my profile | my password | search | faq & rules | forum home

» Film-Tech Forum ARCHIVE   » Community   » Film-Yak   » Plates overheating on a 4-400A Tetrode (Page 3)

This topic comprises 4 pages: 1  2  3  4

Author Topic: Plates overheating on a 4-400A Tetrode Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 01-24-2003 02:51 AM                     William, that last paragraph describes my predecessor exactly to a "T"! He was a very brilliant person, and a very kind and passionate human being. Unfortunately, he has passed away as a young man in his late '40's of an illness. I really admire that person, he would give you the shirt off his back if you asked for it. As a young lad, he had Polio, and he was very crippled, but yet, he forced himself to walk. If he would lose his balance and fall down, he would just pick himself back up and keep going like nothing ever happened. He had a golden sense of humor, and always had a smile on his face, and had a kind word for everyone. I have known him for 15 years, and I have NEVER heard him say so much as an off-colored word. Swear words were not in his dictionary. When he passed away, it was a sad day and a great loss to all of us that knew him. I would like to think that the reason why his workmanship was not the greatest in the world was because he was always in severe pain, but he did not let on to it. If you saw him work and worked with him, you would automatically know what he was going through. Sometimes I seem to forget that, and in one post I did. After feeling like a fool, I edited that post.  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 01-25-2003 03:50 AM                     Update: Power-up by itself worked as advertized. Power down time, well, that's a different story. Seems like the plate contactor does not want to release when the power is removed from it's coil. First, the damn thing does not want to power up! Now when I fix that, the damned thing does not want to power down! Jeeze, that's worse than a woman!!!!!!! It can't make up its friggin' mind!!!! Jeeze, does it want an egg in its beer, too? Now I have to find a contactor that will last another 40 years (but the way this crap is built these days, that will probably never happen).....Maybe I can dress the clappers to buy some time....The Saga continues.... 'Ya know...This is really fun and challenging to work on shit like this... But it is stressful...one slip and I am off the air. It is all a calculated risk. So far, I have been lucky.  |  IP: Logged Kenneth Wuepper Phenomenal Film Handler Posts: 1026 From: Saginaw, MI, USA Registered: Feb 2002 posted 01-25-2003 06:58 AM                     Paul, You are doing this work in the right spirit. You love the pressure and it feeds you. We restoration people in the theatre world have enjoyed a rush from time to time as we get the old organ to play as it was originally intended. Sometimes it is a piece of lighting or sound equipment that we restore. The theatre restoration is likely to be more costly in terms of ingenuity as there is less of the green stuff or it has to be sought through donations. Broadcast electronics is a very nerve intensive business and you are right to look at all of the alternatives before making a move. By the way, do you play chess? It is a good game to sharpen your mind for these decisions you are making. It helps to anticipate what could happen a few moves further up the road. I can't tell from your photos but am I seeing a few new grey hairs from this one? KEN  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 01-29-2003 01:17 AM                     Well, I finally got my coupling capacitor. I'll change it tomorrow, and see if it helps my modulator drive. I didn't get the feedback ladder capacitors yet, but I'll report on the results of the coupling capacitor change.  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 01-30-2003 06:50 PM                     I changed the capacitor today, and it did help the modulation a little. However, I am still driving a little too hard to get the desired modulation.  |  IP: Logged Kenneth Wuepper Phenomenal Film Handler Posts: 1026 From: Saginaw, MI, USA Registered: Feb 2002 posted 01-31-2003 07:31 AM                     Paul, How are you coming on the overcurrent in the quiet state problem? I thought you had made some progress there also. I suspect that you have several problems which are in that modulation power output stage. Did you say that the screen voltage was too high? I believe that the tubes will act more like triodes as your screens approach 50% of the plate supply. The bias should be adequate to keep those tubes near cutoff before they are driven with audio. Did you measure the actual bias from each grid to the high side of the cathode metering resistor? That is the actual grid bias on those tubes. If they are still glowing then the tubes must be bad. (Gas inside the envelope) Still interested in this one! KEN  |  IP: Logged Bernard Tonks Jedi Master Film Handler Posts: 619 From: Cranleigh, Surrey, England Registered: Apr 2001 posted 02-10-2003 05:30 PM                     I thought this might be of some interest to Paul and others on this thread. It is an aerial system, with transmitters and generators on an unmanned platform six miles out at sea. www.longwaveradio.com View Engineering.  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 02-10-2003 08:31 PM                     Ken, I temporarily "bagged" this one. The transmitter sounds really great on the air, has a nice warm "punch" at the low end, and a very nice clean high end. Since I replaced the capacitor on the output of the modulation transformer, the transmitter does sound much better. The transmitter has a better "splatter" specifications than the old Collins, and both transmitters meet FCC requirements. With no audio applied, the plates of the 4-400's cool down, to almost no glow at all. The quescient cathode currents of the modulators and RFPA's under those conditions are very normal according to the manual. However, the harder I drive them, the hotter they get. But as long as the transmitter sounds as good as it does, and it meets all FCC specifications, I'm gonna let 'er run. So I fry more 4-400's - I suppose for high lever plate modulation, I can expect that. The 2 used bottles I matched up seem to be holding their own very nicely, even though they do get hotter than hell. At least, according to the meter readings of today, they have not lost any ground.  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 10-08-2003 01:26 PM                     Bumped for Luciano. Last night, the 4-400 on the right finally went Pbpthbpthbthp! Flatter than a pancake. No cathode current whatsoever. I had a used one and was able to balance. (quick fix) I have two sets of new 4-400C tubes, but I have to check the ratings on them. I am concerned they might not have enough balls. My RFPA'a may be getting a little flat also...Although my RF line current is normal, the negative modulation is about 90% but the positive modulation - that's a different story. If I can get the positive modulation to peak 60%, I am lucky.  |  IP: Logged Jack Ondracek Film God Posts: 2348 From: Port Orchard, WA, USA Registered: Oct 2002 posted 10-08-2003 06:24 PM                        Paul, those "C's" ought to work fine. We usually made a point of replacing "A's" with them, because they seemed more rugged (I don't recall the specs, either). What kind of final readings are you running? Those mod figures are really whacky.  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 10-08-2003 06:53 PM                     Yes, Jack. The readings are really screwy. I just had a shorted 4-400A in the Collins that practically blew the transmitter out the back door this morning. (damned used tubes) I did replace the 4-400A's with a new set of 4-400C's in the modulator holes and they seem to be performing OK. I checked the specs on the "C" version, they should do just fine. The Collins is happy again and making 10,000 watts. For how long remains to be seen.....that's a good question. The next thing to go is the 3CX-10000 - that costs about 1800 bucks now... The remaining new set of 4-400C's I have will be stuffed in the RFPA holes in the ITA. I suspect that will bring my modulation back up to where it belongs. The modulator drive seems to be ok and balanced, so I suspect one of the RFPA's is going goofy. It has all it can do to make 1000 watts. Power change coming up at 1830...I am going to stuff the tubes in there and come back and have my screwdriver handy for screwdrivergetwitzen adjustments to adjust the RFPA Ig current and dip the plate before the 500 bucks worth of new tubes burn up. As an edit, I did stuff the new 4-400C's in the RFPA Holes of the 1KW transmitter. With screwdriver in hand, I got the adjustments made very quickly at power change time. Only one thing. The transmitter output was too "Hot". If I detuned the loading, I could have brought it down to 1KW, but the RFPA Plate current would have been too high. Don't wanna burn up 500 bucks worth of tubes. To add insult to injury, the power ramping motor does not work. It is jammed and stuck. Result was I had to reduce power by using the hi-low toggle switch instead of the ramp motor. I had two options: 1250 watts or 800 watts. I elected the 800 watts until tomorrow when I can fix the ramp motor and the plate current meter. The meter sticks so badly I have to constantly beat on it with the back of my screwdriver to make sure I was getting the correct reading. Gee...Isn't old equipment fun? [ 10-08-2003, 10:19 PM: Message edited by: Paul G. Thompson ]  |  IP: Logged Luciano Brigite Master Film Handler Posts: 277 From: Sao Paulo, SP, Brazil Registered: Jan 2002 posted 10-08-2003 09:27 PM                     Thanks for bumping it up Paul and good luck in having the transmitter back at it's top performance  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 10-08-2003 10:23 PM                     Yeah...nothing like having a dead 10,000 watt transmitter and a 1kw transmitter that had all it can do to hit 60% modulation. Makes for "nice coverage" of the area...and makes the owner quite nervous. Anyway, both the 10,000 watt transmitter and the 1000 watt transmitter seem to be very happy at the moment. Now it is "MILLER TIME" Miller Low-Life...The Champaign of Bottled Pee....now you know why I drink Busch or Budweiser... Same Shit...Different Shovel...  |  IP: Logged Jack Ondracek Film God Posts: 2348 From: Port Orchard, WA, USA Registered: Oct 2002 posted 10-08-2003 10:43 PM                        quote: I did replace the 4-400A's with a new set of 4-400C's in the modulator holes and they seem to be performing OK Glad to hear it all came back up for you, Paul. Is that correct? You're using 4-400s for modulators at 10kW? My favorite old combo was a pair of transmitters I had in Yakima. This one was the 1kW standby. We had the 5kW version of this design (wish I could find a picture of IT) sitting next to the standby (892R mods & final), which made for a transmitter chain about the length of that Ampliphase you were talking about.. I really liked those transmitters. Lots of metering... and all tuning adjustments were motorized. Parts, like that oscillator box, were interchangeable between transmitters. Though we could run the standby on our psa power (a whopping 86 watts), they usually just dropped the 5. We dumped the remainder of the 1kW output into a resistor load, which was mounted back in the "cage", and kept the whole transmitter room toasty!  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 10-09-2003 12:24 AM                     Jack, there are 4 each 4-400's in the Collins. Two of them are drivers to the 3CX3000 modulators, and the other two serve as IPA's for the 3CX10000 final RFPA. The Master Oscillator drives a 6SJ7 buffer which in turn drives an 807. The 807 drives the parallel configuration of the 4-400's that serve as an IPA. The transmitter employs plate modulation. The outputs of the 3CX3000's feed the modulation transformer which in turn injects the modulated signal into the plate circuit of the final. The two "400"'s that drive the 3CX3000 push-pull configuration receive the audio signal from the two push-pull 6SJ7 audio amplifiers.  |  IP: Logged

All times are Central (GMT -6:00)

This topic comprises 4 pages: 1  2  3  4

Printer-friendly view of this topic

Hop To: Select a Forum: Category: Operations -------------------- Digital Cinema Forum Film Handlers' Forum Large Format Forum Ground Level Feature Info, Trailer Attachments & REAL Credit Offsets Category: Community -------------------- Film-Yak Film Handlers' Movie Reviews The Afterlife Bob Maar's Joke-A-Thon Category: Classified -------------------- Equipment and Supplies Wanted/For Sale Help Wanted/Seeking Employment Category: System -------------------- Software Beta Testing Forum

The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion and agrees to release the authors from any and all liability.