Help identifying amp please!

[pede69]

Help identifying amp please!

So I can hopefully fine a schematic.

I need to find the schematic so I can figure out what the value for the burnt register is. (in the pics) And of course I need it anyway.

Pics here: Index of /amp

Pre-Amp is out on amp. I'm hoping the resistor is the issue. Also... am I correct in assuming that the 455 in there is for the pre amp?

Thank you for your help,
John

PS - A manual would be nice too

 

[fnkycoldmedina]

100 ohms
2 watts

could be a 5 watt ,cant judge from here .but just replacing the resistor wont cure the problem as to why it burnt .it probably has a bad pill .

good luck

 

[pede69]

fnkycoldmedina... how can you tell 100 ohms? Is it not burnt too much to tell for sure?


Dead keys over 400. Swings near 500.

If pill is out... must be the 455 I mentioned above, the 2290's all seem to be working.

Thanks,
John

 

[AudioShockwav]

The MRF 455 Is a driver for the 4 2290`s, it has nothing to do with the pre Amp
Hard to tell just from pictures....that looks like the input to the MRF 455 and it has been over heated by too much drive into the driver(455).
I do not think it is burned open, just well scorched....if it was burned open you would have no output.
IIRC Those amps were built by a Guy named Steve that also built Pirate Amps.
TX 500, TX 800/900, and later the LA 500 and the LA 800/900....the 800/900 uses 2879`s and a 2290 for a driver...with fans.
As far as I know there are not any Schematics for these amps unless someone has hand drawn them.
The Small bi-polar transistors ( 2 of them ), one is for the Pre amp, the other keys the relay when you key the radio.
My first guess is the small pre amp transistor is shot.


73
Jeff

 

[fnkycoldmedina]

fnkycoldmedina... how can you tell 100 ohms? Is it not burnt too much to tell for sure?




Thanks,
John

that value is pretty common in most amps .

 

[AudioShockwav]

Be careful when you put the amp back together.
The covers on the ones I have seen are pop riveted on and it is fine until the rivets get drilled out.
In picture http://daytonacb.com/amp/4-burnt.jpg
look above the 455 and just to the left...see where the hole is to mount the case?
It is at board level and you got traces and parts real close.
If too large/long of a screw is used it can cause a short.
The TX 800 i had was a very hot Amp, both in terms of heat and gain.
You only need a little drive with that amp.
If you are hitting it hard enough to dead key 400 watts it will not live long.
I would keep the dead key to around 100 watts or less.
I know it says 500 on the front but that is asking a lot from 4 2290`s.
A fan would help also.
They are ok amps and work well if you do not over drive them.

73
Jeff

 

[pede69]

This makes sense to me. The ding dong I got this from was driving it with a two pill modulator. (455's). Said he kept the drive gain low.

Din din time. more later.

J