what did you use to clean the Chassis like that?
"If it aint broke don't fix it. "If you can't fix it get a bigger hammer."
You could teach some of us a few things! This post begs answers to a few questions...
1. Why would someone have wanted to yank the 6146 modulators?
2. Why would a 'shack' engineer be inclined to use wrong components at the base of the plate choke?
3. Why would someone have wanted to solder two rectifiers to the base of the bias rectifier socket?
Look Honey, it followed me home...
Indeed it did! This was picked up early this morning an hour away from my home. I should have known something was up when I was met outside and the radio was carried out the door for my inspection. "Works fine" my foot--the thing is as deaf as a post. But for another $160, who am I to complain...
The front panel is flawless--nary a nick, scratch, or blemish. A little oxidation on the tuning knob and logo, but that should polish out nicely. A couple minor nicks and blemishes on the case--but a 9 out of 10. Most cases have been beat. All knobs original, no discernable wear, chips or scratches. Included was the ORIGINAL manual, which I thought was a reproduction it looked so new and crisp--but a mimeo insert and rubber number stamp tell a different story. I should put that on ePay and get someone to pay $25 or more for it...
I am beginning to equate used equipment sellers with used car dealers. As advertised, the language stated "no changes", but the original antenna screw strip was missing and a BNC connector added. Other 'issues' say that the rig has not been fired up and used for a very long time. I have a feeling that some of the NC-303 mods were done as well. It also came with the XCU-300 crystal calibrator which is working--lord only knows how far that has drifted. Something else to align...
The inside is fairly clean--just a smattering of dust. It looks like sometime in the very recent past there was an NC-300CC converter cabinet to go with the rig--as demonstrated by the fairly recent disturbance of the dust around the accessory socket. I will be looking for one of these and at least the 6 and 2 meter converters to stuff it with.
I checked for ground leak resistance upon benching it, and spent a little over an hour slowly cranking up the Variac to reform the caps should it have been sitting a mite too long. I hate those loud bangs and foil with bits of waxed paper flying everywhere. Electrolytics are also the ONE SMELL in old electronics that I do not like...
As stated, the thing is almost completely deaf on all bands. The S meter erratically flies to the left and pegs itself until such time as the rig is turned off. Not an issue--as it will be recapped, have resistors whose values have changed outside of tolerance changed--and a full alignment done. The pots are unbelievably dirty and thus noisy--which adds to the conclusion that this honey has not been on in a while. I have yet to peel the case off and look at the chassis wiring & components. That will wait until the Valiant is a bit further along.
I have not found a date code stamped inside yet--this was usually somewhere on the top of the deck chassis. I am sure that I will get to the bottom of it.
More to come...
Last edited by AE1PT; 03-09-2012 at 09:28 PM.
I could not wait--the cover was stripped off this thing late this evening. The answer to why the thing is deaf is quite clear. Some jackass substituted a 6CB6 for the 6BZ6/6JHB that belongs in socket V1. The result is that after a bit no fewer than three resistors became cooked out. BTW, this is the RF Amp tube...
It must have been in the 80M position when the circuit blew out--as T10, which is a small double layer "antenna transformer" wound on a 1" x .25" axial lead core. Each band has one--and this one got a bit toasty. I am hoping that it is still in good enough shape to work--as this bad boy is definitely 'unobtainium'.
I clean chassis with a combination of 409 spray cleaner and hydrogen peroxide. Applied with a toothbrush. Stubborn stuff and mild aluminum oxide get a sprinkling of jeweler's rouge tossed in for abrasive/polishing action. Johnson coated these with a thick plating of Cadmium--cleans up really nice.
The 6CB6 likely got in there the same way the wrong components got into the plate section of of the Johnson--it's what some hammy hambone had kicking about in his junk box--and put it in to make it work. Nobody said anything about well...
Sue, my new Matchbox is the 275W version. It does not have the relays inside the box like its bigger brother.
The next steps
So over the past weeks I have been taking my time--going over every section, checking for resistors that have gone high--and looking at every bit of discussion I could find that addressed issues had over time with the Valiant and the NC-300. It was now time to shop for parts.
It's a whole new world out there kids, from when at least two parts houses were no more than 15 minutes away from me. Even Mouser is getting tight on their inventory--and prices have indeed become startling. But at last I had a list of components that would come from Digi-Key, RF Parts, and Antique Electric Supply. Off and away the orders and everything has now come in:
Included in this is everything for both rigs. All paper caps to be replaced with polyester or polypropylene--depending upon the application. 5 new matched Sylvania 6146Ws. A few other tubes that tested weak, were gassy, and one OA2 replacing the original that one of the cats decided to give the floor test to. Needless to say it did not survive the crash... The moral of this story is not to let cats test tubes.
I decided to go with computer grade 210mf@450WV caps to replace the 80mf ones. One multisection is a direct replacement for the NC-300, and the other ditches two discrete caps. Most of the resistors being changed I already had in stock--these are ones I did not or would have depleted my stock using up. Some are upgrades for poorly specified original components.
The small 300W Johnson Matchbox and the Johnson Directional Coupler/Meter came in also:
There was a sad note to this though. The coupler was fine and cleaned up nicely. The matchbox was very well packed--but the sound of something rattling about did not bode well. Taking out what must have been 20 screws and removing the knobs--the cause became clear. A bright spot was that this particular model does have the relay circuit! But it also has this:
Note the bandswitch and plexiglass rod for the loading coil. Not so good. It is pretty obvious that both had broken in the remote past and a repair done--as evidenced by the grey epoxy smeared on the ceramic body of the switch and plastic cement glooped on the support rod fracture faces. I would certainly like to hope that everything was popped loose from its repair during shipment--and not before... Buying anything of this age is like gambling. You have to invest a bit to become a winner.
I will end up temporarily repairing the bandswitch--and keeping my eye out for a replacement--whole or part--now that we will be getting into hamfest season. More to be posted as the project continues!
Last edited by AE1PT; 03-16-2012 at 05:36 PM.
Oooh! Noice! A Valiant, and an NC-300. And both are in relatively good condition!
It looks like you have the makings for a nice vintage AM station Patrick. Also, you were lucky that you had somebody to carry your stuff. I not only drove to south of Rockford, IL to pick up my Viking II (which I got at a great price - $75 back in late 2008) on a Saturday afternoon, but I had to carry it up out of the guy's basement, to my car (his back was trashed), and up to my 2nd story apartment, from my aprtment building's parking lot (I ended up having an asthma attack [I have asthma], after I got the Viker in my apartment). Like you, sombody hamboned my Viking II to an extent. It hand't been used in at least 10 or 15 years (possibly longer - it was loaded with dust & crud), and had two open holes, and two BNC connectors in the front panel. What the holes and the BNCs were used for is unknown, since the BNCs weren't connected up to anything (the nearest I can figure, from seeing a photo from 50s or 60s of a ham station, with a RTTY setup, that used a Viking II for a transmitter, was that the mods were for RTTY). I just ended up leaving the holes & connectors alone. Also, the finish on the radio isn't pristine, but it's still in very good shape, so that was left alone. As for other hambone actions to my Viking II - after recapping it, I fired it up, only to see the plate current go sky high, no matter what I did tuning wise or tube change wise!. A friend of mine (Rodger WQ9E), whose done tons of restorations (one of his main AM rigs, is a Desk KW), went over it on the phone with me. The only thing we could figure out, was that the clamper pot needed adjusting. Normally it only takes about a half turn on the clamper pot to adjust things. As it is, the pot only has one turn of movement. Well, it took TWO turns before things settled down! Some yahoo in the past, replaced the clamper pot, with a pot that had an audio taper profile. Sheesh! But, once the clamper pot was adjusted, and the 807 modulator tubes were replaced (the ones in the Viking II arced, when I modulated the rig), my Viker selttled down, and behaved itself. 3 years after restoring it from a non-runner, it has become my main 75m AM rig. Coupled with a D-104 mic, and the recent acquisition of a mostly restored Hammarlund HQ-129X (ah luvs muh Hammarlunds!), bought for only $60, and I have fun setup!
Have fun with yours when you get it up and running Patrick! Vintage radio gear is cool!
Getting rid of all those paper caps and out of tolerance resistors is the way to go. Having at least one NOS 6BZ6, 6BA7, 6BE6 and 6BJ6 on hand as benchmarks or replacements when needed will help get things back to normal along with an alignment.
An excellent mod is to replace the free running 2nd conversion oscillator with a crystal as was done in the NC-303 and every 300 that came to National for service. It may even be done but you will have to pull the can apart to tell unless hammy hambone tacked it in at the socket. Current price at International Crystal is $29; I bought 3 last month. They have the specs already and the accuracy is near perfect which makes the IF alignment easy. Stability improves to easy SSB copy even on 10M for long periods. All aligned with selected tubes the 10M sensitivity on the last one I did was .4uV in the AM BW for a 10dB SNR, all others are nearly the same. Not bad for a 1955-56 radio!
If youre real fussy you will likely find several caps and resistors in the IF BW selection way apart in values or simply out of tolerance. The .022 paper caps for Position 3 are the worst. I get kind of fussy and match to 1% or less which really tightens things up especially in positions 2 and 3.
My own 300 is currently on 10M with either a Viking II CDC or a GSB-100 for vintage SSB.
Time to move onward through the rehab. It's now time to change out all of the paper, electrolytics, and carbon comp resistors that have seriously changed value. The operating theater awaits:
All of the paper caps were replaced, and a number of resistors and disc caps as well. Various reasons for this--but testing on the bridge revealed that they were not even close to 20% value...
Finally, this part is complete. Next is removing some discs on the accessory plug, and finishing the work on the VFO. Purists will cry--the two pin Amphenol mic connector has been changed for a three pin, the crystal holder that put 115VAC to the TX/RX relay is now a two pin Cinch-Jones, and a fuse holder is being added to the chassis. There was a new cord and no fuses when received...
All pots have been cleaned, shafts lubricated, and rotary switches overhauled. Soon, off to the top deck!