[ARC5] BC-453 B dynamotor hum

[Michael Hanz]

Typical ripple for a clean dynamotor is usually *less* than one volt per 
hundred volts of output, Jim.

1)  What's the frequency of the ripple?

2)  Is it sinusoidal or pulse-based?

3)  How clean is your low voltage DC supply?  Put the scope on it while 
running.

4)  Have you checked the brushes while running for unusual arcing? 
(Helps to turn the lights off.)  When was the last time you cleaned the 
commutators?

On 11/3/2015 9:44 AM, J Mcvey via ARC5 wrote:
> OK, it's confirmed, it's a stupid problem!!!!  I THOUGHT that I scoped the DC, but when checked again, It has deep ripples, more like alternating DC than DC!I jumped a 0.5 uf to ground at the B+ terminal of the output and the hum volume  dropped dramatically, but there was still an unacceptable 80V ripple.
>
> Question: What is the the ripple normally seen at the dyno output?                 Is there possibly a defect in the dyanamotor where there is a missing winding in the armature causing the ripple?
>   
>
>
>       On Monday, November 2, 2015 11:41 PM, J Mcvey via ARC5 <arc5 at mailman.qth.net> wrote:
>     
>
>   I found an exact replacement audio output transformer in an "extreme restoration challenge " receiver that was way on the back burner.No joy., the problem still persists. I even replaced the 2 meg grid resistor because it seemed unstable and it read 2.85 meg.
> This makes no sense, so its going to be something really stupid!
>   
>
>
>      On Sunday, November 1, 2015 6:57 PM, Kenneth G. Gordon <kgordon2006 at frontier.com> wrote:
>    
>
>   On 1 Nov 2015 at 18:42, WA5CAB--- via ARC5 wrote:
>
>> It would need to be a plate to 70.7 volt line.  Your garden variety 70.7V
>> and 25.? V line transformers are line to voice coil.  A 70.7 volt line
>> happens to be 500/600 ohm line (it's a long story).
> Well, yes, but it also depends on the exact type of 70.7 V transformer. Those
> which are labeled or specified for varoius "wattages" output have
> impedances up to something like 5K ohms. I have forgotten the exact values,
> but can dig out the info.
>
> As I remember it, using the .625 watt output as the primary matches the
> output of the 12A6 stage almost exactly.
>
> I'll dig out the definitive info and post it here asap.
>
> In any case, secondaries are 4 and 8 ohm, and in some rarer cases also 16
> ohms.
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