[Hallicrafters] HT-37 selenium rectifier replacement..HELP!!!!

[Mark K3MSB]

Paul

Look for an old resistance substitution box at a hamfest.   This will help
you find the correct value.

You can find them for under $10;  under $5 sometimes.   After all, who
would ever need such an antiquated device in this day and age, eh ?

73 Mark K3MSB



On Wed, Dec 30, 2015 at 6:43 PM, <a69galaxie500xl at comcast.net> wrote:

> Thank you guys,
>
>      I appreciate the advice and feel comfortable enough now to proceed.
> Like I said, I'm green and am sure I will have
> many more questions. Very happy to have found this forum!
>
> Thanks again & 73
>
> Paul KG5KVW
>
> ------------------------------
> *From: *"Al Parker" <anchor at ec.rr.com>
> *To: *"Mark K3MSB" <mark.k3msb at gmail.com>, "Paul Mobley" <
> a69galaxie500xl at comcast.net>
> *Cc: *"List Hallicrafters" <hallicrafters at mailman.qth.net>
> *Sent: *Wednesday, December 30, 2015 7:53:04 AM
> *Subject: *Re: [Hallicrafters] HT-37 selenium rectifier
> replacement..HELP!!!!
>
>
> Hi Paul, et al,
>         Mark's right.  There's nothing that should confuse you about the
> circuit, but it can be difficult to understand the diagrams sometimes.
> Nothing terribly critical here, it's low voltage, low current.  The
> resistor can go on either side if the diode, it's in series either
> place.  In my experience, I think I've used a larger R value, but
> basically any one that will allow you to adjust the bias voltage to -49v
> (IIRC) at the test point to the finals will do the job.
>         If it hasn't already been done, you should also solid state the HV
> and
> LV rectifiers.  The HT-37 & HT-32 power xfmrs are well know for
> developing a short between the HV winding and a filament winding.
> That's fatal to the xfmr.  Removing the filament winding from the ckt
> will avoid this (I speak from grim experience(s) on this one).  You can
> see some pix and instructions on this at
> <http://www.boatanchors.org/HT37.htm>, about half way down the page.
>         This is a good forum, if you have any questions ask them here.
> 73,
>
> Al, W8UT
> www.boatanchors.org
> www.hammarlund.info
>
> "There is nothing -- absolutely nothing -- half so much
> worth doing as simply messing about in boats"
> Ratty, to Mole
>
> On 12/30/2015 12:13 AM, Mark K3MSB wrote:
> > Paul
> >
> > It's been a long time since I did this to my HT-37.
> >
> > I would figure on a voltage increase of about 10V with the new diode.
> > Since it's a bias circuit,  figure low current, about 10 mA..
> >
> > That would mean a resistance of about 1K.  A 1/2W resistor should be
> fine.
> >
> > What is the RMS voltage of the tap that's feeding the diode?  Whatever it
> > is,  multiple by 1.414 to get the peak rating for the diode.
> >
> > Diodes and resistors as dirt cheap;  I'd oversize the heck out of both of
> > them.....
> >
> > 73 Mark K3MSB
> >
> >
> > Mark K3MSB
> >
> >
> >
> >
> > On Tue, Dec 29, 2015 at 8:14 PM, Paul Mobley <
> a69galaxie500xl at comcast.net>
> > wrote:
> >
> >> Please, can anyone give me detailed info on replacing selenium rectifier
> >> in my HT-37, with diode. I am a beginner with electronics and having
> real
> >> trouble trying to understand the whole bias supply circuit. I don't know
> >> what value of dropping resistor to use and am confused as to weather the
> >> resistor should go to the anode or the cathode side of the diode. The
> whole
> >> negative voltage bias thing is very confusing. Please help!
> >>
> >> Thanks,
> >> Paul
> >>
> >> Sent from my iPhone
> >> ________
>
>