NATIONAL 183D FINISHED AT LAST

[KB5MD]

I have a 183D that has good volume on the broadcast band but very low volume on every other band.  Any ideas, anyone? Its' got me stumped.

[KA0HCP]

Dirty band switch.  Also check the wire connections.

Don't soak it in Deoxit.  The wafer material swells and it takes most of a year to dry out.  (ask me how I know).  

[w3jn]

Could be anything... but the rear wafer of the bandswitch has a resistor network that sets the sensitivity for each band.  Perhaps one of them is bad.  Get the manual and go to town...

[KM1H]

With virtually no info provided it could be anything.

When was the last time it was completely recapped and all resistors checked for tolerance?

Carl

[The Slab Bacon]

Knowing Nationals and their crappy resistors, it could also be a screen dropping resistor in one of the RF amp stages.

[KA2DZT]

Check the screen resistors to the RF and IF tubes.  They usually are way up from 47K.

I modified my NC 183D.  Got rid of the PS rectifier, used two diodes.  Replaced the choke with a better one, went choke input, added a second choke.  First choke and cap went to the 6V6's and second choke and cap to the rest of the receiver.

I added a regulated (105V regulator tube in the rectifier socket) supply to the screens of the RF and IF tubes through separate 2200ohm resistors and .01ufd bypass caps to each tube.

With the reworked PS the whole receiver runs much cooler, before you could fry eggs on it.  The power xfmr runs much cooler, a good thing especially since these xfmrs have a history of failing.

Fred

[AB3FL]

Can a 5r4gyb be subbed for the 5u4?  I figure that with the higher voltage drop and the 2A fil instead of the 3A fil, everything should run a little cooler.


73 de AB3FL

[KM1H]

I use 5R4's most everywhere since I wound up with a load of them some years ago.  Dont expect much if any difference in the drop at the 183D's low current. Going to SS diodes actually increases the load on the transformer.

Bad screen resistors is only a small part of the problem, a typical 183D or HRO-60 will require 15-20 to be changed.
They are also starting to have the mica caps in the IF cans crapping out as well as other circuits.

Carl

[WD5JKO]

Going to SS diodes actually increases the load on the transformer.

   Well, that depends. What Fred did was switch to SS and go to choke input filtering from capacitor input filtering. The B+ done this way will be just shy of stock when the AC line used to be 110vac. Doing this switch usually increases the AC ripple though, and hence the second choke was used for the low level stuff., L-C-L-C.

   I did the same thing with my SP-600, and since it had two chokes already, the ripple was still OK. The B+ as I recall was about 225v. The tranny stayed cool with 120v line voltage.

Jim
WD5JKO

[KM1H]

He could also have used the 5V winding in bucking mode, there are several ways to cool it down.

I run mine as built and each bench has a big bucking transformer feeding it for 109-113V depending on what cheap oddball voltage 15-20A transformer I picked up.

[KA2DZT]

As I recall the B+ was just a little less than stock voltage.  It didn't affect the way the receiver work.  There was no ripple when I finished the mods.  I used a 7hy 200ma low resistance choke for the input choke.  The second choke was a 6hy 125ma 220ohm choke.

First choke was mounted in place of the original, second choke was mounted under the chassis on a bracket.  Voltage off the first choke went only to the 6V6's plates and IIRC the screens.  I may have connected the screens to the second choke, don't remember.

I mounted the diodes on the accessory socket, did away with some of the wiring at that socket, don't remember exactly.

I used the 5U4 socket for the regulating tube (105V 40ma type) for the screens of the RF and IF tubes.  I replaced all the caps and most, if not all, of the resistors.  But then I disconnected the new screen resistors at the sockets and supply screen voltage from the regulating tube circuit.  I used isolating resistors to each screen (2200ohm) and bypass each with a .01mfd cap.

I thought the receiver worked much better including the way the S-meter worked.

With the choke input filter the power xfmr was much cooler and the heat from the 5U4 was gone.

Keeping a receiver all original is not a big deal with me.  If changes need to be made to improve something, I make the changes.

Fred

[KB5MD]

The 183d is gradually coming back to life as each resistor is changed out and the recapping is completed, but, still no AVC.  That is the next hurdle to overcome.  Will start looking for that solution tonight if band conditions are still crappie.  "Slowly but surely", I'll get there!

[KB5MD]

Finally, it's finished.  99% of resistors and caps replaced, volume control replaced, solder bridge removed, avc coil can removed and insides rebuilt, realignment and one bad tube replaced.  After working on it for what seemed like forever, I wonder if it's really worth the effort???  OH YEAH!

  I forgot to mention, the cabinet was bent by UPS and had to be straightened.  I specifically requested that the seller on ebay double box and pack well...NOT!!  Actually packed with a couple of old sweat shirts around it, thrown in a box and shipped.  What a moron!

[KX5JT]

Congratulations "Dr." Roy!  I hope I sound good on it!  Been a while since I've been on 75 Meters, might catch you on 40 sometime soon.

John KX5JT