Silvertone 100.385 schematic/info

Page 2 of 2 Previous  1, 2

View previous topic View next topic Go down

Re: Silvertone 100.385 schematic/info

Post by Chas on Sun May 07, 2017 6:28 pm

Best reflector for IR (heat) is gold, failing that $$$, polished brass panel mounted to the transformer bolts should be effective. A sandwich of two or three brass sheets should be most effective, far enough apart to allow free flow of air. I worked with first surface mirrors trying to get the max. from Xenon strobe to CCD camera, gold plated aluminum mirror greatly enhanced IR reflection.

There is data on tubes about operating them at below specification, has to do with the ion cloud damaging the oxide coating on the cathode, shortens the life of the coating... Simple, if the tube(s) are above filament voltage limits then reduce, never go below the limit, it saves nothing, reduces sensitivity and volume. Exception, thoriated tubes designed to have adjustable filament voltage.

Chas
avatar
Chas
Member
Member

Number of posts : 27
Age : 70
Registration date : 2008-07-24

Back to top Go down

Re: Silvertone 100.385 schematic/info

Post by tubesrgr8 on Sun May 07, 2017 6:58 pm

Thinking for a very quick experiment I could use heavy duty aluminum foil, two sheets with an air gap. Nothing permanent at first, just to see if any effect.
avatar
tubesrgr8
Member
Member

Number of posts : 47
Registration date : 2013-01-01

Back to top Go down

Re: Silvertone 100.385 schematic/info

Post by Chas on Sun May 07, 2017 10:30 pm

Aluminum will work, sheet brass much better, it has to do with the longer wavelength of IR reflecting rather than being absorbed... Crinkling up the surfaces works even better,. I found the reflectance of brass, but copper is the same as gold. Surface has to remain unoxidized. There are ceramic fiber mats available, but the gimmick is keeping air space on both the tube and transformer side.

I would not recommend covering the rectifier tube with a shield. However, there are tube shields that not only protect against magnetic and capacitive coupling but also provide cooling properties.

IERC tube shield:

http://www.qsl.net/kh6grt/page4/shields/shields.htm

Chas
avatar
Chas
Member
Member

Number of posts : 27
Age : 70
Registration date : 2008-07-24

Back to top Go down

Re: Silvertone 100.385 schematic/info

Post by tubesrgr8 on Sun May 07, 2017 10:45 pm

Hi, Chas - I wasn't going to cover the tubes. Just making a temporary shield. Flat pieces, shiny sides toward the tubes, hopefully to reflect their heat and to shield the corner of the xfmr. Pretty flimsy, but no matter at this point. If that makes a noticeable difference then I'll go to something more elaborate.
avatar
tubesrgr8
Member
Member

Number of posts : 47
Registration date : 2013-01-01

Back to top Go down

Re: Silvertone 100.385 schematic/info

Post by tubesrgr8 on Mon May 08, 2017 8:22 pm

Well, the insulator idea didn't help. Folded sheet of heavy-duty aluminum foil was placed between the very hot tubes and that corner of the xfmr. Gave it 1hr 10 min run time, ambient was 71 deg. Final temp was 108 rear corner, 133 front corner. Heat shield wasn't the greatest, but it didn't seem to make any difference. Ugh. Still, probably less than the UL max allowable. I just don't like it to be that hot.

Gonna pull the chassis out and check things previously suggested, and likely lower the AC input voltage for good measure.
avatar
tubesrgr8
Member
Member

Number of posts : 47
Registration date : 2013-01-01

Back to top Go down

Re: Silvertone 100.385 schematic/info

Post by Bill Cahill on Tue May 09, 2017 11:53 am

Could be something is pulling too much current load, and, causing transformer to overheat.

_________________
Please also join us here;  http://videokarma.org/index.php
avatar
Bill Cahill
Admin
Admin

Number of posts : 4585
Age : 66
Registration date : 2008-03-12

Back to top Go down

Re: Silvertone 100.385 schematic/info

Post by tubesrgr8 on Thu May 11, 2017 3:32 pm

Bill, I'm still hoping to find another perhaps easier solution, than replacing this replacement xfmr. Although I know you may be entirely correct. The transformer is a pull, apparently tested good, and a little better current ratings than the original. Also physically a little larger.

Reading other posts about hot running transformers gave me lots more to think about.  Solid state 5Y3GT replacements weren't recommended; what I'd save in filament current would be offset by higher B+ to the radio. If the xfmr is at or close to saturation, the heating goes way up. According to other posts, a small decrease of input primary voltage decreases heating much more, as it's proportional to the square of the voltage. So I ordered a small 12v xfmr to buck the input, still within the original specs for this set. A dropping resistor is initially cheaper but the postage makes if more expensive than the small xfmr! LOL.
avatar
tubesrgr8
Member
Member

Number of posts : 47
Registration date : 2013-01-01

Back to top Go down

Re: Silvertone 100.385 schematic/info

Post by tubesrgr8 on Fri May 19, 2017 11:01 pm

Found the info about the replacement pwr xfmr, Crest #6416, new old stock. Company was in Chicago, but Google turns up nothing current about Crest.  Rated 350-0-350@100mA, 5V@3A, 6.3V@4A. Seems like it should be able to handle a chassis rated as drawing 60 watts. Dropping the input to 110VAC resulted in a drop of 2-3 degrees after 1hr 45min. I can lay my hand on the transformer for 30 seconds or so, it gets uncomfortable, but not blistering. Not what I had hoped for. I guess I'll pull the chassis again and see if there's something I overlooked. Appreciate all the input!
avatar
tubesrgr8
Member
Member

Number of posts : 47
Registration date : 2013-01-01

Back to top Go down

Re: Silvertone 100.385 schematic/info

Post by Sponsored content


Sponsored content


Back to top Go down

Page 2 of 2 Previous  1, 2

View previous topic View next topic Back to top

- Similar topics

 
Permissions in this forum:
You cannot reply to topics in this forum