That would be sad...i have not pulled the legs to check them yet. I did a test awhile back to see if they're leaking, they are not, still holding true to 13.8 continued through the entire system..i still have 6 or so components to replace on my list, play with some capacitance values, then I will pull the legs on the Toshiba's if I don't get results..
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Texas star 350dx high drive keeps burning input rf choke..
- Thread starter Myst-hic
- Start date
I hated to "like" your comment..but I must, 2 votes for bad transistor is nothing i can ignore.i will pull the legs next and give them a test...shucks..thank you for your input!
Are you suggesting that because I could not get my bias up that the 2879s could be fried? My parts cane in, I just replaced c17 with the schematic cap, I think .1 uf, anyhow my voltage just increased to 6.2!! In some ways that is good news, but even if my bias checks out now can they still be fried?
UPDATE!! c22 was shorted, I had 13.8 on my antenna out line. I replaced c2 and the l1 rf choke, went through series of tests for swr, pass through, the gamut. Hooked it up to my test am radio, powered up, no smoke!! 3 watts in, over 100w out, I noticed at that time dial a watt was not working, I wanted to turn it down..so, hooked to my uniden Washington, turned the mic gain to half so she wouldn't push as many watts, and proceeded to chat with my local friends, this puppy was killing it! I jumped at least 3 s units on report. About my forth key up the amp went into a dummy load pretty much, like a 2 watt output..recieve amp works fine, I can power off, just recieve amp on, and talk my regular watts from my Washington. So, transistors seemed to be fine...it worked for a bit, what now? Nothing looks burned inside..this is significant progress, but another step back, where do I go from here?
Key it up to test it again and check R5 and R7 near the transistors for heat or smoke.
Thank you shockwave, there is no sign of burn, the 5w/25 ohm was pretty darn hot though..i have since done a ton of testing, one final is reading 720ohm, the other 125...leakage is .8v at base before pulling the base leads to run the test..they are officially toast after pulling the 125ohm my leakage is still .4..so I have a choice, replace both or throw in my spare parts pile. My concern is, either age and sitting got to them, or there is still another unresolved issue that caused them to blow. My bias checked out perfect before I put rf in, it really did rock the house for 30 seconds! In summary, c17 fixed my bias voltage, c22 fixed my rf choke burn..that was quite the learning experience, I have enjoyed working on the unit..possibly it's worth putting another hundred into it in the future, but for now I think I will just buy a small amp to get me over the static. Thank you so very much for your time spent, 73s!
That was my dead key...when talking briefly with my buds they said I was the most powerful in the group, until it cut out..50 miles away on ssb, I was close to red for them..funny thing is, even running on one weak final the recieve amp still works extremely well. Thank you for your input!
Exactly! I get 1 watt out...even if one is getting me a good recieve amp, it's not pushing back for the output..well said..
The RX preamp functions completely independent of the transmit RF amplifier. They are entirely different circuits. One can work, or not, without the other.
Hey all, I am.gwtting my new finals in the mail today, I would appreciate any info you have regarding testing procedures before or during fire up tests. I plan to install, then check bias resistance and voltage again, then hook up transmitter with swr meters before and after the amp, check with power off, then check again with the power on, if everything goes well in that chain I will wish to transmit. Are there any other tests I should be doing before or during the procedure that I am.missing? Would it be helpful to add a bit of capacitance to c8 to buffer the input? I do not need full power, nor would wish to overdrive the unit...thanks again for tutoring me through this!
Another update, the amp now works, ish...i peak 100w, swr is 3 on input, in a series of hack tests if I pull the stacked mica I get the 100w, if placed I get 60w..that is a clue. Balance of input/output impedance I guess? I have replaced input choke, 25 ohm sandbar, played with c8 values, best I can achieve is the 100 watts and severe transceiver output shunting, I peak 8 watts whereas it does upwards of 20 normally. Everybody says "tune the input" well, other than shadetree's capacitor trim cap install there is little info on how and where to start..i must admit, I'm still a noob when it comes to reading schematics..i do feel accomplished and thankful to you all for helping me get it to this point, any cheat sheets to get that input swr down would be much appreciated! Also, the dial a watt really makes it bad if engaged..i read people saying "bypass" but see no instruction on how it is done..those are my questions for now, 73's!