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Maco 300 help !!
- Thread starter kenny1971
- Start date
Burned the choke there.
There are two versions of that amp. The B and the M. I think it is a 22 mh but can not remember and i am at work and not at the plant.
You will see your has two chokes the same. Lower left hand of your picture.
Go here for the two schematics and figure out which one is yours:
CBTricks.com Maco RF Amplifiers Index
There are two versions of that amp. The B and the M. I think it is a 22 mh but can not remember and i am at work and not at the plant.
You will see your has two chokes the same. Lower left hand of your picture.
Go here for the two schematics and figure out which one is yours:
CBTricks.com Maco RF Amplifiers Index
Clearly, you have the "B" Model (B=Base, M=Mobile) of the Maco 300.
It seems that you have burned the plate choke (where the B+ is fed to the tubes) for your driver stage; this could have been caused by a shorted tube drawing too much current. Find out what caused the problem before you start the repair.
You could either re-wind it yourself of try to find something like a Z-14 choke to replace it (also, two Z-28 tied in parallel would work nicely).
Be careful using the CB Tricks PDF re-draw, it is incorrect; who-son-ever drew that had his head inserted somewhere dark.
Your bad part is circled in green, the B+ line is traced in blue, the red "X" is where the artist had connected the high voltage line to chassis ground thus causing maximum smoke and fire if wired that way.
.
It seems that you have burned the plate choke (where the B+ is fed to the tubes) for your driver stage; this could have been caused by a shorted tube drawing too much current. Find out what caused the problem before you start the repair.
You could either re-wind it yourself of try to find something like a Z-14 choke to replace it (also, two Z-28 tied in parallel would work nicely).
CB Tricky
Be careful using the CB Tricks PDF re-draw, it is incorrect; who-son-ever drew that had his head inserted somewhere dark.
Your bad part is circled in green, the B+ line is traced in blue, the red "X" is where the artist had connected the high voltage line to chassis ground thus causing maximum smoke and fire if wired that way.
.
Glad you cleared that up!
And good to know that some of the re-draws are incorrect. guessing when some one re-drew it they used a modified box?
kenny1971, please do not start more than one post on the same subject.It just causes confusion and makes the thread hard to follow. I answered your question in the other thread you started before I saw this one. :bored:
Kenny,
I think there was a misunderstanding on that. Some one else posted a comment and quoted your pic in it. About the cbtricks.com schematic.
Located here.
http://www.worldwidedx.com/amplifiers/37469-tricky-schematics.html
It is just a misunderstanding that is all.
Sorry about that kenny. I posted that after staying up all night working and then having no sleep. Someone else started another thread quoting you. My eyeballs had been open for nearly 31 hours at that point. The brain was acting a little slow too.
Also need help with a maco 300 ,But orange face
I have an orange face later model maco 300 using the 5- 2057's as soon as i turn it on the tubes randomly turn blue and then after a minute or so start glowing orange. i have checked all the tubes on the tester and show no shorts . i have even only put 2 of the 4 finals in and get the same results . also depending on where i turn the air-variable caps at a certain point the transmit light comes on , but obviously the relay is not engaging and there is no exciter. my first thought was a short to ground on a cap at a socket so i have removed each one , one at a time and checked for short but none. Could it be a bias problem? Also if i try the amp out quickly without leaving it on too long it does work and good numbers too , but when i get it tuned it is at the point where when i un-key it has no receive and the transmit light is on. Any help would be great , especially since i can't find the schematic on the orange face version . Thanks
I have an orange face later model maco 300 using the 5- 2057's as soon as i turn it on the tubes randomly turn blue and then after a minute or so start glowing orange. i have checked all the tubes on the tester and show no shorts . i have even only put 2 of the 4 finals in and get the same results . also depending on where i turn the air-variable caps at a certain point the transmit light comes on , but obviously the relay is not engaging and there is no exciter. my first thought was a short to ground on a cap at a socket so i have removed each one , one at a time and checked for short but none. Could it be a bias problem? Also if i try the amp out quickly without leaving it on too long it does work and good numbers too , but when i get it tuned it is at the point where when i un-key it has no receive and the transmit light is on. Any help would be great , especially since i can't find the schematic on the orange face version . Thanks
Looks like old contact cement used to hold the caps in place, that 1000 mfd down at the bottom don`t look to good.......
I would re-cap the whole thing if it was mine, and clean up some of the soldering in there.
73
Jeff
check the half wave rectifier cap and diode that supplies + voltage to the relay and grid of tubes, could be bad and suppling acv instead of dcv. relay chatter on key up gives a sign of this. been awhile since I repaired one as they are kind or rare. best I can help without it on the bench.