You're the only one that's had the balls to show the world how this is done. Poorly written articles by many hams go way over complicated on explaining with no visuals. But no one has come forward with a video. Until now. I know I speak for countless newcomers in saying: Thank you
This mod is worth doing to any 500Z amp that uses the caps/chokes on the grid pins. An RF engineer Tom Rauch W8JI also backs up what Luke is telling us here so this is not snake oil. I did this mod to my 50 year old 220 and it's never missed a beat since. Having rebuilt a few 220's myself, I enjoy watching Luke work on them too. I've been into radio for over 45 years now, both CB and ham radio. One of my first jobs was working in a CB shop back in the 70's. I can remember when an amp like an SB220 was a monster and only the "Big Guns" had them.
Back in the day...the D&A Phantom was king, until CBers learned that they could use ham amps by driving them with a smaller amp. Ham amps don't have an internal keying circuit, and require a pair of "dry contacts". Some guys added a foot pedal. Other guys added an Ameco PCB receiver preamp that just happens to have a set of dry contacts on the back. This development alarmed the FCC, causing them to force ham amp makers to remove 10 meters and prove that the amp was inoperable above 24 mhz. Well... Along comes the new WARC 12 meter band, and of course hams want to run power, so the manufacturers provided kits to add 12 and 10 meters, upon presenting proof of a license authorizing that power level. Technician class hams need not apply.
Thanks a milion man. I bought just last week from ebay Europe two Heathkit sb220 linears, one in pieces, one complete and i just ground the grids on them. Sad enaugh 3-500z in europe kost legs and arms so im forced to replace them with QB3,5-750 tubes. I know it will be less power but price vise its better option as im gonna sell one and keep other for me.. I have automatic switch board for high voltage tube amplifier with timer so im planing to intercept Primery transformator windings from High voltage and make him start 5minutes later then compleet amplifier so tubes have time to warm up before they are hit by 3000volt. Regards
Thank you for taking your time to make this video..I watched you prior work on several different 220's which on one you showed this and never could find it again..big wave from Tatersalad.S.C..73
Real good info, i appreciate the time you take to explain stuff in your videos. The amount of knowledge i have gotten from your videos, if i had to pay $1.00 for everything new i learnt i would be brokes lol... Thanks much....
Thanks Luke I finally got the concepts of the grounding.,.well I bit the bullet and bought a Henry 2 kd classic .it's a piece of crap..it worked long enough that I'm rebuilding it. It needs work but it blowed a cap . someone unhooked the ALC. And with new strength of mind and taking a 3000 volt hit off a palamar 300.. I'm driving into a Henry...might hollar... 505 ridgerunner and I'm back quiet and back to the drawing board
@@imarat21 I'm trying to get the little 105, and the 505, so I can have complete set. But the funds are unavailable at the time. I was told from a old timer that you could use the 105, to drive the 305, then both into the 505. Not sure but would love just to have the set
Another problem, as discovered by tramdr, is that over time the tube socket connections used by the filaments overheat and lose their grip on the tube pins. The heat causes the metal to lose its temper and it ceases being springy. Squeezing the socket together with pliers in an effort to improve the grip often results in the metal breaking. So...if your amp's tube sockets are blackened from overheating just plan on replacing them. It's the only way.
Hello mister.I write you from Greece (Hellas). After 16 years i want to make AM station. I show some of your beautiful video's.Tell me please this is the right way to ground all the tubes ? And for high voltage which diodes must youse and how many for the bridge. Ευχαριστώ να είσαι δυνατός
I prefer to ground my grids via flat copper bar bolted directly to the chassis and soldered to the tube socket clips. Very easy and very reliable. YMMV.
My SB220 choke on the inside 3-500Z burned up. I'm grounding my grids. Thank you for your video. My SB220 was butchered by many people before I acquired it. I'm basically going through it and rebuilding almost everything. I'm installing the W7RY Qsk upgrade. For ALC and bias I like your way of using full wave bridge rectifier and upgraded 47 uf capacitor. I'm doing Harbach capacitor upgrade and rectifier board and W7ry soft step start board and I'm using two vacuum relays for the Qsk board. I have 3 Eimac 3-500z's. I'm a long way from powering up. Are the 3-500z's toast after they flare up?? How do I test them when I'm done with my rebuild??
I'm sorry because I'm ashamed of myself for laughing at other people's misfortune but, the stories (10:45) of the stubborn guys not grounding their 3-500Z Grids is downright comical because it's so absurd. I'm an engineer with 50 years of hands-on electronics experience with years of semiconductor manufacturing equipment exp. using high voltages up to 225 Kilovolts. I've got a very sharp friend, Dave who said that he wanted to learn about tube amps because he'd never owned one. Among everything else, I told him that he needs to correctly ground the Grids of his 3-500, 811 and 572 tubes and why. There's DC grounds and RF grounds with phase angle to consider in the latter. He did some additional self-study and came back talking about Q-points and Neutralization and never had any trouble at all because he's someone who has the intrinsic intelligence to be safely putting his hands inside a potential Widow-Maker and emerging successful. Sadly, I think there're others who should simply stay out of these amps so they don't end up dead. I mean, if the guy can't even follow simple instructions or refer to reference literature, such as the Radio Amateur's Handbook circa 1966 (i.e. Read), he could kill himself. My buddy Dave can now make any vacuum tube linear amp purr with > 50% more than originally designed power and, he's never been shocked or RF burned by them even once. I'm the same way.
You do want to use a choke and some capacitance to isolate the grids on the 572b 811a tubes if you're going to operate them down in the lower frequencies what I'm talking about his 160m or 80m. Remember the 3-5 hundred Z is a little bit newer tube completely different design
@@BoxBuilderIdaho Oh yeah because of the single, long, thin wire inside the tube assembly that comprises an inductance in series with the Grid. That inductor can develop an RF voltage across it and at a particular frequency provide a 180 degree phase shift to that voltage so that it ends up being positive feedback to cause oscillation in the 811 and 572Bs. Thanks for sharing your videos. They're great.
WRONG The wires are way too small in diameter and highly inductive at parasitic frequencies. Pin inductances are what resonate with internal and external capacitances in and around the tube to cause oscillation. Adding inductance is NOT correct.
Hey you're back welcome back its my negative RU-vid commenter.. the guy that has no operating examples of stuff that he's worked on nor does he have a RU-vid channel of any kind.. well like I said on the last two negative comments that you've left me on other videos. I appreciate your viewing..
