The AM Forum

My father Paul W3VVS is finishing re-furbishing his late 1940's homebrew AM transmitter.  Hopefully we will hear him on 75 meters within a couple weeks.

The transmitter is a pair of 812H's push-pull in the r.f. deck, driven by an 807 crystal controlled exciter deck.  Pair of 807's in modulator deck and a power supply deck.

Let's see if this new photo feature works:

Your piccie must reside on a public server with a publicly accesssible URL.  Posting a pic off your hard-drive won't work.   Maybe if you email your pic to Gary, he can post it somewhere on  Amfone.net somewhere, where it can be accessed?

www.photobucket.com is a good free image hoster.

You can post pictures from your hard drive. Click "Additional Options" below your message box when adding a message. Here's one from my hard drive:

Pete,

Thanks for the tip.   The rig picture is now added to the original posting.

Everyone,

Please scroll back to the top and see the photo edited in to my original posting.

Thanks,
Tom

*That* is a thing of beauty, Tom.  Glad you're getting it back on the air!

73 John

Tom,
      I can't wait to hear it on the air! I had a conversation with your father about the modulation scheme (with the pair of 807's) and am very anxious to hear how it sounds.

The mod scheme is very typical of what a lot of Hams were doing right after WWII.

Thanks for posting the pic and hope to mod-u-sooner-than-later.
Joe Cro N3IBX

Like a good motor real rigs are painted black!

Cool
Fire That Mother Up!!!

As I always say, "Nothing is sexier than Black Crackle and Green Phospher."

Congrats Tom, that rig pretty enough to make a grown man cry.
Its great he could get it back on the air, 60 years later.
Looking forward to hearing it this fall/winter.
Perhaps you could post some interior shots, would love to the details.

As the old bromide says...Everything old becomes new again....
Or in the modern words of the Timtron "Nothing like it, old technology."

I guess I will make an old-time radio serial out of this topic.  Below is a rear view of the 812H rack cabinet just before refurbishing began in February 2005.

Tonight’s episode – The Shack Overview.

By the early 1950’s my father had 3 home-brew HF transmitter racks in his shack on the second floor of our “Cape Cod” in the northern suburbs of Philadelphia.  When my twin brother and I were teenagers about 1968, my father moved the ham shack to the basement (where it resides today) so that my brother could have his own room.  Fred moved into the old ham shack and promptly painted it hyellow.

Anyhow, the original shack in the second floor had a workbench area in addition to the operating area.  There was a 3 ½ foot rack cabinet immediately to the right of the operating desk and a 3 ½ foot rack cabinet immediately to the left of the operating desk.  To the left of that rack cabinet was a 2 ½ foot rack cabinet with a 160 meter 90 Watt AM transmitter.  All 3 rack cabinets are on castors.  (I’ll see if I can dig up a good photo.)

The 160 meter rack (2 ½ foot) consisted of an r.f. deck using an 811 or 812 with a 6AG7 crystal oscillator/driver, a modulator deck using a pair of 6L6s, and a power supply deck.  This rack of equipment was given away to a boy scout group mentored by one of our radio club members when the shack was moved to the basement.  The modulator deck actually returned a few years ago, somewhat rusty.

The 3 ½ foot rack cabinet just to the left of the operating desk was the big HF AM rig, 300 Watts input.  The r.f. deck is a pair of 812H’s in push-pull.  The 812H was solely made by United Electronics Company (UEC) of Newark, NJ.  The plug-in final tank coils are war-surplus BC-610 spares that are modified.  The final is criss-cross neutralized.  The driver coil is the plug-in B&W JVL series.

The plate input power is 1500 Volts at 200 milliamperes.

In those days, the final r.f. deck was driven by an 815 buffer deck driven by a Meissner Model EX Signal Shifter (VFO).  We don’t know what happened to the buffer deck!  Originally, my father had an earlier model Signal Shifter which used a 6L6.  This earlier model Signal Shifter drove the final by itself o.k.  When my father upgraded to the new Model EX instead of the earlier model, he found that the EX put out LESS power, even though it used an 807 instead of a 6L6!  Hence the 815 buffer deck was added.

The EX was the last in the line of the Signal Shifters, but by far the most handsome of the series, in my opinion, with its brushed aluminum front panel and magic eye tube.  The EX sat at the left end of the operating desk.

The push-pull 807 modulator deck design is from a 1940’s ARRL handbook.

The power supply deck and the modulator decks again use United Electric sole parts; Z-225 mercury rectifiers.  They are electrically similar to 866A’s, but are shorter with the T14 bulb.  This helps to keep the panel height down.

The high voltage transformer, filter chokes and oil filter capacitors were all war surplus.

The Meissner EX Signal Shifter was sold off, probably when my father bought a Ranger II in 1967 (which he still runs).  I don’t know if he expected to ever drive the final with the Ranger, but perhaps he felt he would never run the 812H rig again.  The Ranger then sat at the left end of the operating desk instead of the Signal Shifter.  This was all well and good for me for when I became a JN in 1968.  All I needed to do was order some 75, 40 and 15 meter novice crystals for the Ranger and plug them in.  I still have those crystals.

To the right of the operating desk was a 3 ½ foot rack cabinet with a 50 Watt 10 meter AM transmitter.  The 10 meter r.f. deck has a 6F6 crystal oscillator, 6L6 buffer/multiplier, and 807 final with a 6L6 keyer tube.  All coils are plug-in.  This deck is now the exciter deck for the 812H rack refurbishment.

The 10 meter rack cabinet also had a homebrew 6 meter AM r.f. deck.  The final used a 6146.  This deck was built with horizontal orientation.  The panel height was only 3 ½ inches.

There was a push-pull 6L6 modulator deck and a power supply deck also to this rack cabinet.  The rack was primarily used on our radio club frequency of 29.493 MHz. AM.  The 6 meter deck was hardly ever used. 

The Phil-Mont Mobile Radio Club established 29.493 MHz. as their “Channel 1” frequency due to the war surplus FT-243 crystals on 7373.333 kHz.  Phil-Mont was active on this frequency from 1949 until the migration to a 2 meter FM repeater on 147.030 MHz. in the early 1970’s.  For a period from about 1968 until the 2 meter repeater was put in service, the club had a 10 meter AM repeater, split-site, about 1 mile apart in the Roxborough section of Philadelphia.  The repeater work has been mostly the sole efforts of Jim Spencer W3BBB, to this day.

After the shack was moved to the basement, and the 10 meter 50 Watt AM transmitter was not in use any more, I decided one day to try to fire up the 812H rig on 29.493 MHz. for kicks; 200 Watts AM out. This was circa 1970.  I wasn’t on the air more than a couple minutes and the next door neighbor Millie called on the phone to complain about interference on her telephone.  That was the last time the 812H rig was on the air.

I brought the other remaining empty 3 ½ foot rack cabinet to my house when I moved here in 1990.  I hope to build up a Class E legal limit AM transmitter in it.

Next episode – The Operating Desk/Receivers

Below is a rear view of the 812H rack cabinet just before refurbishing began in February 2005.

Close-ups of the rear of the un-refurbished rack:

1. The r.f deck

2. The exciter deck

3. The modulator and power supply decks.

More photos:

1. RF deck close-up

2. Modulator deck close-up

There are 6 crystals in the exciter deck now, all for 75 meters:
3837, 3870, 3875, 3880, 3885, 3890.  BCNU.

Crystal-controlled 807 Exciter Deck Photos:

1.  Top View

2.  Bottom View

Excellent story and great photos, Tom.  Thanks and please keep 'em coming!

Tonight’s episode – The Operating Desk & Receivers

The operating desk acquired in the early 1950’s has a bit of broadcash history with it.  Two neighborhood radio hams who were broadcast engineers at WIBG-AM, George Hooper and Lester Sacks (both SKs now), gave to my father the old engineering console from the broadcast transmitter site in Flourtown, PA, which is just west of the northwestern border of Philadelphia.   (WIBG started out in Glenside, Pa. off of Keswick Avenue as a small religious station - Why I Believe God.  In the baby boom era of the 1960’s, WIBG was the #1 rock music station in the Philadelphia market, transmitting on 990 kHz.  It was affectionately known as “Wibbage”.  By the early 1980’s, this station reverted to Christian music, WZZD as I recall.  Now, 990 is a talk radio station.)

 The desk is a large, heavy metal office desk with a thick black rubber top.  The sloping panels above the desktop went to another ham friend, Jim Spencer, who in turn built a short height wooden equipment shelf to sit on the desk top.  The wooden shelf is designed to take (3) 3 ½ inch rack panels side by side on the front face.

As I recall, the left-hand rack panel and right-hand panels were identical.  They contained volume and squelch pots, switches and pilot lamps controlling crystal-controlled monitor receivers.  The left panel went to a Link 11-UF n.b.f.m. receiver on the local township police frequency of 39.18 MHz.  The right panel went to the 10 meter AM receiver on 29.493 MHz.  The 10 meter AM receiver and Link f.m. police receiver sat on a shelf under the desk.

The center panel has a symmetrical lay-out of 2 main power switches, two classic telephone lever switches, and 4 pilot lamp assemblies.  Two lamps are standby power indicators which come on when the power switch is up.  The other two lamps are transmit indicators which light up when the lever switches are thrown.  The left-hand controls are for the 812H rig to the left of the desk.  The right-hand controls are for the 10 meter AM transmitter to the right of the desk

If either lever switch was thrown, up to 4 receivers were muted.

The muted receivers were:
- the main HF receiver, a  Hammarlund HQ-129X purchased new in 1946
- a home-brew 10 meter AM crystal-controlled, squelched receiver
- a 10, 6 and 2 meter AM and FM receiver using a RME VHF-152 tunable converter 
  feeding a homebrew i.f. receiver with AM and FM modes.  The i.f. receiver was built in
  a cabinet that matched the VHF-152 cabinet.

So occupying the top of the shelf on the operating desk were, from left to right, the Meissner Signal Shifter (or later a Ranger II), the HQ-129X, and the RME 10, 6, and 2 meter receiver cabinets.

The 10 meter AM receiver and the Link police receivers were on a time-clock that powered the receivers from about 4:45 p.m. to 11 p.m. every day.  These two receivers also fed several remote speakers in the house.

About 1969, the HQ-129X receiver was sold after acquiring a new-in-the-box, never used National NC-183D.

The photo below of the operating desk was taken today, August 16, 2005:

On the operating desk shelf is an RME69, the NC-183D and the Ranger II.  The 812H rig will be used with the NC-183D receiver.  The 812H rig will be controlled by the right-hand set of switches of the center control panel.

Also, the left-hand control panel has been replaced to fill in the spot.  The current 3 ½ inch panel is from the old 6 meter Link f.m. receiver that was on 52.525 MHz.   The left-hand meter movement is a zero center meter connected to the discriminator.  This showed the received signal’s frequency relative to the center of the receiver channel.  The right-hand meter was connected to the 1st limiter grid.  This meter showed the relative received signal strength.

All for now.

I found a negative of the old second floor shack desk and scanned it in.  (Not too bad of a rendering for a reflective scan of a negative.)

At the left end of the operating desk is the Meissner Signal Shifter Model EX (vfo) which drove the 812H rack.  The JT-30 microphone for the 812H rack (just to the left of this photo) is in front of the middle of the EX panel.  Sitting on top of the EX is the official Hammarlund speaker for the HQ-129X.

To the right of the EX is the Hammarlund HQ-129X receiver. 

To the right of the -129X is the RME VHF-152 10, 6 and 2 meter tunable converter.  To the right of it is the home-brew a.m. and f.m. i.f. receiver for the VHF-152, built in a matching cabinet.  On top of the i.f. receiver cabinet is a Heathkit Two-er, built for the local township Civil Defense RACES operations.  (Duck and cover!)

To the right of the i.f. receiver, which is the last item on the desktop, is the 10 meter 50 Watts AM transmitter rack cabinet.  Only the top deck of the rack can be seen.  It is now the exciter deck for the present 812H rig refurbishment.  Sitting on top of the rack cabinet is a National FB-7 receiver and a Vibroplex bug.  The JT-30 microphone for the 10 meter rack is sitting in front of the i.f. receiver cabinet.

Back at the left side of the desk, in front of the telephone on the pull-out shelf is a portable typewriter in it’s case.  This may have been called a laptop in it’s day – HI.

When we get the transmitter going on the air, I will take another picture of the finals.  This time the dust is cleaned off of the tube envelopes and the filaments will be lit!  And I will have some “operator with rack” photos.

- This photo taken April 1965 - (see the desk calendar on top of the -129X!)

Nice looking rig Tom .
Give us a heads up and we'll  roll tape on the inaugural key up.

We could alos take this great thread and turn it into a cover story Amfone. Nice project!


And yes you can upload from your machine. No more needing a pic on a url to post .

It was one of the bigger points in the decision making process.

Gary,

Thanks very much for the offer to record on-the-air transmissions from W3VVS.  We may be testing today or tomorrow, then are ready to go full QSO.  I will post a QSO notice here for everyone and send you a PM.

Thanks also for the ability to post photos and files from the hard drive.  This is a great feature!

W3VVS will be on the AWA AM net today (Sunday) at 4:30 p.m. on 3837 kHz. with his homebrew 1940's refurbished 812H rig.

The inaugural transmissions of W3VVS' refurbished 300 Watt 812H rig went very well today on the AWA net, 3837 kHz.   He sounded good and clean to me. 

Gary, thanks again for making the recordings of the AWA net. 

I will get to my father's house soon and do some operating from there with the rig.  I hope that there is no interference to the neighborhood!  We can get on 3870, 3875, 3880, 3885, and 3890 also.

Tom,

I have spent quite some time carefully examining the pics.  They're wonderful!   Your dad is to be congratulated!  BTW, it was a pleasure to talk to you and Wayne this afternoon.  Hope to hear Dad on the AWA Sunday.  Sorry I couldn't be there yesterday.

73,
Herb

Thanks for the comments Herb.  I gave my father a print-out of this thread today.


2 photos taken during today's visit and operation of his station:

1. The shack view with the 812H transmitter rack.

2. Close-up of the push-pull final PA with the 812H's lit up.

Final Episode - Photo Op.

O.K. here is my final posting on this topic.  Below are 2 photos of my father Paul, W3VVS at his operating desk.  One photo was taken approximately 50 years ago.  We finally found 1 photo that shows the original 812H transmitter rack to the left of the operating desk.  The other photo was taken last week operating with the refurbished 812H transmitter rack, to the right of my OM.

1. Second floor shack, circa 1954.  812H rack to left of operating desk.

2. Basement shack, August 2005, 51 years later.  Refurbished 812H rack to right of W3VVS.

Very nice Tom.  That's really great.  Regards to the OM.

K2VHerb

Very nice Tom,
Looking at the pictures was kind of like looking at a 1940's QST...But in Color!
Regards,
BobbyT

Surely a thing of beauty!

Nice stuff Tom, I didn't see this when it was originally posted. That home brew transmitter is a work of art.

Looks like a couple of nice mid-30's HROs in the photo in the first post.  Obvious by the German silver dial.

Wonder if  he still has those.

Don,

My father retains one HRO, the one with the silver dial.  He has sold off much of his collection which included a number of HRO's and many SW-3's.

In the shack photo just above, the RME-69 spot is now occupied by a restored rack-mount HQ-120X.  The Tripplett? modulation meter sitting on top of the Ranger II is gone from the operating position and may have been sold - not sure off the top of my head.

Tom,

Thanks for sharing all of the photos, great looking gear!  It is even better to learn that some of it is going to be active again.

I hope he still owns the RME-69; it looks great with the other black finished gear.  I am a little biased since I live near RME's original hometown.

Rodger WQ9E

Thanks for sharing your great family radio heritage. Cool stuff!

Roger and Steve,

Thanks for the comments. 

The RME-69 was sold recently after my father restored an HQ-120X.  He had a HQ-120X once before and came to regret selling it.

When my father bought the VHF-152 converter brand new from RME back when, supposedly it was picked special from the production line as a unit with above average performance.  He also was able to get a matching cabinet and built an AM and FM i.f. receiver in it to go along with the VHF-152.  The 2 cabinet combination can be seen in two of the old black&white shack photos on page 1 of this thread.

That's one gorgeous rig.  ooo la la  ;)

Rob

WOW! this rig is very close to the scheme I planned on making. Too bad you can't find 812H's anymore; maybe shuguang will start making them? they already make carbon plate 811H's, and metal plate 812A's, just a simple plate swap would work.

My father passed away January 30, 2010.  I am adding a photo below of his first station in Fremont Ohio, November 1941.  Contrast that shack photo with his shack just 13 years later in the northern suburbs of Philadelphia, posted in reply #23.

His first station used a Thordarson All-Star Senior receiver public-domain kit built by him in high school, and his home-brew all-wood rack transmitter with masonite front panels.  The transmitter has a power supply at the bottom with 866 Jr. window, modulator with 46's, exciter with 47 crystal oscillator and 46 buffer, final PA with 46's then upgraded to 6L6GX's, and antenna tuner on top.

Tom,
Neat looking OT set-up for sure.  From the picture it is a bit unclear of what microphone he was using.  I have a 30's D-104 that is on a totally different stand that was used in later years. It may be the same one as in the photo.  When I have a chance I will take a picture and post it. 

I know you have been busy, but I am assuming that your going to get your Dad's 812H rig on the air someday.

Joe, W3GMS

Oh, we enjoyed the China Buffet yesterday! 
   

Tom, those are some fine photos!! I am curious as to the frequency split that was used on the 10m AM repeater.Some friends of mine and I had a 10m FM repeater in Huntsville, AL in the late 1980's. 100 watts with 100 kHz spacing at 1 1/4 mile separation worked out for us.Unfortunately, my friend whose call was on the machine had his job abolished when the state ETV went to sold-state and we had to vacate both sites( he was able to put it back on in south Alabama when he got another job with the state Highway Department maintaining their radios). I understand that there was a 6m AM repeater in CT until recent years.

Love that photo Tom, what a classic!
Sure wish my shack looked like that, simple, clean, focus on radio, not techno gizmos.

I've always had in the back of my mind to set up such a station, think once that was up,
any interest in my modern gear would soon vanish.

Thanks for sharing with us!

-Bruce

Tom,

Your father's legacy is something to really be proud of.  Family pass-downs of ham gear are rare today, just look at all the SK estate sales going on.

a wonderful story, indeed.

73DG

Hi Tom,
Would like to use one or more of the pics in the 2012 WA1KPD Old Tyme Radio Calendar if that is OK.
Thanks and 73
Carl

Tom, that's really great that your Father is still around and active in hamming. You're very fortunate indeed to have him with you in this hobby. I hope to make contact with him in the future. I lost my Dad in 1958, just as I was becoming active in Space technology, but still hamming. I'm attaching a pic of him and his three AM rigs, two having P-P 450-TLs and the other with 250-THs.

Walt

Great stuff Tom.

Great looking xmtr,  real Ham Radio is black wrinkle.

I spotted the HROs in the first photo.

My HRO-M is rack mounted but has the black dial.  I use it as my main-station receiver.

Reading the posts, I didn't realize it was an old thread until I got to the sad news of your father's passing.  Sorry to hear that.

Hope to work you with your dad's black wrinkle xmtr.  We can bang heads together with my black wrinkle 813 xmtr.

We'll smoke the airwaves with this stuff.

Fred, KA2DZT

I like the great pics..........It grieves me to see these transmitters cuz I used to have one that was built by an SK Ham in Ohio. Almost the same design and black crackle. A pair of 4-400's link coupled tank circuit with the B&W plug-in coils modulated by a pair of 811A's.
Back breaker plate transformer..............1 KW of RF of A.M.

Tom, I'm sorry to have learned that your Father has passed away. I didn't read the dates on your earlier posts, so I believed that you and he were working together on the old rig.

Sorry to have misunderstood, Tom, so please accept my belated condolences.

Walt

Very nice history and photos Tom and your dad was way ahead of his time with coax in those days.

That 129X photo is a bit similar to my late 50's station:

HQ-129X, DB-22A, VHF-152A. Meissner EX Shifter into a pair of 813's for CW. AM was a Viking I, 122 VFO and PP 250TH's with 810 mods. The 6 and 2M TX gear was on another table.

Ive had that exact same Steelcase desk since moving back to NH in 73, these days its full of VHF/UHF stuff, it will hold anything.

Carl

I went back through alll the posts and photos again and am impressed all over with the look of ur OM's rig Tom, and all the other station gear.  Vy sri to hear of his passing away.

Rob

I had the distinct pleasure of knowing Tom's Dad very well. He was an extremely competent individual.  He was so smart that he never had to tell anyone how smart he was!  Did you ever notice that some guys get a real kick about claiming themselves as an expert?  The guys that really know their stuff never have to even come close to hinting how good they are.  Tom's Dad was one of those kind of guys.  He was also the ultimate gentleman.  He always took the time to explain things in a way that was easily understood by his audience.  He was an expert in many things, but many of us locals that knew him called him the expert on the National SW-3.  The amount of research he did on all the various versions of the SW-3 was amazing.  I distinctively remember when he was restoring his 812H rig and was one of the first stations to work him when he got it back on the air. 
Tom is a lucky guy to have such a father.

Joe, W3GMS       

Wow!! That is one handsome radio!!  Great you could save it for use on the air, congrats a bunch.

....and I'll be on the local net tonite with a 7.5Watt GRC-9. A tad 'yellowie' as they say but Monday is 'Kids' set night.

EdZ KG6UTS
San Diego/Borrego Springs

That's some of the best looking stuff I have seen lately. Very stately and dignified equipment.

Guys, I would like to keep this thread on topic.  Please use the Private Message system for admonishments.  Please start another thread for computer topics.

Thanks for all of the nice comments about my father and his home-brew equipment.

Joe W3GMS,

I do intend to put the 1946 812H rig on the air someday.

W4AAB,

the 10 meter repeater’s output was on 29.493 MHz and the input was 29.626 MHz., for a frequency difference of 133 kHz.  The spacing was 1 mile between sites and a phone line was rented for the link.  This was 1969 and then the club repeater system evolved to 2 meters FM a few years later when that became the big thing.

The 29493 kHz operating frequency was established in 1949 based on WWII surplus crystals on 7373.333 kHz.

Carl WA1KPD,

I sent you a PM concerning the photos.

Fred KA2DZT,

I have one HRO from my father’s estate – a 1935 HRO Senior he inherited from a legendary “Elmer” of my father’s area.  It has been out of service since 1967 when the original owner passed away.  It is on the workbench now to get all of the capacitors changed.  They appear to have been changed once before, a long time ago.  The receiver filaments were never turned off during WWII by decree of the owner, a Naval officer, away for the war.  It probably ran 24 hours a day after the war too.  Many of the resistors will need to be changed also.

Tom, if you replace any of those white National resistors I'll take them please.

Carl

Carl,

I'm going to try to put new 1/4 watt film resistors in those ceramic tubes when the time comes.  I have read that this can be accomplished.

Walt W2DU,

The photo of your father's shack shows an extremely impressive assembly of gear, equal (or better) to commercial communications stations of the era.

I recognize the "danger high voltage" sign at the lower right of the photo.  It looks identical to one in some of my father's other early shack photos.  He gave me the sign card when I was a kid and was looking for it today but couldn't find it.  I probably threw it out many years ago.

Thanks OM really great pics, the kinda pics a guy could use in private.

 And sure better than pics of kitty cats, doggy woggies and flowers.
 

Tom,

The caps in my HRO-M seemed to have been changed years ago.  They are all the green ones, forgot what brand.  They seemed to be all good as the receiver works fine.  I don't think any of the resistors were changed in mine.  I would have to pull the receiver out of the rack to see if they look original.  You may check them first before replacing them as they may be within tolerance.

Not sure 1/4 watt resistors will be a high enough wattage, especially if you put them inside an old resistor body.

I added an output xfmr in mine, as many HROs didn't have one.  My output tube is a type 42, 7K load to spk.  When I run out of type 42s I'll have to switch to a 6F6 and make a socket adaptor.

I have all nine plug-in coils that were made for the HRO along with two rack mounted coil housings.

Whats really rare is finding an original HRO rack with the speaker.  It's worth more than the receiver.

I don't have the dog house PS that went with the receiver so I built my own PS.  250V at about 80ma.  My receiver had a filament center tap resistor in it.  I think it was 100ohms CT to ground.  I did away with that resistor as the filament winding has a CT.

Someone added a tone control in mine, looks like it may have been something National did.  I redesigned the tone control circuit to make it work correctly.

The last thing, I redesigned the S-meter circuit.  I'm not sure what National was thinking with the way it was designed.  The S-meter works correctly now as it closely follows the S-meter readings on my NC-183D.  The S-meter in your older model I thing differs from mine.  Mine has S9 plus dBs above S9

My HRO had a switch to shut off the S-meter, not sure why I would want to do that.  So, I rewired that switch to turn the receiver PS on and off.

I have an original manual if you need help with anything.  Although, my HRO may differ from yours.

Fred

Fred,

I won’t replace resistors unless they measure out of tolerance.  I already know that many measure way out though. I won’t put ¼ Watt resistors back in the tubes if that value is going to dissipate more than ¼ Watt.  I will use appropriate wattage carbon comps in that case.  I saved my father’s resistor drawers that have old carbon composition resistors.  Although they may not be real reliable, they would be older than new stock

My HRO has 6 volt tubes.  There is an audio output transformer installed under the chassis - a Merit A-3020 7k to 3.5 Ohms.  The output tube is a 42.  The speaker secondary comes out a phone jack/hole that was added.  The two terminal strip on the back for the transformer-less audio output was re-wired to be a Switched B+ terminal.  I do have an original matching National speaker cabinet with output transformer.  When the receiver is restored, I will see what gives with that National speaker assembly (bad speaker or transformer?) and go from there as to whether I run the additional internal transformer or not.  It is convenient though to not require an additional speaker to sit at the operating position.

The doghouse supply I had was the lower B+ voltage (170) output.  You want the higher 240 Volt supply to run an HRO anyway.  When I checked it out, I found one of the output chokes open.  That National doghouse is the cheapest p.s. I have ever seen (Depression market design).  So I drilled out the spot welds on the bottom of the supply chassis and stripped out the potted transformer/choke assembly.  I have a power transformer that is perfect for the job.   And I will use silicon diodes.  Sacrilegious yes, but practical.

Thanks for the offer on manuals, but my father had put together quite a collection of HRO civilian and military manuals.  I have the original serial numbered manual that came with the receiver chassis – matching S/N’s with the entire original set of 4 coils.  I have 3 additional low frequency coils also which cover 2 MHz down to 230 kHz.

Tom,

National must have made a number of different coil sets.  I have nine matching coils, 50-100KC, 100-200KC, 180-430KC, 480-960KC (notice the missing 50KC), 900KC-2.05MC, 1.7-4.0MC, 3.5-7.3MC, 7.0-14.0MC, 14.0-30.0MC.  The last four are the band spread type that can be switched to just cover the 80/75M, 40M, 20M, 10M ham bands.  The coils are switched by moving small flat head brass screws to the adjacent holes on the contact strip.  I'm sure you're probably familiar with this.

My receiver has an original phone jack and the two-terminal strip on the back was wired to cut the B+.  It also has a B+ on/off switch on the front panel.  Use it when changing coils while the set is on.

I mentioned earliar about the on/off S-meter switch.  You may notice that the S-meter will go through a soft pin when the set is first turned on.  Could be the original reason for the S-meter on/off switch.  The S-meter works on a balance of screen currents being drawn by the 6C6s and/or 6D6s and the B+ itself (IIRC).  The point,  I used a 5Y3 rectifier for the B+ supply to retard the rise in B+ which reduced the pinning of the S-meter.

Using SS rectifiers may make the pinning worse.

Fred

National marketed a few 160 and 15M bandspread coils in the 50-60's for use in all the older HRO's. I had a 160 in a 5TA1 many years ago. The HRO-7 had an AC coil available.

There were also speciality coils made for commercial customers.

Ive also made my own replacements for those white resistors, pretty time consuming.

Carl