Airline GAA-2940 - Power Supply 60 Hz Hum

It's a bit of a mess - 120Vac line voltage wires running right next to Vdc wires running close to 6Vac wires - all on two sets of criss-crossing seven lug terminal strips. When I get the new output transistors I'll see if I can try to clean that area up and keep the AC wires as far away from DC wires as I am able.
With what you've done/tried, the birds nest of ac/dc wires may be the cause.
General rules are that AC active and neutral wires should be twisted together, something about cancelling fields. And DC voltage wires should be kept
as short as possible. You might have to rewire the birds nest using these general rules. Maybe someone with more experiance will chime in, fresh ideas welcome.
 
Update: My MJ15016 transistors are on their way - but in the meantime I decided to take one of the DTG110 transistors off and test it.

These transistors are not connected to the heat sink. They are isolated from ground by a thin transparent film. The film has some kind of gel on it - probably old thermal paste. The screws that connect the transistor to the heat sink have isolating washers around them so that the transistor is not electrically connected to the heat sink at all. The isolating washers seem kind of cheap and somewhat misshapen.

(Honestly - the build quality on this Airline is a step below the Zeniths and Magnavox units I've worked on.)

I'm wondering if there could be some short in these isolating elements - or if they are conducting small amounts of voltage across them due to age. Thinking about replacing these parts (isolating film and washers) with higher quality parts just to ensure the new transistors are completely isolated.

When I removed the DTG110 transistor and tested it on my LCR-T4, it measured as a PNP transistor but only registered an Hfe of 15 and Vf = 87mV - that seemed very low. When I tested it a second time, it measured as a PJFET. ??? Wondering if it just went bad due to overheating through the years.

I'll see how the others test - but otherwise will proceed with my plan to replace them.
 
Replacing worn/tired parts on the way sounds like a good plan.
Any AC (ripple?) at that point should be 120Hz after rectification.
Apart from the birds nest wiring you could look at the GND circuit (again).
What you may have is a combination of a multiple of chassis connections and a chain of boards/items connected in series.
Ideally there should be only one chassis connection, the star centre. The chain should be broken up into short segments (star points)
with a connection wire back to the star centre. If you fail to disconnect the chain and connect to the star you will have another loop and
even more hum.

This should only involve relocating wires. Important to test/ohm all segments have a connection to GND.
 
Replacing worn/tired parts on the way sounds like a good plan.
Any AC (ripple?) at that point should be 120Hz after rectification.
Apart from the birds nest wiring you could look at the GND circuit (again).
What you may have is a combination of a multiple of chassis connections and a chain of boards/items connected in series.
Ideally there should be only one chassis connection, the star centre. The chain should be broken up into short segments (star points)
with a connection wire back to the star centre.

Good advice, mbz.

After carefully tracing the entire power supply circuit and GND connections throughout the unit, I have determined:
  • The power supply circuit has no less than five different ground points on the chassis. This seems like a prime candiate for ground loop hum.
  • The Volume and Balance pots are both grounded to the chassis at two different points (this is in addition to the grounding point for the amplifier board which is on a separate point)
I've held off replacing output transistors until I clean this up. I am going to focus all power supply grounds to a single point and see if that helps.
 
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I will follow with interest to see if the theory and practice align.

Recently I had success with a humble Marantz 1050. it used a chain as described, broke it up into
segments connected to star point, I was surprised how well it worked in reducing hum. Your case
is slightly different, everthing is connected to the chassis rather than the chain, however this "must"
cause GND loops. A star system still appears the way to go.
 
UPDATE: After rewiring the power supply to a single chassis ground, grounding the pots + tone board + amplifier board to a single chassis ground point, replacing all four Germanium DTG110 transistors with MJ15016 silicon transistors, and rebiasing the circuit to eliminate crossover distortion (for reference, I changed R19, R21, R39, and R41 from 2.2 ohm to 10 ohm resistors), the console NO LONGER HAS HUM!!!

When I first turned it on with volume at zero I thought I must have broken something because it wasn't making any noise. That was just the wonderful sound of silence! It's nice and quiet now. Sounds good too! The silicon transistors are clean and clear - sounds better than it ever did.

Thanks everyone for your help!
 
Congradulation on this huge effort. Now that you have this first hand knowledge you can help others. Hums come up frequently.
 
UPDATE: After rewiring the power supply to a single chassis ground, grounding the pots + tone board + amplifier board to a single chassis ground point, replacing all four Germanium DTG110 transistors with MJ15016 silicon transistors, and rebiasing the circuit to eliminate crossover distortion (for reference, I changed R19, R21, R39, and R41 from 2.2 ohm to 10 ohm resistors), the console NO LONGER HAS HUM!!!

When I first turned it on with volume at zero I thought I must have broken something because it wasn't making any noise. That was just the wonderful sound of silence! It's nice and quiet now. Sounds good too! The silicon transistors are clean and clear - sounds better than it ever did.

Thanks everyone for your help!

What was the actual cause of 60Hz hum? Transistors — or grounding issue?
 
Dang, I wish I was talented and persistent enough to fix something like that. And I have a couple sitting around half-done.
 
What was the actual cause of 60Hz hum? Transistors — or grounding issue?
60Hz hum means the hum is finding its way into the audio path before rectification so generally speaking it was a
grounding issue though that can be a massive generalization. Problem could be bad GND screw/contacts, multiple GND
contacts, poor wiring layout eg, mains voltage wires in close proximity to audio wires, failed rectifier and much more...
 
Both. Fixing grounding issues reduced hum - and replacing output transistors eliminated it.

Hello Cecik!

I have the exact same problem as you with my Ward's Airline Console. Model number

I go into more detail in two blog posts I wrote about the repair:
https://www.tubesandtransistors.com/airline-gaa-2940-console-part-1/
https://www.tubesandtransistors.com/airline-2940-console-part-2/
Hello Cecik!

I have the same humming problem that you fixed on yours. I have a Ward's Airline Solid State as well, model number GHJ 2647A.

I'm not sure how much different mine is from yours, but here is the audio output from the schematic.

Also, here is a YouTube link I uploaded.
 

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I have the same humming problem that you fixed on yours. I have a Ward's Airline Solid State as well, model number GHJ 2647A.

I'm not sure how much different mine is from yours

From your video, your model is quite a bit different than the one I repaired. My advice would be to start a new forum thread with the model number in the thread title, upload a clear image or PDF of the schematic, and go from there.

Before you go to the great lengths I went, I'd say start by 1) Replacing electrolytic caps - especially in power supply stage, and 2) doing a deep clean of all switches and connectors with DeOxit D5 and pots with DeOxit Faderlube. You might find just doing that will make a difference.

Worst case, you eliminate a ton of variables as you continue to troubleshoot - best case, you solve the problem. ^_^
 
From your video, your model is quite a bit different than the one I repaired. My advice would be to start a new forum thread with the model number in the thread title, upload a clear image or PDF of the schematic, and go from there.

Before you go to the great lengths I went, I'd say start by 1) Replacing electrolytic caps - especially in power supply stage, and 2) doing a deep clean of all switches and connectors with DeOxit D5 and pots with DeOxit Faderlube. You might find just doing that will make a difference.

Worst case, you eliminate a ton of variables as you continue to troubleshoot - best case, you solve the problem. ^_^
Thank you for your reply so quickly!

I've tried soo many things to get rid of the humming, one of which was getting the caps and power cord professionally replaced, so I came across this post and figured I could try it.

Thank you for your advice!
 
I've tried soo many things to get rid of the humming, one of which was getting the caps and power cord professionally replaced, so I came across this post and figured I could try it.

One thing I learned about the Airline brand - they were made cheaply for sale in department stores and not known for their build quality or use of high-quality parts.

As you read from my post, I had to replace all electrolytic caps (nearly every single one had drifted out of tolerance and was leaky), redesign the PSU, rewire the grounds, replace and re-bias the output transistors to get rid of the noise.

Good luck!
 
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