 | R-25/ARC-5 | |
| Communication Receiver | 3.0 - 6.0 | CBY-46105 | BC-454-(*) | R-26/ARC-5 |
| Communication Receiver | 6.0 - 9.1 | CBY-46106 | BC-455-(*) | R-27/ARC-5 |
(*) A (basic model) or B (1st revision). (#) No letter (basic model) or A (revision).
Differences between the ARC-5 Receiver Series:
(I will summarize the information below at the end of this section)
1. Front Panel Plug wiring:
Both the ARA series and the SCR-274-N series bring the headset audio output signal to pin 4 of the front-panel connector (audio also appears on the rear panel connector). The AN/ARC-5 series has no audio connection to the front panel! Audio for this series only appears on the rear panel connector.
2. Automatic Volume Control (AVC):
Of the three series, only the AN/ARC-5 series (i.e. R-23 through R-27 receivers) has Automatic Volume Control (AVC) circuitry. You should be able to quickly identify if a radio has this functionality (and thus is part of the AN/ARC-5 series) by looking for the following differences:
- 12SF7 replacing the 12SK7 tube in the Second IF Amplifier stage.
- C26 (a capacitor connected between pin 2 of the 12SR7 (middle tube, last row) and the middle terminal of Z-4, i.e. L12) does not have a resistor attached in parallel across it (R14).
For comparison, here is an example of the wiring for non AN/ARC-5 receivers:
3. Filament Voltage:
Per my reading of the ARA, SCR-274-N, and AN/ARC-5 manuals, only one receiver was designed for 14 V operation, and that was the R-148/ARC-5X receiver, covering 0.19 to 0.55 MHz.
In this receiver, 12V filament tubes were used, and all filaments were wired in parallel.
All other receivers used 28 volts for their filament voltage. Given that the tubes are 12V filament tubes, the filaments of pairs of tubes were first connected in series (the RF Amp & Mixer pair, the 1st IF and 2nd IF pair, and the Det./Osc. & Audio Amp pair) and then each pair was fed with 28V.
Never assume that a receiver has been wired for 28V filament voltage! I have made this mistake! Always verify filament circuitry before applying power to a newly acquired receiver. Previous owners might have modified it.
For example, my R-27 AN/ARC-5 receiver should be wired for 28 V filament voltage, but all filaments are wired in parallel, while my CBY-46106 ARA receiver is also wired with all filaments in parallel and the original 12V tubes were replaced with 6V tubes!
4. Audio Output Transformer and Impedance:
Of the three receiver series, only the SCR-274-N series was designed for connection to high-impedance headphones (e.g. 8000 ohms). Of this series, the "-A" version was designed for use only with high impedance headphones, while the "-B" version could be used with either high-impedance or low-impedance (e.g. 600 ohm) headphones, depending upon how the Audio Output Transformer T1 was wired.
The other two receiver series (ARA and AN/ARC-5) were designed for use only with low impedance (e.g. 600 ohms) headphones.
Audio Transformer (T1) Summary:
ARA receiver: The Audio Transformer should have a "5613" part number. Its primary to secondary turns ratio is 8:1, and spec'd for low impedance headsets (e.g. 600 ohms). (See Table 19 of the Instruction Manual).
SCR-274-N receiver: Audio Transformers can have two different part numbers:
- "6308": Used only with high impedance headsets (e.g. 8000 ohms). This transformer was used in the "-A" revision of the receiver.
- "ES-691027": Provides connection to either a high impedance headset (e.g. 8000 ohms, via terminal 3) or a low impedance headset (e.g. 600 ohms, via terminal 6). This transformer was used in the "-B" revision of the receiver. Refer to Table 20 of the Maintenance Instructions. (Note, the turns listed for the secondary's tap were most likely counted from the "hot" end of the secondary (terminal 3), rather than its ground end, meaning that the tapped secondary would actually be 475 turns rather than 1325 turns).
The illustration below shows both the schematic and the wiring diagram for ES-691027 transformer in the "-B" revision of the SCR-274-N receivers:
AN/ARC-5 receiver: Audio Transformers support low impedance headsets (e.g. 600 ohms) and, per Table 20 of the Maintenance Instructions, can have one of two part numbers:
- "5631"
- "640268"
An example of the different T1 part numbers in different receivers:
(By the way, for an interesting discussion of military headsets circa the 1940's, go here).
ARA Series:
- Audio Line at Front Connector (pin 4): Yes
- AVC Circuitry: No
- Dynamotor (Filament) Voltage: 28 VDC
- Headset Impedance: Low Impedance (e.g. 600 ohms)
SCR-274-N Series, "A" Revision:
- Audio Line at Front Connector (pin 4): Yes
- AVC Circuitry: No
- Dynamotor (Filament )Voltage: 28 VDC
- Headset Impedance: High Impedance (e.g. 8000 ohms)
SCR-274-N Series, "B" Revision:
- Audio Line at Front Connector (pin 4): Yes
- AVC Circuitry: No
- Dynamotor (Filament) Voltage: 28 VDC
- Headset Impedance: Can be wired for High or Low Impedance
AN/ARC-5 Series:
- Audio Line at Front Connector (pin 4): No
- AVC Circuitry: Yes
- Dynamotor (Filament) Voltage: 28 VDC (Note: R-148 wired for 14 VDC)
- Headset Impedance: Low Impedance (e.g. 600 ohms)
Identifying a Receiver:
The receiver should have an attached metal tag stating its series, receiver identification, and sometimes its operating voltage (i.e. dynamotor voltage). The tag for the ARA and AN/ARC-5 series should be on the receiver's top cover, while the tag for the SCR-274-N series should be on the right side of the chassis, near the front panel.
Here are the steps I would take:
1. Ignore the receiver tag on the top of the radio (if it exists); after all, someone might have put the wrong cover on the radio. Instead, look at the front dial and identify its frequency range. This narrows the selection down to one of four receivers (ARA, SCR-274-N ("-A" revision), SCR-274-N ("-B" revision), and AN/ARC-5).
2. Is the chassis bare aluminum or painted with black-wrinkle paint?
2.1. If bare aluminum, the receiver is either an SCR-274-N ("-A" revision) or an SCR-274-N ("-B" revision) receiver.
2.1.1. If the SCR-274-N receiver has no side-mounted ID tag, we will need to determine the receiver's revision by examining the audio transformer under the chassis. Remove the bottom cover. If the Audio Output transformer (T1) has an "ES-691027" part number, it is the "-B" version of an SCR-274-N receiver (e.g. BC-454-B). Otherwise, if the P/N is "6308", the receiver is an "-A" version.
If the radio is the "-B" version, now would be a good time to check if the audio transformer, T1, is wired for 8000 ohm or 600 ohm impedance.
2.2. Otherwise, if the chassis is not aluminum but instead painted with black-wrinkle paint, the receiver is either an ARA receiver or an AN/ARC-5 receiver, or it could even be an SCR-274-N (although I personally have not come across a "BC" prefixed receiver in black wrinkle, I have seen some pictures).
2.2.1. Is the black-wrinkle receiver of the SCR-274-N series? Check the side of the chassis for an identification tag. If there is one (and it starts with "BC"), then the receiver should be of the SCR-274-N series. You can double-check this conclusion by removing the bottom cover and examining the Part Number of the Audio Transformer, T1. If this P/N is either 6309 or ES-691027, then the receiver is of the SCR-274-N series.
2.2.2. The receiver will be in the AN/ARC-5 series if the second IF tube is a 12SF7 (either pull the tube out or check its filament wiring -- a 12SF7's filament pins are pins 7 and 8, while a 12SK7's filament pins are 2 and 7).
Alternatively, you can remove the bottom cover and check C26. If there is no resistor across C26, the receiver is an AN/ARC-5 receiver (with AVC).
2.2.3. If the black-wrinkle receiver isn't an SCR-274-N receiver nor an ARC-5 receiver, then it is an ARA receiver.
And finally, an important note regarding receiver identification!A caveat regarding these checks: modifications made by later owners might have substituted parts from other series, changed circuitry, or...? There are any number of reason why a receiver that appears to be of one series was actually born of another.
The three IF transformer housings should each have a color dot in one corner on their topside. These three dots should all be the same color, and they should match the front-panel's tuning dial per the following table:
- If a dynamotor is used, its Low Voltage (LV) power (e.g. +28V) must be applied via the Rear Panel connector (J3).
- If an external power supply is used (supplying both LV and HV), this power can be applied either via the Rear Panel connector (J3) or via the Dynamotor connector (J2).
- If the Rear Panel connector is used for power without the dynamotor installed, then the HV and LV pins on J2, the Dynamotor connector, should be covered (heat-shrink tubing?) to prevent accidentally shorts or shocks!
- Also, if the Rear Panel connector is used for power (with or without the dynamotor), pins 6 and 7 on the Front Panel connector (J1) must be connected together to route +LV to the tube filaments.
- Pin 1: Gain Control Line
- Pin 2: Ground
- Pin 3: (not used)
- Pin 4: Headset Audio Output (Note: the AN/ARC-5 receivers do not have this signal).
- Pin 5: CW Osc. (i.e. BFO) Shut-Off Line
- Pin 6: +L.V. to receiver circuitry
- Pin 7: +L.V. from rear-panel connector
- Pin 8: (not used)
The following schematic shows how controls can be wired to this connector:
Front Panel Connector Notes:
- ARA series and SCR274-N series of receivers provide audio to pin 4. Note that the load on the audio signal is expected to be either 8000 ohms or 600 ohms, depending upon the receiver.
- AN/ARC-5 receivers have no internal connection to pin 4, and so audio cannot be accessed via the front of an AN/ARC-5 receiver.
- If +LV (low voltage power, e.g. 28 V) is applied via J3 (the Rear Panel Connector), then pins 6 & 7 of the Front Panel connector must be connected together (either via a wire or a switch), to route +LV to the tube filaments (and Dynamotor +LV input).
- Gain control is provided via a potentiometer (20K or 50K ohms), and should be wired so that, in its position of maximum gain, resistance is at its minimum.
- The CW Oscillator (BFO) can be turned ON or OFF via pin 5. Note that the BFO is OFF when pin 5 is shorted to ground.
Connecting to the Front Panel Connector's pins:
Use a jeweler's saw (see below, available inexpensively from Amazon) to cut the 1/8" O.D. tubing to length!
Here is my control panel for my BC-454-B receiver:
Rear Panel Connector:
- Pin 1: Ground
- Pin 2: Headset Audio Output
- Pin 3: Gain Control Line
- Pin 4: CW Osc. (BFO) Shut-Off Line
- Pin 5: + Screen Grid Voltage (not used)
- Pin 6: +L.V. (i.e. Low Voltage, e.g. 28 VDC or VAC)
- Pin 7: +H.V. (i.e. High Voltage, e.g. 250 VDC)
- Pin 2 is the Audio Out signal. Note that the load on the audio signal is expected to be either 8000 ohms or 600 ohms, depending upon the receiver.
- Pin 3, Receiver Gain can be controlled via an external potentiometer (20K or 50K ohms), and it should be wired so that, in its position of maximum gain, resistance is at its minimum.
- Pin 4, the CW Oscillator (BFO) can be turned ON or OFF via pin 4. Note that the BFO is ON when pin 4 is OPEN.
- Pin 6 is the +LV pin (low voltage power, e.g. 28 V). Note that if +LV is applied via this pin, then pins 6 & 7 of the Front Panel connector must be connected together (either via a wire or a switch), to route +LV to the tube filaments (and Dynamotor +LV input). The image below shows an FT-230-A Adapter, which can provide this function.
- Pin 7 is the +HV pin. No connection from an external high-voltage source should be made to this pin if a Dynamotor is installed. If there is no Dynamotor, then +HV (e.g. 250 VDC) can be applied to the radio via this pin.
I prefer to use an 8-ohm speaker instead of a headset (even though I do have a 600-ohm headset) and I find that the receiver, connected to the 8-ohm speaker via an impedance transformer designed for the appropriate impedance ratio, can drive my 8-ohm speaker to quite loud levels.
With a 600:8 ohm Impedance Transformer between radio and speaker, and measuring voltage with an oscilloscope at the speaker, the speaker's signal starts clipping at at about 3 Vpp (i.e. about 1.07 Vrms if the signal were a sine wave), which equates to a speaker drive power of about 0.14 watts. With my speaker, this is VERY LOUD -- I need to wear ear plugs! A 1 to 1.5 Vpp signal is more comfortable.
The following Audio transformers, available from Mouser (if in stock), should be able to transform an 8 ohm speaker to 600 ohms (or 500 ohms, which should be close enough):
Xicon 42TL series (75 mW max output drive):
- 42TL001-RC: 500 ohm primary, 8 ohm secondary.
- 42TL003-RC: 1.2K ohm primary (for 600 ohms, connect between one end of the primary and its center-tap), 8 ohm secondary.
Xicon 42TM series (200 mW max output drive):
- 42TM001-RC: 500 ohm primary, 8 ohm secondary.
- 42TM003-RC: 1.2K ohm primary (for 600 ohms, connect between one end of the primary and its center-tap), 8 ohm secondary.
Xicon 42TU series (460 mW max output drive):
- 42TU400-RC: 500 ohm primary, 8 ohm secondary.
The image below shows the relative sizes of these three transformer families:
I chose the Xicon 42TM003-RC because physical size wasn't an issue and it could handle the maximum output from the receiver, if I accidentally left the receiver unattended, set to maximum volume, and tuned to a carrier.
Below is a schematic showing a possible wiring diagram. Note that the receiver is connected to the primary's center-tap (i.e. 600 ohms), not across the entire primary winding (i.e. 1200 ohms).
If using a 4-ohm speaker in lieu of 8 ohms, connect it to the secondary's center tap, rather than across the entire secondary.
Adapting an ARC-5 Receiver for Ham Use demonstrates how a small audio transformer (Xicon 42TL series) can be installed behind the front "adapter panel" and held in place with hot-melt glue.
1. Verify Filament Wiring:
As I mentioned earlier, always first verify receiver filament wiring before applying power to a receiver. A common modification was to rewire 28 VDC filament circuitry for 14 VDC (in practice, 12.6 VAC) by connecting all six filaments in parallel. You do not want to apply 28 VDC to a receiver that has had its filaments rewired!
Also check if the original 12V tubes were replaced with 6V tubes.
For 28 VDC operation the following pairs of tubes were connected in series:
- 12SK7 RF amp & 12K8 Mixer
- 12SK7 1st IF Amp & 12SK7 (or 12SF7) 2nd IF Amp
- 12SR7 Det./CW Osc. & 12A6 Audio Amp
The quickest way to verify if a receiver has all six filaments wired in parallel is to check the filament wiring of the following tubes:
- 12K8 Mixer, pins 2 and 7.
- 12A6 Audio Amp, pins 2 and 7.
- 12SK7 First IF Amp, pins 2 and 7.
2. Check Capacitors:
Over time capacitors can degrade and fail. All capacitors should be checked with a good capacitance meter (that measures loss, or dissipation factor, as well as capacitance -- I use a GenRad 1657 RLC Digibridge).
The most likely failures will be the electrolytic capacitors (C5, C30, and C32), so I would start with those. For the caps in the "tubs" screwed to the chassis, I simply unsolder the wires from their terminals (or terminal) and measure capacitance (and dissipation factor) from each terminal to chassis (ground).
Also look for capacitor "tubs" that might be leaking (these should be fairly obvious). Check these, too.
Some authors recommend replacing all of the capacitors. I prefer to just replace those that measure poorly. But replacing them all would be a suitable tactic if you don't have a good way to check the capacitors.
If you find faulty caps, replace them. For faulty capacitors contained in the metal tubs (for example, C6A, C6B, and C6C)), I would simply remove the tub and add a terminal strip with new capacitors wired to it (see: Adapting an ARC-5 Receiver for Ham Use). I'll show an example later in this post, when I describe my efforts with my BC-454-B.
Some restorers prefer to stuff the original capacitor metal "tubs" with new capacitors to retain the look of the original receiver (see: https://www.antiqueradios.com/forums/viewtopic.php?f=5&t=288697&start=0). I am not such a purist, preferring an easier route, myself.
3. Check the Receiver's Audio Impedance Requirement and add an Audio Transformer, if necessary.
The load required by the receiver's audio amplifier will be either High Impedance (e.g. 8000 ohms) or Low Impedance (e.g. 600 ohms). Refer to the discussion earlier in this post regarding how to determine your receiver's requirement. Note that a radio might have been modified by a previous owner. It's good to verify!
If your headset or speaker is not the correct impedance (if it's close to the correct impedance, it should be OK), you should use an impedance transformer to transform its impedance to the impedance that the receiver wants to see. For example, see discussion, above, regarding transformers that will transform an 8 ohm speaker to 600 ohms.
4. Should I Attach Control & Audio Signals to the Front or to the Rear Connector?
Connect the Control functions (Gain Control, BFO On/Off) to either the Front Panel connector or the Rear Panel connector, per your preference. Refer to the appropriate sections, above.
5. How will the Receiver be Powered?
Determine how the receiver will be powered (refer to the "Powering the Receiver" section, above). Here are three choices:
- Dynamotor (installed on the receiver), with +LV applied from an external supply to the Rear Panel connector.
- External power supply providing both +HV and +LV, attached to the Rear panel connector.
- External power supply providing both +HV and +LV, attached to the 3-pin Dynamotor connector.
Refer to the "Powering the Receiver" section earlier in this post.
Only after I've gone through all these steps do I then apply power.
Example, BC-454-B Revivification:
Here are the steps I took to bring my BC-454-B back to life.
1. Verify Filament Wiring
The receiver is one of the SCR-274-N series of receivers and therefore should have its tube filaments wired for 28 volts. In other words, the filaments of each of three pairs of tubes should be wired in series.
I removed the bottom cover and visually checked to see if any tubes had no filament pins tied directly to ground. At least one tube fit this criteria, confirming that the radio was wired for 28 VDC.
2. Check capacitors
With the bottom cover off, I first did a visual inspection of all of the "tub" capacitors (note: anti-fungal coating can possibly mask leakage). The C7 capacitor tub (containing three caps: C7 A, B, C) looked like it had leaked a bit since the radio was first manufactured (in March, 1945), but unsoldering the wires to the three capacitor terminals and measuring their capacitance to ground revealed no problem. They all measured in the range of 60 nF (spec'd to be 50 nF (i.e. 0.05 MF). Close enough!
Without any other tubs looking like they had leaked, I decided to focus next on the electrolytic caps, assuming that the other non-electrolytic caps were probably good. One electrolytic cap, C32 (spec'd 5 uF) measured 6.7 nF (off by a factor of 1000 !!!), with a Dissipation Factor of 1.78.
The values of all other electrolytic caps measured OK, with DFs of sub 0.02.
Not willing to go through the hassle of trying to fit a new cap into the original tub, I removed C32 and replaced it with a 2-lug terminal strip. The cap filters the +HV line, so larger is better for this application. I dug up a 50 uF, 360 WVDC cap (from my junkbox), which I soldered in to replace the original 5 uF cap.
Note: the receiver manuals do not specify capacitor working-voltage, so I simply use parts that are rated (by a comfortable margin) above the receiver's +HV rating of 250 VDC.
3. Check Audio Transformer T1 for Impedance Requirement.
A quick verification of T1's Part Number (P/N ES-691027) and a check of its wiring, per the schematic notes in the SCR-274-N manual (see illustration earlier in this post) confirmed that the audio transformer's wiring had not been modified and that it was setup for a low impedance (e.g. 600 ohm) load.
Thus confirming the decal on the side of the chassis!
4. Fabricate and Connect the Front Control Panel
One of my six receivers had a filthy control panel with an old pot, BFO switch, and audio jack attached.
I cleaned up the panel, installed a new pot from the junkbox (with power switch on its back), new BFO switch, and new audio jack. Then I attached wires and home-made "pin-sockets" (from 1/8" O.D. copper tubing) to slip over the Front Panel connector's pins.
5. Rear Panel Connections
To use an 8-ohm speaker, I chose a Xicon 42TM003-RC transformer to transform an 8-ohm speaker to 600 ohms. The center-tap of the transformer's primary connects to pin 2 (Audio Out) of the Rear Panel connector. Pick one or the other of the remaining two primary pins (it doesn't matter which one) and attach it to pin 1 (ground) of the Rear Panel connector.
The '+' terminal of the 28 VDC supply connected to pin 6 (+LV) of the Rear Panel connector, and the supply's '-' terminal connected to pin 1 (ground).
6. I decided to first test the receiver my high-voltage "lab" supply (a Heathkit IP-32, set to 250 VDC), and so I connected its =HV to to pin 3 of the Dynamotor connector, with supply's ground attached to pin 1 of the same connector.
7. I attached my antenna to the Receiver's antenna connector.
8. And then the big moment -- I turned the Gain control on the front panel clockwise, turning on the power switch. +LV current (filament current) initially rose, but settled to under 0.5 amps (it might have been significantly under, I don't recall), and +HV current was on the order of 40 to 50 mA.
And as the tubes warmed up, I started hearing signals on the 80 meter band. It worked!
9. Check with Dynamotor
Next, after powering down the receiver ,I disconnected the Heathkit High Voltage supply and attached the Dynamotor to the back of the receiver. It spun up as soon as I turned on power and again, as the tubes warmed up, signals began appearing.
Final Configuration:
The diagram, below, shows my BC-454-B setup, including power supply (but not the antenna).
My BC-454-B, On the Air (YouTube Video):
Below is a video showing my BC-454-B in operation, powered by its dynamotor. Both AM and LSB reception are displayed.
Note that this receiver has no AVC, so some "riding" of the Gain control is necessary.
Also, note that the tiny impedance transformer (600 to the speaker's 8 ohms) is temporarily connected between the radio and the speaker using clip leads.
Thoughts on Modifications:
Personally, as an engineer, my feeling is that if modifications can improve the performance of a radio, why not make them? But I'm also sympathetic to those who want to keep their equipment in original condition -- à chacun son goût.
1. Bringing Output Audio to the Front Connector:
I haven't tried this yet, but if you have an AN/ARC-5 version of the receiver without the audio-out connection to pin 4 of the Front Panel connector J1, it should be possible to run a wire from the Rear Panel connector pin 2 (J3) to pin 4 of J1.
This will require removing the RF Coil Unit (Z5A, Z5B, and Z5C). Hopefully this is straightforward. I plan to find out when I start working on my R-27 receiver.
2. Adding AVC:
Lack of good AVC in the BC-454-B is certainly noticeable, and it might be more annoying if this were my only receiver.
There is a simple modification for adding AVC to receivers without it.
All the essential a.v.c. components are incorporated in all receivers, but there is no connection between them. The purpose of this conversion is to provide a.v.c. action to the r.f. and i.f. amplifier stages by completing the a.v.c. circuit. It required two additional resistors and a capacitor. Refer to figures 11A and 11B (not shown in this post, k6jca). First, unground pin 5 of the 12SR7 (VT-133). Connect the 100 uuf (i.e. 100 pF, k6jca) capacitor across pins 4 and 5 of the tube socket. Connect the 470K resistor from pin 5 to an adjacent ground lug. Connect the second 470K resistor between pin 5 and the junction of C-15A and R-11. Remove R-11 from the circuit to increase the effect of the a.v.c. action.
Note: I haven't tried this modification. I imagine it would be satisfactory for AM (where there is a carrier present), but perhaps not for CW or SSB signals. For those modes, you'll probably still need to keep one hand on the gain control.
Resources:
A Google search for various ARC-5 terms will return a plethora of hits. Below are some of the sites I found useful.
Command Set Summary. A good summary (from Australia) of the various ARC-5 receivers.
T.O. 12R2-3SCR274-2 (formerly 16-40SCR274-5). Handbook, Maintenance Instructions, Radio Set SCR-274-N (revised 25 July 1956). Note that this handbook only applies to the SCR-274-N equipment (e.g. receivers BC-454, BC-455, etc.). As such, for example, all receiver schematics show the second I.F. tube as being a 12SK7, not a 12SF7, as seems to have been used in the ARC-5 (not SCR-274) series of receivers. 228 pages.
AN16-30ARC5-2. Handbook, Maintenance Instructions, AN/ARC-5 Aircraft Radio Equipment, LF, MF, HF Components. Note that this handbook only applies to the AN/ARC-5 equipment (e.g. receivers R-25, R-26, etc.). As such, for example, all receiver schematics show the second I.F. tube as being a 12SF7, not a 12SK7, as seems to have been used in the BC-series of receivers. 354 pages.
The Instruction Book (including schematics and wiring diagrams) for the ARA/ATA series can be downloaded as five PDFs via the following links. Note that this is the manual for the R.A.A.F. (which I assume is "Royal Australian Air Force").
- ARA/ATA Manual, Part 1
- ARA/ATA Manual, Part 2
- ARA/ATA Manual, Part 3
- ARA/ATA Manual, Part 4
- ARA/ATA Manual, Part 5
NAVWEPS 16-30ARC5-501. Handbook, Bench Test and Alignment Procedure, Radio Equipment AN/ARC-5. Specifically for the AN/ARC-5 series, but can probably be used for the SCR-274 series (e.g. receiver I.F. schematic shows 12SF7 as the second I.F. tube). 56 pages.
List of component differences between the various receivers. Lists the C, L, and R component values for the different receivers in the ARA, SCR-274-N, and AN/ARC-5 series. (However, I don't believe this list identifies the differences in T1 between the series).
Adapting an ARC-5 Receiver for Ham Use. AD5X. Among other things, describes using 1/8" O.D. copper tubing for connectors and also a nice home-brew tuning knob.
https://www.antiqueradios.com/forums/viewtopic.php?f=5&t=288697&start=0 A thread showing an example of recapping a receiver using the original capacitor housing.
http://jlandrigan.com/files/BC%20453/The%20ARC-5'er%20Power%20Supply.pdf 1966 article of a power-supply design. Also discusses impedance transformation if using a speaker.
Stevens (G2BVN), The Command Set Receivers, R.S.G.B. Bulletin, February, 1957. Discusses the command set receivers (does not mention the variant with the 12SF7 as the second I.F.) and modifications thereof.
Stanley, J., K4ERO, "Using Unmodified Command Set ARC-5 Radios on the Ham Bands," QST, January 2016
Surplus Radio Conversion Manual, Volumes 1, 2, and 3. Originally published as paperbacks by Editors and Engineers. Note that Volume 3 contains a simple AVC mod on page 15 (for the SCR-274N receivers, such as the BC-454 and BC-455, that lack AVC).
Command Sets (CQ Magazine Article Reprints). Mostly transmitter mods, but some receiver information, too.
Standard Caveat:
As always, I might have made a mistake in my equations, assumptions, drawings, or interpretations. If you see anything you believe to be in error or if anything is confusing, please feel free to contact me or comment below.
And so I should add -- this information is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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