BTA 250L

[John K5PRO]

I may have an opportunity to purchase a clean RCA BTA250L, I think it is. It may be missing a tube or two, I will go look at it this week. Its at a B'dcaster who can use the $ more than a museum piece, but I am not sure what these thangs go fer. Haven't seen this particular one on EPAY, usually see the BTA1R1 model. Besides, I don't trust EPAY for value judgements. This has 810s. Any tips or ideas of value? I am not wanting to restore the monster, just want to help move it along to a good home.

[K6IC]

Hi John,

I know nothing secifically abt the value of this rig.

Am sure that U know what it looks like and/or have Googled it ... but if not ...  a fuzzy image:

http://www.oldradio.com/archives/hardware/RCA250L.jpg

ca  1947  looks Decoesque kinna ala 20 V2 ... do not see any windows ... looks HEAVY !

73  GL   Vic   KF6RIP

[KR4WI]

John: I have a 250L. I picked it up last yr, Sorry, I cant help with price. I have posted pics hr on amfone qso section page 3. Just a few pics I put on a couple weeks ago. It is heavy 1360 pounds, 810s modulated by 828s. Matthew KR4WI

[flintstone mop]

Hey John,
Make an offer of $200 and see what happens. Gently tell the owner you are coming to his TX site to remove it. The only thing you are asking is to disconnect from the mains and disconnect the antenna. Remember some of those TX sites are a disaster getting ready to happen.
Sounds like a nice rig.

Fred

[John K5PRO]

Matthew, Thanks for linking me to your note on the QSO page on the RCA rig. I remember reading and seeing that, but couldn't remember where it went. Yes, that is the beast. I am going to look at it later this week, am told it is very clean. I downloaded the schematic (manual is there too) from Patrick J's website. I see it has 828 for the driver and pair 828s for the modulator in AB1. 828s have been out of production for many years, in my RCA transmitting tube manual TT5 (dated 1960s) it is marked discontinued. In RCA tube handbook HB3 it is covered, datasheet is dated 1939. Antique Electronic Supply has them for $62. Thomas Brukner has them online for $120 each! I think the audiophools have jacked the price up. Yikes!

Here is an 828.
http://www.dogstar.dantimax.dk/tubestuf/pinups/828.jpg

It is a beefier version of an 814, looks like the same filament and socket. The 814 goes for $21 at AES. It has zero voltage rating on the beamforming plate, whereas the 828 has a true suppressor grid with 100 volts or so, if needed. Has higher transconductance too, being operated as a pentode. In the RCA 250L G3 voltage is coming off a tap off the screen supply for the same tube. The The 814 may be usable in the RF driver stage, with some modifications. Not sure if it would handle the modulator however. I was told that the 250L I am going to see is missing some tube, and I fear it might be these. 810s are a little easier to find.

Too bad RCA didn't have windows in front to see the glow on that rig. Good luck with yours, I will let you know how things go here.

73
John
 


Th

[W3SLK]

828 are double the 814. Other than that its pretty much the same tube only heftier. Maybe a better analogy would be the difference between 811A's and 572B's. But remember if you get them from Antique Electronics, you will have a guarrantee and chances are you probably would never need anymore. Plus it will buy you some time to scarf a few at the hamfests.

[KR4WI]

Howdy again John: Mine was missing a tube also, it was the 807 in osscilator, I wanted to tell you that for a positive note, I have had a lot of fun and learned a ton with mine this yr, I am looking for resistors at present and I hope that will be the last of replaced parts I need. I had to get 828 tube for driver on mine, I found one on epay for 17 bucks and I hope it is good, when time comes to fire it up. Thats interesting about the 814 tube, we may need it some day. I found a raytheon  ra1000 and they ask me 500 bucks for it, so the 200 is a good offer for the bta250L I would think. I will post on hr when I get mine going. So stay Tuned. 73 Matthew KR4WI   Oh: I have a manual also, if the one on web dont turn out for you, I would be happy to make a copy at work, and put it in mail for NO CHARGE.

[flintstone mop]

Hi John
I had a nice GE AM transmitter that had the appearance of a refrigerator. N3DRB cleaned it up and I had to buy some tubes. Heavy box and it was just 250 watts. A pair of 810's modulated by a pair of 828's. I forget the exciter/driver.It was a neat box during my beginning days. I learned a lot of things with that Tx and the help of Steve Huzman. 250 watts and a good antenna for 160M will get you nice reports.
Good luck
Fred
When you get it home and you are ready to throw the big switch, after the usual setup and checkouts, hook the beast to a dummy and tune it up and then hook your audio chain to it and play some oldies R&R music and watch the needles jump around and the mercury rectifiers flicker to the music. It's quite an RF high!!!!!

[John K5PRO]

Yes, I think the GE was very similar to the RCA if not the same design, repackaged. The push pull modulator (828) are driven by pair of 6J7, RC coupled, so it would be disasterous to try and run class B with 838 or 805 triodes (same filament again) in the 828 positions. Without a speech amp stage, the 6J7s are all there is for audio drive. The 838 and 805 have different socket also. The manual from Patricks' website is low resolution, so if I did get this thing, I will let you know Matthew, for a copy of the book. I got the schematic fine though. Quite a simple thing, why did the box have to be so friggin big and spacious? I have a Continental 314R1 right now, which is smaller, lighter, and does 1 kW with PDM!

[flintstone mop]

John
You would love a Gates BC1-H. Very nice 80's transmitter with a window. The early vintage transmitters were a "showcase" when clients would come to the station and buy advertisement time. THey would oooh and WOW looking at the meters dancing around and the pubes lit up and blushing a little and the Mercury vapor tubes flickering to the modulation.
Later................Fred I'm going to check on 160M for the first time in 2 1/2 weeks.

[John K5PRO]

I looked over this BTA250L today. The iron has already been removed and stacked in the corner. It has the 828 and 810 tubes all in 'er. I didn't realize that the 250L was not very deep, the cabinet doesn't stick out so much. Its just big and tall and wide! So thats why its so large, everything is on the one big panel, including the iron. Its got a rather appealing 1940s design to it, not far off from old Collins cabnetry.

[WA3VJB]

John,
A reminder that I'd enjoy including your story if this rescue mission comes to pass. Get someone to shoot lots of pictures come Moving Day, both where it sits, around the station itself, and a couple of good shots from outside the building. Any history you can collect from engineering, sales and owners may tell whether they bought this new, etc., and who knows, someone may unearth the original bill of sale for the thing, HA! hopefully after you've closed the deal..

Paul

IN CASE YOU MISSED IT       ---------          Check the NEW story for Mark K3MSB's "shutter door" RCA the BTA-1M at this link:
http://amfone.net/amradionetwork/index.htm

[VE7 Kilohertz]

HI JOHN,

That's a nice looking TX. I had my head in one a few weeks ago. Very easy to work on and they were designed to run 550KHz to 3MHz out of the box. Should be a breeze to put on 160M and only a few changes to put it on 75M.

If you want a different approach, to get it for free, tell the owner you are saving him a costly environmental nightmare by removing his PCB laden transmitter at no charge. Although even $250 is a steal for what you are getting. 

Keep us posted on your acquasition.

Paul
VE7KHz

[Steve - WB3HUZ]

Wow. I pity the poor bastard on a dial modem trying to view that link!

That's a neat looking TX. Similar to the 1MX but with the flexi-door instead of a viewing window. Some interesting trivia: RCA made a HF transmitter (2-26 MHz) that looks almost exactly like this one. It had 4-400s in the final and 833s a modulators.

[John K5PRO]

Station has been dark, coming out of bankrupcy court, so things aren't for sale right now. But I offered to do some engineering help, maybe will try for a trade or something. Their MW1A won't kick on the air right now, and they need to get it back up real soon. Speaking of which, that MW1 is quite a finicky box from what I could read on the Harris website.

Glad to hear the BTA250L is simple, it sure looked it inside. So much air and space in there, with large bus wires connecting sections. With a pair of 810s and the 828 modulators, it should be theoretically possible to raise the HV a smidgen and get a solid 375 carrier out of it, plus good modulation depth. I didn't see air variable caps in the output, mostly variable inductors with a wheel rolling on the coil.

You can download complete manuals and many tech supplements/notes for the Harris Gates One, the SX-1 and even a bit of the MW1 at the Harris Broadcast Div website. You have to find the Radio>Transmission page, then look for techical support, and find the manuals. You must log in as a premium customer to look. Thats not so hard, just go through, create the profile, and get your password assigned. Then login and change it to something you can remember.

[Powell]

Station has been dark, coming out of bankrupcy court, so things aren't for sale right now. But I offered to do some engineering help, maybe will try for a trade or something. Their MW1A won't kick on the air right now, and they need to get it back up real soon. Speaking of which, that MW1 is quite a finicky box from what I could read on the Harris website.



Indeed it is. At WJES's unit on 1190, it has a mod for it to say  POS MW-1. But it operates fine at 380 watts.

What station is that you are doing work for? is that the graveyarder that went dark in your area?


Powell W4OPW

[WA3VJB]

John I have a 1948 RCA catalog featuring advertising photos and spec sheets of the 250L.
Once you get the thing let me know if  you want a "wall size" poster photocopy.

[John K5PRO]

Thanks 'VJB. It will be a while as the lights have to get turned on first, then the license transfer made, etc. I may or may not get ahold of it. Either way, it won't get turned into pot metal - for certain.