[Drake] follow up TR4c AC hum

[WA2DGD]

My original post:
Hello,
I have been using a tr4-c without any problems. I always listened using the speaker. I started using headphones and notice a significant hum with the volume fully ccw. To hear weak cw signals, I have to raise the volume to an uncomfortable level to get the weak signals above the hum noise level. 
I checked the AC4 and all the voltages are proper. I put a scope on the +250v line and can see about 2 volts p-p of ac ripple. I see the exact same waveform if I connect the scope to the audio output.
Can I simply put new caps of the appropriate values across the caps in question on the underside of the AC4 chassis? I would like to reduce the hum significantly. Are there any other known causes likely to produce this hum?
Thanks,
Larry 

Follow up:
I replaced the electrolytics in the 250v supply (C3 and C4a,b) with new electrolytics and the ripple went down to about 1v p-p. The hum improved but still not comfortable enough to listen to low level cw signals with headphones. 
I also put a 3 wire grounded AC cord on the power supply.
Any other suggestions, or is this standard for this vintage equipment.

Thanks,
Larry
WA2DGD


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