NC-183D Modification; Comments

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W3SLK:
So I have not had much success finding a power transformer for my NC-183D. Hammond doesn't list it as being made and back in the day, Peter Dahl would sell you one if you sent the old one in. The cost for it in 2004 was $165 plus shipping. I would think that to have Hammond redo it would be very costly. So what I am now considering is to use an Antek AS-2T350-200VA toroidal transformer. It will give me 700VCT @ 0.250mA and 8A of 6.3 filament current. Along with that I will solid state the rectifier whereby eliminating the need for a 5.0VAC filament. Opinions or other considerations are invited.

w4bfs:
Quote from: W3SLK on March 25, 2023, 09:55:34 AM

So I have not had much success finding a power transformer for my NC-183D. Hammond doesn't list it as being made and back in the day, Peter Dahl would sell you one if you sent the old one in. The cost for it in 2004 was $165 plus shipping. I would think that to have Hammond redo it would be very costly. So what I am now considering is to use an Antek AS-2T350-200VA toroidal transformer. It will give me 700VCT @ 0.250mA and 8A of 6.3 filament current. Along with that I will solid state the rectifier whereby eliminating the need for a 5.0VAC filament. Opinions or other considerations are invited.


the National manual calls for 6.3 Vac @ 5.25A and 260Vdc @ .14A plus more for receiver powered accessories about 70W.

the receiver internal supply is cap input full wave center tap with filter inductor.

the Antek toroid spec'd will generate B+ too high even if the input filter cap is removed (about 315 Vdc).

a better choice is the AS-2T200 .  to 'dial' this one in will require some experimenting.  I assume that you are recapping your receiver if not at least the caps off the B+.  be sure to get the ones at the transformer connections as these are likely the one(s) that killed ur stock xfmr.
since you are going solid state ps I would go to a bridge with secondary windings paralleled.
leave off the input filter cap for now.  when you power up you will get around 180V of B+
this is basically ok for now and check out the radio circuits for normal voltages.  then as the circuits check out you can vary the value for the input filter to bring the B+ to the desired 250/260V desired.  start with 2ufd or so minding polarity and be Safe

W3SLK:
W4BFS said:Quote

the National manual calls for 6.3 Vac @ 5.25A and 260Vdc @ .14A plus more for receiver powered accessories about 70W.

the receiver internal supply is cap input full wave center tap with filter inductor.

the Antek toroid spec'd will generate B+ too high even if the input filter cap is removed (about 315 Vdc).

a better choice is the AS-2T200 .  to 'dial' this one in will require some experimenting.  I assume that you are recapping your receiver if not at least the caps off the B+.  be sure to get the ones at the transformer connections as these are likely the one(s) that killed ur stock xfmr.
since you are going solid state ps I would go to a bridge with secondary windings paralleled.
leave off the input filter cap for now.  when you power up you will get around 180V of B+
this is basically ok for now and check out the radio circuits for normal voltages.  then as the circuits check out you can vary the value for the input filter to bring the B+ to the desired 250/260V desired.  start with 2ufd or so minding polarity and be Safe
I have a 200ohm 20W WW ceramic to drop about 50V. The secondaries didn't go bad, it was the primary! I was hoping I could find the issue near cover but it was all potted.

W1DAN:
Hi:

I may (?-gotta look and ohm it to see if it is good) have an HRO-50 or HRO-60 power transformer. Please check to see of one of these would work for your NC-183D. If so, I can drop it off at my local UPS Store and have them pack and ship at your cost. There would be no other charge for the transformer.

Dan
W1DAN

W3SLK:
W1DAN said:Quote

Hi:

I may (?-gotta look and ohm it to see if it is good) have an HRO-50 or HRO-60 power transformer. Please check to see of one of these would work for your NC-183D. If so, I can drop it off at my local UPS Store and have them pack and ship at your cost. There would be no other charge for the transformer.

Dan
W1DAN
I would appreciate that Dan. I have an HRO-50 that may have met the same fate. So either way I would need one. Let me know the shipping costs and I can send a cheque to you or any other form of payment you prefer.

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