11m and 10 m amp conversion to hf.  - Page 1
Forum section: electronics / rf-microwave

author: Jesset1996.5
author_rank: Regular Contributor
timestamp: October 06, 2016, 03:43:50 am
content: Hello everyone, im currently working on converting a 11m and 10m amp to hf and possibly 6mjust for kicks. It uses 7 24lq6 tubes in a 2-5 configuration, it was designed to put out 700w with 5w input from my understanding but is capable of much more.It also has a rf relayand no keying line which i might use only when the radio im using has no relay line(like the prc 320, 0r the vrc 321 that i own)I will be adding a relay line. posibly 1.2kw could the part that im confused and need help with is the tank coil and the band switching. I understand that the band switch simply changes taps on the tank coil but im stumped on how exactly i get the length and the taps on the coil right. Also i would be replacing the original band curcuit with a much larger one if i understand correctly right? I can draw up a scematic of the rf curcuit if needed however i do not have any equipment yet to measure the values of any coils. Im an electrical engeneering student but im new to building and modifying rf equipment. AC8WP

author: ChristofferB
author_rank: Frequent Contributor
timestamp: October 06, 2016, 09:40:12 pm
content: When you say "hf" what exact bands are you talking about? 11m is already in the HF region, and 10m is right on the edge. I assume you mean lower, ham stuff like 20m, 40m, or so?Depending on the tank coil's construction, you could just calculate the number of turns needed for your specific bands. and get pretty close. Or build a jig for measuring inductance.

author: Jesset1996.5
author_rank: Regular Contributor
timestamp: October 07, 2016, 06:17:46 am
content: I intend on going to the lower end of the band yes. the plan was 160 -10. Im guessing i would have to just replace the tank coil but for 80 and 160 i do believe i would need caps. I should probably draw out the scematic and post it on here just so everyone is on the same page. Unfortunatly i am new to building rf equipment so its problably best i post a scematic.

author: CJay
author_rank: Super Contributor
timestamp: October 07, 2016, 07:33:45 am
content: I'd suggest having a look at a few websites like this one:https://pa0fri.home.xs4all.nl/Lineairs/Frinear750/FRI750uk.htmHe has a vatriety of designs for valve based HF amplifiers which show the coil construction in great detail.

author: Unknown
author_rank: Unknown
timestamp: October 07, 2016, 09:45:58 am
content: To answer your question, the output LC circuit is just a low pass filter and serves 2 purposes:1) To filter the harmonics and clean up the output2) To match the impedance of the valve anodes to the 50 ohm aerialCalculating the L and C values is thus just designing a low pass filter with an output of 50 ohms and an input of whatever your anodes are sitting at. The anode impedance depends on the power output and the peak voltage applied.If your amplifier is a single band CB set, it might not be this simple however. You will likely need to provide a tuned input stage for each band with attenuation to compensate for the increased gain (depends on what circuit arrangement is being used). You will also most likely need to change the anode choke, especially if you want to go down to 160M. The choke must have a high enough impedance at the lowest frequency so as to not load the anodes and have no self resonances in any of the frequency ranges you will use and of course be capable of passing the peak anode current without burning up!I'm sure you're already aware that the power supply in that will kill you without asking so take care.I'll second taking a look at PA0FRI's web site. I built a variation on his 150 Watt design and it works great, there is lots of good info there.

author: cncjerry
author_rank: Unknown
timestamp: October 07, 2016, 03:54:21 pm
content: I would make sure that amp isn't class 'C' biased.