Sender: |
|
Date: |
Fri, 27 Nov 2015 22:01:16 -0800 |
Content-Disposition: |
inline |
Reply-To: |
|
Subject: |
|
MIME-Version: |
1.0 |
Message-ID: |
|
In-Reply-To: |
|
Content-Type: |
text/plain; charset=us-ascii |
From: |
|
Parts/Attachments: |
|
|
It is just possible that each of the 4 transistors has a seperate emitter
resistor. These might be very low resistance value high power resistors one
from each emitter to a common point. This helps ballance current flow
between the transistors.
If one or more of these resistors were open, it would keep that transistor
from carrying any of the load current.
Also if replacing the transistors, there might be insulating washers between
the screws and the heat sinks. You must assure that none of the transistor
cases is shorted to the heatsink on which it's mounted. You need heat flow
there not current flow.
I aggree with Buch, replace all four transistors if any appear bad. But I'd
do my best to replace with the exact number unless you are really able to
compare specs.
Tom fowle
On Fri, Nov 27, 2015 at 03:08:43AM -0800, Butch Bussen wrote:
> The hot ones are likely good as they are in series with the load, that is
> why those supplies are called series regulaters. I'd replace all four
> from the same vendor so you have sort of a matched set. Should be able to
> get those from mouser or some one. You will also need some silicon
> grease. When you pull the transisters, watch for the thin mica insolater
> that is between the chassie and transister. Some times these stay stuck
> to the chassie, or heat sink, and some times they come with the
> transister. You don't want the transister actually touching the heat
> sink. A small bit of silicon grease is used between insolator and
> transister and between tinsolator and heat sink to help with heat
> transfer. I'll have to see if I can find the number, but if I were doing
> it, I'd go with darlingtons, I think e c g 247 or e c g 249 which are the
> same, but higher current.
> 73
> Butch
> WA0VJR
> Node 3148
> Wallace, ks.
|
|
|