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Repair: Airline GA 2940 Console (Part 1 of 2)

tubesandtransistors 6

The Airline 2940

Today on the bench is an Airline model GAA-2940 console produced sometime between 1966-67. Airline was a brand used by the Montgomery Wards department store.

This unit features AM/FM radio, a Voice of Music turntable, and a line level input for tape (which can also be used to input audio from a digital device such as an iPod).

Airline model 2940 console

The owner had just bought it to feature in their new home: a midcentury gem that this would feel right at home in. My task was to ensure it had another 50 years of life in it.

After turning it on and listening, it was clear that it needed some TLC. The unit had a slight hum, and the overall sound quality was just a little “off”.

Technical Specifications

The Airline model GAA-2940 console is a solid state amplifier, AM/FM radio, and turntable with the following specs:

  • 10 Watts per Channel Audio Power Output at 10% distortion
  • 30 – 12kHz frequency response
  • Delco DTG 110 Germanium Output transistors
  • Class AB configuration

These specs should tell you that this unit is not a real performer in terms of output power or high fidelity audio reproduction. However, its midcentury modern style is not without charm, so we’re going to try and make it sound as good as we can.

The 2940 came with a nice original schematic (with parts list) and a cool owner’s manual.

Airline GAA-2940 Schematic (click for larger version)

First things First: Rebuilding the Power Supply

The first order of business was to look into the source of the hum, which often indicates an issue in the power supply – often old leaky filter caps. With electrolytic capacitors in a unit this old, I generally replace them with modern high quality capacitors (long life, high temp). So my first task was to rebuild the power supply.

The power supply circuit of the Airline GAA 2940

C17A, C17B, and C17C were a multisection can capacitor which was removed. C18 was a very large electrolytic which was also removed. I prefer not to use replacement multisection caps for two reasons: 1) Multisection can caps are expensive and 2) Multisection can caps are generally only rated for 1000-2000 hours at 85 degrees Celsius.

For power supply replacement caps, my preference is for using individual Nichicon UPW series caps mounted on a terminal strip. These are rated for long life (2000-8000 hours) at high temperature (105 degrees). You get a more reliable, rugged cap for a price a fraction of what you might spend on a multisection can cap.

In this power supply circuit I also replaced R96, R97 and R98 with metal film resistors, as the carbon composition resistors in the unit had drifted out of tolerance.

The new power supply caps – replacing the multisection can cap.

Ciao, Ye Olde Electrolytics

I then replaced the electrolytic capacitors on the preamp/amp board. The old caps had drifted quite a bit and were very leaky.

Cleaning Pots & Switches

I always clean all switches with DeOxit D5 and potentiometers with SuperWash (or other contact cleaner that plays well with carbon such as DeOxit F5).

But… The HUM!

After rebuilding the power supply and replacing the electrolytics, the sound was much improved – however, with the volume at 0, a mysterious hum persisted that drove me to look deeper into the cause.

Using an oscilloscope, I was able to visualize the hum and it appeared to be a combination of 60 and 120 cycle frequencies.

In order to ensure this hum was not coming from the power supply circuit at all, I replaced the rectifier diodes, which looked a little scorched, with 1N4004 diodes.

I also implemented best practices for grounding components after finding that there were many points on the chassis that different components were grounded to – including the 6.3VAC lamp circuit. I unsoldered the pots from the chassis and connected them to a star ground, along with the preamp board.

After many hours of work, the hum was only reduced slightly. None of these things eliminated the hum entirely. Using an injected sine wave and oscilloscope, I was able to isolate where the hum was coming from – the output stage.

Learn how I solved the hum problem in Part 2 of my repair saga.

  1. Andrew Kimball Andrew Kimball

    Hi, caution, many questions coming.
    I recently purchased a Wards Airline Solid State console although much smaller. I am struggling to get the record player to work. The radio works but audio isn’t the best. I have replaced all the electrolytic caps except the amp ones. I do have a lot of questions and comments from this write up. Our chassis’s appear very similar from the few pics you posted.
    1. One I don’t have the circuitry next to the two amp circuits on the same board with the 2 orange wires. What is this for? My board simply has pre-cut holes in that approximate 2″x2″ section. I am wondering if this is the “tape input” amp or something? My console does have 2 additional input (assumed) ports just below the record player inputs but no dial position for tape. These ports connect straight to the black wires on the germanium transistors
    2. My radio has similar Germanium transistors outputting to the speakers. These have identical first two sets of numbers: 466 2780 followed by 6707. Do you recommend I do the same the MJ15016 PNP silicon transistor swap? I do not have an oscilloscope to play with.
    3. What record changer did this have and what cartridge was in it? Mine is a BSR UA25 with the SX1M cartridge rated at 250mV at 1cm/sec. I am guessing my cartridge is faulty as no sound emits beyond whats at the needle only. When I plug my other BSR in with a Pickering V-15/AT-2 I get plenty of good sound from the record but probably not as loud as the radio can go, maybe about 75% loudness.
    4. One of the 4 visible coils has the internal loop lead broken. This is a red single coil. There is also a green coil and a double stacked red coil on the same board. I strongly believe this is L2 in the schematic on the PC3 Multiplex circuit board. My board is stamped A1-4. Do you know what this coil does?
    5. Does the FM stereo light bulb do anything to the circuit. It’s busted and I plan to replace it. I know the older tube radios the bulb was integral to the circuit but not sure about the solid state circuits.

    Thanks for all the help. I might have more questions in the future.
    Andrew

  2. Hi Andrew,
    I’ll first say that if you have a different model entirely, the circuit could be radically different than this one. I’d try to seek out a model number and appropriate schematic if possible. You might need to dig up a SAMS Photofact at https://www.samswebsite.com/ if your unit did not come with documentation.
    1) The board with the two orange wires you menion is PC-1, the audio circuit board. You can see it referenced in the lower right of the full schematic. It is basically some preamp stuff and the main power amp circuitry (minus the power transistors). The tape input does not have a separate amplifier circuit associated with it – that input goes directly into the input selector switch.
    2) The 6707 is likely a date code – mine was 6625 (25th week of 1966) yours is 7th week of 1967). So your transistors are the same. The MJ15016 will work as a replacement – provided you re-bias as I describe in part 2 of this post. The trick is: if you don’t have a scope, it’s gonna be tough to see when you’ve eliminated the crossover distortion and properly bias. If you overshoot, you could risk driving the transistor into “thermal runaway”. So I’d be conservative here.
    3) I don’t remember what changer or cartridge this had in it (this is not my console so it’s now at the owner’s home). Looking at the circuit, there is no phono preamp that I can see. The phono inputs are treated the same as tape inputs! So you might experiment with adding a phono preamp stage in between the phono and the phono inputs. That would definitely raise the phono volume compared to other inputs. You could also add a RIAA EQ which should improve tonal balance on LPs. Something to tinker with.
    4) I can’t comment on this without seeing it and knowing the schematic of the circuit. But if the radio works fine I wouldn’t worry too much about this. Usually those coils were part of the tuning circuit.
    5) If your model is like mine, you’ll see the two bulbs in the lower left of schematic – they come directly off of the secondary windings of the power transformer. If one goes out – no worries. It won’t hurt anything or affect other parts of the circuit. You are right in older tube radios that do not use a power transformer, sometimes the light was wired in series with the tube filament heaters so if the bulb went out, the whole circuit was dead. But this is not the case here.
    Best of luck with your repair work – glad to help!

  3. Andrew Kimball Andrew Kimball

    Do you have any pictures of the chassis you saved elsewhere? From what I have cross referenced on my chassis, I believe these are much the same circuits. I have checked many of the resistor and cap values in their relative areas with the schematic and the values match. My chassis also shows the 8 boxed coils on the main board called the AM-FM Circuit board. I downloaded the 3 page schematic from radio museum. My end coil on my chassis is stamped 1457 which matched T3 (far right) on your schematic as this is also next to two diodes.
    1. Is the tone control board an amplifier in a way? I am still new to the different type of circuits and trying to reverse engineer each.
    2. I will hold off on the germanium replacement PNPs until the rest works.
    3. I could get a pre-amp for mine and see if it helps. Do you have a cartridge recommendation? I was thinking the BSR SC5H at .59 V with 1.5-3 grams force or the Pfanstiehl P-132d Phono Cartridge at .4V at 4 grams force. I think both could fit my single screw mount tone arm.
    5. Mine only has one bulb that I can find… Interesting.
    6. Are the voltage values on outside the individual circuit boards where are the connection points cross the dotted lines for voltage readings only? If so I could use these to help troubleshoot any issues.
    Thanks, Andrew

  4. I do have additional photos of the chassis, which is stamped B33A56 7002 on the side in black ink. Unfortunately, I cannot add these photos to a comment. I may not have any shots of the AM-FM circuit board, as the radio circuit was working fine in mine and I didn’t touch anything on that board. I will add a few photos to the end of Part 2 of this blog post when I get a chance.
    1. The tone control board is simply a set of RC filters with variable resistors (pots) that controls how the circuit handles different audio frequencies. It is not an amplifier – and you will notice on the tone control board there are no transistors. Thus, gain actually *decreases* across the tone control board – the opposite of amplification. The tone stack in this amp is known as the “James tone stack” and you can learn more about how it works here: https://www.ampbooks.com/mobile/amp-technology/james-tonestack-analysis/
    2. If your circuit sounds good and noise is minimal you may not need to replace the germaniums at all. In general, I like the sound of germanium transistors – nothing wrong with them – but mine were noisy and caused an audible hum, likely due to overheating over the years. If you’re happy with the sound of yours – keep them in.
    3. I have no cartridge recommendation off the top of my head. Just remember this is not a HiFi console – as I point out in my post. I wouldn’t spend money on high end components when the unit itself is only rated up to 12 kHz frequency response.
    6. The voltage values are indeed for voltage readings. Set your multimeter for DC V and connect your negative lead to the chassis and positive lead to the appropriate point on the board. Measured values that are more than 5-10% off spec will definitely help you identify trouble areas.

  5. M M

    So I came across one of these and am going to refinish it. As far as I can tell its in working order the radio works but record only plays for a second or so before the spinning stops. I think it just needs a new belt. I can’t for the life of me find any info on what size belt it needs. I’ve scoured the internet and can’t find a thing. I have the exact same model as you have in the pictures. Any help would be greatly appreciated.

    • Sorry for the late reply – this record changer does not have a belt at all – it runs via an “idler wheel” which is coated in rubber. The motor spins the idler wheel, which in turn spins the platter. Sometimes these idler wheels dry out and lose their ability to turn the platter. Other times old hardened grease in the changing mechanism can cause issues. Best to completely remove, degrease, and re-lubricate the entire mechanism – and then get the idler wheel replaced. Contact Gary at Voice of Music and he can help you with the idler wheel part.

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