Re: [AMRadio] Modulator feedback
, The UTC may work so don't discount it. Those I and H model transformers were only about half the size as the D and E models. I can't think of the company that made them but they were substantially different then the earlier models. The potted versions are made by Chicago Transformer Co. They are indeed much smaller than the older end-bell model like what is used in the E model. I suppose they work OK, because I have not heard a lot of complaints about blowing them, but I am still amazed at how TINY those things are. Don K4KYV
Re: [AMRadio] Modulator feedback
I agree, they are very small for a 250 watt transformer. I made a few more adjustments such as line voltage and tightening up the old E model tranny. Hopefully, when I get the back on it will be usable now. I sure appreciate all of the suggestions, advice and experience I have received here. Rick/K5IZ Donald Chester wrote: , The UTC may work so don't discount it. Those I and H model transformers were only about half the size as the D and E models. I can't think of the company that made them but they were substantially different then the earlier models. The potted versions are made by Chicago Transformer Co. They are indeed much smaller than the older end-bell model like what is used in the E model. I suppose they work OK, because I have not heard a lot of complaints about blowing them, but I am still amazed at how TINY those things are. Don K4KYV __ 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
Re: [AMRadio] Modulator feedback
Rick, Unfortunately, you are plagued with the same problem dozens of -610 owners have. The only way to resolve it is to get an I or H model modulation transformer. They are potted and hermetically sealed and don't talk back near as much. Other than that you are SOL. Mod-U-Lator, Mike(y) W3SLK - Original Message - From: Rick Brashear [EMAIL PROTECTED] To: Discussion of AM Radio amradio@mailman.qth.net Sent: Thursday, March 16, 2006 10:42 PM Subject: [AMRadio] Modulator feedback I've posed a couple of questions on some other lists and received some good advice, but I am still in need of more. My BC-610-E has a bad feedback or talk back problem. I've placed a capacitor across the overload relay (RY-5) and that did eliminate a little of the talk back. However, with much audio gain at all, not nearly enough to attain 100% modulation, I get feedback. Not just talk back, but feedback. I have to assume it's coming from the modulation transformer. The modulator bias is set for 40 ma as specifications state. The bolts on the modulation transformer are all tight. What am I over looking here? I'm using a BC-614-E speech amplifier with a D-104 non amplified mic. I did a few modifications to the dynamic input circuitry of the BC-614 to better match the D-104, but that is the only modification in either the speech amp or the BC-610-E. 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
Re: [AMRadio] Modulator feedback
Rick, The UTC may work so don't discount it. Those I and H model transformers were only about half the size as the D and E models. I can't think of the company that made them but they were substantially different then the earlier models. As always, your mileage may vary. Mod-U-Lator, Mike(y) W3SLK - Original Message - From: Rick Brashear [EMAIL PROTECTED] To: Discussion of AM Radio amradio@mailman.qth.net Sent: Friday, March 17, 2006 4:25 PM Subject: Re: [AMRadio] Modulator feedback Wow! Not exactly the news I wanted, Mike, but thanks for the honesty. It looks like I may have to move the speech amp and mic considerably further away from the E model. I have an H and I model, but they are still in the refurb process. Potted modulation transformers or any modulation transformer for the 610 series is scarce. I have a UTC that will work, but it's not potted and I have an oil filled military transformer that would work if I had room on the chassis. I wonder what the guys in the SCR-399 did to contend with this issue since they were in such close quarters? Anyway, back to the drawing board and thanks again for the info. 73, Rick/K5IZ Mike Sawyer wrote: Rick, Unfortunately, you are plagued with the same problem dozens of -610 owners have. The only way to resolve it is to get an I or H model modulation transformer. They are potted and hermetically sealed and don't talk back near as much. Other than that you are SOL. Mod-U-Lator, Mike(y) W3SLK - Original Message - From: Rick Brashear [EMAIL PROTECTED] To: Discussion of AM Radio amradio@mailman.qth.net Sent: Thursday, March 16, 2006 10:42 PM Subject: [AMRadio] Modulator feedback I've posed a couple of questions on some other lists and received some good advice, but I am still in need of more. My BC-610-E has a bad feedback or talk back problem. I've placed a capacitor across the overload relay (RY-5) and that did eliminate a little of the talk back. However, with much audio gain at all, not nearly enough to attain 100% modulation, I get feedback. Not just talk back, but feedback. I have to assume it's coming from the modulation transformer. The modulator bias is set for 40 ma as specifications state. The bolts on the modulation transformer are all tight. What am I over looking here? I'm using a BC-614-E speech amplifier with a D-104 non amplified mic. I did a few modifications to the dynamic input circuitry of the BC-614 to better match the D-104, but that is the only modification in either the speech amp or the BC-610-E. 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 __ 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 __ 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
RE: [AMRadio] Modulator feedback
Get a high inductance choke (modulation reactor) to shunt the DC out of the secondary of the modulation XFMR. It will kill about 75 % of the talk back. What's left is all second harmonic talk back and it won't feed back. Did you ever use an old speaker that required DC to get the magnetism (no permanent magnet)? Not much sound comes out until the DC goes in to make the magnetism for the voice coil to work against. John, WA5BXO -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Rick Brashear Sent: Thursday, March 16, 2006 9:43 PM To: Discussion of AM Radio Subject: [AMRadio] Modulator feedback I've posed a couple of questions on some other lists and received some good advice, but I am still in need of more. My BC-610-E has a bad feedback or talk back problem. I've placed a capacitor across the overload relay (RY-5) and that did eliminate a little of the talk back. However, with much audio gain at all, not nearly enough to attain 100% modulation, I get feedback. Not just talk back, but feedback. I have to assume it's coming from the modulation transformer. The modulator bias is set for 40 ma as specifications state. The bolts on the modulation transformer are all tight. What am I over looking here? I'm using a BC-614-E speech amplifier with a D-104 non amplified mic. I did a few modifications to the dynamic input circuitry of the BC-614 to better match the D-104, but that is the only modification in either the speech amp or the BC-610-E. 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
Re: [AMRadio] Modulator feedback
Thanks John, that's a good idea. Rick John E. Coleman (ARS WA5BXO) wrote: Get a high inductance choke (modulation reactor) to shunt the DC out of the secondary of the modulation XFMR. It will kill about 75 % of the talk back. What's left is all second harmonic talk back and it won't feed back. Did you ever use an old speaker that required DC to get the magnetism (no permanent magnet)? Not much sound comes out until the DC goes in to make the magnetism for the voice coil to work against. John, WA5BXO -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Rick Brashear Sent: Thursday, March 16, 2006 9:43 PM To: Discussion of AM Radio Subject: [AMRadio] Modulator feedback I've posed a couple of questions on some other lists and received some good advice, but I am still in need of more. My BC-610-E has a bad feedback or talk back problem. I've placed a capacitor across the overload relay (RY-5) and that did eliminate a little of the talk back. However, with much audio gain at all, not nearly enough to attain 100% modulation, I get feedback. Not just talk back, but feedback. I have to assume it's coming from the modulation transformer. The modulator bias is set for 40 ma as specifications state. The bolts on the modulation transformer are all tight. What am I over looking here? I'm using a BC-614-E speech amplifier with a D-104 non amplified mic. I did a few modifications to the dynamic input circuitry of the BC-614 to better match the D-104, but that is the only modification in either the speech amp or the BC-610-E. 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 __ 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
Re: [AMRadio] Modulator feedback
Thanks Mike. I just made a discovery about the 2A3 A-F drivers. I had a set of matched NOS RCA tubes in there. The feedback seemed to be coming from the area of those tubes more so than anywhere else. So, I exchanged them for another pair I have and it seemed to help quiet the feedback. Obviously, microphonics in the 2A3's is a factor. Next I looked for shields for the tubes, but have none, so I used a poor man's shield, a couple of pieces of aluminum foil. It helped considerably! As a matter of fact, I could then advance the audio of the speech amp enough to achieve good modulation. So, I am now on a quest to find some way of shielding the 2A3's. I'm afraid my temporary foil shields would cause the tubes to over heat, plus it's not the best way of doing it. Have you had any experience with this? I wonder if the 100th's are also part of the problem. I really think the talk back is coming from the modulation transformer, which I can live with. I just have to get the feedback out of it. Thanks for your assistance and advice, Rick/K5IZ Mike Sawyer wrote: Rick, The UTC may work so don't discount it. Those I and H model transformers were only about half the size as the D and E models. I can't think of the company that made them but they were substantially different then the earlier models. As always, your mileage may vary. Mod-U-Lator, Mike(y) W3SLK
RE: [AMRadio] Modulator feedback
How much capacitance did you use? It should be at least 20 mfd. A cheap electrolytic should do ok, since there is only a few volts across it. Put it between the midtap of the plate transformer and ground. The positive side should go to ground, and the negative side to the transformer. In all the BC-610E's I have ever seen, that capacitor eliminates 95% of the chatter. Don k4kyv ___ This message was typed using the DVORAK keyboard layout. Try it - you'll like it. http://www.mwbrooks.com/dvorak/ http://gigliwood.com/abcd/
Re: [AMRadio] Modulator feedback
Thanks Don. I used a 100 uf capacitor at 160 vdc, so it should be sufficient. I hooked it up exactly as you stated, positive to ground and the negative lead toward the center tap of the HV transformer. I wish I could say it stopped it, but I still have problems. It did stop a lot of the talk back, but the feed back is still there albeit not nearly as prevalent since I switched the 2A3 driver tubes. I made a couple of modifications to the dynamic microphone input to better accommodate the non amplified D-104, but I can't see how that would have anything to do with it. I can move the mic several feet away (it has a long cord - possibly too long) and turn the audio up enough to get 100% modulation on the scope. The 614 has a pretty high output and it takes little to overdrive the modulator. Rick/K5IZ Donald Chester wrote: How much capacitance did you use? It should be at least 20 mfd. A cheap electrolytic should do ok, since there is only a few volts across it. Put it between the midtap of the plate transformer and ground. The positive side should go to ground, and the negative side to the transformer. In all the BC-610E's I have ever seen, that capacitor eliminates 95% of the chatter. Don k4kyv ___ This message was typed using the DVORAK keyboard layout. Try it - you'll like it. http://www.mwbrooks.com/dvorak/ http://gigliwood.com/abcd/ __ 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
Re: [AMRadio] Modulator feedback
I'll bet you a nickel the bias supply has a problem, the plate supply for the 2A3s is not normal the plate supply is achieved by putting a negative voltage on the 2A3s cathode to raise hte plate to 360 volts. Sounds like the bias supply voltage is off. Check the manual and then the components that provide voltage to the 2A3s Jim WB2FCN YMMV - Original Message - From: Rick Brashear [EMAIL PROTECTED] To: Discussion of AM Radio amradio@mailman.qth.net Sent: Friday, March 17, 2006 6:10 PM Subject: Re: [AMRadio] Modulator feedback Thanks Mike. I just made a discovery about the 2A3 A-F drivers. I had a set of matched NOS RCA tubes in there. The feedback seemed to be coming from the area of those tubes more so than anywhere else. So, I exchanged them for another pair I have and it seemed to help quiet the feedback. Obviously, microphonics in the 2A3's is a factor. Next I looked for shields for the tubes, but have none, so I used a poor man's shield, a couple of pieces of aluminum foil. It helped considerably! As a matter of fact, I could then advance the audio of the speech amp enough to achieve good modulation. So, I am now on a quest to find some way of shielding the 2A3's. I'm afraid my temporary foil shields would cause the tubes to over heat, plus it's not the best way of doing it. Have you had any experience with this? I wonder if the 100th's are also part of the problem. I really think the talk back is coming from the modulation transformer, which I can live with. I just have to get the feedback out of it. Thanks for your assistance and advice, Rick/K5IZ Mike Sawyer wrote: Rick, The UTC may work so don't discount it. Those I and H model transformers were only about half the size as the D and E models. I can't think of the company that made them but they were substantially different then the earlier models. As always, your mileage may vary. Mod-U-Lator, Mike(y) W3SLK __ 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
Re: [AMRadio] Modulator feedback
Jim, you have a dandy idea there. The plate supply for the drivers is kind of weird. When I was going through the transmitter I replaced most of the components in the modulator section as most were out of tolerance. Maybe I made a mistake, I'll sure check. Thankfully, the modulator deck can be accessed (by standing on your head!) without breaking down the entire transmitter. If that bias is off it could sure cause some strange happenings. Thanks a million, I'll follow your advise. Rick/K5IZ James M. Walker wrote: I'll bet you a nickel the bias supply has a problem, the plate supply for the 2A3s is not normal the plate supply is achieved by putting a negative voltage on the 2A3s cathode to raise hte plate to 360 volts. Sounds like the bias supply voltage is off. Check the manual and then the components that provide voltage to the 2A3s Jim WB2FCN YMMV
[AMRadio] Modulator feedback
I've posed a couple of questions on some other lists and received some good advice, but I am still in need of more. My BC-610-E has a bad feedback or talk back problem. I've placed a capacitor across the overload relay (RY-5) and that did eliminate a little of the talk back. However, with much audio gain at all, not nearly enough to attain 100% modulation, I get feedback. Not just talk back, but feedback. I have to assume it's coming from the modulation transformer. The modulator bias is set for 40 ma as specifications state. The bolts on the modulation transformer are all tight. What am I over looking here? I'm using a BC-614-E speech amplifier with a D-104 non amplified mic. I did a few modifications to the dynamic input circuitry of the BC-614 to better match the D-104, but that is the only modification in either the speech amp or the BC-610-E. Rick/K5IZ
