Glowing 3-500z's are beautiful and do a great job. The tubes in the picture are over 40 years old and still have full output. To keep them working that way, tubes of any kind must be operated correctly.
Hi Jim, Hope you are doing well. Thanks for the refresher. I think it was in the 90's last time I tuned up the SB-221. Shouldn't be much longer it will be back on the air as an SB-220. Stay safe. 73 WJ3U
I always tune plate for maximum grid current and load for maximum output within the specified limits for those currents. With tetrodes for maximum screen current of course.
"Sincerely Yours" From W1VTP, Al. The answer to your question is no - but there is a procedure as delineated by Jim that *must* be followed to reduce distortion products (some say 'splatter' - I don't agree with the term but an adjacent 'channel' user, splatter fits the bill. I follow Jim's approach - feeding the output into a 50 ohm termination that is built for the job. A final thing I do is using a scope that has a trapezoid mode - I transmit a full power signal with an extended "FIIIIVE', 'SIIIIX' while watching the trapezoid pattern. The unparalleled lines should be straight with no bending at the top of the trace. Any bending of the lines should be either a biasing or more likely a non-linear output due to a bad tuning sequence and the whole procedure might have to be done. I have achieved greater than 1,500 watts on my termination with a pair of 3-500ZG's. Jim could done things slower but watch his original video that goes into more detail. I have normally achieved > -50 dB/ full output on my distortion products on my amplifier.
My L4B puts out about 1200 watts when tuned. While the 3-500 tubes will put out more power safely many of the older amps were designed when the input power rule was 2000 watts and that meant the output would seldom go much over 1200 watts. The plate voltage of that era was the limiting factor. The 3-500 needs 3000 or more volts to put out the power. To be legal back then for SSB you had to tune up on the antenna on the low voltage setting and then switch to the high voltage for SSB and not retune.
Interesting. Does it appear to be rather finicky or is that normal when tuning these amps? Also, are you keying a mic or something in short bursts to keep the amp from delivering constant max power, or is that an effort to keep the dummy load from overheating, or both? Sorry for the newbie questions - it's because I are one. ; )
Hi... I'm a Spanish follower of yours. I have a request. you could make a video about the equalization parameters of the equipment with the micro. Cheers
Some times there is more than one path. Some times the amp, even at low power, has huge IMD issues and distortion due to poor tuning and overdriving. Some times they are using tons of processing. 73, Jim
