W8KHK Restore of W8YNG 1937 250TH AM Transmitter

[WZ5Q]

Excellent and well thought out restore Rick, Thanks for sharing!

It has been a year now since we moved our QTH and moth balled all the Heavy Metal Projects. Renovating always has hidden issues and the old QTH at the River House was no exception. We hope to list the River House this month and when it's finally sold, I can get to work on building the shack at the new QTH. Once this is accomplished, I can then start again on the Heavy Metal Projects.

Rick, your project has inspired me!
I can hardly wait.

[W3GMS]

Rick,

Well your data shows all is as it should be thus far.  My mentor Harry-W3FDY used a pair of 250TH's in push pull in his KW rig.  Had a pair of 450TL's as modulators.  It also used the B&W HDVL push pull coils and the Faraday shielded link.  His did not have the link control so one had to go behind the transmitter and manual push the link in and out to get the correct loading....yikes!!

Keep up the great work and we need to mark the occasion with a special day on 40M when you put an antenna to it and fire it up! 

73,
Joe - GMS

[w1vtp]

From the looks of the link coupled output the output connector seems to be a BNC connector.  I suggest that be a UHF SO-239.  The modulation peaks depending on the Z of the load can be as high as 377 volts assuming a Z close to 50 ohms.  The BNC might work but a safer bet for legal limit output would be a SO239 / PL-259 combo.

Nice detail Al

[w8khk]

Excellent and well thought out restore Rick, Thanks for sharing!

It has been a year now since we moved our QTH and moth balled all the Heavy Metal Projects. Renovating always has hidden issues and the old QTH at the River House was no exception. We hope to list the River House this month and when it's finally sold, I can get to work on building the shack at the new QTH. Once this is accomplished, I can then start again on the Heavy Metal Projects.

Rick, your project has inspired me!
I can hardly wait.

Mike, thanks for the kind words of encouragement.  I know it can take a long time to get around to some of these big projects, this and another one have  been waiting for many years.  I am glad I inspired you to press on.  Brett, N2DTS, has inspired me to get back to work on the 4-1000 screen modulated rig, and to try another transmitter with a quad of 4x150s, also screen modulated.  Several other heavy metal projects in the wings, but I must get out and get some antenna work done now that it is warm, before the leaves are on the trees.

[w8khk]

Rick,

Well your data shows all is as it should be thus far.  My mentor Harry-W3FDY used a pair of 250TH's in push pull in his KW rig.  Had a pair of 450TL's as modulators.  It also used the B&W HDVL push pull coils and the Faraday shielded link.  His did not have the link control so one had to go behind the transmitter and manual push the link in and out to get the correct loading....yikes!!

Keep up the great work and we need to mark the occasion with a special day on 40M when you put an antenna to it and fire it up! 

73,
Joe - GMS

Joe, dad used the same technique for adjusting the loading with a wood stick on his 304TL rig.  It did not have the HDVL coils, just homemade coils with banana plugs and jacks on polystyrene strips, and a loop of hookup wire for the link.  Later on he used the faraday shielded links. 

I have been more forgetful as I age, and that is why I put the HV interlock switch on the door, so an external control for the swinging link seemed to be a necessity.  Boy, 450TLs would certainly make fine modulators!  Dad's P-P 304TL rig was modulated by a quad of Taylor TZ-40s in push pull parallel.  I modified it some time ago to use another pair of 304TLs in the modulator.  It needs the power supply reworked with the soft start and overload circuits to protect the vintage components.  Not sure which project will be next, but I will have the 40M 250TH rig on the air soon.

[w8khk]

From the looks of the link coupled output the output connector seems to be a BNC connector.  I suggest that be a UHF SO-239.  The modulation peaks depending on the Z of the load can be as high as 377 volts assuming a Z close to 50 ohms.  The BNC might work but a safer bet for legal limit output would be a SO239 / PL-259 combo.

Nice detail Al

You are correct, Al, that is a GR adaptor from 3/4" spaced banana jacks to a BNC.  The BNC connects to an "N" connector feed-through in the top of the cabinet.  I plan to use all "N" connectors instead of SO-239 and PL-259 connectors.  I will mount an "N" coax relay inside the top of the cabinet with an "el" type "n" connector.  The open terminals at the right of the control deck are reserved for the antenna relay, and the sequencer logic is in the control deck.  The challenge will be mating the leads from the swinging link to the male "n" connector.

I used BNC connectors almost exclusively with my dual 4-400A linear at legal limit, and never had a problem.  But I will go with "N" for the output circuits on the AM rigs.

[W2VW]

Great looking project. Maybe it will make it through a few more generations!

[Steve - K4HX]

It's a family heirloom now!   

Thanks everyone for the kind comments!

Great history and a great story. Thanks for sharing and congratulations on bringing the transmitter back to life. Not too many 3rd generation transmitters out there!

Steve, I did not even think about a third generation transmitter.  My daughter and grandson have just recently become interested in ham radio.  Makes me wonder just what is in the future for this rig!

[KA2DZT]

What I like about the project are the pictures.  Seeing the rig in the 1937 photo with Rick's grandfather, then with Walter, Rick's father.  The xmtr has a great history and it's nice to know, with all of Rick's efforts, it will live on for more generations.

Fred
KA2DZT