BC-799/SP-200 Hammarlund Recondition/Mod Project

[WBear2GCR]

Oh yes, Al, as I mentioned in the first post (I think) this receiver appears to have been worked on by someone - perhaps the NEARFEAST seller - and then never finished because it is/was deaf on all except the 10-20mc band. So, the caps NOT in the tuner unit have been swapped out. I see some resistors that I will likely spot check with an ohm-eater, because past experience has shown that a lot of 60+ year old carbon comps are a wee bit off center value. So, that caps were already swapped.

Also, note the genuine vintage 12kt gold filled Cross pen with RCA logo that was used to point to the blocking cap. You newbies, take note, always use genuine vintage pens to point with when working on vintage gear!  

WARNING: do not point with metal pens when voltage is present.

[WBear2GCR]

Back to the front panel... I'll be posting some pix of the new front panel after a while. It needs a trip into the oven for a few hours. It's still "outgassing" solvent. If it was summer or even sunny I'd put it in the sun all day.  I'll fire up the lab's special junker electric oven this weekend and bake it for a few hours. If the weather holds, I may bake and put another coat of paint, bake more.

But Al, perhaps you can look carefully at the layout, IF the 200 and 400 are the same or close enough you might find a 799/200 panel and repaint it, put the 400 tag on, and ur good to go??

The other option is a virgin aluminum front panel, find an outfit that does CNC engraving (Front Panel Express does exactly this) and have a duplicate made, get it anodized and dump in the color for the labels. If you do a few, you could doubtless sell them and recover your costs.

                     _-_-bear

[WBear2GCR]

Pulled one of the HF Osc coil modules.

Pix to come along later...

The cap is fine.
Very very close to spec on my DVM cap checker position.

So, back to looking at the issues. Now I think what is needed is a re-check of the ground or not grounded with the switch theme. Without the module in there, it had better not show a short. But if it does, then either someone has hamboned the wiring or else there is a mechanical problem with the switch.

It never goes simple or fast, does it?

 

[N8ETQ]

  I wonder if you pulled the hfo coil from the
working band? Perhaps you could roll a couple into
the same "Slot" so to speak and see if they work
there. A lot of good info can be learned by knowing
what's NOT broke.

   It also appears that the Band spread cap is only
in circuit on the 3 highest bands.

/Dan

Pulled one of the HF Osc coil modules.

Pix to come along later...

The cap is fine.
Very very close to spec on my DVM cap checker position.

So, back to looking at the issues. Now I think what is needed is a re-check of the ground or not grounded with the switch theme. Without the module in there, it had better not show a short. But if it does, then either someone has hamboned the wiring or else there is a mechanical problem with the switch.

It never goes simple or fast, does it?

 

[WBear2GCR]

Yeah Dan, I played it safe, I pulled the middle coil. No possibility of getting it wrong, since the only working band is the 10-20mc band, and that's not the middle one.

I'm thinking about "Sven's fingers" right now, but some probing about will likely show up the problem. The other thing I noticed is that the CT ground for those coils is achieved through one of the two screws (and a solder lug) holding the coil module in place. So, now I know enough to pull the CT ground and see how things measure WRT the switch operation.

It's going to be something simple, because there's not much else there for it to be.

            _-_-

[w1vtp]

After checking with Bear, I am uploading the panel of my SP-400.  Note the same flaking off of the paint.  What part of the fabrication process failed in the original manufacture of these panels.

Al

[WBear2GCR]

My last post on the ground from the coil module was bass-ackwards, the ground lug goes to the end of the coil, the CT goes to the switch. So with the ground lug lifted the only proper path to ground will be through the switch and "Sven's fingers".

Al, and everyone else, seems fine to come in with related material and things.
I'm re-doing the front panel on this one, so it works in fine.

As far as failure mode, as far as I can tell it's a nickel plated panel, and that may play a role in the paint losing some grip after all this time.

Here's what I said to Al in an email about his panel.
This is only my opinion and what I've done.
By no means the only approach.

I'll be getting into the panel after I get mine baked, a second coat added (maybe tomorrow) and then re-baked.
Then the finishing, I'll put into the blog. So yours fits right into the whole thing.

But, and I'll repeat this on the thread if you post, yours is engraved (looks nice, btw!). So, all that is needed isto strip the paint with paint stripper. The "green" stuff (non-methylene chloride) seems to work ok on Hammarlund paint. Then see what the surface looks like. if there are small scratches or pits, fill those with automotive scratch filler paste (it comes in a tube), it slides on with a plastic trowel very thin. Sand that with a flat block, very very fine paper, like 800 grit. When the pits are gone, spray with automotive primer. Bake @ ~150deg for a few hours. Let cool a day, then sand again with 800, then finer... if you don't find any flaws you can proceed to color coat(s).

If there are flaws then hit them with the scratch filler paste OR spray with automotive "scratch filler primer". You could have done it the first time with this stuff. It fills voids. But you have to sand flat to get the filled holes flat with the surface - standard automotive methods here.

Anyhow after all that is done, the intermediate coats baked (for dryness and hardness), and the color coat(s) done and baked. You fill the labels with color. There are different ways to do it. My current favorite is the acrylic "fabric paint" that all the crafts stores sell. It comes in hundreds of colors. Some REALLY nice. They have metallics, pearlescents, translucent, transparent and regular colors. Several coats are needed, the stuff goes on high and then shrinks when it dries. I use a Qtip shaft cut at 45 deg and dab it in. But you can just squeegee it on too, and wipe or let it dry and then sand/polish/buff to remove the excess. No matter what you do you have to do that last step, but I've found the better you do the getting it into the right spaces and wiping the excess (Qtip again) the easier it is to finish...

So you could do as many or as few colors as you wanted to. You could make red stripes there, and make the Hammarlund one color with the labels another, etc...

It looks sweet!!

Best idea is to try the acrylic fabric paint on an unimportant panel that happens to have engraving to see what it will do.

Btw, regular crayon also works... lasts forever.  
It's the easiest because you can just buff the excess off with a rag.
So called lacquer sticks work too.

I was going to add, IF that panel is aluminum, then you'd probably want to go with one of these newer automotive primers that are "self etching". Permanent grip there. Also, to my eye, yours is actually engraved. The one I have looks stamped. They look different if you know what to look for.

[WBear2GCR]

Big palm slap to the head!

DOH!!!    

Been chasing my tail the whole time. Probably.
Dan, I'm thinking your post about the bandspread was a hint.
Like maybe this was YOUR radio?
Or perhaps this is a well known mod?

So, I'm not so bloody smart then, eh?  
Yeah, right.

Ok so go back to the post with the picture about the wire that was clipped.
Note that there is another wire attached to one of the screws on top of the ceramic
insulator there? That's the top of the bandspread cap. It's attached to the end of
the grid blocking cap C15, and goes to one section of the bandspread cap.

So, what it looks like is that in order to give bandspread to other bands, a wire was run to one
section of the bandspread cap and the wire that normally want to the switch assembly was cut, as it would be shorted to ground on all bands other than the one selected.

Bandspread cap is C2, C2D is this section, there is a wire/clipped wire for each section.

Think maybe the wrong section was picked as this section is small and there is a fatter one... but anyhow that's what it looks like.

I did look suspiciously at the wire immediately, when I opened the radio to look. But what threw me is that this is NOS cloth covered wire,  looks the same as the rest of the wire in the radio.

Now I don't recall if I saw these clipped wires first and "fixed them" or if the radio was still deaf and then I fixed them. Kinda think it was the latter...

Pix to follow... and a "retest" to see if the bands have awakened or not.

YIKES!

GEENUS AT WROK!!  


_-_-


PS. If ur wondering, it worked on 10-20mc. because that was the one band where the grounding "Swen's fingers" were lifted for that particular bandspread section, all other bands had ALL of the grids shorted to ground. Ha ha ha. This is why I get the big money!

[WBear2GCR]

It Dont' Come Easy - Ringo Starr

Last update before hitting the hay.

Top two bands and the lowest band, alive.
2.5-5.0mc band and 200khz-400khz, no HF OSC action at all.
Switch contacts ring out ok.
Or so it seems. They don't appear to have a problem with Sven's fingers.
Will double check it tomorrow.
Swapped in a new 630v 1220pf cap in the 2.5mc band, no change.

Not much in the circuit. Must have missed something.

[N8ETQ]

  Cool,  Is that a light at the end of this tunnel?

/Dan

[WBear2GCR]

No.

Obviously a mud slide into the tunnel, trapping the occupants. Quicksand. The dark and slippery slope.

Btw, watch out, the little variable trimmer caps sticking out of the IF cans?
Electrically hot! Grrrrr... thanks Hammarlund!

As of this moment, there is no good reason that it should not be oscillating on the two dead bands. There are not even any bad reasons. Of course there must be a reason.

You wanna stop over and have a look at it Dan?

                    _-_-

[N8ETQ]

   It's Cool, You have him 60% functional at this point. Much
better than it was. Sounds like it's been Hammy-HamBoned!

    May I suggest just rolling a known good HF Osc assembly
say the 5-10 into the 2.5-5mc slots and see whats up. I would
pull the 100-200 HF Osc coil for inspection as he's the logical
choice for hacking, Maybe someone just clipped all the padding
caps off it.

     I would clearly mark each coil assembly with some sequence
and take a digital photo of it for reference. Maybe there screwed up
now.

     OTOH if you have a "Fancy-Dancy" DMM with a "C" meter
on him, I could Measure the PF's I see on mine from V4 Pin 8
to chassis. Mine has the dust cover on it so I'll need a little time.

     I just got home from work and want to get to church, then
over to KD8FVJ's qth for antenna stringin', Then Beer and Football.

GL and Keep the Faith!

/Dan

[WBear2GCR]

A little more headbanging.

THe 200-400kc. band shows HF OSC action when the bandswitch is not quite at the
dentent. Actually, quite a bit off the detent. Soooo... looks like the cover is coming BACK off the top of the mechanism. Could it be a slipped cam? What holds the cams in place? Friction fit??

But the 2.5mc band is still dead. Possibly the same reason, but it does not show any signs of popping to life as the bandswitch is rotated.

Since the lowest band works, I'll leave it in peace. Going to pick up a NOS 200-400kc module from W2TRH hopefully later today, and plop that in place of the wayward 2.5kc module, and maybe it will spring to life! But I think this one is going to be mechanical and in the switch, which is not exactly good news.

Otoh, the switch "rings" ok with the ohm-eater, or give the appearance.

Poke, poke, poke. Poke around.

The only way I found to test the series caps is to pull them or pull the module to get them free of other connections and parallel caps.

Took a metal version of the 6K7 HF OSC tube (hope that was the right number, the next tube over is a 6L7, iirc) from the rust-o-bucket chassis and dropped that in. If the numbers have not been scrubbed, the tube type is printed on the upper rim of the octal sockets! Nice, good idea Hammarlund! Bins of them sitting in the factory, one bin per tube type. Made no difference.  One can hope.

Will go back to the 12ga. shotgun troubleshooting. But this is looking now like the switch, at least it is on the 400kc band.

I was thinking, change out the 100-200kc band for a 1.0mc-2.0kc and the dial would sort of be ok...

[WBear2GCR]

If no one is that interested, I can QRX/QRT.

Any comments or thoughts are appreciated.
I suppose anyone who has done a few of these Hammarlunds is biting their tongues as
I stumble around this one... but I'm not one for stage fright, and don't mind looking a bit foolish.

There are a number of reasons that I decided to document and post, but at the moment they are not so important. The main idea is that this isn't my private monologue and that it's an "open frequency" and we're running break-in. Over?

[w1vtp]

Im for keeping this thread going from time to time as it could turn out to be a good resource for later time.  I'd put some stuff up but my SP400 is on the rack waiting for some TLC

I am looking for a phenolic strip where I can make up the connection for the cable that goes from the RX to the PS. I'm looking for either hardware or an idea how to make one.

Al

[N8ETQ]

    Yes, keep it going! Problem is that I did the work on mine
20 years ago,   I couldn't recall how I
lashed up the power connections either so I moved him out
a bit this morning to get a PIX for Al.    My other "motivation"
is a CE-100V TX I may pair him up with.

    Al,  I got a chunk of 16 cond. Military cable from something
and just connected the thing to the P.sup with spade lugs
on both ends. The cable is fastened to the back of the RX.
You only need 9 wires from the psup to the rig for operation
but I brought the "SPKR" and "BK IN" lines down as well.(unused)
A "PHONO" input and "PHONES" connection are also available
on the BC-779. I have an ICE-Cube relay hanging off the "BK IN"
terminals.

/Dan

    

[WBear2GCR]

Attached is the basic circuit.

In the actual radio it is bandswitched and the values for the coil, shunt and series cap are changed for each band.

Ok, so forget about how the values they have used for a minute. IF one wanted to set up this HF OSC (VFO) for a different band or to cover a different *range* of frequencies, what are the considerations?

For example if you wanted to go for 3.0mc to 7.0mc instead of the 2.5mc to 5mc they have, what would need to be changed, and what controls the high freq side and what controls the low freq end??

The three main components are L23 (the coil) C76 (the shunt cap - air variable) and C81, the series cap. The tuning cap itself (main tuning knob) appears to consist of three physical sections, so whichever band is being used must use some combination of the three sections.

One problem that I see is that each band must more or less tune linearly across the band and go from one end of the main tuning cap to the other in doing this. Then too how arethe trimmers are used to set the band ends?

At the same time one wants the output of the HF OSC to be relatively constant, which means that the "Q" of the tuned circuit needs to stay fairly constant across the range.

For most bands C81 is the same 1220mmf (pf)! What happens if that is changed?
Also C76 remains the same value trimmer for a number of bands.

Of course I get that the coil gets changed to different values, higher L for lower bands.
Does more of the C1D (main tuning cap) cause the freq to go lower or higher? I'm guessing lower, so then the coil is spec'd for the high end of the band??

So, I'm entirely unclear on how the oscillator is set up given what it needs to do.

Insights and explanations appreciated.

                       _-_-

Actual circuit, pdf,  added for reference...

[w3jn]

Just because it works on some bands don't assume all the parts associated with the oscillator are good.

Plate voltage OK?  Screen voltage OK?  No leakage in C13 or C15?  Any or all of that could kill the oscillator, and it all depends upon the Q of the L/C circuit whether the oscillator will fire off or not - and I'm betting the Q ain't the same for every oscillator coil.

Yes, you found one of the many hidden hazards of the SuperPro with those hot trimmers.  First radio I recapped was a SP400, i was about 12 and it was one of those hot humid days and I was sweating up a storm.  Grabbed the little screwdriver and held it by the shaft for extra sensitivity and my other hand was clamped firmly on the front panel.  Got the screwdriver on the trimmer and the 300V right across the heart about knocked me out - I was sick for a couple days.  Had I been older I probably wouldn't have survived that.

[WBear2GCR]

Whoa, JN! Serious tale there. Glad you made it through ok... nasty stuff.

Yes, the osc is osc'ing ok as far as the tube and the stuff around the tube.

I've worked out the problems as far as getting the bands to work. I think I may post the details of the rest of this romp through Hammer-land (is that where Thor comes from?) via some other means...

...but the short version goes like this; one of the bands, the 200-400kc. band upon closer inspection, and after some actual sleep, looking at it with the brain engaged,  turns out to NOT be the 200-400kc. band any longer! The coils were all rewound! The new range is not quite spot on where it needs to be, but undoubtedly was intended to be 20-30mc, to finish the high end (extending the range of the receiver now to cover 15m and 10mc).

I did find some bad caps in the HF Osc coil modules, and actually replaced one module with a NOS one (acquired by luck locally), which worked perfecto.

There's a whole lot more detail to this, but I'll leave it for now unless someone has other thoughts, questions or comments.

[w2emn]

Keep going- I've got two BC779s, a SP-400 and a SP-600 so I'm really into Hammarlunds.  The first BC-779 was badly hacked and took me months to restore it to original.  The SP-400 was almost pristine except that when I fired it up, it had bandspread on the two lowest bands (broadcast), and none on the highest SW bands.  I did a LOT of head scratching over that.  Finally I pulled the cover on the bandspread capacitor, and found four clipped wires... Some prior owner had switched the wiring to the bandspread cap.  Fortunately, it was a simple process to reconnect the wires.
I've spent a lot of time restoring the radios to original (took years to find an original power cable and the knurled nuts for the cover).  So if you need advice I'll keep watching this thread.

Pic of my SP-400 is on radioblvd hammarlund page

Ed  W2EMN

[KL7OF]

I have a real hack artist BC 779 that plays very well.....It is ugly and the unknown artist removed the push pull audio  and put a power supply in its place....the audio is now single ended and the power supply is on the chassis......Hack and whack job, but I really like the RX and the adjustable bandwidth...Good Luck with yours..

[Todd, KA1KAQ]

I've got a pre-war 200SX that someone did the miniature tube mods to in the RF section. Fortunately they left the rest alone. Still contemplating converting it back but Johnny convinced me for the time being at least that since the work has been done and it probably works a little better, why bother?

I did find some bad caps in the HF Osc coil modules, and actually replaced one module with a NOS one (acquired by luck locally), which worked perfecto.

Keep your eyes peeled online if you discover more parts are needed. NOS Super Pro parts turn up quite often on ebay and elsewhere cheap. The gov't procured plenty-o-spares once they got up to speed. The harder things to find end up being knobs, meters, and so on. Even at that, numerous parts sets surface too.

Once it's all dialed in, there's nothing quite like an old Super Pro with shove/yank audio output driving a big old Jensen or EV speaker to fill a room with sound. I'm forever in debt to 'JN and the artist formerly known as the HUZman for steering me back toward the old SPs some years back after I'd dismissed them. One of the finest receivers ever made, can't imagine radio life without one.

[WBear2GCR]

Just an update picture.

Working on the dial assembly now - the plastic part with the dial legend is warped. May try heat to "relax" it back to flat, and/or swap out dials from the parts unit. Pix shows unit ready to pull the main tuning module to get access to the dials. The rest of the chassis has been cleaned and you may spot some shined up hardware too... front panel is painted and legend filled in, ready to go.

            _-_-

[n1ps]

Bear I think you are spending about as much time authoring this thread as it takes to fix up this radio.

Good read though.  Any of these period higher end receivers are always an experience in frustration and then relief when you have one of those DOH moments when the fix presents itself.  I have a SP400 which I have to get at as the evinrude circuit motored to life.  Fixing these 2 piece receivers with the separate PS is a PITA.  Its like trying to work on a vacuuuum cleaner made of iron. 

So I recently completed a sx42.  Bought it sight unseen.  Turned out to be mostly a basket case.  It sat in may garage weeping every time I drove in.  I finally gave in after 12 years and put it on the bench last winter.  The only good item in the unit was the bandswitch, it being the most important.  The front panel was a disaster.  The chassis I'm  pretty sure hosted some rodent races.  Electrically it showed signs of being worked on by the kid next door in Toy Story (one).  But got it all going despite the roadblocks.  Also TNX to Bill K1BF who dropped off a parts rig with the only nice piece of it being the front panel.  Electrical-wise, the BC band was weakest.  The rest of the bands were OK but not great.  The fix - an IF amp was weak and needed all new components ( I reworked all 3 amps).  So happiness now with the 42.  The sp400 iron vacuum with the evinrude motor is next up.

Peter

[WBear2GCR]

Peter, thanks for the kind words. I type fast. Learned that when I was doing computer graphics all day, can type almost as fast as I can think it...

I think that the SP400 is very similar to the SP200, but as I noted, I am a Hammer-Land newbie. Now I be na expret!

This one is actually almost done. (Famous last words) Just the dials, alignment, and putting the front panel back on, polishing the knobbers. Got some parts set to come via wagon train, so that will but the gilding on this old gal.

Gotta say that the Nev-R-Dull on the toggle switches sure made the bat handles gleam! Sweet! Nothing quite so nice and satisfying as good polished nickel plating.

                        _-_-