National HRO-50-1

[KE7KPB]

I did a cap replacement on my receiver and I did a very careful job of it also. I wouls clip the leads of the cap very close to the ends of the cap so this would leave a tail where the cap was soldered and that way I would not get lost on the location. After a total recap and I replaced the 100 ohm resistor on pin 7 on v-1, cathode. Turned the set on and nothing. EGAD. I put the scope on the pins 1 on the v-1 v-2 v-3 with no pattern. RATS. I even ran the voltages on the pin outs and this bird is dead. I guess this a good lesson on replacement of a few components and check operation and if it doesn't work, well you can back track. Back to the drawing board. Any hints would be help lfull  also. The gray matter is getting foggy with all of the cold here in Montana.
KE7KPB
Bob.

[WQ9E]

Is the octal shorting plug in place on the back?  If I interpreted your post correctly you are missing B+

If you haven't done so already remove the .1 cap from the rectifier plate to ground.  You don't need it unless you are addicted to the smell of burning transformer

[KE7KPB]

funny. c-118 will go by the wayside. thanks.

[w3jn]

OK, time to start looking at voltages.  B+ at the filters first, then go to the audio and backwards toward the RF section.

You have a scope - that's good!  If you can't find the trouble with the VOM, it'll be invaluable.

Let us know what you find.

[KE7KPB]

Sorry for the mix up. the select-o-ject. is installed in the back with an antenna, speaker.
Stupid question, Why would I remove c118 from the 5v4? Did the engineers mess up on this? I did check the voltages on the 6ba6s and 6be6 and they were good. The meter I am using is a Fluke 73.
Just asking.

[VA3AEX]

Reminds me of my restoration of a National HRO Senior.  Built a power supply; then did a complete recap and replace a couple of resistors and..... nothing...  Put it aside for a couple of weeks, and then when back on the bench realized there was no B+.  The 'had worked' power supply and given up the ghost.  Rebuilt the power supply (with an 'on' light for the B+) and the receiver sprang to life...  Or maybe my first transmitter refurb, a Halli HT-40, and after much head scratching and help from the forum, realized that I didn't have the shorting octal plug plugged in the back...     

[WQ9E]

Why would I remove c118 from the 5v4? Did the engineers mess up on this?

If it shorts (and it commonly does) it will take out the plate transformer before the fuse opens.  It really serves no useful purpose and was deleted by National in later production; I believe they also clipped it out on the NC-183 and HRO series receivers that came back for transformer replacement

[KM1H]

C-118 was installed to KEEP the 5V4 and transformer from blowing in 3rd world slums with power like we have today....full of big spikes. Unfortunately people today seem to thinks its just fine to turn on a 60 year old radio with no grey matter working and kill the transformer.

Replace it with a good 1600V poly Orange Drop or similar.

Carl
National Radio 1963-69

[KE7KPB]

Hi Carl, since I am still on the learning curve of the HRO Receiver I have ran into a puzzle. So I am going to take a break from it for a day or so. Recapped the radio, not no sound. I get meter action, and checked all of the tube voltages and they are all good. No signal. Hooked up the heathkit signal generator to the antenna and the scope to pin five of the v-1 and nothing. Even went to the V-2, and V-3 on pin five. Even hooked up to the other pins on the 6ba6, even checked with different filters. I am getting a very low noise when I hook up the headphones. 
I am going to change the C118 to a 3000 volts cap. All I have with the high voltage. A few days off will be good.
Good learning tool, After working on the antique radios.

[KM1H]

Make sure all tubes are warm to the touch, maybe an open filament or socket corrosion. Ive also seen a tube with a broken key put in wrong.

Other than that there may be a cap installed to the wrong place or unsoldered.

Touch your finger to the center tab on the volume control, if there is a loud hum the audio section is OK. Then take a hunk of wire and touch to a grid pin starting with the last IF and working foreward. A working stage will cause a noise increase.

And dont forget to turn the B+ switch On on the front panel Thats always a good gotcha with HRO's.

Carl

[KE7KPB]

I want to thank everyone for there help on this receiver. This dog hunts. I found why I lost the signal through the filter stage. When I was clipping off the extra leads during the recap, A small piece dropped into the filter coils ares and shorted out the signal. The piece was so small that if I didn't look through every inch, I wouldn't have found it.
This is a good lesson in making sure you get every piece and don't work on one when your tired. Anyhow, time to attack the Johnson Viking 2. This should be fun. Again Thanks for the help.

[WQ9E]

Bob,

Glad you found the problem!

For your Viking II start with a check/cleaning of the 5R4 tube bases and sockets to clean/prevent carbon tracks.  If they haven't been replaced already then replace the filter caps in the B+ and bias supplies (C10 through C13).  The filter cap in the plate supply (C9) is an oil type and should be fine.  Don't forget the electrolytic cathode bypass caps in the audio section.

If you have to adjust the tap on R-13 (modulator screen) make sure it is properly loosened and use caution since the winding is very fragile and easy to break.

[KM1H]

And put metal or even heat dissipating plate caps on the 6146/807's. Those ceramic caps look nice but really raise the tube seal temperature. While 807's are everywhere the 6146 is getting scarce and expensive as speculator type tube bandits have scoffed up huge stocks.

Carl
KM1H
Johnson Viking I and Viking II CDC owner

[KE7KPB]

I put open end caps on, They don't look as nice but like you said it's the heat. I got a new development in the HRO.
I would be listening to a local radio station an I noticed that the meter would slam to the left with a strong signal and then it would go back to mid point. Kinda strange?

[Todd, KA1KAQ]

Sounds like an issue with the AVC/AGC. Shorted cap or other component?

While 807's are everywhere the 6146 is getting scarce and expensive as speculator type tube bandits have scoffed up huge stocks.

Makes good sense from a business standpoint. If you're a tube dealer, who will be the next big batch of likely customers? The guys who grew up using or wanting S-Lines, KWM-2s, Drake 4 Lines, TS-520s, 830s, FT-101s and so on. Sweep tube and 6146 users. The 'real radio' gang isn't being replaced at the same rate of thinning it's experiencing. Though the audio crowd seems to be holding steady or even gaining a bit.

[KM1H]

Id start by swapping all tubes on the AGC line one at a time to eliminate a HK short or leakage driving a grid positive.

Next would be doing AGC voltage measurements and find where its lost.

Carl