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THE AM BULLETIN BOARD => Military Amateur Radio Section => Topic started by: SM6OID on August 01, 2019, 04:08:43 AM

Title: BC-375-E, wisdom needed...
Post by: SM6OID on August 01, 2019, 04:08:43 AM

A future upcoming project is to put a BC-375-E on the air.
A believe that I have a good set of tubes, so that is a good start.

It appears as if a couple of "big resistors" are junk, but other that that, I have no idea of what to find.

So, on top of the list is to find a couple of TU's, at least 80 and 40 meter units.
The question is, has anyone tried to operate CW on 30 meter with a -375?
I would expect "some chirp", but is usable or..?

Any words of wisdom that I will be needing on my journey?

By the way, the transmitter will be using a power supply not dynamotor.
If I find a dynamotor, I might be using it.

Title: Re: BC-375-E, wisdom needed...
Post by: KA3EKH on August 01, 2019, 08:59:34 AM
have you looked at:

That and the BC-191 are a challenging transmitter to use, also expensive considering what the tubes sell for these days. I have run several ART-13 transmitters over the years and played around with a lot of the ARC-5 stuff but not attempted the big MOPA.
Good luck!

Title: Re: BC-375-E, wisdom needed...
Post by: SM6OID on August 02, 2019, 05:52:35 PM

Yes, I've read all(?) the information I can see on that page, I do believe that I have an idea of what to expect with the -375.

I do hope that the tubes I've got will last, if not for ever, a long long time.
Considering that the limited duty of a rig like that, tubes once acquired, is a small problem?
Need a couple of tuning units and there is a good chance I will be on the air with the -375 in a not too distant future.

I also have an ART-13 up and running, mostly CW but some AM, there are few AM folks around here.
But, it has a problem, the frequency range switch is partly defective, it will only work on "even numbers".
And, it looks like a pain in the a** to do something about it. I run it using the dynamotor, and it does well!
I'm also into "ARC-5" transmitters, actually I have ATA and SCR-274-N transmitters, no ARC-5, but anyway, great fun!

I'm close to the "finishing line" brining back a Marconi T1154 (WW2) transmitter to active duty, so far I have only fixed mechanical issues, the age of the transmitter and unqualified fingers in it can cause a lot of weird and strange behavior.
However, the last issue to solve (?) for now is to check voltages around the PA tubes, it's suppressor modulated and sounds absolutely horrible, carrier is too high. Do not expect this to be too much of a headache.
And by the way, it chirps and drifts, not bad on 80 m but on 14 MHz, it has a "unique" tone...

Title: Re: BC-375-E, wisdom needed...
Post by: SM6OID on August 14, 2019, 05:26:56 AM
So, I have opened up the BC-375-E, it has been stored under less than ideal condition for a while, but I guess that it is mostly a cosmetically “problem”. Exterior is ok, front fascia not repainted but side panels has seen “new paint”. Some of the big resistors at the rear suffers from mechanical damage.
I'd say that the condition is "Not Great, Not Terrible", I've seen much worse...

However, what will be become somewhat of a headache is to rewire the filament circuits. At some time in the past, someone put in a lot of work changing the original circuit, the workmanship is not top notch, not even close, rather the other way around. A number of wires has been cut while others relocated.

Those of you familiar with the BC-375-E knows that it is “densely wired” some soldering joints are a real PITA to reach. The preliminary plan is to go the original route regarding the filaments, unless I’m advised not to or I come up with a brilliant idea myself…

The conclusion is that it shouldn’t be a too much of an effort to make it run, but I really do hate to clean up after “previous users” no matter if it at the toilet of an old transmitter!
If anyone has some detailed pictures of internals of the transmitter, I would really like to see them!

To Be Continued…

Title: Re: BC-375-E, wisdom needed...
Post by: SM6OID on August 29, 2019, 05:01:22 PM

Dear All, I hereby announce that it is officially alive!
After some work, it takes a wile to clean up after a "conversion/modification wizard"... 

It will give me 65 W on 10.1 MHz, CW.
The AM part needs some attention, it's not working...
But never the less, it's alive!
Chirp is not too bad, it's better than expected, drift is "clearly noticeable".

So far, the power has been dumped in to a dummy load, will hook it up to an antenna tomorrow, it's 23:00 here so, I will do a few other things then it's bed time.

I'm looking for TU's, so far I have the TU-10B 10-12.5 MHz, hope to find drawers to cover 160/80/40 meters.

To Be Continued!

Title: Re: BC-375-E, wisdom needed...
Post by: SM6OID on September 11, 2019, 11:59:42 AM

So, I have modulation, of course there is a FM component present, but considering I have done the tests at 10.12 MHz, it is to be expected. But it is not horrible.
I can get 80-90 W of carrier.

Title: Re: BC-375-E, wisdom needed...
Post by: KC4VWU on September 22, 2019, 10:29:32 AM
That sure is a beautiful sight to behold!

Title: Re: BC-375-E, wisdom needed...
Post by: SM6OID on September 24, 2019, 06:49:38 AM

Yes, it sure is!
And I might add, the BC-375 is a very practical transmitter.

How many times have we not been late for dinner?
As a result, having to eat cold food...
With a BC-375 this is no longer a problem, put the plate on the top of the transmitter and having to eat cold food is just a distant memory!

Or, if you during a long evening/night session get hungry, a couple of pizza slices on top of the transmitter will solve that problem. After a decent rag chew transmission, the pizza is ready to eat!
Needless to say, put the coffee mug on top of the transmitter and you won't have to drink cold coffee anymore!

I have now had it on the air on 40 meters now, CW so far.
AM to be evaluated, but it seems like it acceptable, some FM.
Drift is less of a problem, but still VERY noticeable...
Chirp is there, adding personality to the transmission.

My conclusion is that this is one of the best transmitter ever made, looking at the glowing triodes is a real feel good experience, and then the ability to take care of the "food issue"...

Title: Re: BC-375-E, wisdom needed...
Post by: SM6OID on October 28, 2019, 06:38:00 PM

Project update!
A number of CW QSO's has been done on 80 meters as well as a handful of AM conversations.
Mostly within Sweden, but some with Norwegian station and one in England.

Feeding the audio from a ElectroVoice 638 via W2IHY EQ into the microphone transformer makes the thing to sound quite good!
Have also been using a T-17 microphone, and that work quite OK that too, but there is a difference...

By now, I do think that most of the old dead spiders has been zapped into smoke, yes... I have had a few flash overs.

Title: Re: BC-375-E, wisdom needed...
Post by: K4RT on November 15, 2019, 12:11:31 AM
Congratulations getting it working and making QSOs! Thanks for posting the pic.

Title: Re: BC-375-E, wisdom needed...
Post by: KA3EKH on November 15, 2019, 10:15:35 AM
What receiver are you using with the transmitter? If you add a BC-312 or BC-342 receiver you can be well on the way to having a SCR-188 or SCR-193 set for the entire WW2 radio experience!
Any WW2 reenactors or events local to you?  Operating the radios in the field is always a fun challenge. The only issue may be that you have a BC-375 that was aircraft version of the BC-191 and where it would not be an issue finding a BC-348 aircraft receiver to pair with the transmitter and give you a SCR-287 aircraft set finding a B-17 to put it in may be a problem.

Title: Re: BC-375-E, wisdom needed...
Post by: SA2CLC on November 18, 2019, 11:38:56 AM
Haha, great use.
"I'll just put the food on the shortwave oven"

Maybe we should try a 40m am qso soon,
Still haven't gotten anything up for 80 yet, but have
a vertical up for 40.

Title: Re: BC-375-E, wisdom needed...
Post by: SM6OID on November 23, 2019, 02:24:34 PM

I use different receivers, BC-348-Q is one of them, but mostly R-390A.
B17 are getting scarce, but I have a Meteor V12 that can power a 28 V generator, at least I have a noisy power source...
The dual ignition system is completely screened, so reception should not be a problem.

Since a few days back, I’m on the air using a PE-73 dynamotor, works fine on both CW and AM.

CLC, we have to ask the propagation gods for advice...

Title: Re: BC-375-E, wisdom needed...
Post by: Opcom on November 24, 2019, 01:51:54 PM
you know an engine is serious when the camshafts drive the accessory pulleys. Reminds me of a video of a guy starting up a turbo jimmy and getting a suprise from a stuck rack.
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