ZETAGI B300P - TRANSISTOR REPLACEMENT -MRF455.
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- Опубликовано: 27 авг 2024
- ZETAGI B300P in need of new transistors, owner admits to over driving the amp which destroyed the SD1446 original devices.
Using MRF455's as replacements which were the original devices used in these amps before they were discontinued by Motorola. 
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did you try the 100 watt transistors it would be interesting too see the results
It's best to remove the transistors to test them correctly, i recently repaired one of these where the relay would not switch in on TX but it was just a dry solder joint on the board.
The only issue could be matching which may require some cap changes but it would be worth trying first to see how it works, i may have a RM-KL500 coming in shortly so may give it a go myself....
i've already got a matched pair and just bought another matched pair as the 550 runs two matched circuits, i'll give it a go and see if it works..
also changing the input resistors may make it handle more input power, so i'll have a look into it..
i already have an 8 pill using 2SC2879 so wouldn't be to hard to possibly get some measurements from that..
@juckelscorey According to ZETAGI the input power should be 1-10 watts AM/FM and 1-20 watts SSB, this is for settings 1 - 5.
I have a few of these kicking around, will probably improve the bias circuit, the temptation to use my FT817 in the car with a tray of amplifiers is getting too much.
I loved Zetagi
I wounder what happened to zetagi after the CB era.
It was quality, it was the best transistor amp ofcourse not as good as the electron tube amps
I think they are 15 ohms, they are colour coded brown-green-black.
Hope this helps.....
Another good vid
Right next to the on switch i see a little 1/4" inch jack. What is that there for?
What about the Zetagi B5550P ??
runs four MRF455 all blown, only did around 200w, was going to change to MRF454, but then can use 2SC2290 as a replacement..
so what about going the whole hog with four 2SC2879 ??
on paper then seem to be all around the same with voltage differences from 40v to 50v to 60v amp and current seem around the same..
so what you think, B550P with four 2SC2879 ??
should see 300w at 10w drive...
can you see any problems ??
thanks mark all done with new resistors i have also put in pair of
MRF 421s i will let you all no the outcome in a few days
sorry no way of making a video :D
nice but I just rather use my yaesu stock power and use a nice clean microphone.
Danita CB similar to the ham multimode 2 tight :)
cant tell what colour they are :D burnt too badly but on the opposite side of the front board there are 2*47 and 2 *27ohm
anyone got the schematics for the front board on the zetagi B300p i can find loads for the main and rear boards but not for the front
i basically need too find out the value (ohms)of the 2 resistors on the far right of said board behind the selector switch as you look @ it from the font
I love this vid !! You give the operators a well deserved spanking !!
throw the crap away, class C Amplifier are ok for FM but not worth in AM/SSB
I tried a lot of those Zetagi Amps.
Afaik there are no Zetagi Amps with AB Bias circuit available.
I suggest spend a little more money into a quality brand, maybe 300$ for a good 100W Amp. believe me, Zetagi sucks!
my 455s seem to be gone and am going to try the 421s any tips :D
I have one of these how do I get the most out of it on sideband? I have a superstar 3900f and a lincoln! just getting back into the hobby and thinking of buying loss loss coax but to make my b300p last?
haters gonna hate, i wounder why he approved your comment
Remote power switch.
A lot of those cheap Italian amps are biassed more like class C than A or Ab, hence they sound like shit when used for SSB & AM. You may get near 200 watts from a couple 455s, but it'll be a dirty old 200 watts & on a scope it'll be ugly.
I usually mod the bias in these amps to put them into Ab, & while you lose some output power, you sound much nicer, you gain a pretty picture on a scope & happy neighbors on a crowded band. No kidding, these things are wide. Better output filtering is nice too.
get a hd cam
What a waste of transistors lol
italian schrott!!!