Re: [AMRadio] BTA Mods
Hi Jim, I don't have the schematic yet, but the input to the trace on the board that goes to the coil goes thru a rectifier diode then on to the coil. The relays are both marked "Potter & Brumfield SL4349 Reversing Polarity Latch". I have been unable to find any information on the relays themselves thus far. They are very small plug in type relays and the diagram on the case indicates they are DPDT. I have not tried to power the relays to see if the contacts are working properly since I'm not sure of the voltage of the coil. I am assuming they are 115 v, but I don't want to chance it. 73, Rick/K5IZ Jim Wilhite wrote: That is interesting about the relays Rick. Are you sure they are DC coils? I have a P&B LK 17A relay here that NIB. It is the same setup but has 115 V coils. They are marked AC but I wonder if the BTA ran them off of DC? 73 Jim W5JO
Re: [AMRadio] BTA Mods
That is interesting about the relays Rick. Are you sure they are DC coils? I have a P&B LK 17A relay here that NIB. It is the same setup but has 115 V coils. They are marked AC but I wonder if the BTA ran them off of DC? 73 Jim W5JO Steve, That could very well be true. When I receive the schematic I'll know more about exactly what the work is all about. There are very few differences between the BTA models circuit wise, but it seems the oscillator is one of them. The BTA-1R1 uses 4PDT AC relays to switch the crystal frequency and the R2 I have uses DPDT reversing latch relays with DC coils. I'm not sure exactly what else is different, but I have found some of the edge connections to be different. Thanks for the insight. 73, Rick/K5IZ
Re: [AMRadio] BTA Mods
Neal, Thanks so much for the insight and advice. I think first hand experience and advise from that experience is most valuable. Larry Will, another fine engineer, has also given me some great advice and help. Hopefully, with the things I've learned thus far and the help and advice from you guys who have "been there and done that", I'll be able to get this old gal back on the air. I really don't want to make any major modifications in the layout or circuitry if I can help it. I have always thought it a great challenge to retain the original design and layout while achieving my goals. Whether it will be possible in this case remains to be seen. I'll keep you guys posted on my progress and I'm sure I'll be tapping into your vast experience for help and advice. 73, Rick/K5IZ neal Newman wrote: Hi Rick No matter what I tried to Fix what was done to this transmitter. It would Put out Spurs all over the place. Yes It got to 75 meters...looking at the spectrum analyzer It was all over the place. these spurs were causing High currents and arcing. in the output Network. self oscillations the transmitter was what I call a Runaway. you Could pull out the crystal and it would still deliver full output Not a Good sign.. thats when I decided to Build the output network back to the RCA design. and try 160 meters.. it worked first shot. Clean spectral. If you like to Tinker with High voltages and networks. and not worried about Blowing out coils. Cool Go for it. I would recommend you put a spectrum analyzer on it when your Done. best to cover your butt.. and If you Do get a clean Output on 75 meters. Let me know Ill try it on another Rig I just picked up.. Now I know the Gates BC-1H can go to 75 meters I know one down south where its a dual bander it does 75 and 160 meters. going through a Divorce right now. so eventually Ill get to working on the Gates..
Re: [AMRadio] BTA Mods
Steve, That could very well be true. When I receive the schematic I'll know more about exactly what the work is all about. There are very few differences between the BTA models circuit wise, but it seems the oscillator is one of them. The BTA-1R1 uses 4PDT AC relays to switch the crystal frequency and the R2 I have uses DPDT reversing latch relays with DC coils. I'm not sure exactly what else is different, but I have found some of the edge connections to be different. Thanks for the insight. 73, Rick/K5IZ Perhaps someone needed more capacitance to net the crystal on frequency... and two of the three crystal sockets more or less taken out of use Perhaps someone cut out the "Conelrad" crystal switching... Steve WD8DAS
Re: [AMRadio] BTA Mods
Hi Rick No matter what I tried to Fix what was done to this transmitter. It would Put out Spurs all over the place. Yes It got to 75 meters...looking at the spectrum analyzer It was all over the place. these spurs were causing High currents and arcing. in the output Network. self oscillations the transmitter was what I call a Runaway. you Could pull out the crystal and it would still deliver full output Not a Good sign.. thats when I decided to Build the output network back to the RCA design. and try 160 meters.. it worked first shot. Clean spectral. If you like to Tinker with High voltages and networks. and not worried about Blowing out coils. Cool Go for it. I would recommend you put a spectrum analyzer on it when your Done. best to cover your butt.. and If you Do get a clean Output on 75 meters. Let me know Ill try it on another Rig I just picked up.. Now I know the Gates BC-1H can go to 75 meters I know one down south where its a dual bander it does 75 and 160 meters. going through a Divorce right now. so eventually Ill get to working on the Gates.. --- Rick Brashear <[EMAIL PROTECTED]> wrote: . What seemed to be the them on 75? My goal is 3.880 thru 3.890, so I would > be very interested > in any experience you can share. > Thanks, > Rick/K5IZ > __ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
RE: [AMRadio] BTA Mods
Please forward any info on the RCA BTA 1 r, BTA 500H and if anyone has info on a BTA 5F need to move all of theses to 75 Thanks Brad KB7FQR -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Rick Brashear Sent: Sunday, May 28, 2006 6:06 PM To: Discussion of AM Radio Subject: Re: [AMRadio] BTA Mods Thanks for the tips, Neal. What seemed to be the problem with getting them on 75? My goal is 3.880 thru 3.890, so I would be very interested in any experience you can share. I am now in the process of refurbishing the oscillator board, but I have to wait until the R2 schematic arrives before I can go much further. Thanks, Rick/K5IZ neal Newman wrote: > I have 2 RCA rigs. a BTA 500R and a BTA 1R1 >Neither Rig worked well On 75 meters. > so I put them on 160. >The very first thing I would Do after determining If >the Rig works on its origonal frequency. I would >replace Every Resistor and cap on the Exciter board > Less than $50 to do this. >makes the oscilator back to New tolerance. and will be >stable. > Neal-ka2caf > > > > __ AMRadio mailing list Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net AMfone Website: http://www.amfone.net AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb -- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.1.394 / Virus Database: 268.7.3/350 - Release Date: 5/28/2006
Re: [AMRadio] BTA Mods
Thanks for the tips, Neal. What seemed to be the problem with getting them on 75? My goal is 3.880 thru 3.890, so I would be very interested in any experience you can share. I am now in the process of refurbishing the oscillator board, but I have to wait until the R2 schematic arrives before I can go much further. Thanks, Rick/K5IZ neal Newman wrote: I have 2 RCA rigs. a BTA 500R and a BTA 1R1 Neither Rig worked well On 75 meters. so I put them on 160. The very first thing I would Do after determining If the Rig works on its origonal frequency. I would replace Every Resistor and cap on the Exciter board Less than $50 to do this. makes the oscilator back to New tolerance. and will be stable. Neal-ka2caf
Re: [AMRadio] BTA Mods
I have 2 RCA rigs. a BTA 500R and a BTA 1R1 Neither Rig worked well On 75 meters. so I put them on 160. The very first thing I would Do after determining If the Rig works on its origonal frequency. I would replace Every Resistor and cap on the Exciter board Less than $50 to do this. makes the oscilator back to New tolerance. and will be stable. Neal-ka2caf __ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
Re: [AMRadio] BTA Mods
> I have found traces cut and spliced to other traces, a >small variable capacitor replacing a compression trimmer Perhaps someone needed more capacitance to net the crystal on frequency... >and two of the three crystal sockets more or less taken out of use Perhaps someone cut out the "Conelrad" crystal switching... Steve WD8DAS
Re: [AMRadio] BTA Mods
Rick, Just a thought on the osc circuit. You could always disconnect the osc board and use a signal generator to feed the grid of the 6146. This will let you test out the remainder of the transmitter on the AM broadcast freq. I would think that the crystal osc will be removed when you move it to 75M, so fixing it may not be worth the effort. 73's Roger KC8OPP --- Rick Brashear <[EMAIL PROTECTED]> wrote: > Well... I have investigated the printed circuit > board on the 1R2 on > which the crystal ovens are mounted and find there > have been several > modifications and/or repairs made through out this > old girls life. My > intention, as advised by much more knowledgeable > people on these > transmitters, is to put it back to it's original > state, be sure it's > operating at the original specifications, then begin > the conversion to > 75 meters. My concern is that some of these mods > may have been handed > down by RCA and should possibly be left in tact. > Does anyone know of > any modifications that RCA issued concerning this > portion of the > transmitter? I have found traces cut and spliced to > other traces, a > small variable capacitor replacing a compression > trimmer and two of the > three crystal sockets more or less taken out of use > with that fact > marked in pencil on the board. My inclination is > these are repairs made > due to failure of components, but with no > documentation on the repairs > it's very difficult to be sure. The board is badly > scorched beneath the > 4000 ohm 10 watt resistor, but I have read this is a > common issue. > There is no trace damage to the board from the heat. > > Any advice will be very much appreciated. For those > who subscribe to > more than one list, I apologize if you receive this > post more than once, > but I want to reach the largest audience possible > for assistance and advice. > > Thanks, > Rick/K5IZ > > > > > __ > AMRadio mailing list > Home: > http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami, Paul > Courson/wa3vjb > __ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
[AMRadio] BTA Mods
Well... I have investigated the printed circuit board on the 1R2 on which the crystal ovens are mounted and find there have been several modifications and/or repairs made through out this old girls life. My intention, as advised by much more knowledgeable people on these transmitters, is to put it back to it's original state, be sure it's operating at the original specifications, then begin the conversion to 75 meters. My concern is that some of these mods may have been handed down by RCA and should possibly be left in tact. Does anyone know of any modifications that RCA issued concerning this portion of the transmitter? I have found traces cut and spliced to other traces, a small variable capacitor replacing a compression trimmer and two of the three crystal sockets more or less taken out of use with that fact marked in pencil on the board. My inclination is these are repairs made due to failure of components, but with no documentation on the repairs it's very difficult to be sure. The board is badly scorched beneath the 4000 ohm 10 watt resistor, but I have read this is a common issue. There is no trace damage to the board from the heat. Any advice will be very much appreciated. For those who subscribe to more than one list, I apologize if you receive this post more than once, but I want to reach the largest audience possible for assistance and advice. Thanks, Rick/K5IZ
