[Milsurplus] WWII Navy RAL-8 Receiver Project

[Richard]

Nice work on the RAL.  A few more things you might want to try: There 
are capacitors plate to ground (C124 & C133) in the audio amplifier to 
roll-off high frequency response, carried over from the RAK.  This is 
why there isn't a big difference when the low pass filter is switched 
out.  I took 'em out and had a vicious supersonic oscillation with 33 
volts across the 'phones, due to about five feet of unshielded low level 
AF wiring.  I lifted one end and covered them with braid from RG-58 
coax, which dropped it to 17 volts, which was due to the output tube 
"looking" at some nearby low level AF wiring.  I shielded the 41 output 
stage and it was stable.  I now had an imbalance between RF and AF gain, 
changed the AF input resistor to a pot, and put it where the ac/dc 
switch was.  The RAL is now a joy to listen to, and decodes SSB better 
than any other receiver I've used.

Another thing:  At the high end, 21-23 Mc, there is a grid squeal a bit 
beyond normal regeneration level.  Looking at the detector, the grid 
capacitor is 500 pf, also carried over from the RAK, and much more than 
needed at HF.  Experimenting showed 80 to 120 pf was optimum, so I used 
120 pf because i had one.  The squeal now occurs much higher than the 
normal regeneration level, so I don't see it.

Years ago some people removed nameplates in an attempt to make surplus 
look less military. (curse them!)  If you can borrow a plate from 
another set, copy and laminate it, and you will have a nice plate that 
at first glance looks authentic.

Richard, AA1P

On 7/5/19 1:27 AM, David Stinson wrote:
> Got the RAK working and finished, covered in wrap
> to keep dust (and mice) out of it and back on the
> storage shelf.  It was in pretty nice shape and
> didn't need much work- ground fixes and alignment,
> mostly.
>
> Now I'm working on the RAL-8, and that one is in
> rougher shape.  Unlike the RAK, the low-pass audio
> filter can be switched out-of-circuit, so no need
> to bypass it for decent audio as we did with the
> RAK.
> https://photos.app.goo.gl/EawDbZrmw5AuoBXh8
>
> Needed the usual De-Ox-It treatment, lubrication,
> some tube, capacitor and resistor replacements and
> the grounds refurbished.  Haven't gotten to
> alignment yet.  The band switches needed a good
> dose of De-Ox-It.  Slow-bring-up of B+ displayed
> no unusual current leakage or spikes.  Powered-up
> to check basic functions.  Receiver did sorta-play
> on all bands except band 7 (5-8 MC).  The Detector
> would not oscillate.
>
> With the RAK, internal resistors divide the 180V
> B+ and apply it to the Detector and this seems to
> be "good enough" to run the set.  This is not the
> case with the RAL; you need to supply High B+
> (normally 180V but can be anywhere around there as
> long as it's regulated) to terminal 6 of the
> power/audio connection strip and 90V Low B+ to
> terminal 5.  Fortunately, this is very easy and
> cheap to do; you don't need a dual-voltage supply.
> A single 1N53xx series 5-Watt Zener diode, widely
> available for pocket change, can do the job.
> https://photos.app.goo.gl/pFKzvEUZFukAUpLo8
> In this photo, terminal 9 (ground) is at top, 8
> and 7 are Audio Out, 6 is High B+ (180V from a
> regulated variable supply in this case) and 5 is
> Low B+.  The Zener is a 1N5375, chosen because it
> was the closest I had available.  This Zener is
> rated at 82 Volts.  The diode drops 82 of the B+
> volts, leaving an nice clean 100V for terminal 5
> from a single B+ supply.  The diode runs cool
> since the Detector draws little current.
>
> Say you have a supply that will source 150V B+,
> which will run the RAL just fine.  You need to
> drop 60 Volts to supply the Detector Low B+.  You
> could do it with a two-resistor voltage divider,
> waste power and generate heat, or go with a
> cheaper, easier alternative.
>
> Check the spec sheet for the 1N53xx series of
> zener diodes:
> https://www.onsemi.com/pub/Collateral/1N5333B-D.PD
> F
> Scroll down to page 3 of the PDF.  Note that a
> 1N5371 is rated at 60 Volts and is available in
> quantities of 1 from Mouser for the terribly
> expensive sum of 45 cents.  Connect the cathode of
> this diode and your 150V B+ supply to terminal 6.
> Connect the Anode of the diode to terminal 5 and
> you will have a nice, working 90V for your
> detector.  Unless something shorts the 90V buss,
> the diode will outlast us both.
>
> As noted above, the receiver did play except on
> band 7 and the Detector would not oscillate.
> Regeneration is controlled by varying the screen
> voltage on the Detector and this voltage was low.
> The main problem was a very leaky C118, a 1 mFd
> oil-filled cap which is the Detector screen
> bypass.  This turned-out to be only oil-filled cap
> in the entire set to be defective.  Decided to
> "err on the side of caution" in the Detector
> stage, replacing resistors more than 20% out of
> tolerance and the low-value silver micas.  The
> Mica-Mold .01 bypasses all checked like new, so I
> left them in place.  If one fails, it will tell
> me.
> The 2.2 Meg Grid resistor in the Detector was
> fine, but the 1 Meg grid resistor in the preceding
> stage (R107) was 1.8 Megs and was replaced.
> Powered-up and the Detector now oscillates
> normally.  However, band 7 was still dead.
>
> With the top cover off the tuning capacitor
> compartment, I connected an Ohmmeter to the
> stators of the three tuning capacitor sections and
> ground, each by turn.  This reads across the
> selected band's coil section for each band.
> Turned the band switch and all coils showed proper
> low-resistance paths except for the Detector
> stage, on band 7, which showed open.  Turned the
> radio over and removed the bottom cover over the
> RF stages.  Then carefully removed the panel with
> the set screws in it that keeps the band switches
> in alignment.  Be very, very careful here.  If you
> twist or pull any of those switch segments, they
> have to be mechanically re-aligned and you will be
> very unhappy.  Don't "gorilla" anything.
>
> Used and ohmmeter to check continuity through each
> band switch set of contacts (2 per switch on band
> 7) but didn't find a problem.  However, on switch
> S111, I noticed there is a mica, C142, 510 pFd,
> which is connected only when on band 7.  I
> carefully unsoldered one end and connected the
> ZM-11 cap tester.  Sure enough, the little bugger
> was leaking badly.  The manual says the function
> of this cap is to "Detuning cap on primary winding
> of the LF Detector Coil when using Band 7."  I
> don't know why but it must be important.  Maybe
> the stage oscillates and blocks on band 7 without
> it?  Replaced it with a 560 pFd silver mica, put
> the switch alignment plate back on and band 7 came
> alive.
>
> Did a few other misc. fixes.  Replaced the 100K
> grid resistor in the Audio Output stage, corrected
> cold solder joints at a couple of tube sockets,
> disconnected the .01 uFd RF bypasses across the
> Audio Output transformer secondaries to ground to
> improve high-frequency audio response.  Will be
> playing the set a few hours tomorrow as a "burn
> in" to make sure there aren't any surprise smoke
> signals.  Rig sounds really nice when the Regen
> control is set properly.
>
> Which brings me to a request:
> https://photos.app.goo.gl/C5wBpK7j6EbvW6YW8
> Need a couple of knobs.  One large, one small.
> Enough RAK/RAL sets were scrapped that surely
> someone out there has a couple of knobs.  I
> *think* I have the Output meter.  Still digging.
> I do have have freq chart holder, just removed it
> for painting.
>
> Also:  The nomenclature tags on the case are the
> fiber-board type.  They've got that "faded" look
> that so common with these:
> https://photos.app.goo.gl/h2G31zrpTCZGtWC77
> Don't know if the ink fades of if it's MFP that
> gets cloudy.  Has anyone succeeded in getting
> these tags to look decent?
>
> Hope this encourages someone to fire-up their set.
>
> GL OM ES 73 DE Dave AB5S
>
>