[Boatanchors] National HRO-5RA1 Revive and Serial Number Strangeness

[David Stinson]

Been resurrecting the pretty, very clean HRO-5 from that last

auction in Garland, Texas.  Found out why it didn't sell:  It actually

got bids, but only to $50 and the owner "passed."  I think maybe the

bundles of wires hanging out had something to do with that.  

 Called Jim and negotiated its release.

 

https://photos.app.goo.gl/Qu9pFESJeNAZtoME3

 

The "Doghouse" power supply with it is actually a 6 VDC

RAS Vibrator supply.  I got that working, but will need to 

replace the vibrator.  This one just isn't going to live.

Any tips on the "best" of the Sandy-State replacements?

 

The rig had some really hair-brained "improvements," like

un-grounding the cold end of the Mixer input coil and attempting

to run AVC voltage to the mixer grid and to the BFO grid (HUH??)

Some Franken-fiddles in the Audio stage, attempting to run

external audio from the Noise Blanker (??) and assorted other

nit-wittery.  Of course, when none of the "improvements" magically

transformed the radio into a Drake R4-B, it went on the junk pile.

 

Clean/Lube/De-Ox-it, check all the grounds, replaced bad caps

and resistors, fixed all the quackery, installed a Audio Output xfmr

(B+ on one bare spot is bad enough, thanks ),

aligned and now it sounds sweet.  A well-revived HRO

is one of the best sounding classic radios ever, IMHO.

 

Video of tuning 5 - 6.5 MC AM:

https://photos.app.goo.gl/r37W6SPrqCDNxCcn1

 

Serial number strangeness:

This is an HRO-5RA1, built in 1946.  But the serial number

is "L230."  I thought the "L" chassis was mid-1930s?

Perhaps this was one of the "leftovers" from which the

-5s were supposedly made?  Also- I read that the -5s 

dispensed with the center-tapped filament resistor,

returning one side of the filaments to ground. 

 But this one still has it and it's in the manuals.

What do you National HRO gurus know about these?

 

P.S.  You've likely heard the joking advice: "Don't put

the cover back on!  It will never work if you do!"

Well,  the first time I put the cover on, 5 mins later the

filament opened on the 6J7 BFO tube.  Ack!  Fixed 

that.  Put the cover back on.  3-4 minutes later, 

the BFO alignment shifted.  Fixed that

(de-ox-it on the trimmer cap rotor contact).

Then a fixed cap in the "F" LO coil can started leaking,

jumping the LO all over.  At least I didn't have to

pull the cover to fix that one.  
Put the cover on for the third time.  So far, so..


73 OM DE Dave AB5S