The AM Forum

Got an old Ratty NC300.. Covered in nicotine, years of Grime..  So bad I figured this was the last ditch effort.. Put it in the dishwasher.. Pots and pans heavy cycle with a couple packets of Cascade ultra.  

To say it came out nice is an understatement.. Its like new!  I dont think 2 hours of hand scrubbing would compare to this!  I am running it again for good measure.. Removed the racks and put pieces in as sections.   All Knobs and controls when into the basket that holds the silverware..

Obviously... Remove items you feel might get damaged.  

I will post pics of the thing when its all done.  Gotta run to AES and pickup the Hammond 600 ohm to 4 ohm transformer for the audio output.  Should be up and running tonight.  It will be used with the GK 500C as that is what leo used in the adds from the 50s.. :)

This is a BEFORE cleaning picture..

Clark

Oh, I thought you put the entire rx in the dishwasher!

Brett

I did..  LOL. Thats the case and the knobs in that picture.. Just remove items you think might get damaged.  Transformers.. Tubes,  Dials ect.. 

This one was a mess.  Looks like it had been in a barn or patio for 20 years.  Sprayed it down with soap and hit it with a paint brush to get Grime off.. Then tossed her in the dishwasher.. Shes on the second cycle now..

I chose not to do the heated Dry cycle.. I have had a couple cheap kitchen knifes get melted with this machine.. So I turned that feature off.

When it comes out this time.. I am going to wipe it down with some Furniture polish to shine up and to stop rust
Clark

I think you'll like the NC 300, having a boatanchor with a backlit, analog tuning dial that actually shows you what frequency you're on is worth the price of purchase.  ;D

If you can get hold of the multi-tap RadioShack 10 Watt 70 Volt Audio Transformer, #320-1031, it will also do your speaker output impedance conversion much cheaper than the Hammond.

To late on that info.. I already drove up to AES and got the Hammond.  $20.. Ouch.  Case and knobs came out nice.  All that dirt and Crap is gone.  Just plastic and metal inserts.  The Big insert on the main knob is real bad.  Might look for a replacement.

Got the caps in.  Going to fire it up in a few minutes.  Wish it had BC band for testing. Going to have to get the Sig gen out I guess.  Or an HF Rig and Dummy load.

Question..  This  NC300 is light and Dark grey.. All the ones I have seen are brownish two tone color.. Does this signify a year or version?

C

The one I had was light/dark grey. Don't know serial #'s.

The other nice thing about the 300 is that it was designed for ham bands, unlike other older band cruisers, it's "hot" all the way up to 10 meters. When 10 AM opens, you'll appreciate that.

Why do you need a matching transformer? It should have an 8 ohm output.

73
Darrell, WA5VGO

Was kind of shocked to see this one go all the way to 225 meg!  THat means I can use it with my Heathkit 2 meter AM Transmitter.  

Only problem I have now is I cant seem to figure out what holds the DRUM.. It moves along with the band switch as normal.. but if you let off the Drum then it derails..  

C

This one is clearly marked "600 ohm" on the back Darrell.   

C

Here's some info on the paint colors and year models.

http://www.virhistory.com/ham/nc300/nc300.html (http://www.virhistory.com/ham/nc300/nc300.html)

600 ohm speaker: y'know, come to think of it, I've never heard of an NC-300 or 303 with a speaker output other than 8 ohm. The antenna terminals should say "300 ohms" on it, and it looks a LOT like a speaker terminal, so maybe...... ???

Specs for the NC-300 say 8 ohm voice coil for speaker

Specs for the NC-303 say 3.2 ohm voice coil for speaker

Here are the final pictures..  Very little testing done..  No BC band.. Have to drag it in the main room and hook it to the big antenna.  It came out spotless clean..  1000 times better.  All bands working up to 10 as normal.

Not sure what to tell you guys about the speaker. This one is labeled 600 ohms and required the transformer.  Maybe older? 

I have one 6BJ6 that is testing 10 on the TV7. I dont have another one.. Still seems to work though!  I will have to locate one and replace it.

In the case..  Maybe one day I will paint the case. It needs it.

C

No..   Mine has 600 OHM audio output. Its not line out.Its powering the speaker loud. There are no other connections on the back for a speaker.  Just the normal strips for Mute/standby and antenna.  Its not modified. Its clearly original with no extra holes.  I traced this line back to the audio tube directly before we put it in the case because you guys had me wondering.  If I hook the speaker up I get no sound.  If I hook the 600 Ohm transformer up its super lound like it should be.  Not sure what else to say on this.  Maybe they made a few at 600 ohm and then changed them?  Maybe they made some this way to use older speakers? I just do not know.

Someone will probably read this and have an explination.. I am all ears!

I had an nc300 and a 303, and both were 8 ohms.
Maybe they made some special ones for the govt?.

If it was me, I would replace the output trans with an 8 ohm output one and do away with back to back transformers, or just take audio off the detector and feed it to the marantz.

I liked the nc 300 and 303, but dont think the audio amp was anything to get excited about.

Brett

I will look into that. Not much low end on this reciever. 

I just got it to sit next to the King 500 as that is what he used.  If it works decent and sounds good on 160.. I am good.    I have other recievers that are better.  halli's Hammers and 390s.   Dead tired.. I spent alot of time on this thing compressed into two days. Once I start something, I like to finish it..




C

Yes, the r390 is a better receiver, and I never liked the art decco style of the 300 series receivers, but it was stable and had that very nice freq readout.

I think it was also a little narrow for AM, no?

Brett

Some Hallicrafters had 500 ohm outputs, the matching speakers had a transformer in the cabinet. That would be like a 70 volt / 600 ohm PA system output capable of driving a multi speaker distribution system or a very long speaker lead efficiently.

The small cheapo 70v/600 ohm transformers have poor frequency response, no lows at all, as they were intended for pa horns.... the 10watt or higher tranformers usually sound much better.

Those are converter bands.  The radio itself doesn't go up that high; it's just calibrated as such for the accessory VHF converters.

Also a 120V/6.3V fil xformer makes a great replacement audio output for a 6AQ5 to 8 ohms.  

You put the whole thing in the dishwasher... chassis and all? ??? 
I have  a '303 that could use that treatment!

Its alot of work..   This one was a mess.  Transformers, tubes, IF cans dials ect.. All should come out..  Like I said, use your discretion on that :) 

I am going to listen to it for a while later tonight.. Time for a late dinner.

Thanks for the tip on the Fil trans!!!
C

The speaker terminal strip on my NC-303 was stamped with 3.2 ohms. From the parts list, the audio output transformer in the 303 was labeled B19435-E whereas the audio output transformer in the NC-300 was labeled A13615. National also used the same part numbers for parts that were common to both units so obviously these two audio transformers have differences. Also there was a slight difference in the output circuitry. In the NC-300, a 100 ohm resistor was bridged across the output of the audio transformer, whereas in the NC-303 a 33 ohm resistor was bridged across the output transformer. The factory service document that I have for the assembly line test and alignment for the NC-300, says an 8 ohm speaker. I don't have any factory assembly line docs for the NC-303. For all practical purposes whether the audio output is 3.2, 4, or 8 ohms, hanging a 4 or 8 ohm speaker on the output wouldn't make any difference  especially on a communication-type receiver.

I have several versions of the NC-300 manual and none of them have a 500 or 600 ohm output.

National also issued a bunch of service addenda on the NC-300 during its life-cycle. It had problems.

on a really nasty radio, thats the only way to go. take out yer dials, xfmrs, ,etc, anything that would be damaged by water and detergent.

you gotta watch out for eh wrinkle though, sometimes it will soften it up. Usually a a few hours in da oven at around 200 degrees will lock it back down again.

teh best ever drying method is a professional force dryer for dog grooming. it has heated air at about 100 degrees with a hose, much better and safer than a air kompressor. faster as well, point it into the radio and let it blow. will totally blow a chassis dry in about 15 minutes. They are like the better hand air dryers in yer restaurant bathrooms. Dry- Eaz is a good brand.

A good working 300 is a pretty pleasent rx to use. Be sure to check the tone and sensitivity switches on the backs of the tone and RF gain potz. Mine has crapped out 2 12AT7s in the detector / meter amp. Also if you have a low sensitivity problem, check out the grid parasitic and screen dropping resistors on the first RF amp, IIRC they are a mother to get to.

my biggest dislike for the 300 is that damned 6BA7 first mixer. They are just noisy tubes, and you offtimes still hear some background noise, even with a needle bending signal! !

                                                           The Slab Bacon

Clark,

   I once had a HQ170 that had been through a flood. I should have tried your trick.

I do wonder though, If I put radio gear in the dishwasher, the XYL here would have my head. :'(

So do the dishes now taste like cigerettes?

Running a few cycles through the dishwasher after such a project might be wise. You don't want to leave some chemical film on the dishes..

I always enjoy your posts,

Take care,
Jim
WD5JKO

It looks like I have an ULTRA RARE NC300!   Its serial number 1!!!!    That explains the 600 ohm output. 

Maybe I should ebay this for $1000?  $1500?  $2000?  ;D ;D ;D   Then just buy another ham fest special and save it from the scrap heap!

The IF and RF filters where confusing at first..  I had my Brother Transmit on the Champion and I sat in the other room with the manual and played with settings. Once I got it out to 8K wide, I got decent tone out of it. 

This set is SUPER sensitive.  It over loads very easy.  With a 20 ft piece of speaker wire flung over the door, I copied SSbers on 75 meters ulra clear..  They came up to 20DB over.  Its nice to have a Boat anchor with built in SSB.  We sat and listed to them for 20 minutes. No Drift.

Problems I need to address:

1. TONE CONTROL Does not do anything for the sound.. I hosed it with Deoxit. I just cant hear a difference.

2. DIAL DRUM HITS the edge on the Big rotating pulley!.  This Derails the Cord.  To get past 40 meters, You gotta lift the top and help it along.  This one has a Slight bevel to the edge of the Drum.  I wonder if thats factory or not?  I cant see any possible way to adjust this.. It must be slightly warped.. Going to have to file it down a bit so it clears. 

3. I am missing the LEFT SIDE CHROME STRIP.  Never noticed this before.  I thought it was there.. but now its not. Anyone have one? Probably not.. Oh well. It sits next to gear anyways.


On the dishwasher.. DONT DO this when anyone is home..  LOL.   After I was done, I sprayed the dishwasher down with cleaner and ran a Full HOT cycle.  I dont even think that is needed.  This is a new Whirlpool... It was clean inside anyways.

Clark

          " DONT DO this when anyone is home..  "

Clarks's Rule #1

This should be one of the things in the front of the ARRghL Handbook. It saves one from a lot of grief and angst.

klc

I don't know if this applies to the dishwashing method and antispotting rinse stuff, but after washing a radio I allows follow the last rinse with a distilled water rinse (it's cheap at the supermarket or use water from a dehumidifier) in case your tap water leaves mineral deposits/spots on the item.

You can find reproduction "donut" polished trim rings for the main tuning knob on your NC 300 from Charlie Talbott, K3ICH. He advertises in Electric Radio Mag and on eBay all the time. They are a perfect fit and absolutely beautiful. Priced at just a few bucks. He has many different polished inserts for many different radios. Shoot him an email for current pricing. You'll be glad you did! 73, Bill, w0ng

Yep.. Use distilled water. I also scrub with Furniture spray. Leaves a nice light oil and shine.

I will look through ER for the inlay.. I need that.. Mine is pitted bad.  I saw a guy on ebay. Not sure if that is the same guy. Its a BID auction.

C

My 5Y3 rectifier is SUPER HOT.   So hot it made the top of the case very warm in one spot..  This tube is beyond what I would say typical.

Can any other NC300 owners tell if that tube in fact runs real hot?  I better plug this thing into my Eico signal tracer and check current!

C

Eico shows 75 watts power consumption.   Manual states 60 APROX.   The Eico is pretty accurate..  My halli said 45 watts and it was right on the 45 line when tested. 

Should I be concerned?? Or just let it run?

C

did you test yer power supply filters? you didnt run them thru the washer too, did ya? That would b a sin.

Naw man.. I just tossed the entire radio in.. LOL.


Its got new caps and no hum!

I think I figured it out.. 128 volts at the wall socket!   Put on a variac and she came down.  Man the power company must ramp up during the winter to run everyones heaters.

I put a meter on the Lamp lead and set the variac for 6.3 volts.. It was running the fils up at 7.7 volts.. That cant be good for any of the tubes. 

Clark

yeah that's high line voltage for a set designed for 110.  I was jackin ya about the caps.  :D I know you done passed thru old radios 101.

Actualy its 115 volts :)    The way I do it, Is to tap onto the Fil line, Normaly the Lamps are on the fil supply.  Then turn the variac down so you get the correct voltage.   On my SP600, This was 117 volts,  On my NC300 this was around 114 to 115 volts.  If you set your variac to 115 your probably good :) 

C

I've done several R-390 RF decks in the dishwasher. Just make sure you pull out all the cans. The gears come out looking like new. Bake in the oven on the warm setting for an hour or two. Just make sure the YL isn't home. She thought I was making dinner. Not!

National NC-400 receiver has 3.2 and 600 ohm audio outputs. Probably wasn't that difficult for National to tailor a receiver for a specific customer needs even in the NC-303.

600 ohm speaker outpoot YES. AES had nice Hammond transformers for that job.

BTW what does she look like inside???  The cabinet is great!
The NC300 was a little drifty on warm-up

Fred

Its all back in the cabinet now. I have not used it much Fred.  Been using the SP600.   I( listed to hams on SSB with some speaker wire antenna. Thats about it.. I need to carry it in here and give it a real test tonight.  I have been busy building my Freq display for my Sp600.  AADE's DFD1.  I got the backlit version.. Works perfect with a simple Tube shield pickup! No wiring or soldering to the RXer!

C

Clark,

Rectifier tubes run extremely hot so it is most likely normal.  You will also find the 6AQ5 output tube runs hotter than the other tubes.

 If you didn't already replace them, two "good to replace" caps are the coupling cap to the control grid of the output tube (C-56) and the cathode bias resistor bypass cap (C-62C).  Leakage in either of these will increase current draw of the audio output tube (which is the single biggest B+ current "sink" in a receiver) leading to excess heating of the power transformer, rectifier, filter choke, output tube, and audio output transformer. 

I like my NC-300 a lot; I never have had a chance to try out the NC-303 replacement.

Rodger WQ9E

I checked overall current draw and it is exactly what the manual states.  I guess that tube just runs hotter then hell in there.  Its not cherry but its making alot of heat. 

C

Clark,

If the current draw is good then don't worry and use the radio because AC straighteners do run hot.  Two receiver tubes guaranteed to give you a blister if you touch them are the rectifier and the output tube.  They are generally near each other and as far as possible from temperature sensitive circuits. 

One of my friends from high school got in a bit of trouble with his mother when he decided to do an alignment on the FM tuner section of the family console stereo.  He pulled the chassis out of the cabinet and had it operating upside down on the nice soft living room carpeting.  He decided to look underneath after noticing a scorched odor and when he picked it up there were 4 small and one large circle burned into the cream colored carpet.  You could easily tell where both pairs of 6BQ5 output tubes and the 5U4GB rectifier were located for a long time after that repair job.  He was lucky the Vietnam war was over by that time or his mother probably would have signed him up AND provided some free ammo for charlie.

National kept a lot of the heat out of the earlier HRO's by keeping the power supply external.  My Pierson KP-81 has both the power supply and audio output stage separate from the main receiver so the big heat producers aren't in the same box as the tuned circuits.

Hahah.. Funny story.. I did the exact same thing to my moms carpet.. Except it was truly an accident.. I was BIG time in RC cars.. I plugged a battery pack in to charge and set the 15 min timer and left.  The timer failed and it never hit OFF. It fast charged that battery until it scorched the carpet in the living room.  Lucky I did not burn the house down. I was not out of trouble until my dad verified that timer was defective and then stood up for me.

Or have your JN 30 ft of RS mast and 2 meter collinear drop onto the parents roof during a midnite storm when u were 15!

Not a happy parent

Carl,

So being a very quick thinking novice, I bet you used this occasion to explain why they needed to buy you 60 feet of "real" tower so this won't happen again  ;)

But now spouses take the place of the parents.  Early one Saturday morning a couple of years ago my wife was slowly waking up when she heard Anna loudly ask, "Daddy, why is your transmitter on fire?"  Maureen came flying into the radio room as I will killing the power to the Desk KW.  One of the cooling fans went up in smoke and created a few minutes of excitement.  My wife went into the kitchen and gave Anna (who was 4 at the time) the fire extinguisher and told Anna it was her turn to babysit daddy to keep him from going up in smoke.

LOL..  I had a DC choke in my valiant go out as I took a nap on the couch.  The smoke detector when off and woke me up to a hallway full of smoke..  I always hated lugging that Valiant around.. This time, I picked it up and ran it out side like it was empty cardboard box. That smell was around the house for days and in this room for a week. 

How about reaching over to pick up a Screw driver off the work bench and Grabbing a 50 watt iron directly with your bare hand?


C

Clark,

One drawback of the Desk KW is you can't pick it up and run outside with it.  I opened the windows to ventilate before the smoke detector and ADT/fire response got involved. 

After this incident I decided to only use one of the two thumbscrews that lock the works into the pedestal so it is possible to quickly slide out the works and use a fire extinguisher.  One of my colleagues, a former USMC pilot, suggested an on-board extinguisher for the transmitter.

Rodger WQ9E

I think the key is to use variacs that are accessable.  If you pull the power to the unit, There is not much inside that will keep burning. Power strips by your foot is a good idea.. Something to kill the power fast. Never leave this stuff running alone.  Turn it off when you leave.. Going to have dinner? Shut it off at the source. NOT the switch on the unit. My Dog turns my Globe king on.  I dont know why.. but he does.  I now have it on a switch so he cant turn it on. I have come back in and found the switch ON again.. Lucky for me, The power was not available to the king.

C

I have outlet strips in the bottom of each rack, the one next to the desk also does all the desk top equipment.
The only thing I ever set on fire is the heathkit antenna tuner.

I also have a few large halon fire extinguisers around...

Brett

Brett,

Your use of outlet strips allows quick shutoff in case of smoke and more importantly a non-technical type can easily kill the power if you get in trouble without having to find a power switch on a piece of gear.

For my main room radio room, I have several pieces of gear running on 240 volts (Johnson Desk KW and Viking 500, Collins 30S-1 and 30L-1, and a Drake L-7).  The 240 volt 30 amp line to this room has a separate shutoff switch and the I added fuse holders to the Desk KW power cord since Johnson depends upon the home breakers to protect the amp.  I wanted to be able to use low current fuses during restoration/testing of the Desk KW and once it was working properly I use a pair of 20 amp fuses in my cord mounted holder rather than depending upon the 30 amp breaker.  The associated exciters and receivers are plugged into power strips into regular 120 volt outlets.  One of my Christmas planned projects is to see how difficult it will be to provide separate power to the radio outlets in this room so I can use a single "kill" switch for the gear in it also.

Most of the gear is in a dedicated basement shack and I use a separate sub-panel for this room with a shutoff switch feeding it.  This switch is thrown when I am not using the gear and the lights and a couple of marked outlets in this room are the only thing not powered from the sub-panel.

I have seen several A/C switches fail on old gear and most of them have line bypass caps (some on the non-protected side of the fuse).  I don't trust the older components enough to leave AC power to the rigs when I am not around.

Rodger WQ9E

You should get him his own rig, maybe a DX-100 or a Valiant.

(But seriously, maybe he likes the heat?)

He lays around on the floor and flips the switch.  I got a real strong table rated for 700 lbs. We planned on raising the king up on the desk. But it was smaller and would not hold the CHamp.  So I have decided to redo the Store room with shelvs, Valiant, ranger and Champ will be in one room.  King and SS HF gear in the other. Probably complete this after the hollidays.

I dont use the King as much as I would like. Its on the floor and difficult to operate.

C

Ah. In that case maybe one of these would help.

(http://www.autotoys.com/pics/thumbs/t_plsw26.jpg)

I have that same switch on my race Car to control the 90hp shot of nitrous :)  You can see it to the left of the steering wheel.

C