Gates BC1H conversion to 160 & 75 meters: What's involved?

[N6YW]

Greetings
I have been considering a conversion project for a while now and the Gates BC1H seems like a perfect
candidate. It's footprint is manageable, tube cost is easy on the wallet and it looks easy to work on.
In fact, at 72" in height, it can roll right through my shop door with ease.
I have the concept down but there are some specific rules involved here, so that's what I would like to discuss.
This would be my first BC transmitter conversion project.

Here is a link to the schematic diagram:
http://www.bobgroome.us/Schematics/Gates%20BC-1H%20Schematic.pdf

What I would like to consider is the feasibility of such a scheme. Switching from 160 to 75 meters.
Frequency control and excitation.
Band switching.
Tank circuit modifications.
PTT.
 
I am aware that every transmitter design is different, & each model presents it's own set of challenges.
So, what do you gentleman have to say about this project? Looking forward to the comments.
73 de Billy N6YW

[KL7OF]

Do the oscillator first... cut the fixed cap value in half...and remove turns from the small coil until it is resonant on 75....Then move the tap on the 2 in diameter driver tapped coil until it resonates on 75 meters...  You will be removing some of the big fixed micas from the tank next..C1 shud be around 125 pf for 75 meters..set L1 to about (roller)  25 uHy...remove the "L" coil completely  C2 will have to be reduced in value and the tune Inductor L2 can be adjusted for 80 meters...Be aware that there is a huge circulating current in the tank circuit and you must use big fixed micas with Hi current and voltage ratings...  That is the quick and dirty description...Somewhere on the web I found a site where a ham describes in great detail how he converted a Gates BC1....If you want to make a two bander , you will have to switch the fixed caps in and out with some max scrote relays or switches...the roller coils have enough range to accomodate 160 and 75...Good Luck......Steve

[N0WEK]

Do the oscillator first... cut the fixed cap value in half...and remove turns from the small coil until it is resonant on 75....Then move the tap on the 2 in diameter driver tapped coil until it resonates on 75 meters...  You will be removing some of the big fixed micas from the tank next..C1 shud be around 125 pf for 75 meters..set L1 to about (roller)  25 uHy...remove the "L" coil completely  C2 will have to be reduced in value and the tune Inductor L2 can be adjusted for 80 meters...Be aware that there is a huge circulating current in the tank circuit and you must use big fixed micas with Hi current and voltage ratings...  That is the quick and dirty description...Somewhere on the web I found a site where a ham describes in great detail how he converted a Gates BC1....If you want to make a two bander , you will have to switch the fixed caps in and out with some max scrote relays or switches...the roller coils have enough range to accomodate 160 and 75...Good Luck......Steve

The very first thing before all of the above is to check it over, clean it up and get it fired up on the original frequency first before you start to change things. Otherwise you'll be chasing both the original problems and the troubleshooting of the changes and unable to tell them apart.

[W7TFO]

Yep, power it up on the original freq for sure to begin with.

Keep in mind that 1H uses a solid-state mod driver circuit, and while it sounds really great on the air, it can not take the fiddling the older tube-based scheme can.

You might call KO6NM and run through the procedure with Mike, he is in your area and has done a lot of these.

I have a 1H-1 here if you need and goodies.

73DG

[flintstone mop]

Depending on the original on-air frequency, there are three ranges in the broadcast band, that were listed for the fixed mica caps. The manual would be very nice to have.
If the TX is already in the upper range you will not have to do anything for 160M. The BC1-H I had was on 570kc, and it took about $200 of fixed micas to get to the upper range, which allowed me to slip on up to 160 with no sweat.
The Exciter is the only possible trouble maker. 75M will be the usual challenge of switching in/out inductance and capacitance in the exciter and PA.
I do not know why someone would spend the time to convert a BC TX to 75M. All of that effort and great audio where it is la-la land filled with carriers and jamming.
I'll take the solid state driver over the 807 mess any day. PLENTY of audio drive to those mighty 833's.
Do you have a single hole or two 833's in the final?
Fred

[N6YW]

Depending on the original on-air frequency, there are three ranges in the broadcast band, that were listed for the fixed mica caps. The manual would be very nice to have.
If the TX is already in the upper range you will not have to do anything for 160M. The BC1-H I had was on 570kc, and it took about $200 of fixed micas to get to the upper range, which allowed me to slip on up to 160 with no sweat.
The Exciter is the only possible trouble maker. 75M will be the usual challenge of switching in/out inductance and capacitance in the exciter and PA.
I do not know why someone would spend the time to convert a BC TX to 75M. All of that effort and great audio where it is la-la land filled with carriers and jamming.
I'll take the solid state driver over the 807 mess any day. PLENTY of audio drive to those mighty 833's.
Do you have a single hole or two 833's in the final?
Fred

Fred.
It has 2-833's in the final. The one I am considering has (6) 807's, so it does not use solid state in the audio path. The exciter circuit is solid state. My reason for putting a box on 75 is because it's where I operate most of the time and 160 is only useful for certain times of year. Very noisy here during the Summer months. The transmitter under consideration was recently taken off-line, so it was producing power on air. It's currently tuned up in the upper portion of the BC band. It is in what I would call Pristine condition compared to most of the units I have seen. It was impeccably maintained and was evidently taken care of
with a high level of professional pride.
I also like to be different.
Most guys like to run the Collins, Bauer stuff. I have several AM transmitters, but this is one of my bucket list projects and I have never done this before. If you look at my QRZ page,
you will notice a beautiful Gates "Yard" audio console. The appeal of completing this lineup is strong
within me. But, I need to know how feasible this project is by having band switching capability.
Also, and this is big plus for me... I really want to piss off my neighbors, so I might as well do it right.
I would also be content with it being on one band as well, so this conversation is all about the exploration
of what's involved and I really appreciate the comments from everyone.
Billy N6YW

[N6YW]

Yep, power it up on the original freq for sure to begin with.

Keep in mind that 1H uses a solid-state mod driver circuit, and while it sounds really great on the air, it can not take the fiddling the older tube-based scheme can.

You might call KO6NM and run through the procedure with Mike, he is in your area and has done a lot of these.

I have a 1H-1 here if you need and goodies.

73DG

Dennis.
Yes, you bet I will. The effort in traveling well out of my area to acquire it is worth it and I am sure
Mike would be pleased to know of this agenda of mine. In fact, I think he would expect me to do
this sort of thing.
Thanks.
Billy N6YW

[W7TFO]

I've heard of BC-1H rigs with all-tube modulator drivers, but never run across one.  Early production no doubt.

We out West have a lot better time on 75m, our condolences to Fred.

One needs a good half-gallon at least to cover the distances encountered, even across the metro in LA.

A single 833A would signify a BC-500H.

73DG

[N6YW]

All...
According to the photos that were sent to me, it's in as close to a factory state of operational
correctness that would be considered normal. No obvious signs of repairs or modifications.
The traces on the boards are clean, no signs of flash over and is very clean inside the cabinet.
Meaning, no accumulation of large amounts of dust and assorted debris.
In my mind, it seems to have lived it's operational life under optimal conditions and not subjected
to harsh operational hazards.
So, maybe this one falls in the category of "saving a BC rig" and I might just record the events in blog,
video and photo formats to share. I mean, this is all about AM in it's various forms of survival.
I like this very much...
Billy N6YW

[W7TFO]

It will pay you to pay attention to the 833 sockets.  Gates cut corners there, making them out of aluminum bar stock and a cheap phenolic mounting scheme .

One side of each will be held tight, the other should slide around a bit to accommodate expansion and tube variances. 

What happens is they can fail, either from the thumbscrew galling and making you think the connection on the tube pin is tight, or the terminal lug on the wire(s) can work loose and heat up.

73DG

[ka4koe]

"Also, and this is big plus for me... I really want to piss off my neighbors, so I might as well do it right."

Oh, I wish I had the scrote to do this. Sheri K4SMN and I are troublemakers in our neighborhood since we object to the BS actions of our HOA board.

[N6YW]

"Also, and this is big plus for me... I really want to piss off my neighbors, so I might as well do it right."

Oh, I wish I had the scrote to do this. Sheri K4SMN and I are troublemakers in our neighborhood since we object to the BS actions of our HOA board.

It's quite simple really. Play along with my sense of humor if you can.

I am THE guy in our neighborhood who has the ability to actually use tools, can make stuff and make it work. In other words, I am a doer. Most of my neighbors are well to do trust fund idiots with a college education who think the world is at their bidding. So, this means if I cause a little disturbance with their cheap cordless phones (which I fixed) that I am a liability in their precious world. I have been the subject of numerous complaints (computer speakers are my favorite, again fixed) BUT... "Billy, could you fix my CD player???". So, I figure this is the win win for me. I mean, the look of amazement and terror on their faces is
priceless when they come over to my shop and see my equipment lined up, ever ready for deployment to devour their imported Plasma TV's. The warm glow of vacuum tubes pays homage to the mental picture in their feeble minds that I am some crazed mad person hell bent on destroying their universe with Ham Radio. Oh! You should have seen my neighbor freak out when I put up that 43 foot military mast for my new dipole antenna! HAHAHAHAHAHAHA!!!! you would have THUNK he would stroke out. I was hoping he would too, the little imbecile. The big box transmitter is the perfect addition to this carefully crafted image I have painstakingly created to insure my neighbors will stop screwing with me. I tell them it causes cancer.
All of sudden, they stop coming over to ask me to fix their stereos for free.

I have the satisfaction of knowing that if I were to suddenly leave this life, I at least had the satisfaction of doing exactly what I love to do, enjoying it immensely... BECAUSE I COULD, while my useless neighbors spend their lives complaining about what they don't have. None of these people have a clue of what it means to hear the clunk of a contactor make closure as the RF circuits pump out Angle Music. Nobody in the hood gets it and they never will.

So, this is part and parcel of the journey. My tongue and cheek response to the question is by definition, accurate. Life is too short for QRP and it's always better with a carrier and two sidebands. Those who know me well will most definitely chuckle at this because they know all too well.
Now, onto collecting some parts and vacuum relays etc.

73 de Billy N6YW

[Jim, W5JO]

I am THE guy in our neighborhood who has the ability to actually use tools, can make stuff and make it work. In other words, I am a doer. Most of my neighbors are well to do trust fund idiots with a college education who think the world is at their bidding. So, this means if I cause a little disturbance with their cheap cordless phones (which I fixed) that I am a liability in their precious world. I have been the subject of numerous complaints (computer speakers are my favorite, again fixed) BUT... "Billy, could you fix my CD player???".
73 de Billy N6YW

I fixed consumer equipment for complainers a long time ago but quit.  It seems that if you fix interference then it blows a fuse for another reason, you caused it and they want it fixed for free.  I am not in the consumer repair business so I began to proved them written instructions from the ARRL and other organizations on how to fix the problem themselves.

[N6YW]

I am THE guy in our neighborhood who has the ability to actually use tools, can make stuff and make it work. In other words, I am a doer. Most of my neighbors are well to do trust fund idiots with a college education who think the world is at their bidding. So, this means if I cause a little disturbance with their cheap cordless phones (which I fixed) that I am a liability in their precious world. I have been the subject of numerous complaints (computer speakers are my favorite, again fixed) BUT... "Billy, could you fix my CD player???".
73 de Billy N6YW

I fixed consumer equipment for complainers a long time ago but quit.  It seems that if you fix interference then it blows a fuse for another reason, you caused it and they want it fixed for free.  I am not in the consumer repair business so I began to proved them written instructions from the ARRL and other organizations on how to fix the problem themselves.

Same here, but the problem remains with them, not me. Anyway, back on topic.

[N6YW]

I will be traveling to see the transmitter within the next 10 days. I'll have some photos to share then.
The iron and the tubes have been removed, so it's ready to move into it's new location
I have to perform some logistic modifications here at home, so the the journey begins.
73 de Billy N6YW

[W0BTU]

I'm pretty sure my HB linear amplifier was made from Gates BC1H parts. I can say from experience that two 833As in parallel can be made stable up to at least 75 meters. The stock plate choke works just fine on 160 and 75. I used the Gates 30uH rotary inductor in the tank circuit, along with junk I had on hand. You'll almost certainly have to neutralize it, unless you can somehow copy my swamped grid circuit.

Maybe looking at what I did will give you some ideas. http://www.w0btu.com/833C_linear_amplifier.html

Here's a quick link to the photos, sorted by newest on top.
http://www.w0btu.com/files/misc/833C_linear_amplifier/?C=M;O=D

And DO pay attention to the advice above about the 833A sockets! Several of mine needed a lot of help. I even had to stone off some of the pins so they would make good contact.

Be careful running that rotary inductor all the way to the ends! You can ruin the contacts instantly.

[N6YW]

I'm pretty sure my HB linear amplifier was made from Gates BC1H parts. I can say from experience that two 833As in parallel can be made stable up to at least 75 meters. The stock plate choke works just fine on 160 and 75. I used the Gates 30uH rotary inductor in the tank circuit, along with junk I had on hand. You'll almost certainly have to neutralize it, unless you can somehow copy my swamped grid circuit.

Maybe looking at what I did will give you some ideas. http://www.w0btu.com/833C_linear_amplifier.html

Here's a quick link to the photos, sorted by newest on top.
http://www.w0btu.com/files/misc/833C_linear_amplifier/?C=M;O=D

And DO pay attention to the advice above about the 833A sockets! Several of mine needed a lot of help. I even had to stone off some of the pins so they would make good contact.

Be careful running that rotary inductor all the way to the ends! You can ruin the contacts instantly.

Mike
Thanks for the reply. I will pay attention to all of the parameters concerned. There is a pretty good article on converting the BC-1H for Amateur use in Electric Radio #195 November 2005. There are two treatments described in the conversion project covered then. I am sure there are others. It's pretty early in the project for me now. I went ahead and committed to becoming the new owner, and will retrieve the transmitter next month from the San Diego area. This is a big step for me because of it being the first BC transmitter conversion I have ever attempted. My working skills are very good to excellent, so performing the tasks aren't the hard part. It's knowing what NOT to do, so I will take my time.
Fortunately, the transmitter was making rated power when taken offline a couple of months ago. This is a very good thing as it will likely limit the possibility of some ugly surprises. It's in immaculate condition and I am blown away at how well it has been cared for since new. Some of these boxes were abused and neglected in ways I could never imagine, but it's by sheer luck I found this one in such fine shape.
Check it out:

[N6YW]

More shots:

[N6YW]

And more:

[W0BTU]

Looks like it's in good shape, but it looks like some things are missing in the bottom. Where's the HV power transformer?

[N6YW]

All of the iron was removed when the box was moved from the TX site to storage.
It's 100% complete.

[KA3EKH]

I played around with the BC-1H in broadcast service and it’s an all right box, never liked the 120 volt AC interlock or remote control functions being you tend not to expect 120 volts on control lines but that was fairly common of the Harris – Gates stuff back in the seventies. 833 is a great tube, almost indestructible in broadcast service and have to wonder if they are still in production today although cannot imagine anyone still using a tube base transmitter in broadcast service today except maybe as a backup.

[W0BTU]

They are still made -- in China.

Mine are Chinese 833Cs. Graphite plate.

[W3GMS]

Billy,

Those pictures look great!  Some dirt, but as you said its in immaculate condition and working on the BC band.

Should be a snap to get working on 160/80 meters.  In fact, I have used 833's up to 20 meters and they played very nicely. 

Joe, GMS

[John K5PRO]

Good luck with 'er, OM. My 1H1 is still on broadcast band. I did replace the warped phenolic bar stock that held the 4 833 sockets in a row. The 1H had tube audio drivers and the 1H1 was with the silicon audio drivers. I imagine the 1H had a slight edge over the 1H1, more "natural sounding distortion" as pube audipiles are frequent to say.