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NC-183D Modification; Comments




 
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W3SLK
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« 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.
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« Reply #1 on: March 26, 2023, 05:55:48 PM »

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
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Beefus

O would some power the gift give us
to see ourselves as others see us.
It would from many blunders free us.         Robert Burns
W3SLK
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« Reply #2 on: March 26, 2023, 10:17:17 PM »

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.
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Mike(y)/W3SLK
Invisible airwaves crackle with life, bright antenna bristle with the energy. Emotional feedback, on timeless wavelength, bearing a gift beyond lights, almost free.... Spirit of Radio/Rush
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« Reply #3 on: March 27, 2023, 07:19:58 AM »

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
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W3SLK
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« Reply #4 on: March 27, 2023, 10:32:19 AM »

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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Mike(y)/W3SLK
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Bob W8LXJ
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« Reply #5 on: March 27, 2023, 11:35:38 AM »

Mine died in early 1970s.  Found a dead tube tv set, pulled transformer, checked good, still running in my 183d today.

  Bob W8LXJ
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« Reply #6 on: March 27, 2023, 06:01:22 PM »

about having design center power supply voltages - the National rx uses push/pull 6V6 tubes.

Have you priced a pair (matched) lately?
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Beefus

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It would from many blunders free us.         Robert Burns
Detroit47
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« Reply #7 on: March 27, 2023, 11:30:58 PM »

Tube matching is a scam. In my opinion.

N8QPC
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« Reply #8 on: March 28, 2023, 09:29:27 AM »

Tube matching is a scam. In my opinion.

N8QPC

Yes, most are done with the tube tester 'figure of merit' numbers and are of very limited value.  better than nothing.

if the tubes are matched at operating conditions by quiescent current and then equal gain, then u have something of worth

Mike = digging that Rush lyric  Grin
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Beefus

O would some power the gift give us
to see ourselves as others see us.
It would from many blunders free us.         Robert Burns
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« Reply #9 on: March 28, 2023, 11:43:03 AM »

To reply to a few comments:
WA1GFZ:Hey Frank! It's been a long time since we talked! Yeah, I was recommended to use the 200VA Antek on the antiqueradio.com forum. So I'll probably go that way. In doing so I remove the heat from the rectifier which creates less stress. I've heard nothing but good things about Antek so that is why I will go that route. Since you mentioned the 'Hot Rod' Valiant, I may use your audio board in mine. I may use WA5BXO's driver circuit also. Its not as complex as yours. I gutted the speech amp because of 60Hz hum on the audio. Bob, W2ZM(SK), did some serious BE mods complete with a tube of RTV. It has the 6146Bs in for modulators and a beefier HV transformer. So half the work is done. BTW my brother-in-law who you met when we had our eyeball passed away last year. He was 67, too damn young!
Mod-U-Lator.
Frank I tried to respond directly but got the 'Message Blocked' indicator.

N8QPC said:
Quote
Tube matching is a scam. In my opinion.
I agree 100% Bob. My friend Eric, WB4VVI(SK) taught me that a long time ago!

W4BFS said:
Quote
about having design center power supply voltages - the National rx uses push/pull 6V6 tubes.

Have you priced a pair (matched) lately
Yes, most are done with the tube tester 'figure of merit' numbers and are of very limited value.  better than nothing.

if the tubes are matched at operating conditions by quiescent current and then equal gain, then u have something of worth

Mike = digging that Rush lyric


I have a nice supply of 6V6's that I recently found in a box of tubes I had for years. So long as you don't abuse them, they will last forever.
BTW I'm a big Rush fan and thought the lyric was 'apropos'! Wink
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Mike(y)/W3SLK
Invisible airwaves crackle with life, bright antenna bristle with the energy. Emotional feedback, on timeless wavelength, bearing a gift beyond lights, almost free.... Spirit of Radio/Rush
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« Reply #10 on: March 28, 2023, 05:02:27 PM »

Mike:

The transformer I have looks to be an HRO-60 power transformer as it has the 11VAC winding for the regulated filaments. I tested the transformer and it seems to be good, no promises. Old style with no end-bell. Please be sure whether this will work in your NC183D or HRO-50 (that does not need the 11VAC winding).

I went to my local UPS Store and they quoted $42.04 to box and ship to Danville PA. Or I can bring it to NEAR-FEST.

I am a big fan of removing the 6V6s as they draw almost half the current in an HRO-60. I then use an external amp tapped from the volume or limiter potentiometer.

Dan

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W3SLK
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« Reply #11 on: March 29, 2023, 11:51:37 AM »

W1DAN said
Quote
Mike:

The transformer I have looks to be an HRO-60 power transformer as it has the 11VAC winding for the regulated filaments. I tested the transformer and it seems to be good, no promises. Old style with no end-bell. Please be sure whether this will work in your NC183D or HRO-50 (that does not need the 11VAC winding).

I went to my local UPS Store and they quoted $42.04 to box and ship to Danville PA. Or I can bring it to NEAR-FEST.

I am a big fan of removing the 6V6s as they draw almost half the current in an HRO-60. I then use an external amp tapped from the volume or limiter potentiometer.

Dan
I would say "Winner, winner, chicken dinner!", Dan. Let me see if anyone is passing nearby me on the return trip from NEAR-Fest and get it via 'Pony Express'. Hopefully that will save us both the expense of S&H. If not, then I'll send you the money to ship it. Either way it is greatly appreciated. The only amp I have is a Heathkit AA-14 with a pair of 6BQ5's in P-P. I found it and the matching speaker after an auction. It was sitting on the curb for the trash! Not exactly a McIntosh or Dynaco but it will suffice, (not that I would turn down one of those mono-block amps!).
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Mike(y)/W3SLK
Invisible airwaves crackle with life, bright antenna bristle with the energy. Emotional feedback, on timeless wavelength, bearing a gift beyond lights, almost free.... Spirit of Radio/Rush
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« Reply #12 on: March 30, 2023, 01:16:47 PM »

Mike:

OK, let me know what delivery method you would like.

For one of my HRO-60's I have solid-stated the HV rectifier, removed the audio 6V6's, clip-leaded from the top of the limiter pot to a 100k resistor then a 1uf mylar capacitor. This feed the instrument (hi-z) input of a tabletop powered speaker similar to a Fostex 6301. The audio is cleaner, louder and with more headroom.

I also reduced the rear chassis fuse from 2A to 1A to help save the power transformer. On another HRO I added a 1/4a fuse from the HV secondary center tap to ground.

Dan
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