[Drake] follow up TR4c AC hum

[WA3FIY]

Hello Larry,

You are probably using low impedance headphones and the 
Drake is WAY over driving them.   For much better signal to 
hum ratio and to protect your hearing against overly loud 
signals, may I suggest you put about 220 to 470 ohms 
resistance in series with the phones.  If they are stereo, put a 
resistor in each circuit.

-73-

-Lee-

On 30 Jul 2002 at 16:24, WA2DGD wrote:

> 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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