Paramount 220v version

[Demsy]

Grainger, our line voltage here is 220v daytime and could go down to 200v at night. For this I already use a 5kVA automatic voltage regulator, which is now set at 220V. I also connected a manual slide regulator, set at 240V, to it. Of course I can bring the voltage up to 250V, but the point is to find out first why the filament voltage is still below the specified 5V even at 240V. I really don't have the desire to keep the chain of regulators in my music room.

[Grainger49]

Ok, I had not read that you had brought your input to the Paramounts to 240V and still not brought the heaters to spec.  Sorry!

I'd say Paul Joppa will come up with the answer.

[Demsy]

PJ, if the line voltage were set 250V, would there be any negative consequences for the transformator and it's other outputs?

[Paul Joppa]

>>> "PJ, if the line voltage were set 250V, would there be any negative consequences for the transformator and it's other outputs? "

No, none.

I have developed a preliminary set of recommendations to give the 5.00 volts with line power of 220, 230, 240, and 250v, and interpolation will allow intermediate voltages to be accommodated. I am not yet ready to post them.

[Demsy]

Thanks PJ. Good to know that the recommendations are on it's way!

[Demsy]

Any progress so far, PJ?

[Doc B.]

PJ is away for a week or two.

[Demsy]

Hi PJ,
How's the development of the recommendation?

[Paul Joppa]

Sorry for the delay; several of us have been absent off and on and out communication is a little haphazard!

I have given Doc B a draft writeup which he will probably post on the site once we are all agreed it's satisfactory. Meanwhile, for the specific problem of a Paramount on 220v, the best solution is fairly simple:

1) Wire the filament power choke as if it were for a 2A3. This will reduce the DC resistance from 0.6 ohms to 0.15 ohms, raising the voltage about 0.55v. The exact change depends on some uncontrollable variables such as the amount and type of distortion on the power line voltage.

2) It will also increase the hum a bit; if this is a problem you can place a 10000uF/10v to 16v cap across the output of the choke (positive to choke terminal 6, negative to terminal 1). This capacitor can be used with any Paramount to reduce the very small residual filament hum.

[Demsy]

Will the final solution be the same as what you've written? I'm not comfortable with the increased hum and additional components. I plan to use a high sensitivity (105db) loudspeakers in the near future.

[Paul Birkeland]

I'm not comfortable with the increased hum and additional components. I plan to use a high sensitivity (105db) loudspeakers in the near future.

I would recommend trying the choke rewiring.  If it does elevate the hum, then pop the cap across the output of the choke.  (10,000uF/16V)

[Paul Joppa]

With 105dB speakers (!) I would certainly add the capacitor. It will then be much quieter than the normal (240v) stock build.

In the proposal I made (the draft article) I tried to avoid using complicated or difficult modifications. The suggested mod will work well *5.00 +/- 2.5%) for voltages in the range 220-230 volts. There are different versions for 230-240v and 240-250v, and the stock circuit is excellent at 250-260v.  In my opinion greater precision is not warranted in light of fluctuations in available power.

[Demsy]

Thanks PJ and PB.
Would this apply for both of the 300B and 2A3 tubes?

[Paul Joppa]

No, the 2A3 is different and more complicated.

[Demsy]

PJ, easiest for me is to bring the line voltage up to 255v instead of the other mods, as you mentioned that for 2A3 it's different and more complicated changes are needed.