HRO50T. Need some help.

[ke7trp]

Carl, and others:

   I just recapped an HRO50T.  I replaced shorted caps and then fired it up.  After that, I replaced them one or two at a time and checked the rig. 

I found some bad resistors but did not replace them all.  I have a couple questions:

Pin 2 of the 6sn7 has 22.5 volts listed in the manual but my rig has 70 volts. All other voltages are very close to being spot on.  Is this a printing error?  I do not get 0.2 volts on the phase converter either.  Just 0.

The audio in my opinion is not even close the sound off the 28A or 42 I have recapped.  There seems to be very little mid to high range. I swapped cathode caps for 100s. That got some bass. I also changed the coupling caps to .47s.  Some more bass. I swapped out and changed the "TONE compensator.

Trying to figure out the phase converter issue but I would like some opinions on the audio once repaired.  I am thinking of changing the trans out for a Hammond.  Maybe a 1608?  I have an SX28A that had the audio trans swapped due to failure and it is the benchmark of sound.
 
This radio is in perfect alignment and runs great.. Just not happy with the sound.
Thanks for the help!

[KM1H]

The audio should sound as good as any other PP 6V6 National so Im not sure what is wrong but Id replace all out of tolerance resistors first.

And then maybe swap some tubes, The Hammond wont buy you anything unless the original is only half working.

[w3jn]

The NBS-1 (essentially a NC-183 with some differences in the IF) I did a while back had one terminal of its tone control shorting to the chassis due to the entire control being rotated and that really killed the high frequency response.  You might want to check that.

The resistances in the phase splitter are fairly critical for low distortion, check and replace any out of tolerance resistors.  Would be good to look at it with a scope and see where you're losing highs. 

[ke7trp]

Thanks guys. 

Yesterday, I checked the Two GE 6v6s  80 on the TV7.   I ran one at a time in each location and had audio.  Here is the odd thing.  There is no difference in plugging in the second tube. 

You can have one tube and running along.. Put the other in and here no difference. Pull the other tube out and it runs along fine.  So both postions work but with both tubes I see no difference in sound.  Bith run the same temp. Super hot.  Some blue.   I tried another set of RCA tubes. Same thing.  The audio has to be up to 5 on the dial to get a loud roof full of sound. 

I think I need one more round of resistors checking on this rig and also it might be time to check that Audio transformer.  Maybe today.

 Also. Thanks alot for the tip on the TONE control! 

C

[w3jn]

1/2 of the audio transformer primary might be open.  Voltage checks are the order of the day.  If you have no plate voltage on one tube, that's probably it.

[ke7trp]

Ok. this afternoon, I will pull the cover back off and try again!  Thanks for the help!

C

[ke7trp]

Had an hour to kill before lunch.  Its the Trans. Its shorted on one side.   Can you help me pick the one I need from Hammond?

http://www.hammondmfg.com/125a.htm

Or these:

http://www.hammondmfg.com/1608.htm

I was thinking of the 1608 or 1609. 

C

[KM1H]

Had an hour to kill before lunch.  Its the Trans. Its shorted on one side

No surprise there, that was high on my list.

Id go with the 1609 but be sure to get the total plate current down to 80-85 ma for long life, you dont need 10-14W and the iron running on the edge. Increase the value of the cathode resistor is the simplest way. If you want to get fancy use a seperate resistor for each and set the value so that both tubes draw equal current. Bypass both with 50uF. Be sure all paper caps are replaced and those resistors checked before doing any iron swapping.

[ke7trp]

Ok.  I will order the 1609.  Tomorrow, I will replace all the resistors.  I have the day off and nothing to do so why not.

I have 100UFs in the Cathode now.  I will take your advice on lowering the current.

Thanks alot everyone.

C

[ke7trp]

I made a rookie mistake on checking the transformer.Its ok.  Still learning. 

This morning I spent another 4 hours on the old girl.  I decided to check/replace all of the resistors.  I found about 10 that where out of spec and 2 that where torched.  I also found that I missed TWO .01 caps that where hidden from view down by the MODE switch.  I got those replaced as well.

Now the S meter  does not peg on every station.  The Radio is noiseless with out an antenna now. SILENT.  Hook a piece of wire up and big sound and signal on the meter.

The audio gain troubles where traced to the two 100K resistors on the audio amp tube. Plate load and cathode( I think, The manual is not in front of me).  These resistors are 100K in the manual. Mine where factory installed 300Ks that where checking around 580K.  I put in 100Ks like the schematic and the sound is much much better and there is more gain.

I believe now the radio is working as it should.  Maybe better then it ever has.  However, The audio of the rig is not up to the quality of the SX28A with Hammond transformer. That rig has AM so clear you would swear it was hifi FM. The second SX28A sounds about like this HR050T.   I have asked the person who restored the SX28a with hammond and was told that the 1609 transformer makes a WORLD of difference on the sound.

So that explains it. I  am thinking of ordering a couple 1609s and installing them in the SX42 I just restored and the HRO50T.  I have been spoiled by that HiFi SX28A.  However, Its probably a waste of time and money.  All of them sound great and work as they should.

The last issue I have with the HRO is the arcing on/off switch.  I picked up a replacement pot/switch yesterday at Tubesandmore.com since they are down the street.  Its going to be a bear of a job but I will tackle it tonight or tomorrow.

THANK YOU for the help!



C

[Jim, W5JO]

Just by chance you didn't cross the grid input to the audio finals did you?  If so it sounds like you describe and it is easy to do.  Make the audio out of phase.

[ke7trp]

The caps are installed exactly the way they where from the factory. Just removed old and installed new.

C

[ke7trp]

Calling this one done. Thanks for the offline/online help.    Learned alot this resto.   Audio is better then new now.   

All caps
All resistors
Switches, pots changed
Tubes replaced.
Knobs cleaned, repainted
cabinet cleaned and detailed
Alignment.

Anyone know W0FTJ?  I have to guess he is SK now. He purchased it new in 1950 and sold it in 1954 to a guy that responded to his add. He wanted a Collins Receiver. Probably a 75A-X.   This radio sold used with a Viking 1 and a dow key for $380 in 1954.   

Youtube video of the HRO50T.

http://youtu.be/H8LhEAAiLqQ

C

[ke7trp]

SOME IDIOT turned all the trimmers on all the ham band coils.     

I spent 6 hours going through those coils. I have all the Bandspread coils working and aligned. What a pain in the neck!  Lucky for me they did not turn the L in the back. They only turned what they could get to. The top trimmers.



C