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Timtron WA1HLR Featured in ARRL Newsletter




 
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Author Topic: Timtron WA1HLR Featured in ARRL Newsletter  (Read 1634 times)
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« on: March 08, 2018, 05:53:17 PM »

ARRL Repurposes AM Broadcast Transmitter for Ham Radio Use

Thanks to a joint effort by ARRL and the Vintage Radio and Communications Museum of Connecticut (VRCMCT), a classic Gates BC-1T AM broadcast transmitter will enjoy a second life on the Amateur Radio bands for occasional use under W1AW or under the ARRL Headquarters Operators Club call sign, W1INF.

Tim "Timtron" Smith, WA1HLR, digs into the Gates BC-1T broadcast transmitter.

Spearheaded by broadcast engineer Dan Thomas, NC1J, VRCMCT volunteers restored the1 kW transmitter to operating condition, after obtaining it from the National Capital Radio and Television Museum in Bowie, Maryland. The VRCMCT will retain ownership of the transmitter, while the League houses and maintains it on loan. The transmitter will be located in the ARRL Lab, and Assistant Lab Manager Bob Allison, WB1GCM, said the transmitter could be on the air as W1AW during such operating events as the AM Rally and the Heavy Metal Rally.

ARRL turned to AM guru and veteran broadcast engineer Tim "Timtron" Smith, WA1HLR, of Skowhegan, Maine, to handle shifting the BC-1T from 1,340 kHz to the ham bands. Timtron not only has been an AM mainstay on 75 and 40 meters over the years, he's engineered all manner of AM, FM, and HF broadcast transmitters in his extensive career. This combination of familiarity and experience made him a logical choice to handle the conversion to amateur use of the Gates BC-1T.

Various stipulations added a level of complexity to the endeavor. First, the transmitter had to be modified as little as possible, retaining original components. The 833 final amplifier tubes (left), better suited for broadcast-band use, would be retained as would the inductance-heavy tuning circuits. Another requirement -- this one set by Smith -- ambitiously called for the transmitter to function on 75 as well as on 160 meters.

Each RF stage was converted, starting with the Colpitts oscillator -- which offered two octal tube sockets to hold broadcast crystals, and a selector switch. More complicated was changing out feedback and loading capacitors in the oscillator stage, along with the buffer tank circuit. The driver tank circuit was next. Removing one-half of the windings on the multiple tank, changing some connections, shortening long leads on RF bypass capacitors, and modifying the neutralization circuit were necessary.


Assistant ARRL Lab Manager Bob Allison, WB1GCM, at the helm of W1INF at ARRL Headquarters. The BC-1T is on the right.

The output tuning circuit proved to be the easiest to convert; parallel capacitors that enabled broadcast-band operation were rewired in series to resonate on the amateur bands. A spare inductor, not required for higher frequencies, was repurposed in place as a dc safety shunt. The modulator just needed only minor changes. All was documented.

Initial tests at 250 W on February 22 demonstrated the success of the modifications and marked completion of the first phase of a new lease on life for the BC-1T as ARRL's flagship AM amateur band transmitter. "It took many volunteers and their resources to make this project come together," said Allison, who calls the BC-1T "The Ambassador."

"It's an ambassador for the AM mode, reaching out a friendly hand to radio amateurs old and new," he said.

The project began in ARRL Lab on February 18 with the presentation to "Timtron" of an official ARRL Lab coat. As if stepping from the pages of a 1960s ARRL Handbook, he looked the part and was ready to begin the operation. -- Thanks to Clark Burgard, N1BCG, and Bob Allison, WB1GCM

http://www.arrl.org/news/arrl-repurposes-am-broadcast-transmitter-for-ham-radio-use


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« Reply #1 on: March 08, 2018, 06:48:36 PM »



We are living the end times.


klc
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Steve - K4HX
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« Reply #2 on: March 08, 2018, 09:19:27 PM »

Fine Business. Why was the Timtron Institute of Technology not mentioned?

http://www.arrl.org/arrlletter?issue=2018-03-08#toc04
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« Reply #3 on: March 08, 2018, 10:18:42 PM »

Why was the Timtron Institute of Technology not mentioned?

No worries. The institute is mentioned in the soon-to-be-released movie...

https://youtu.be/K8cbRCIZ2FA?rel=0
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WA2SQQ
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« Reply #4 on: March 09, 2018, 10:40:23 AM »

Cant wait - the legend at work!
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kb4qaa
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« Reply #5 on: March 09, 2018, 12:06:54 PM »



We are living the end times.


klc
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WA1LGQ
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« Reply #6 on: March 09, 2018, 12:21:02 PM »

Also on QRZ Now:
http://qrznow.com/arrl-repurposes-am-broadcast-transmitter-for-ham-radio-use/
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« Reply #7 on: March 09, 2018, 11:44:21 PM »

I guess 80M and 40M should work well. How is the spacing between parts, lead lengths, when higher frequencies are wanted?
It's very pleasing news in any case!
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« Reply #8 on: March 10, 2018, 01:29:03 AM »

The video will give the complete story, but in the meantime, here are some of the modifications that were made:

OSCILLATOR:

C3 - Changed to 10pF

C4 - Changed to 200pF

L3 - Modified (although I need to get a clarification from Tim on the particulars... TBD)

R3 - Changed to 37k @ 2W (R5 removed and added in series with R3)

R7 - Added 0.01uF in parallel for RF bypass

R9 - Changed to 37k @2W

DRIVER:

C7 & C17 - Moved connection to L8 one tap in from end. Other lead of C7 moved in one tap from end. Neutralizing cap connection remains at end of L8.

C16 - Added new 0.006uF cap at L8 to provide more direct RF bypass

L8 - Removed two turns between each tap (one on each side of taps)
833 grid connection moved to tap next to center tap (bias point)

FINAL:

C11 & C12 - Changed to 375pF (160M) or 125pF (75M)

C13 & C14 - Changed to 1750pF (160M) or 1000pF (75M)

C23 & C24 - Replaced with 0.01uF from each filament lead (4) to chassis via short leads. A chassis extension was fabricated for this purpose.

L13 - Changed to DC shunt/safety between chassis and C13 & C14 which are now in parallel

OTHER:

1) There's an audio attenuator module located near the input audio transformer. It's used to reduce the modulation level for 250W operation. Bypassing this will greatly reduce the amount of audio drive needed to reach full modulation at 250W.

2) Some changed components can be reused, ie, C11 & C12 placed in series and C13 & C14 placed in series, etc.

3) Backfeeding the antenna connection with an antenna analyzer and placing a 2700 ohm non-inductive resistor between the RF plates and chassis will allow adjustment of the output tuning circuit without power applied. Be sure to remove these when done!

4) Proper neutralization is achieved when the grid current peaks concurrently with a dip in final plate current.



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« Reply #9 on: March 10, 2018, 12:02:14 PM »

That can't be right! There's nothing about deyellification, drilling & blasting, yanking out parts by their roots.....  And most importantly, it didn't start out with, So what ya need to do.....
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« Reply #10 on: March 10, 2018, 12:51:59 PM »



     "    That can't be right!   "

Shhhh.... he got in the door, and They must be watching........  I'm sure the ArrL has lots 'o stuff......  be patient and keep your glasses and hearing protection Handy.


klc
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« Reply #11 on: March 10, 2018, 04:32:40 PM »

So far, only the promo video (trailer) is out. The full-length feature film includes scenes of transmitter in Maryland prior to its arrival at the ARRL, the mods, testing, the first contacts, and an operational overview from the head of the Timtron Institute of Technology.
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W1RC
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« Reply #12 on: March 10, 2018, 04:32:54 PM »

I guess 80M and 40M should work well. How is the spacing between parts, lead lengths, when higher frequencies are wanted?
It's very pleasing news in any case!
The transmitter is operational on 160 and 75m. 40 would be very difficult and more of a “cut and hack” job than the owner would allow.
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« Reply #13 on: March 11, 2018, 11:22:36 AM »

 Any guesstimating on when the video will be out?
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« Reply #14 on: March 11, 2018, 12:17:06 PM »

Any guesstimating on when the video will be out?

Well, it's being put together by North Korea's propaganda studio during their down time, and despite the language barrier and having to explain Tim's unique terminology, it's almost finished with just a few tweaks remaining. It also has to be approved.

What can be said is that it starts with the acquisition a year ago from the National Capital Radio and Television Museum in Bowie, MD and ends with Tim's summary of what was done, how it operates, and why it's so special.

There's a BOOT copy out on the net already, can you believe it, of segment 2 although it's an early version featuring sample rate tests. The five segment video wasn't put together in chronological order, so ironically, the beginning was the last segment to be done.

Truly a fun and educational filmshow (at least I hope others will feel that way too).


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« Reply #15 on: March 11, 2018, 04:54:44 PM »

Prof. Tim looks way cool with a lab coat.
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« Reply #16 on: March 11, 2018, 07:20:44 PM »


It wasn't too many years ago this would have been a good subject of an April Fools article in QST...  For several decades ARRL tried really hard to ban AM from the bands, and even when they did relax, they taught newcomers that AM "old fashioned" and a "bandwidth hog". 

Steve WD8DAS


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« Reply #17 on: March 11, 2018, 10:42:29 PM »


It wasn't too many years ago this would have been a good subject of an April Fools article in QST...  For several decades ARRL tried really hard to ban AM from the bands, and even when they did relax, they taught newcomers that AM "old fashioned" and a "bandwidth hog". 

Steve WD8DAS



I sure enjoyed that video. Hat off to Timtron and the ARRL guys for making a nice public project of it.

My take on the old anti-AM stance is that the league likes advancements and saw only that SSB theoretically lets two stations into the space. They had perhaps not remembered the level of technical art that goes into a high level modulated transmitter and the good communications quality signal that comes out nor the fun and historical aspects of it.

When thinking about old anti-AM attitudes, I should not leave out the strong push from AM to SSB done by the many equipment manufacturers. Many gear-makers did throw AM operators a bone, so to speak, with the ol' carrier+USB trick while doing away with the big expensive power supply and modulation transformer. It's almost like that is where the "100W PEP transmitter" got its start. Anything bigger with a linear amp as the final and it was off into duty-cycle land. Remember all the trade-in ads in the magazines? Basically you would trade in 600 lbs of AM stuff and get a 100 lb SSB rig and a discount. HT-32 anyone?

As for the media.. pah! they'll parrot anything that rolls off the tongue and makes them seem smart. Not like in the old days where editorial items were researched and compared to the facts.

Over the years AM has proved its worth as many of the same hobbyists who play at the bleeding edge have also devoted resources to building their own stuff and maintaining the antique gear in order to keep up standards.

I guess it's more 'cool' and historical now and enough hams want to tinker with it that the ARRL sees the potential to serve or please more of their members and potential customers. They are not stupid, and they like to have a good time as much as anyone else. Not much you can do with a board full of 0203 parts and postage stamps, but a project like the Gates, they can really enjoy and and get their hands into. The hobby's lucky to have Timtron to help make this happen.
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« Reply #18 on: March 12, 2018, 09:01:43 AM »

If you wait long enough, what’s old becomes new again. Look at the resurgence of vinyl in the music industry and film in photography. The youngsters that are just getting into the hobby are showing an interest in AM. Restoration projects are an excellent way to teach electronics. This weekend I spent about half an hour talking about AM to a newly licensed 16-year-old who admitted that he never knew AM was a mode used on the ham bands! It seems we are now the messengers who have been entrusted to reintroduce AM to the next generation. It seems like only yesterday that I had my first phone contact (as a novice) on 2M AM using a Gonset Communicator!
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« Reply #19 on: March 12, 2018, 12:36:51 PM »

I've been on AM since shortly after i got licensed in 2007 at age 13. Still working on my homebrew transmitter, also have a few old military rigs to get going. My wife is working on getting her license, i have a DX-100B and SP-600 here that belonged to her dad that I'm working on for her.
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« Reply #20 on: March 12, 2018, 08:38:31 PM »

I've been on AM since shortly after i got licensed in 2007 at age 13. Still working on my homebrew transmitter, also have a few old military rigs to get going. My wife is working on getting her license, i have a DX-100B and SP-600 here that belonged to her dad that I'm working on for her.

Realized i forgot to finish my train of thought. Anyway, part of what appeals to me about AM is working with these old transmitters and receivers, especially the vintage military stuff, sure class E might be nice for those that like to experiment, SDRs might be fun for those that like messing with computers and software, just like for me the antiques are fun for those who like running tube gear. There's something for everyone. Even my wife likes the older radios, she doesn't have much interest in newer stuff, there's even been times she's suggested getting certain rigs because she liked them. New people coming into the hobby are going to follow into whatever appeals to them.
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