The AM Forum

I recently agreed to restore this HART-75 Transmitter for a friend and I'm trying to find as much information on it as I can.  It looks home brew, but it is, in fact a commercially-built transmitter that is 1956 vintage and was available then in kit form for $69.95 from Hart Industries, 467 Park Ave, Birmingham, AL.   According to the owner, this particular unit was purchased by his Dad in 1956 as a factory-built rig.

Two tubes were missing and I'm guessing that they might have been a 6AG7 oscillator and a 6146 final amplifier.  A type 83 rectifier tube remains in place.  The only reference that I have found is a short paragraph and a photo in Raymond S. Moore's book: Transmitters Exciters and Power Amplifiers. This reference identifies the HART 75 as a CW transmitter that is capable of 80 watts (max) input and 55 watts (max) input on AM with an accessory AM modulator.  It is also stated that the rig used two 807 tubes, but it is obvious that this is incorrect, as the two sockets are octal-type and not 5-pin sockets, as would be used for 807s.

I have successfully repaired the power supply and I am getting approximately 500 V.D.C. from it, but I need to confirm the tube types for the oscillator and final stages and, perhaps get some more info on the rig.

Does anyone else have one of these transmitters?  Anyone have a manual or addditional info?  I would appreciate any help I can get.  I would also really like to obtain info on the accessory modulator.  I suspect it was a screen modulator that plugged into the accessory socket on the rear of the rig.  This is a really interesting and certainly rare little rig that would be fun to get on the air.

73,  Jack, W9GT

Lew McCoy reviewed the Hart 75 in QST February 1956.  His review and photos show 6AG7 driving twin 807's.

It's a nice looking rig, very clean design.

Jack,

Wasn't there a predecessor in kit form that appeared in Popular Electronics in the 60s?  I am pretty sure I recall a Hart 65 construction article in one of my old copies of PE.

I ran a search of the CQ archives.  The search machine is not very selective (precise) so it is time consuming.  I searched the returned table of contents from September 1954 thru 1958 without luck.

Two other sources that have helped me in research, are the advertising in the ARRL Handbook, and the Engineers & Editors (West Coast) Handbook.  The other is to manual look up the advertisers index for each issue of QST, to see if HART is listed, then pray the listed page is included.   (When will ARRL, scan in the full issues?!!!!)

bill

The Hart-65 is in Popular Electronics October '67.  I will take a look at it tonight.

Jack,

I checked and I believe the only relationship the HART-65 has to the HART-75 is a fairly similar name.  The HART-65 uses a single 6BH5 tube and was designed/constructed by Hartland B. Smith W8VVD.  He also published the HART-25 in April 1955, this was a 25 watt one tube transmitter.  Given that these were produced on either side of the HART-75 I wouldn't be surprised if Hartland was the designer of your HART-75 but it sounds like the one you are restoring is a revised version of the original reviewed in QST.

Yes....very interesting.  The QST review shows the parallel 807s in the final, but the unit that I have has only a single octal socket and the larger plate connector that would be associated with a 6146.  I thought briefly that the final could have been something like a 6DQ6, but the large diameter plate connector seems to indicate a 6146.  The circuitry does not entirely make sense if it is a 6146, but I need to look at it more and try to draw a schematic.....that is more difficult than it might seem when tracing wiring in a crowded area of a chassis.  Other differences that I have noted are that the rectifier looks like a 5U4 in the QST review instead of an 83 and this unit does not have the keying relay that was described in the article.  The description of the modulator was interesting.  Apparently it was a Heising modulator using a modulation choke.  The modulator tube line-up was a 12AX7 and a 6550.  It would probably be quite easy to duplicate that circuit (or come up with something very similar) that would add AM capability.

Apparently, the transmitter I'm working on was a later version that had several design changes.  Perhaps these changes were only in a factory-built unit.  The article stated that the Hart 75 was only available as a kit, but the owner insists that this one was factory-built.

I might add that (with the modulator) there are a great number of simularities to the venerable Globe Scout.  Especially the Scout models that included 160M!

Thanks for all the valuable input!  Keep those cards and letters coming!   ;D

73,  Jack, W9GT

Well, this project is becoming very interesting!  I received an email from an AMer in Alabama who had attempted to locate Hart Industries in Birmingham, AL .  He found out that Hart Industries was actually located in Birmingham, Michigan.... apparently confirming that the original reference in the Moore Transmitter Guide was incorrect.  I then looked-up Hartland Smith, W8VVD in my 1957 Call Book and found him listed at the 467 Park Avenue address in Birmingham, MI!!!  Wow! Now we're getting somewhere.

Checking W8VVD in QRZ.com indicates that Hartland is still listed and his call has changed to W8QX.  My next step will be to attempt to contact him and see if he is still around and if he might be able to provide info on his Hart-75 Transmitter.

Isn't this fun?   Sometimes it takes a combined research effort to come-up with info, but it pays off to keep at it.  Thanks everyone for helping put the puzzle together!

73,  Jack, W9GT

Jack,

Sometimes I find the research one of the most enjoyable aspects of the project.  Circuits are circuits, but finding the history along with the players, providing they are still around can be quite exciting! 

Enjoy the quest and don't rush the trailblazing otherwise you may miss a turn!

Joe, W3GMS

Good luck with that. I have a very nice 6/2 meter transmitter made by Amplidyne Labs. I finally reached the guy who manufactured the transmitters but he could not remember much about it even though he had one on his shelf?

Maybe the poor guy had one of those brain diseases? Well anyhow, good luck with it. Lots of room to put other parts on if you wanted too.

I sent a couple of emails to Hartland Smith, W8VVD/W8QX to two different email addresses.  Still have not received a response.  I may also try snail mail.  Any other suggestions?

73,  Jack, W9GT

more pictures

Call him up.
Maybe this is his son. Both have the same address.

Hartland B Smith Jr 65+ years old

Phone number  248-644-5042

Address:   1510 Buckingham Ave Birmingham, MI 48009-5882

I'm happy to report that Hart, W8QX responded to my email and has agreed to dig-up the information on the transmitter.  He seems like a very nice gentleman and I hope to possibly converse on the phone, or in-person with him in addition to exchanging emails.  He confirmed that the unit that I have was a "factory-built" unit and possibly an earlier model.  The "factory" was his home and ham shack and he started producing kits in the 50's after helping a budding novice get a Globe Scout kit running.  I will keep everyone informed as I receive more data from Mr. Smith.  Thanks again to everyone for the encouragement and kind suggestions as I have conducted this search for information.

This has truly been quite a journey and an interesting puzzle to solve.

73,  Jack, W9GT

Fantastic news Jack!  Keep us posted and I do hope you can chat with him on the twisted pair.  It sounds like it may have been a side line job for Mr. Smith in that not many were made.  I am sure he could give you some great background information on his cottage industry. 

Joe, W3GMS

Excellent detective work Jack!  This sounds like it could make a great Electric Radio article.

Fun thread, tnx! :)

The power supply is fixed and the 6AG7 oscillator is working, when I get more info on the final, I should be able to fix that, as well.  It does not appear to be a 6146....the circuitry is not correct for that tube.  It has to be an octal tube, but don't know for sure what type.

73,  Jack, W9GT

Maybe a 6BG6?

73DG

Jack,
Although it would not be my choice in building such a rig, but could the 6AG7 be driving a 2E26?   It could produce in the 20W output power range.  I forget if the size of the plate cap is smaller on the 2E26 as compared to the 6146 but that might be the clue. 

Joe, GMS

The 6BG6 is a possibility, although there are a couple of problems:  1. The existing plate lead is too short for the tall envelope, even though the plate cap is the correct size.  The 6BG6 that I found in my tube stock looks like an octal-based 807 and has the tall envelope.  I wonder if they ever produced a 6BG6 in the shorter envelope?   2. The plate disipation is only 20 watts which could be a little low (maybe, just barely enough?) for a 80 watt input rig, however, for amateur service it might be OK for CW.  It was specified at 55 watts input for AM.

The 6146 and its little brother 2E26 are definitely out.  The base connections are incorrect for those types.

73,  Jack, W9GT

Cute rig and will be a nice piece of revived history.

Ok, what is the pin-out of the final?  Does the circuit match 5BT ?
#'s 2, 7 being filaments,  Plate cap being the anode, #1 probably empty or used as additional terminal, etc..
- the rest ?

The more modern type 6BG6GT is 4.438 tall.

http://www.nj7p.org/Common/Tube/SQL/Tube_query.php?Type=6BG6GT (http://www.nj7p.org/Common/Tube/SQL/Tube_query.php?Type=6BG6GT)

First of all.....Hoorah .....Woopie....Celebration!  The Hart 75 is on the air!  I had a nice 40 CW QSO with Fred, K9YII in Southern Ilinois this afternoon and he said the CW note sounds great and he gave me  599.  I still need to do some repair on the panel meter and attend to cosmetic restoration details, but the old girl is on the air and working great.  It puts out an easy 50 watts on CW.

After much pondering, I finally decided to just plug-in a 6DQ6 in the final and get on with seeing how things would work.  I just used a slip-on small tube-cap connector to adapt to the larger size plate connector that was in the rig.  I'm still wondering what the mystery tube for the final should be with a 6AM basing diagram and the larger diameter plate cap.  Of course there must be some explanation or solution for this, but my search has not turned up the right combo yet.

The other big news is that I was actually able to connect with Hartland Smith, W8QX ,the owner of Hart Industries and builder of this rig, on Skype last night. We had a wonderful visit!  What a nice guy, and a truly friendly and helpful gentleman!  I believe he is 91 now , and he is as sharp as a tack and it just was very nice to talk with him. He said that I brought back many memories by inquiring about his creation, the Hart 75.  He identified the unit that I have as one of only a handful of early pre-built units.  These transmitters were built using "some sort of TV sweep tube" in the final (he couldn't remember what type) and then later he sold about 100 or so of the kits, which used the later design with a pair of 807's in the final and a keying relay for CW keying.

He sent me the schematic (for the 807 model) and info and a schematic for the matching AM plug-in modulator which uses a 12AX7 and a 6550 in a Heising configuration.  The modulator should be easy to duplicate, as it is relatively simple in design and built on a 5" x 7" x 2" (nominal) chassis.  He even sent me the proof for an ad in QST in 1956 for the transmitter kit.  Unfortunately he hasn't located the specific data for the sweep tube unit, but it looks to be virtually the same except for the 807s and a keying relay that was added to eliminate safety concerns with voltage across the key in cathode keying.

Hart has been extremely helpful and I am very grateful to him for spending the time to help with this project.  At Rodger's suggestion, I probably will put an article together for Electric Radio detailing this experience. I have to finish up another piece on the Mighty John Meck T-60-1 to perhaps answer some questions left open by a previous article in ER.  This stuff is loads of fun and the research takes many unexpected twists and turns, but what is great are the results and the return of a rare and classic rig to the air after many years of silence.

73,  Jack, W9GT

Wonderful news Jack that you got it fired up and made a CW QSO on 40M.  I was on yesterday around 7.032 having several QSO's, but it would have been icing on the cake to hear your CW signal from the Hart 75.

Equally great is that you had further dialog with Mr. Smith - W8QX.  Hopefully you can give him some pictures of your restoration effort on the 75.   

I second the nomination that Rodger made concerning documenting your story and restoration of the Hart 75. 

Keep up the fun! 

Joe, W3GMS

Possibly a 6DQ5?

Here's an online pdf of a similar xmtr from that era that uses a 6DQ5.

http://www.arizona-am.net/PHOENIX/NA7RH/6DQ5_Charlie_Pics_rev3.pdf

see page 9.

The 6DQ5 is a great suggestion, but the base connections are not correct for this rig.  The 6DQ6 works fine, but the plate connector is the small size which is different from the existing connector in the rig.  I just used a slip -on small connector on the tube then attached the larger one over that.  Of course, we could just change out the connector, but I was trying to keep things original.  Still trying to identify the "mystery tube".  A 6DQ6 with a large plate cap??

That 6DQ5 (and 1625 modulator) rig is a really nice example of a great home brew project.  That would be a nice one to build!

73,  Jack, W9GT

I will have a rummage, but I am sure I have versions of the 6DQ6 here with a large top cap.

Will report back once I have nosed through the valve store.

Sean

I'm still searching for the EMICO 0-10 mA panel meter to replace the original one that opened up.  Seems that those cheap meters were famous for that, in addition to their total lack of damping and questionable accuracy.  I did find a 0-1 mA model on EBay and I can change the shunt resistors to accomodate that range, but I would still like to find one like the one that came in the rig.

73,  Jack, W9GT

Looks like I finally found the Emico meter for the Hart 75 and it should be on its way to me shortly.  Thanks everyone for looking!  I also have gathered all the parts for the AM-1 Heising modulator and I will put that together over the next week or so....maybe I will have the Hart 75 on AM soon.

73,  Jack, W9GT

I just realized that I had not informed everyone via this thread that I successfully completed the electrical restoration of this rig and also constructed the matching Heising modulator.  I got it on the air and had several good AM contacts including one with the owner of the rig.  The owner is having the front panel professionally re-done and it will be a real show piece and a great example of a really rare mid-fifties rig.

Hopefully, I will soon submit an article to ER outlining the story behind this rig and my adventures in researching it and getting it running.  Thanks again to everyone for your kind suggestions and comments during the process!

73,   Jack, W9GT

Nice!...Very cool setup........Steve

Another view of modulator and PTT control box for Hart 75.  

Congratulations!  I was afraid you would not make much progress due to lack of information.  Another piece of history gets saved from a dark corner or the dumpster.

As a gentle suggestion, please consider posting whatever schematics and information you received from the designer here and on the BAMA Mirror for posterity (if you have permission).

b.

Jack,
Congrats on finishing up the project. You did some great research including finding and ultimately talking to the owner of the company and that makes it all the more fun. 

Doing an article for ER is a great idea and I can't wait to read it. 

Hopefully the owner will put it on the air and use it.  Who did he find to redo the panel? 

Joe, W3GMS 

My article describing the Hart 75 project is in the August 2014 issue of Electric Radio.  Also check out an article in the same issue by Don, K4KYV regarding putting a BC xmtr on CW.

73,  Jack, W9GT

Congratulations Jack!

bill

ER came today and that is the first article I read.  You did an excellent job and the story for me was somewhat familiar since we followed the trail on AMfone.  Congrats on taking the time to write up the story.  ER has a great audience and I am sure many of the subscribers will enjoy reading the story.

The second article I read was the one Don wrote.  Very interesting article and a practical and novel way to modify the choke input supply in order to not need the typical value of bleeder resistor required on a choke input filter. 

Joe, W3GMS 

 

I also very much enjoyed the August ER article.   Very nice Jack.

Got the "ER" out of the mailbox yesterday and immediately crossed the road over to the Maple Lake club house porch to read it. Didn't wait to climb hill back to my house.

"Hmm, where have I seen this before?" In somewhat of a déjà vu fog...

..lights back on in there somewhere.   ..."Oh yeah!"

The documentation and confab with the original builder just about puts the little Hart 75 in priceless territory ; these days worth a video trip with him holding his creation along with a little show and tell interview.

I too look forward to reading your article. ER has become my favorite ham rag. QST is a distant, DISTANT, second.

  Got my copy of ER late yesterday, Great Story!!

  If only these old radios could talk, what stories might they tell??

Good ER article Jack.  While I was reading it I thought I had seen parts of it before.  Now I know why.  FB work.

In response to several requests for the schematics, here they are.  Please notice that the transmitter schematic is for the two 807 final version and not for the single 6DQ6 version that I restored.  Also the keying relay was added to this version. This drawing was sent to me by Hart Smith, W8QX.

73,  Jack, W9GT

Thank you Jack
Carl
/KPD