From: Chris Wilson <dead.fets@gmail.com>
Date: Sat, 10 Jun 2017 14:18:36 +0100
Message-ID: <1557864643.20170610141836@gmail.com>
To: Lawrence Galea <rsgb_lf_group@blacksheep.org>
In-Reply-To: <CAFDVXLkiP+bL2eV4uRog4UG6cwVzqvmnfqXmFr1bQsqETqi=oA@mail.gmail.com>
References: <953388818.20170606163952@gmail.com> <CAFDVXLkiP+bL2eV4uRog4UG6cwVzqvmnfqXmFr1bQsqETqi=oA@mail.gmail.com>
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Subject: Re: LF: Decoupling linear PSU
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Hello Lawrence,

Sorry  for  late reply, work and a dodgy e-mail service from something
gone wrong at my ISP. I haven't as yet tried any caps on the LV output
terminals,  would 1uF ceramics be appropriate? The PSU has 0.1uF and a
huge      choke     on     the     mains     input,     please     see
http://www.gatesgarth.com/H60001.jpg   for   schematic.  I  have  also
discovered  a  Schmidtt  NAND IC has, by design, some floating inputs,
one  goes  to a long un-terminated trace on a PCB, I think some pull up
resistors  might  be  appropriate,  the  device  is  part  of  the SCR
secondary  voltage  control  keeping  the pass transistor drop voltage
around 8.5V, until it has one of its fits :) Thanks for the advice.

Wednesday, June 7, 2017, 8:12:15 PM, you wrote:

> Hi Chris,
> Did you Try capacitors across the supply lines right at the output
> connectors and also from both + and - to earth?
> Did you try the same at the mains input with suitable voltage rating?
> Regards
> Lawrence

> On 6/6/17, Chris Wilson <dead.fets@gmail.com> wrote:
>> Hello LF'ers,
>>
>>  I have had a few issues with my lovely old Farnell H60/50 linear
>>  bench power supply. It'll do 60V @ 50A but I suspect it's last couple
>>  of uncontrolled output voltage failures may have been caused by RF
>>  getting into it, maybe up the output leads, maybe elsewhere. The
>>  manual makes mention of using caps of "a suitable value" across the
>>  output, or each output pin to ground, when used to power "transient
>>  loads" ; it's far from clear what's meant. The -ve floats relative to
>>  chassis ground. What do people recommend as a means of stopping RF
>>  getting in via the + and - output leads please?
>>
>>  It has SCR control on the transformers primary to keep the voltage
>>  drop across the huge pass transistor tunnel down to around 8V, this
>>  seems to go haywire at random times when powering my TX, and the
>>  2N3055's don't like 103V into them. Worst case scenario should be
>>  73V, but I am pretty sure SCR control fails and the secondary rises
>>  to its full potential. Thanks.
>>
>> --
>> Best regards,
>>  Chris                          mailto:dead_fets@gmail.com
>>
>>
>>


-- 
Best regards,
 Chris                            mailto:dead_fets@gmail.com