Marshall design fault.

[nigelwright7557]

Bought in a Marshall guitar 100 watt amplifier.
Got it cheap as fun is very noisy due to knackered bearings.
Managed to find another fan on ebay.
Opened up amp to get old fan out.
It was then I noticed while there is an in vent for the fan there is no out vent in the casing !
On my own design amps there is always in and out vent to get a good air flow through the amp.

 

[tubelectron]

@nigelwright7557

Well...Which Marshall amp model is it ?

To my knowlegde - but I may be wrong - there's no vintage Marshall fitted stock with a fan... Hence my question...

The JTM60/100 combo series amp with horizontally mounted tube have a problem of overheat due indeed to a design failure :

A+!

 

[ohdsp]

Doesn't positive air pressure help keep dust out? Therefore if the air cannot flow anywhere you have infinite air pressure and it will be like new on the inside forever?

 

[Mooly]

To maintain positive pressure you would need a source of clean air (under pressure) to vent into the cabinet 24/7 ...and that thing will be as leaky as sieve if you even tried

 

[nigelwright7557]

Its a Marshall 100 chip amp model.

 

[JMFahey]

To my knowlegde - but I may be wrong - there's no vintage Marshall fitted stock with a fan... Hence my question...

Who says it´s a vintage Marshall?

"Small fan" stinks of TDA7294 in a TINY CPU type heatsink and with a small fan to match.
As to exit vents somewhere else in the cabinet, tis is supposed to work similar to CPU cooling: fan mounted on or VERY close to heatsing, blowing 100% into it, hot air spreading in all directions, it does not matter muh where to, as long as it´s away from chipamp.

It´s not a large heavy heatsing assembly which needs a careful airflow path for maximum efficiency.

Of course, end result is barely adequate and those amps die like flies.

 

[tubelectron]

Who says it´s a vintage Marshall?

I agree : any Marshall built after the JCM800 series in not worth to be considered, except for some reissues. So when I speak about a Marshall, it's a tube amp indeed, not a solid state.

A+!

 

[Tarzan]

If my memory is correct, that fan is 10mm thick.
Whenever I get these in repair I change the fan for a 20mm model (again, if my memory is correct). Fits very nice.
I also replace the nuts and bolts of the alu bracket (that holds the power amp pcb) so that I will not get mad because the originals are of such a bad quality.
(Again, my memory...) Maybe the bolts that hold the fan have to be replaced to.
If I can find my notes on this amp, I will post them. But I may not forget...

 

[Mario Pankov]

Its probably a MG - the winner of the contest "can you design the crappiest guitar amp and have it build by people that discovered electricity 2 years ago".