Great video, learned a lot! I'm still classified as a "newbie" to electronics, but it's videos like these that go a long ways in teaching the skills needed for ham radio operations. Thank you Tom!!!
what should be the setting of the loading capacitor during the passive test ? should both plate tune and loading be varied first until maximum feedthrough is obtained ?
Thank you for clearing up so much of my confusion with tuning my LA! I was intimidated by it and always worried about damaging the tubes. Your clear explanation has saved me a lot of worry!
I found your video while researching an issue I'm having with a new ALS-500M. Powered by the Ameritron SPS-75MV, its meter registers nothing at any power setting, on any band, when the IC-7300 is keyed, even though the ALS relay clicks clearly. Any ideas? I would be most grateful.
Was the TOF always in the AL-80B? I had one about 14 years ago, but only for about a year, and I don't recall ever seeing a red light come on. But having owned two AL80-A's if many years, I always kept an eye on the grid current when tuning and stopped before hitting max. I pulsed mine with the CW keyer for tuning. 73 DJ0IP
I can't not express how much knowledge I've learned from you over the years, sir. Nor can I thank you enough for the patience in which you teach, especially with "dummies" like me, or "newbies". 73 DE N4ZAW
Tom, what would prevent me from getting Grid current above 40mA on my 20Meter range please? My 40m will get >150ma Grid & >450plate? Thanks great video. So many other videos talk of peaking plate & not grid. Any help would be greatly appreciated
My Amp is 25 years old. I have no clue how long both of my needles have been moving in unison! My output has dropped to just almost 400 watts and I thought it was just weak tubes ( probably still is) but I have ordered a 1N4007. Thanks for the insight.
No. A copper spreader is not necessary with four and the transistors spread out over the heatsink. If all of the heat was in one spot a spreader would be required. The major thermal issue, if the heatsink finish is good, is thermal resistance inside the transistor.
Honestly, I went from not having a clue on how to set up a tube amplifier to completely understanding from this video. Amazing presentation and perfect layman explanation, thank you.
Tom, I just want to thank you for this video! Dang, the manuals and other well-intentioned hams would have new-to-amp folks like me thinking that proper turning is some kind of esoteric activity. You have simplified it quite a bit. Question: I have an 811H that I picked up used and will be installing a new set of 572B tubes. What mA value am I shooting for with the 572's? Thanks for your videos. They are very helpful. Sub'd.
If I follow the procedure in the video works flawlessly and I get the 800 watts (happy about that) but then when I’m reading the manual it says about never exceed 80 watts so that confuses me because I want to treat well the amp but with 80 watts I don’t get more than 550watts. So do I trust the manual that should be the gospel or this video?
I have one that i convert to GI7B tubes but i would like to ask you about the transformer, do you use the stock one or something different? I can't decide if i will use a bigger external power supply or the stock transformer. Thanks, Chris
I have a AL-811 Ameritron amp. For some reason, it started blowing fuses. I have 20-amp fuses in it and it runs on 120 vac. I just put 3 new tubes in it today. It tuned up ok and had a idle plate current at 60 ma like it supposed to have. Everything seemed ok and I made one short contact and after setting there for a few minutes it blew both 20 amp fuses. I wasn't even keying the mic or anything. Looks like I changed the tubes for nothing. Any ideas?.
Thanks Tom for uploading this very informative video. I don't have an AL-811H, but some of the content is applicable to my amp. I have the following thoughts after watching it: 1) How is the 200 ohm value of the resistor that is added to work with the neutralizing transformer determined? (E.g., if one desires to have less effect on gain, would a lower resistance such as 100 ohms be appropriate?) 2) For some of us, a quick pictorial to illustrate the suggested circuit modification (such as the insertion of the 200 ohm resistor mentioned above) would be useful during the explanation of each modification. 3) Good point about the potential problem with loose/overlapping windings on the plate choke. The next time I have my amp open for maintenance, I plan to check the security of my plate choke windings.
I have been afraid of a tube amp due to this issue with the tuning. But at the price point per watt it makes sense to get the tube type. A solid state is ok but then they get you with the power supply and screw that. Not paying another grand for a power supply. Thanks for the good info
Hi Tom, quick question, I had to replace the tuned input board on the 811h I picked up. Tuned input was fried. The new generation board seems to have a different hookup location for the blue grid wire, which was by the relays, and is now marked to place by the rest of the wires by the transformer side. D16 is fine, loads fine with palser with full output, but I get no or very little grid current, lol, did that make sense? Is it correct that they changed the grid, blue wire that goes straight to the grid meter, from the relay area to the string of wires connected on the right side of the back board, thanks Tom for all your help.
Hi Tom, in the event the diode is open would it be possible to have a trigger circuit that turns on an led using the votlage ir current level present when open? It would only indicate an open diode while doing your test scenario, not used or pay attention to while in normal operarion? Jim WB8ZLK
Honestly, in over 50 years of doing this and using that form of protection, I have not ever seen a diode open. The only common diode failure is a short. We use a 1N540x or a 6Ax diode to improve immunity to shorts. Mostly we use a 1N5408 (because we stock them by thousands) or a 6A10 (because we stock them) in real big amplifiers
@@Jerrythenerdful ah ok, could think of a way to use the potential difference that is present when diode is ok but then adding anything into this pathway adds more potential for shorting failures, where the simple test you suggest just needs to become SOP.
I like the idea of tinning the braid before cutting it back, which keeps the braid strands from fraying out before cutting. And by scoring the tinned braid annulus with a blade it leave a clean end as opposed to picking the braid strands apart and then cutting them with a scissor. But this technique only works with a teflon dielectric, as you have noted.
Tom, let me make some suggestions. 1.The PTFE outer sheath is really tough and not easy to slide out once the circular cut is made; yes, you have to make the longitudinal cut and split it while removing and at the same time you should not damage the double layer braid. It is better to trim the shield and then tin it. Using a plier to rip it off is not a great idea, though. Again, to expose the required length of center conductor one has to cut through the tough PTFE dielectric carefully lest the chances that some of the strands are lost. And once exposed, it is better to tin all the strands in one bunch at once. 2. Please get the camera focus right and see that you do things within the camera field. 3. Please avoid the annoying AC hum picked up in the audio. De VU2RZA
I would like to see the rg 400 coax and reducer assembled . How do you stop the cable from rotating at the reducer . heatshrink works. i am speaking of on - off and constant movement. Tape works ok . It is basically tolrence in the reducer. It is hard to get a reducer that will fit tight............
