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Rebuilding another LK cap here and another Plate Tuning cap with nasty pits and therefore....arcing. Any info to secure those rotor and stator plates appreciated. Rich k0zx

Hi guys, I have been subscribed to this list and reading messages for some time, but I believe this is my first message, so hello all. I am a ham based in the UK and have been interested in amplifiers for some time. I have a somewhat basic understanding of their operation if I'm honest, and currently own a linear amps UK 811 hunter. It uses 4 off 811 tubes, and runs very well. I understand 811's are somewhat delicate, and so I tread lightly with them. I have always had a notion of building my own hf multiband amplifier covering 80 to 10 ideally. I have been gathering parts that might someday be useful such as hv transformers, power supply hv capacitors, door knob caps of various values and some big vacuum caps etc. I don't have everything, but I guess I'm on the way. This approach makes things seem less expensive :) . When it comes to tubes, I have also managed to collect some "interesting" items. I have a 3cw 30,000 and some gu5b's. The 3cw30,000 is clearly way too big (is there such a thing :) ) but the gu5b's might be about right. With the power supplies I have I can supply options. 2.8kv DC, 4.7kv DC, 5.5kv DC. All from a 20kva rated transformer, and voltages quoted are bridge rectified at zero load, not voltage doubled, so I have plenty of supply capacity. I could tweak things to get intermediate voltages if useful. I am yet to collect filament supplies, and the thought of a 6.3v or similar high amp supply puts me off so I guess that rules out the 3cw30,000 or similar. I have been told to start with a triode amplifier as a tetrode is a much more complex beast, which with it's screen supplies etc I can understand. I have good metal working tools and equipment (Bridgeport mill and welding kit etc) and some electrical test kit including HV probes and a nano van and an old scope. Anyhow, I'm keen to learn as much as I can before I start off on this adventure, can you recommend any good books that are practical in their approach to hf amplifiers? I don't mind maths, I'm an engineer , but practical examples helps set context in my mind. I have seen this diagram (attached) to an amplifier based on 2 off gu5b tubes. Obviously input circuits aren't described, but I guess it's a start? Goal is something that will easily do the new 1kw UK limit. 2kw might be a nice max power rating. Am I mad? Seasonal greetings all, des.

Ok, how does one go about building a tuned input for a 144 mhz amp, using a YC-156 tube ? The input C on the YC-156 is huge, 92.5 pf ( grid to cathode). This is for a cathode driven YC-156 ( The 1/2 wave tank for the output side is fine, and tunes up fine, with calculated RL.... to the 50 ohm output.) The output is not the issue, it's the input. What options, if any, do we have ? What's the fix ? Jim VE7RF

Metering, Power Supply, control circuitry, everything from the utility input to the HV of your choice. 230vac Single phase HV transformer rated at 1 amp continuous at 3000/3500/4000/4500 secondary 197/208/219/229/240/251 primary Currently on 97 Mhz six meter or two meter conversion or add your favorite tube(s) for 160-10 meters. Don W4DNR W4DNR

Hi Everyone, I built this little 2m amp a couple of years ago, it works perfectly in every way..... except for the thermal drift. Tuned up with key down, 300W out with 12W drive, within a few seconds it droops to under 150W. Keeping the power up requires *constant* re-tuning of the plate. The drift is so fast I think it must be within the tube or close to it, there just isn't time for the tank circuit to heat up. I don't know if I made a mistake in the engineering of the tank circuit, or if the tube is faulty Open to all ideas about how to fix it. Thanks Tim G4LOH

Tim and anyone interested : Here’s looking inside the RF box. You can see the original blocking cap - just like yours ! This is a YU1AW “Lazy Builder” design. Suited my construction capabilities perfectly ! You can see the thick Teflon sheet insulation between the tune (right) and the”load” caps. I was so dumb back then, I thought I could adjust the loading like a HF triode amp. As Lou said, we all still learning about amps. The lower pic shows the RF box inside the amp cabinet. The large blower feeding cooling air into the bottom of the RF box, Russki REW14 input and output relays, many 6A10 diodes for operating bias, toroidal filament tranny, metering, etc. are visible. The only other stuff up I made was not using proper terminated cables for the input and output N-Type connectors. I’ll fix that soon. Good luck with it, and let us know how you go. Cheers, John VK6JX

Tim - here’s what happened to my 2200pF blocking cap. Cracked and a little burnt. This caused ALL of the “thermal” power output drift in my 2m amp. She’s rock solid now, for complete JT65B overs. Love it ! John