Forums :: NEW! Web Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Dec Sun 05, 2021 5:38 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 14 posts ] 
Author Message
 Post subject: National NC-270!
PostPosted: Sep Wed 15, 2021 10:03 pm 
Member
User avatar

Joined: Jul Fri 21, 2017 9:58 pm
Posts: 3090
Location: Erie, Pa.
With matching speaker.

What a gorgeous radio, in Cosmic Blue!

The radio stirred some controversy here...

viewtopic.php?t=91498

Description -

"National NC-270 Ham Radio Receiver. IN pretty good ship, no scratches, all functions work, built in calabrator, changed 5Y3 to solid state rectifer to lessen heat, sprayed controls, manual included, works ok, like all vintage equipment could use a tuneup! chassis is clean, paint ok also"

Judging from the ARF thread, alignment can be tricky, but not impossible, but is vital for performance.

Did I misread, or does this want a 72 ohm unbalanced antenna? Can someone enlighten me?

I deaerve to be flogged with a Transoceanic whip for buying this, but what a beautiful piece!


Attachments:
Screenshot_20210915-163955_eBay.jpg
Screenshot_20210915-163955_eBay.jpg [ 196.79 KiB | Viewed 890 times ]
Screenshot_20210915-164002_eBay.jpg
Screenshot_20210915-164002_eBay.jpg [ 181.27 KiB | Viewed 889 times ]
Screenshot_20210915-163726_eBay.jpg
Screenshot_20210915-163726_eBay.jpg [ 196.33 KiB | Viewed 888 times ]
Screenshot_20210915-163756_eBay.jpg
Screenshot_20210915-163756_eBay.jpg [ 202.38 KiB | Viewed 888 times ]
Screenshot_20210915-163803_eBay.jpg
Screenshot_20210915-163803_eBay.jpg [ 188.79 KiB | Viewed 888 times ]

_________________
"Invisible airwaves crackle with life
Bright antenna bristle with the energy"


Last edited by Dalton on Sep Fri 17, 2021 10:09 pm, edited 1 time in total.
Top
 Profile  
 
 Post subject: Re: National NC-270!
PostPosted: Sep Thu 16, 2021 1:07 am 
Member
User avatar

Joined: Jun Sun 19, 2011 2:31 pm
Posts: 8072
I have one along with some of the other cosmic blue National receivers.

It is like other radios of that era and type, you do NOT need an exact antenna match for it to work OK. Practical antennas will present a complex impedance that varies widely across the operating range. If you want a perfect match, get a dummy load :)

I have seen the articles on the work some people have done with the 230 khz. inductors in these National radios. Maybe I am lucky but I have never had an issue with the IF strip alignment in these. My biggest criticism of these is they aren't as mechanically robust as some of the older and/or more expensive National sets. They work fine but the build and operation doesn't have the feel of a HRO, NC-183, NC-300, etc.

Rodger WQ9E


Top
 Profile  
 
 Post subject: Re: National NC-270!
PostPosted: Sep Thu 16, 2021 1:42 am 
Member
User avatar

Joined: Jul Fri 21, 2017 9:58 pm
Posts: 3090
Location: Erie, Pa.
rsingl wrote:
I have one along with some of the other cosmic blue National receivers.

It is like other radios of that era and type, you do NOT need an exact antenna match for it to work OK. Practical antennas will present a complex impedance that varies widely across the operating range. If you want a perfect match, get a dummy load :)

I have seen the articles on the work some people have done with the 230 khz. inductors in these National radios. Maybe I am lucky but I have never had an issue with the IF strip alignment in these. My biggest criticism of these is they aren't as mechanically robust as some of the older and/or more expensive National sets. They work fine but the build and operation doesn't have the feel of a HRO, NC-183, NC-300, etc.

Rodger WQ9E



"If you want a perfect match, get a dummy load :)"


ROTF

A few complain that this and similar sets are weak receive on 10 and 6 meters.

Could it be this is because they are using antennas optimal for HF?

I'm going to experiment! :D

_________________
"Invisible airwaves crackle with life
Bright antenna bristle with the energy"


Last edited by Dalton on Sep Fri 17, 2021 10:11 pm, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: National NC-270!
PostPosted: Sep Thu 16, 2021 7:19 am 
Member

Joined: Apr Sun 08, 2007 6:47 am
Posts: 5208
Location: British Columbia
I can never figure out the propensity towards introducing "sand" in tube equipment. Why is it considered a worthwhile improvement replacing a common full wave rectifier tube, like a 5Y3/5Y4 or a 5U4 with solid state rectifiers? I've seen this advocated with a National NC-183D as well, supposedly to reduce heat inside the cabinet, and transformer. But given the fact the the transformer is heat sinked by being bolted to the chassis, the cabinet is spacious and extremely well ventilated, the mod seems rather fruitless. They even include dropping resistors to keep the plate voltage from going too high, which sort of defeats the aspired goal.
If the intent was to boost the B+ voltage, for enhancing performance, well maybe? If the tubes were rare, expensive, or failed easily, certainly! I have a feeling that there are some people that just have to mod things for the sake of claiming they improved something, even though there is nothing really to be improved, the set was designed to operate at a certain temperature, in a given voltage range. If preserving the transformer is the goal, well the ones in the NC-183Ds didn't fail because of having a tube rectifier, they failed from the pair of bypass caps, between each leg of the H.V winding to ground, shorting out, replace them with safety caps or clip them out. Also I have never had a directly heated rectifier tube fail by shorting out, but silicon rectifier diodes do.
Regards
Arran


Top
 Profile  
 
 Post subject: Re: National NC-270!
PostPosted: Sep Thu 16, 2021 10:10 am 
Member

Joined: Dec Sun 14, 2008 3:33 pm
Posts: 1198
Location: Tokyo
Dalton, in case you have not seen these notes:

https://people.ohio.edu/postr/bapix/NC270.htm

There is mention of the power transformer getting very hot, suggesting a reduction in line voltage would be a good idea. I think it's a good idea in general, line voltage today being higher than it was in 1960.

The QST reviewer (Jan 1961) thought highly of the NC-270's 6 meter sensitivity. Which suggests your receiver on 10 and 6 may not be performing up to its original level. Or perhaps that the reviewer was not hard to impress.

Something I thought interesting in the design: V6, a 6BA6, is referred to as a pentode product detector. Yet it looks to me to be an ordinary IF amp stage, with the BFO coupled to its control grid through a small cap. I believe that used to be called 'enhanced BFO injection' back then. The heterodyned CW/SSB signal still ends up going through the AM detector diode. The later economy version NC-155 used a separate product detector, the output sent to the audio stages. Not a criticism, btw, just a detail I found interesting.

Rob


Top
 Profile  
 
 Post subject: Re: National NC-270!
PostPosted: Sep Thu 16, 2021 4:34 pm 
Member
User avatar

Joined: Jul Fri 21, 2017 9:58 pm
Posts: 3090
Location: Erie, Pa.
Arran wrote:
I can never figure out the propensity towards introducing "sand" in tube equipment. Why is it considered a worthwhile improvement replacing a common full wave rectifier tube, like a 5Y3/5Y4 or a 5U4 with solid state rectifiers? I've seen this advocated with a National NC-183D as well, supposedly to reduce heat inside the cabinet, and transformer. But given the fact the the transformer is heat sinked by being bolted to the chassis, the cabinet is spacious and extremely well ventilated, the mod seems rather fruitless. They even include dropping resistors to keep the plate voltage from going too high, which sort of defeats the aspired goal.
If the intent was to boost the B+ voltage, for enhancing performance, well maybe? If the tubes were rare, expensive, or failed easily, certainly! I have a feeling that there are some people that just have to mod things for the sake of claiming they improved something, even though there is nothing really to be improved, the set was designed to operate at a certain temperature, in a given voltage range. If preserving the transformer is the goal, well the ones in the NC-183Ds didn't fail because of having a tube rectifier, they failed from the pair of bypass caps, between each leg of the H.V winding to ground, shorting out, replace them with safety caps or clip them out. Also I have never had a directly heated rectifier tube fail by shorting out, but silicon rectifier diodes do.
Regards
Arran


I jnow what you mean. I have 2 183D's, one of which has a toasted transformer.

_________________
"Invisible airwaves crackle with life
Bright antenna bristle with the energy"


Top
 Profile  
 
 Post subject: Re: National NC-270!
PostPosted: Sep Thu 16, 2021 4:39 pm 
Member
User avatar

Joined: Jul Fri 21, 2017 9:58 pm
Posts: 3090
Location: Erie, Pa.
shinkuukan wrote:
Dalton, in case you have not seen these notes:

https://people.ohio.edu/postr/bapix/NC270.htm

There is mention of the power transformer getting very hot, suggesting a reduction in line voltage would be a good idea. I think it's a good idea in general, line voltage today being higher than it was in 1960.

The QST reviewer (Jan 1961) thought highly of the NC-270's 6 meter sensitivity. Which suggests your receiver on 10 and 6 may not be performing up to its original level. Or perhaps that the reviewer was not hard to impress.

Something I thought interesting in the design: V6, a 6BA6, is referred to as a pentode product detector. Yet it looks to me to be an ordinary IF amp stage, with the BFO coupled to its control grid through a small cap. I believe that used to be called 'enhanced BFO injection' back then. The heterodyned CW/SSB signal still ends up going through the AM detector diode. The later economy version NC-155 used a separate product detector, the output sent to the audio stages. Not a criticism, btw, just a detail I found interesting.

Rob


Thanks, Rob!

I do have a variac, so I will run this set at lower voltage, which hopefully will extend it's life.

Thanks for the notes and other information.

_________________
"Invisible airwaves crackle with life
Bright antenna bristle with the energy"


Top
 Profile  
 
 Post subject: Re: National NC-270!
PostPosted: Sep Fri 17, 2021 2:42 am 
Member

Joined: Apr Sun 08, 2007 6:47 am
Posts: 5208
Location: British Columbia
I would try running the transformer with the tubes pulled, if it still gets warn it may have a short in the H.V secondary, or the heater wiring.
Regards
Arran


Top
 Profile  
 
 Post subject: Re: National NC-270!
PostPosted: Sep Fri 17, 2021 3:19 am 
Member

Joined: Dec Sun 14, 2008 3:33 pm
Posts: 1198
Location: Tokyo
Not 'enhanced' BFO injection, 'exalted'. Exalted BFO injection sounds much better.


Top
 Profile  
 
 Post subject: Re: National NC-270!
PostPosted: Sep Fri 17, 2021 10:06 pm 
Member
User avatar

Joined: Jul Fri 21, 2017 9:58 pm
Posts: 3090
Location: Erie, Pa.
Arran wrote:
I would try running the transformer with the tubes pulled, if it still gets warn it may have a short in the H.V secondary, or the heater wiring.
Regards
Arran

Thanks, Arran.

_________________
"Invisible airwaves crackle with life
Bright antenna bristle with the energy"


Top
 Profile  
 
 Post subject: Re: National NC-270!
PostPosted: Sep Fri 17, 2021 10:07 pm 
Member
User avatar

Joined: Jul Fri 21, 2017 9:58 pm
Posts: 3090
Location: Erie, Pa.
shinkuukan wrote:
Not 'enhanced' BFO injection, 'exalted'. Exalted BFO injection sounds much better.


It does have a ring to it! :lol:

_________________
"Invisible airwaves crackle with life
Bright antenna bristle with the energy"


Top
 Profile  
 
 Post subject: Re: National NC-270!
PostPosted: Sep Sun 26, 2021 12:20 am 
Member
User avatar

Joined: Jul Fri 21, 2017 9:58 pm
Posts: 3090
Location: Erie, Pa.
rsingl wrote:
I have one along with some of the other cosmic blue National receivers.

It is like other radios of that era and type, you do NOT need an exact antenna match for it to work OK. Practical antennas will present a complex impedance that varies widely across the operating range. If you want a perfect match, get a dummy load :)

I have seen the articles on the work some people have done with the 230 khz. inductors in these National radios. Maybe I am lucky but I have never had an issue with the IF strip alignment in these. My biggest criticism of these is they aren't as mechanically robust as some of the older and/or more expensive National sets. They work fine but the build and operation doesn't have the feel of a HRO, NC-183, NC-300, etc.

Rodger WQ9E


Well, I finally got the rig and speaker hooked up, and am listening to Vermont calling CQ on 40 meters! (AA1SU.)

My only gripe is that I'm not getting a lot of sound from the matching speaker. I'm probably just spoiled by my NC-183D, which I had driving a KLH bookshelf speaker, that would blow you out of the room.

I even tried reversing the speaker wire hookup, made no difference.

Could just be the age of the matching speaker.

Will try hooking another one up.

_________________
"Invisible airwaves crackle with life
Bright antenna bristle with the energy"


Top
 Profile  
 
 Post subject: Re: National NC-270!
PostPosted: Sep Sun 26, 2021 4:50 pm 
Member

Joined: Jul Tue 21, 2009 1:38 pm
Posts: 1010
Location: SW WA 98565
Dalton,

Nice looking receiver!
Reversing the leads on the speaker should have no effect on the audio.
Is it the correct speaker for the radio?
Has the speaker been replaced with a different one?
Have you checked the audio power tube (and the rest of the tubes?)?
Best of Luck,

-Tom


Top
 Profile  
 
 Post subject: Re: National NC-270!
PostPosted: Sep Mon 27, 2021 2:53 pm 
Member
User avatar

Joined: Jul Fri 21, 2017 9:58 pm
Posts: 3090
Location: Erie, Pa.
Tom Herman wrote:
Dalton,

Nice looking receiver!
Reversing the leads on the speaker should have no effect on the audio.
Is it the correct speaker for the radio?
Has the speaker been replaced with a different one?
Have you checked the audio power tube (and the rest of the tubes?)?
Best of Luck,

-Tom


Thanks, Tom!

I suspect that an incorrect speaker (ohms) was put in the matching cabinet. I will rectify this. (full pun intended.)

I set it up Saturday night, and the magic happened. From my notes on Sunday -

"Last night around 8:30, was listening to W6TA, Rancho Palos Verdes, CA. at 14.19 MC, SSB, on my 1960 NC-270. California to Erie on a 60 y.o. piece of gear, with 15 feet of wire for an antenna. Nerd heaven."

_________________
"Invisible airwaves crackle with life
Bright antenna bristle with the energy"


Top
 Profile  
 
Post New Topic Post Reply  [ 14 posts ]  Moderator: Sandy

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 4 guests



Search for:
Jump to:  




































Privacy Policy :: Powered by phpBB