The AM Forum

Greetings once again from Venice.
The Hammarlund SP-10 was an integral product that redefined Hammarlund as a leader in communication receiver design in 1936, the year of it's unveiling. It was in production for just a short period of time of which the SP-100 took it's place. Very few examples of this fine receiver exist, and I am proud to say that
I am now the owner of one such example. It's complete with the rack mount power supply. It has the variable IF gain, the variable crystal filter and of course, that beautiful black box look. The problems it has
is what I would call, the curse of CQ magazine "modification" articles on how to "improve" something that was so prevalent after WWII. This example is unfortunately a victim of attempted hellification of an otherwise brilliant design. I have to remove two very seriously bad modifications that resulted in the use of 7 pin miniature tube substitutions. Fortunately, these mods can be removed with the old 6 pin sockets reinstalled and wired to original stock form using the correct materials and lead dress. I have every reason to believe that this wonderful receiver will back to it's original form and function in under 3 months.
The cosmetics are fine and even though there are some scuffs here and there, it's in remarkably great shape considering it's age. I spent 6 hours installing replacement driver and output transformers that were shot, so I could hear if it worked. Well, it didn't work as far as RF was concerned but I did hook up an iPod to it so I could play some Joe Walsh through the output stage! The 6F6's drove  the speaker nicely.
The original output transformer leaked it's PCB laden contents all over the place, so it will be baked to remove and properly dispose of the offensive guts in order to save the very rare transformer cover.
A modern replacement transformer will be "potted" inside the old cover so I can maintain the look of the original. The steps needed to make this fine receiver work again will be worth it. To me, it's a once in a lifetime chance to own, restore and use something that many have never seen, used or touched.
So, if anyone has any parts from an SP-10, SP-100 in whole or part, please let me know. This will be part of an article I plan to submit to Electric Radio in the coming year.
Thanks for reading.
73 de Billy N6YW

What an awesome radio.  I like the separate supply.  Joe would be proud to know his music is being honored with a hollow-state analog piece of history.  I look forward to hearing about your progress on the restoration.

Congratulations!

Sharp looking radio!  I"m sure you will have the insides just as spiffy in short order.  Congratulations.  b.

Very nice acquisition. Bet your very proud of it and will be more so after restoration.

I don't thing the output xformer was laden with any type of PCB oil; not sure that type of oil was even available or invented in '36.  Probably More like a bitumen impregnation. 

The driver and output xformers in later SP 200's etc. were far beefier, both black and both same sized. They were potted with decent potting compound with cardboard covers on the bottoms.

I don't know what it is but it's disgusting and very very messy. Someone tried to make it work but clearly had no idea what they were doing. Thanks for the comments too. This is going to be one of my favorite projects of all time. I will of course keep you informed of it's progress. :)

Actually on closer inspection the footprint of both those transformers look suspect.  The driver clearly doesn't match the embossed footprint. One corner of it hangs over on an angle with no screw. Stuff I used to do in JS days to use existing holes the lazy way.

The output xfor footprint and input xfor footprint in your picture are the same, just about the size of the ones in the SP-200 where the lugs come out under the xfor's with no flange.  

I think you already have a kludged output where someone has installed an open frame transformer inside a suitable expanded aluminum case, both smaller than the original.  Then they potted it with homemade beeswax or wrong melting temp. compound.

The input xfor is obviously a kludge either added at the factory when nothing else was available for this early model or more likely added later after someone sold both really decent transformers.

I've let my SP-200 go long ago but perhaps someone will measure the footprint of their transformers and send you the results. Both originals in the 200 had expanded steel shells, same size in and out, with lugs coming out the bottom with no outboard flanges.  I'm pretty sure a set of these are what you will find is required.   Possible a museum has an original SP-10 that you can compare.

BTW yours looks more like an SP-100 with octal sockets , a host of kluges and only a few six pin tubes. The SP-100 does seem to have smaller audio transformers than the later SP-200 though.

The power supply appears to have been removed from its case and homemade mounted on the panel too.  Screw holes don't match or are open with faint marks from some previous chassis, etc.
 Very interesting pieces nonetheless.

See a SP-10 and model indentifications here:
http://www.skywaves.ar88.net/commrx/Hammarlumd/SP-10/Super-Pro_SP-10.html (http://www.skywaves.ar88.net/commrx/Hammarlumd/SP-10/Super-Pro_SP-10.html)

Model ID chart for all Super Pro's:
http://www.skywaves.ar88.net/commrx/Hammarlumd/SP-10/Super-Pro_Data.html (http://www.skywaves.ar88.net/commrx/Hammarlumd/SP-10/Super-Pro_Data.html)

edited after a little research later: This nails it . You have a 1937 SP-100X.  Look about 1/3 way down page.
http://www.radioblvd.com/hammarlund_super_pro.htm (http://www.radioblvd.com/hammarlund_super_pro.htm)

Rick
You are quite correct. Both of the transformers you see in the photo are now removed and temp adaptor
plates have been added for using period correct non-stock transformers for interim use to get it up and running so the process can begin. My approach (was) is to allow monitoring of the radio as I go through each stage to get it operational one stage at a time. Right now, the first order of business is to make a notebook to keep track of what's stock and what needs to be returned to stock. I am sure that over time, the needed parts to make it correct will be found. The metal chassis cover needs to be completely repainted as it's the wrong color. It's ugly and because it's a table top model, that certainly needs to be addressed.
I got real lucky with the power supply though. It's right as rain and was recapped in the 70's and fortunately the original can capacitors were not removed. They are the screw on types with locking nuts and the wires of the caps exited through the bushing, which were simply cut. Sprague tubular electrolytics were installed flying lead style. That will be addressed. The plan is to open up the old cans and install new caps inside and redo the cloth wires just like stock. That will be fun and even though no one will ever see it until it's out of my hands, I figure a little extra effort will be justified.
Like the HRO radios of the day, the SP-10 & 100 enjoyed the benefit of external power supplies. This resulted in quieter operation and better performance. This is something I truly enjoy about my HRO 5TA1. It's super sensitive with a dramatically low noise floor. According to Henry Rogers, the performance of the SP-10 is truly wonderful to behold. I am looking forward to that and I hope I can muster the same amount of return on my restoration endeavor.
The way things are going, I am going to need a bigger shop. Really, my radio sickness is spreading out.
:)

I've owned a SP-200 and currently have a 400 but never a 10. Very cool find Billy. IMO, of the receivers made during the tube era, the SP10/200/400 are probably the best sounding for hi-fi AM use. It's heard to beat continuously variable bandwidth up to 16 kc and push-pull audio!

edited after a little research later: This nails it . You have a 1937 SP-100X.  Look about 1/3 way down page.
http://www.radioblvd.com/hammarlund_super_pro.htm (http://www.radioblvd.com/hammarlund_super_pro.htm)

See my add'l edited remarks and referenced sites earlier while you were typing away.  ;D

Your SP100X is certainly worth the TLC your planning. Great rig.

--From above site which appears to be "the Bible" on HQ series.


Someone added the larger tuning knobs later, a common practice and the semi-calibration scale marks don't seem to show up on your receiver.

It clearly started out as a SP-10, but it has a lot more hacking than you think. The quick ways to differentiate the -10 from the -100 are the front panel (-100 has scales over the controls, -10 only has labels), and the -10 used all big pin glass tubes, no octals. This one has everything - glass big pin tubes, octals, and miniatures. Someone has swapped the tuning knobs, but that looks like the least of the problems. They also added an octal socket to the back. One nice thing I see is the then-optional crystal filter installed. This became standard on the SP-100.

The remaining audio transformer is correct, IIRC it's the 600 ohm sealed version. They also used an open frame variation for 8 ohm(?) output, or at least something considerably lower than 600. My -10 has the sealed type, -100 has open frame. And as you said Rick, the goo under the remaining transformer isn't oil but tar. Probably it was hooked to an improper load for some length of time and started the fry off.

Power supply appears to be hacked as well, tube swaps, chassis chops and so on. Something to keep in mind is that the SP-10 used a slightly lower B+ than the -100 or -200 models. With all the hacks in place there's no way to know for sure and it might not matter, but if the goal is to return everything as close to stock as possible, it becomes important. Check the serial number on the receiver (stamped into the back apron) against the one on the supply (looks like it might be under the power connector hack) and see if they're close. Quite often they became separated and some later owner just located a supply for a -200 and hooked it up. If it's the original supply, it's really a shame it got hacked but that's what you did back then. You updated your rig, you didn't have $$$ to go buy another in most cases.

I know there are at least two other list members who have SP-10s. Steve/W8TOW has one with matching supply he got at Dayton some years back in nice shape and I'm pretty sure Dennis/W7TFO has one as well. Mine is sans supply and needs a good clean up (looks far worse than it is) but it's untouched otherwise. I'll post a couple shots of the grubby innards for comparison along with the SP-100 front panel with its scales.

Probably the best place for info is Henry Rogers' site:

http://www.radioblvd.com/hammarlund_super_pro.htm

Excellent technical and historical information including serial number tracking.

It's definitely an interesting rig, the most advanced and best you could buy back in the day. The only other thing that came close was the HRO, out a year earlier. Henry provides good comparison data on his pages as well.

Looks like a few of us were typing at the same time.

Here's a side shot of the audio section along with the SP-100 showing the difference in the front panels and correct tuning knobs (fairly common and easy to find).

Good luck with it. I've gotta go haul branches and brush to the landfill, woohoo.  ::)

I want one of those SP-150s!

Here ya go!

This Jensen 15" speaker is the one you want to hook to a Super Pro. JHP-51 or -52. They sound great.

I forgot to add, aside from the front panel and tubes, another way you can tell your radio is indeed a SP-10 is the pair of cans with thumbscrew adjustments on top. These were removed for the -100 as it was a PITA to remove the cover to reset them. Henry covers this on his page, too.

Those 6F6s were originally 47s.....

Perhaps the whole front panel is a hack too then?  because I think the crystal mounting board looks original from the rear complete with missing shield cover holes and faint shield markings.  "Selectivity" instead of "Bandwidth" also matches the SP-100X notes too.
See the notes on the site we mentioned.

Someone must have had great fun in the day.  ;D

Todd
Mine is a bit of a mongrel, but it is a later serial number according to Henry. He wrote me back after Gary and I submitted photos of my radio. I think mine falls under the category of a CQ magazine modified "special". Thanks for your photos and input. I feel better now that I posted the project here as a sort of landing for information acquisition. Perhaps this resource (here) will yield more information and possibly some parts. According to my research, this SP-10 came stock with the variable crystal filter as it's a later version kind of a crossover to the sp-100. There is one thing that clearly marks mine as an SP-10...
The meter is the plate current type as found on the SP-10. Later models used meters with the more familiar S unit scaling. This type of meter is apparently very difficult to find so I hope mine works!
This will be a challenge worthy of the sport.
I plan on reinstalling the #42 output tubes of which it's clearly evident by the holes in the chassis that mine is an SP-10. Several sockets were replaced with newer Octal style types.

What exactly is your chassis serial number? 
--following from site above.

The 2nd receiver I posted with 'Bandwidth' in place of Selectivity is the SP-100, Rick. The first, SP-10, matches Billy's perfectly if you don't count the paint chips on mine.  ;D That's basically a quick 'from a distance' way to spot the difference at a hamfest or such. 100 has numbered scales over the knobs, too.

The crystal filter is correct, it was originally offered as an option on the SP-10 so that's no surprise. Mine doesn't have it and a friend who has a couple 10s only has the filter on one. My understanding is that it either became standard equipment late in the run of -10s or early in -100 production.

The 0-5 tuning meter was actually used through 100 production as well. It changed with the advent of the 200 series, maybe even late in the 100 line, with the illuminated S meter. Another meter change I discussed with Henry relates to the enclosing of the meter adjusting screw. Early meters had all glass, later ones had a small metal surround holding the screw in place.

It's definitely a great receiver to restore as much as you're content with doing, Billy. They made a lot of SPs and as a result, many ended up hacked. I have two pre-war 200SX models here that have been hacked, but the chassis are pretty clean as are the beautiful wrinkle black panels. Wartime versions went to smooth paint I'm sure for ease of painting maintenance/re-lettering. The pre-war panels were engraved through the paint exposing the shiny aluminum. Someday I need to decide which one to keep and restore, and send the other down the road.

Back then if you had a Super Pro, you had something. Even post-war, many used Command sets or if they were lucky, a BC-348. I'm sure they weren't cheap, so as improvements came along it was much more cost-effective to 'incorporate' them than to buy a new receiver (that might not work as well as the SP). So as nasty as some of it seems to us now from a historical perspective, it's all part of the history. Even my SP-100 has a couple modifications, fat pin to octal conversions. Someone blasted a hole in front to move the headphones from the rear apron too, but I already reversed that. Just need to fill the hole.

And yes.....the audio output used 42s, not 47s. Need.....more.....coffee before typing.

Got another load of brush to move, couldn't resist checking back. Really love the old Super Pros, and I always hold W3JN, K4HX, and WD8BIL responsible for contributing to my delinquency in that respect. 

Steve,

What version SP did I provide pony express service for?  It was the one from Dee-W4PNT (sk). 

Joe, GMS

Rick & Todd...
This is turning into an excellent thread.
My serial number is #996. As to the hack jobs, yes. An unfortunate sidebar to Ham Radio but in some cases actually benefited us along the way by inspiring future engineers who helped to develop new technology. I am trying my best to keep it positive, Hi. It is sickening in retrospect that so many radios were hacked, many of which can never be brought back. Up until now, I have never seen an SP-10 or at least recognized one at a swap fest or online. I know that I am now on the constant lookout for these including the 100.
I really can't imagine what it must have been like to be around back then, at over 200 dollars, the SP-10 must have been out of reach for most people. Kind of like the common middle class Ham of today wishing they could afford a $10.000+ radio currently being offered. But then, we know better don't we?

It was The Derb that turned me on to the prewar receivers, especially the silver dial Hallis and the Super Pros. He had a SX-11 with a Magic Eye. Cool is the rule.

(http://www.radioblvd.com/photos/sx11b.JPG)

Steve
It doesn't get much cooler than that. Beautiful!

Always fun giving signal reports like, "You're closing the eye three-quarters of the way OM!"

I have three SP's. two 100's and a 200'
The serials are 1937, 3255 and 16116.
16116 is a 1943 civilian unit.  Not sure how rare it would be?
I have started replacing capacitors in 1937.  When I bought it it sort of worked but I discovered a wax puddle on the lower cover plate.  I have started on the job of replacing all of the capacitors.
I can take some pictures if anyone is interested.
73, John

Billy, looks like Todd and your ser.  no.   ID it as a late SP10.

If you can obtain a good set of AF transformers which most output tubes work into well enough,  I think I'd replace a few caps and stuff just enough to getting the CQ mods and rest of receiver working FB, enjoy it for awhile while girding up and obtaining parts for the complete restoration.

There will be a ton of work going back to the six pin variation.  Btw I have Five or six , six pin ceramic sockets I'd picked up at cowboy Gathersburg several years ago. Your welcome to them if you want to do the full restoration.

Looks like wire hanging off IF cans may have been rerouted underneath for the min. Tubes, etc. Hope the IF cans haven't been partially bypassed, etc.

Please post some pictures!!! Any and all.
Rick, I appreciate the offer. I actually rummaged through one of my parts boxes and low & behold, I found several of the correct fiber type 6 pin sockets. Not sure how good they are but I'll clean them and see.
Some have the tube numbers stamped onto them like the stock ones were, but not the correct numbers for this set.

Hey Billy,

I have an SP-10 S/N 674 (PSU 804), and two SP-100's...I feel your frustration at not having it back to year one already.

My SP-10 had the leaky transformers as well, but that is just tar, no PCB's in there.

If you need some parts, I have a few extras.  The crystal filter insert on yours was an option on factory orders.

Get it going with care, you will be rewarded with a rare collectable.  The powerful eolution of the Comet Pro.

My research says there was a 19" rackmount version of the SP-10, but it is really rare.

It will be really stable, hi-fi when you need it, or single signal as well with the turn of a knob.

Mind those little thumbnuts for the cover, a set is hard to find and VERY expensive (>$50! :o)

They were usually supplied with an electrodynamic Jensen 12" that you got to mount as desired.

Dennis

Yeah, but that 15" JHP they used in the -150 sounds soooo nice. I've got one hooked to the SX-62B. My -100 came with what appears to be an original Jensen field coil speaker, 10 or 12 inch. Have never tried it. The cone looks like leather.

To Rick's comment about finding replacement transformers: I *think* they used the same transformers in the SP-200 series, along with the open frame type. Keep an eye out on ebay and online for SP-200s for sale just to see what they look like inside. There are a LOT of rough SP-200/BC-779 variants out there that might yield a set of transformers.

I have a really amusing story about a SP-100 but I'll save it for later. Got a ceiling fan replacement about half done, need to go finish it up. Legs were getting a little wobbly being on the ladder too long.

Todd,

The audio transformers on the SP-10 were unique to the series.  They are indeed potted, but have a smaller case than the wartime SP-200's, and mount via a flat plate on the bottom.  Also, they have an 8-Ohm speaker impedance, unlike the SP-200 with the 600-Ohm line.

The iron in the 100's were open frame, so were the pre-war 200's.  Potted jobs appeared for the military application, and carried on thru the 400's.

I built a rackmount "docking station" for repair of these radios, with a homebrew 15" Altec 515 and a Maggie multicell horn.

On top is a recent purchase SP-200 military rebuild, and one of my SP-100's below awaiting all new caps.  Somebody (not me) put in an eye tube....oh well :P.

This is one RX that can really use the Hi-Fi speaker on a clear music station.

Billy, remember the signal meter in the 10 reads delta IF current, so will read backwards.

73DG

DG

What impressive speaker system!!

Al

Thanks for the compliment Al, but it is just equal to the RX.

Can't play it thru some cheezy little cone!

73DG

Wow!
Stand up dispersion.
--Watch your ears.

Where's the 78 changer
  For the phono inputs?
Of your dual Supers
  In push pull parallel?

Dennis
That's an appropriate setup considering it's lineage. Gary K6GLH uses an Altec Voice of the Theater in his "Studio G" :)

Yep, been there, seen and heard it.  Muy buen! :D

Got room for yours?

73DG

Did not know that, but it makes sense. Considering the -10 was their first step so to speak in a new design, they likely changed the transformers to something more available in numbers and quality. Perhaps that had tar leakage issues early on?

I was under the impression that the open frame units, regardless of model, were 8 ohm, while the potted can type were 600. It's been a while and I don't recall where I got that impression - Henry's page, manuals, old sales brochures....

My SP-100 is S/N 2174 with a universal military power supply that works but doesn't come close to matching it. Ironically, I just got back from putting it into the storage unit along with a few other items. SP-10 is S/N 701, also sans supply. I do have one doghouse supply that looks to be pre-war, but it's missing the multi-tap resistor and a few other items. Fortunately no one drilled or blasted it. Can't get to the -200s right now.

Todd
You have a nice collection to get running with. If I end up with surplus parts sets, supplies etc, I want to make sure you get what I have excess to my needs in order to get yours running. Perhaps I need to issue a challenge to AM Fone to assist in the scour the collections of people who may be able to help these radios see the filaments lit and beautiful audio issuing forth. That rust bucket will turn into perfection some day.

Some pictures of my three SP's
The first one is Sp100 2955
The second is SP 100 3255
The third is SP 200 16116
Has anyone developed an errata sheet on the radioblvd site?
I noticed that it states the all Sp 200's from 1942 on had potted audio transformers.
Mine has an open frame.

The third picture in my prior post is a top view of SP 100 2935 showing a replacement audio transformer.
Sp 100 3255 has an origional that I will probably swap over.  It also has a potted audio output transformer.
The firstpicturee is the SP 200 16116
The second shows the output section in SP 100 3255.

Thanks for the kind thought, Billy. I think my receivers are in fairly complete shape, I'm more 'power supply'-challenged. Finding the early models with the doghouse vs. the more prevalent military rack mount versions usually requires buying another set to get the supply. Same goes for the knurled nuts for the covers. Need to track down a set of those for the SP-10, it came with acorn nuts at least.

John, I'd be reluctant to yank any parts from a SP-100 unless it was badly mauled to start with, extra holes & missing crucial parts, etc. Dennis can probably confirm if the SP-200 transformers will interchange with the -100. There are plenty of SP-200/BC-779 donors floating around.

Also curious about those elusive knurled nuts - IIRC, the ones on the -10 & -100 are flatter (not as tall) than those used on the later 200 models. Of course, any are better than none.

Could you post a photo of what a Hammarlund Dog House supply looks like? I have never seen one.
I could likely fabricate the original if I had the specs.
Billy

I'll dig it out in the next day or so. It's basically the same as a rackmount supply without the panel, and with a louvered 'doghouse' covering the top of the chassis. Hence the nickname.

IIRC, the supply for the SP-10 used a 1V rectifier in place of the 80 seen later.

With all of the rain on the way, I think tomorrow evening will a nice time to break out the SP-10 and give it some going over, make notes etc. I will be taking some photos and in case anyone needs it, I can take photos of the interior of both the receiver and power supply and post them here.
I also need to finish up the SP-600 which needs at least 2 days plus any possible troubleshooting.
These projects are as addicting as collecting the radios themselves. I just wish I had more space for laying out these projects.
73 de Billy N6YW

The SP-10 got a thorough once over last week before I began clearing out excess equipment which I sold. It is in need of a complete rebuild back to original specs, which means most of the tube sockets need to be converted back to the original 6 pin wafer types that have the tube numbers stamped on them. This is going to be a pain to source but I think I can do it.
I will post a want when I collect the numbers needed.

Here are a couple of photos.
One is my SP-10...great sound and amazing signal rejection ability
and my SP-200 (AKA BC-1004) from WWII
The SP-10 required only slight cleanup...the BC-1004 got the full
treatment inside and out...
The front panel was stripped, painted 3 times if I remember right
and then a overcoat of Krylon clear-coat...
well, the photo of the BC-1004 escapes me right now...post it later...sorry

a shot of the interior...This rx was originally the station monitor for a
AM BCer in NY!

The SP-10 got a thorough once over last week before I began clearing out excess equipment which I sold. It is in need of a complete rebuild back to original specs, which means most of the tube sockets need to be converted back to the original 6 pin wafer types that have the tube numbers stamped on them. This is going to be a pain to source but I think I can do it.
I will post a want when I collect the numbers needed.

Another anomaly with the 10 is the signal meter reads backwards, or delta RF AGC level.

Can get quirky if you hit the bench thinking of how the 200 reads 'right'. ???

73DG

Fortunately, my SP-10 has the original meter which by most accounts are very difficult to source. Henry Rogers has a serial number survey on his pre war Hammarlund page that lists the various models and production numbers. There were a good many of these made but very few seem to exist today. Unwinding the mess made by a former owner will be a tedious (not difficult) task that will require some good parts sourcing. I have some of the original type tube shields and various misc parts that Gary K6GLH gave to me with the receiver.
If and when any of you have your SP-10 out on the bench, please send me the gut shots. The lead dressing is pretty lousy in mine and will straightened out as I go through each stage replacing and repairing the sloppy mods that were done.
Onward through the past!

I've got a very scruffy BC-779 that works OK and has the rack mount supply that must weigh 60 lbs.

I've also got a 100 or 200 in black in very nice shape with the dog house supply that weighs less than half of what the military supply does. I was told when I bought it that the supply needed a recap so I haven't tried it yet or checked the supply. Hopefully the transformer is OK.

I'll check the serial numbers when I get back off the road (I'm working in Roswell, NM for a couple of weeks) although the BC-779 may not have one since the data plate has been disappeared.

I do have a spare meter, although I don't remember which type, for these that I picked up somewhere, I'll check that too. I'll check my tube socket supply as well.

Greg

The military SP's data plate does not have the Hammarlund SN on it, rather the Signal Corps one.

The Hammy # is stamped on the rear apron of all of them.

73DG

Great looking SP-100 you gots there Todd!!

Thanks Buddly! Clearly you and the original owner took good care of her. I restored the headphone connection to the original rear apron and removed the jack added to the front panel, just need to fill the hole and touch it up.

Sadly, the old girl is in storage as I type this. One of the first sets to go over since it developed a problem and I didn't have time to troubleshoot it. Needs some new caps at some point.

Sure sounds sweet driving a big EV or Jensen speaker!

Did you finish the SP-10?
I just received a chrome plated chassis SP-10, and was wondering how well it works

I just got in 4 Super-Pros, and a SP-10 is in there.

Sadly, it is beyond restoration but should yield some bits of unobtanium if needed.

73DG

I'm going to need pics and pieces to finish mine, but I'm not sure if I should start a new thread, or add to this one, as there are many others in this thread with SP-10s.
 I also have a chrome BC-779 that Henry WA7YBS (www.radioblvd.com) believes may have been done by the signal corps, the tube numbers were stamped in the chassis in a very professional looking (factory looking) way

I still have my unmolested SP-10, and will be happy to E-mail you pix. :D

Easiest ID of all for the 10:  It has a tone control, the others don't.

Also in my collection is the SP-100 with the eye tube modification shown on Henry's site.

73DG

Mine has a tone control, and the knurled nuts on the IF cans, the crystal filter and plate are missing, and the Audio was changed to 6F6, or that was the tube in the socket, just the audio(4 tube sockets) was converted to octal.It looks to have been rebuilt in the 50-60's by the type of coupling caps installed.
I would like pics of the crystal filter, and the connections of the tuner, mine arrived with the tuner just sitting on the chassis, wires everywhere.
I may be in over my head, I have been repairing and building tube amps for years, but this is a little more complex. Henry WA7YBS said I may be able to use the BC-779 as a partial guide to generally figure out where things connect.

a couple more pics.
I am unable to find the serial number on this unit

The caps, and some resistors appear to have been replaced in the 50-60's
I really haven't found a decent schematic for the SP-10 yet.
Where is the serial number usually located on the SP-10?
on the BC-779 it was over the speaker connections.

The more I look at it, the more I realize that this was a never finished rebuild done in the early 60's-ish, it may have been chromed then, there are many never soldered connections on tube sockets and terminal strips.

I had the BC-779 and traded it to a Hammarlund collector for a BC-774(?) It had a chromed front panel. When I asked him why he told me that this was made specifically for the Admiral's quarters onboard ship. I do have the separate power supply that I use for the BC-774. It is a good AM receiver but its BFO is a little on the weak side.

I will start a new thread about the Chromed BC-779, as I wanted to keep the op's thread about the SP-10 on topic, Do you have pics?

In the tube socket picture, what is the red stuff? Apparently it is put on tube sockets and other terminals on very old gear, and it's soldered right through so it remains. Only seen it on really classic stuff.

The terminal boards, like 'pcb' but with upright pins - are these original to this radio or a product of the earlier resotation? I'm curious as to when they came into use.

Anyway that chassis looks pretty clean, will be very nice when completed.

Guessing, I think the person rebuilding the unit marked the terminals with magic marker, or nail polish to verify they were soldered, or tested? I have never seen old equipment with these markings, but have seen it on other, more modern equipment, especially something that was worked on, and many kits when someone marks an assembly manual to keep track what was done.
I don't have a good picture of an unmolested SP-10 in this area, but I think those terminal strips look more modern than 1936, they look the same age as the capacitors to me.The small nylock nuts are certainly not original.
The turret boards look like some version of fiberglass possibly, and I believe they are not original as well.Turret boards are quite old as a construction technique,
but phenolic was the likely material used when this was built.

Don’t think I posted a picture of this for a while; it’s my 1939 National HRO military RAS receiver. On the side of the rack is a autotransformer and voltmeter so it runs on 105 volts. I use to use it a lot on both 7290 and for a long time when I was on 1885 as the AM receiver. I replaced all the old wax capacitors about twenty five years ago and have not touched it from that point in terms of any other work and noticed its sensitivity is down a little so think it will have to come apart to resolve the loss of sensitivity but still very useable and has a great feel to it when running AM on non crowded bands. The IF filtering leaves something to be desired and the military version of the HRO has a 175 KHz IF so images can be an issue on strong signals but for doing easy AM QSO its hard to beat. It dose have the military noise limiter kit that helps a lot with static crashes on 160.
Its almost like there was a short period of time in the late thirties when National, Hallicafters and RCA were producing high end receivers where they have not learned about value engineering yet and tried to produce quality products that were capable of running forever. I have an old 1936 RCA commercial marine receiver that was never placed in service and think that may have to be the next project for the New Year.
Another interesting question, on the old HRO in the rack mounted power supplies there are four 8 Uf electrolytic capacitors that are now like seventy five years old and still are solid working electrolytic capacitors, how is this possible?

old-time Made in U. S. A. and not abused much..

That is in beautiful condition, museum quality! I like it!

I'm putting this aside until I get some more parts, and info to start putting it together.

    Check this out if u havent already....


http://www.radioblvd.com/hammarlund_super_pro.htm

GL
/ dan

Finally, got all the old ones together

3 10's, 3 100's.

73DG

I have been to that site, and have been conversing with Henry WA7YBS for a while now, that was the first site I visited.
Thanks for the suggestion.

That's a beautiful stack there!

Are those called 'super pros? Have separate power supplies?
Do those have interstage transformers from one 6F6 to push pull 6F6 grids?

Sp 10s have push pull 42s, they all have interstage transformers, and use separate supplies. The supplies are almost interchangeable(some modification depending on whether a field coil speaker is used with some supplies, and B+ needs to be lowered if using a later supply on a SP-10)

Here is some info on the SP-10 and SP-100 beginning on page 213
https://radionerds.com/images/3/31/TM-11-310-SCHEM.PDF
The schematic is pretty clear compared to the one I already had.

I was wondering if you could post a picture of the chrome panel.

Sorry Scott, I traded it away for the BC-794, because it didn't cover the 160M band. The fellow I traded it to is up Maine but I forget his name.

So, the front panel was chromed, what colored lettering?

Scott said:If I remember correctly the letters had like a smooth round etching or stamp that was filled in with black enamel.

I think I have to rob the cam switch from this to fix the BC779, since that is the only thing holding me up on getting that unit finished.

What a nice thread to find. Thanks to all who contributed.  I picked up what i think is an SP-10 yesterday. Previously occupied by a lonely mouse, but it should clean up ok.

The rear of the cabinet has an id plate.  I read the Type as BL. With a serial of 637.  Sadly the power supply is not consecutively numbered having a serial of 672. The ID plate on the PS is bolted on not rivited, but is period correct I guess.

Anyway, thanks again, Mark. K7MD. 73

The easiest way to know a SP-10 is it has a tone control