Holiday greetings to my friends at the forum. My 42-1015 seems to have a crashing/cracking sound most of the time when first powered up. It seems to disappear after a few minutes and is there regardless of the band or phono position. It is recapped, and all tubes test strong. It plays great with good volume and no distortion . Any suggestions on how to approach this issue?
Are there any silver-mica caps on the IF transformers?
Has the Cand-ohm bias resistor (item 91 on schematic) been replaced? I have had these go intermittent in the past and cause the same sound that you describe. I have made it a habit to replace these regardless of if they measure OK or not.
Thank you Sean,
No, I did not, but I will get it done. Thanks for the info. I remember that you have one of these and you have helped me in the past with my other BOL changer issues. Have a great holiday!
Probably most likely micas. Impossible to test, just carefully replace them. I'm a believer.
(12-22-2015, 02:52 PM)codefox1 Wrote: [ -> ]Probably most likely micas. Impossible to test, just carefully replace them. I'm a believer.
Can you read the specs on #91, the bias resistor? It looks like 8-192 ohms, is that just 192 ohms? Thanks,
Those values are correct, 8 and 192 ohms. I would replace the 8 with a 10 ohm 1/2 W resistor and the 192 with a 200 ohm 5W resistor.
You could replace the fixed mica capacitors in the IF transformers. There are only 2, one across the primary of the 1st IF and one on a secondary winding of 4th IF transformer. You would have to pull those IF transformers to get to the caps. The Candohm is easier to get at.
Given that this is an early 1940s model with loctal tubes dirty contacts in the tube sockets can be a problem, as well as oxidation on the tube pins themselves. You may also have a problem with a cold solder joint or even one that you forgot to solder. The Candohms are worth checking as well. As far as I know Philcos of this era did not have many problems with the mica caps, except the ones that are wax dipped and used on some pushbutton banks, I think that the IF cans mostly used trimmers rather then permeable slugs for adjustment, even so they would have used molded micas inside anyhow.
Regards
Arran
Agree ,soap before surgery. Loctals can be difficult, of course press towards dimple before removing, and if it's still stuck, a blast of WD40 should make things easier. Pins can become encrusted and best scraped off gently with a curette begged from your dentist or hygienist and some WD40. Precious sockets (ain't many of 'em floating around anymore,) WD40, old school pipe cleaners, or quadrupled up unwaxed dental floss could help. If you blast out the tube sockets, allow a day to dry out.
If the set only has a few mica capacitors in the cans, carefully replace them. That means ancient heat clips (remember roach clips?) so the connections to the windings are not overly disturbed. I'd also replace any old carbon resistors while I was at it, and we assume all other caps have been renewed.