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

[a69galaxie500xl at comcast.net]

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 

----- Original Message -----

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 
>> ________