The transistor you selected should work fine but for the fact that the 2N5201
has higher gain. It is possible that your supply could be in oscillation as a
result.
Why did you pick the 2N5201? The 2N3771 is the accepted higher current
replacement for the 2N3055.
I’d be pretty suspicious about having experienced a second 2N3055 showing a
Base to Collector short in only a year.
The 2N3055 is more than adequate for this supply though the 2N3771 (below)
would be a better choice as it has twice the current rating.
Was the failure in there previous bad transistor also Base to Collector?
This is a VERY simple supply. It simply regulates by looking at the Zener
potential across D7, compared with the Emitter output of Q1 (the 2N3055) fed
through a voltage amplifier (Q2) then through Darlington connected pair (Q3
and Q4) to give sufficient current to set the Base current of Q1 and bring
about voltage regulation.
If the current across the ammeter shunt exceeds the limit set by R8, the SCR Q5
closes and pulls supply voltage to near zero and it will not come back on until
power is cycled.
I would power the supply with no load (radio disconnected) and see if the
ammeter is showing current. It should not show very much. If is does show
current, C2 could be shorted or very leaky.
Gary
W0DVN
> On Jan 31, 2016, at 8:58 PM, Chris Howard w0ep <w0ep@w0ep.us> wrote:
>
>
>
> Follow-up on this old power supply issue from a year ago...
>
> I had the 2n3055 in there as the main pass transistor for just
> under a year. I usually operate QRP, turned down to 5 watts.
> Things seemed to go along fine. Then, one day I turned on
> the power and it immediately died again.
>
> I ordered a 2n5201 from digikey. I have now installed that.
> Sure enough, the 2n3055 showed a dead short from base to collector.
>
> I'm still having trouble though. I hooked the supply up and
> it seems to be sagging badly if I try to turn up the power above
> about 10 watts. The meter light dims and it just doesn't look
> good.
>
> Is there anything about the 2n5201 that is different from the 2n3055
> that requires adjustment?
>
> Here's a datasheet that shows both:
> http://www.mouser.com/ds/2/68/lssgp082-54678.pdf
>
> I think I need to dig into it again, maybe something else failed.
>
>
>
>
> On 2/26/2015 12:15 PM, Al Gulseth wrote:
>> Chris,
>>
>> If it's the main pass transistor it shouldn't be a 2N3055: they aren't
>> enough
>> to handle the load. From what I remember the original device may have been a
>> 2N6258(?) but a 2N5301 would probably be the best readily available sub.
>>
>> 73 es GL, Al
>>
>> On Thu February 26 2015 10:37:14 am you wrote:
>>> My bridge rectifier seemed to be ok.
>>>
>>> But the big pass transistor was reading dead short
>>> between collector and base.
>>>
>>> I replaced that with another 2n3055 that I had on hand.
>>> That seems to have done the trick.
>>>
>>>
>>> Chris
>>>
>>> On 2/9/2015 1:24 PM, Chris Howard w0ep wrote:
>>>> Thank you Ralph!
>>>>
>>>> I hooked the Omni up to a Pyramid linear supply
>>>> that I have here. I can run up to about 10 watts
>>>> and then the voltage sags enough to cause the frequency
>>>> to change. So, I am ok if I stick to lower power.
>>>>
>>>> I'm going to dive into the 252mo supply and see
>>>> what is what.
>>>>
>>>> Do you think it would be better to get a switching-type
>>>> supply? Should I be worried about noise on the power
>>>> line?
>>>>
>>>> Chris
>>>>
>>>> On 2/8/2015 9:22 PM, Ralph Arnold wrote:
>>>>> I had the same problem with my OMNI D the PS is bad mine blew the
>>>>> Bridge Rectifer and the 3055 Voltage Regulators were leaky I also
>>>>> replaced the electrolytic cap it was old Now it works like a champ Oh
>>>>> BTW check output with a known good DVM and I also Scoped PS for clean
>>>>> power.(no 60 cy ripple. Im an old USN Aviation Tech KD8BTQ ---Ralph
>>>>>
>>>>> On Sun, Feb 8, 2015 at 11:41 PM, Chris Howard w0ep <w0ep@w0ep.us> wrote:
>>>>>> I was tuning up the antenna with my Omni-D yesterday
>>>>>> afternoon and everything went completely dead.
>>>>>> I was not high on SWR and not turned up to maximum power.
>>>>>>
>>>>>> Turning things off and on I was able to get the power
>>>>>> supply meter light to come on, but nothing on the rig.
>>>>>>
>>>>>> I have the light in my SWR meter hooked up to the supply
>>>>>> also, and that is not working. I think the supply has
>>>>>> problems.
>>>>>>
>>>>>> -- later --
>>>>>>
>>>>>> I jumper the "SW" ports of the connector, plugged in
>>>>>> in the supply and fired it up. Sure enough, the supply
>>>>>> lights up but no output.
>>>>>>
>>>>>> Any advice before I dive in?
>>>>>>
>>>>>> Chris
>>>>>> w0ep
>>>>>>
>>>>>>
>>>>>>
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