tube amp schematic -"DL" - Page 1
Forum section: electronics / beginners

author: pak
author_rank: Newbie
timestamp: January 25, 2021, 08:04:13 pm
content: Hi, forgive me, and this is a simple question which probably has an obvious answer, but I'm fairly new to this and while I think I understand the rest of this schematic, I haven't been able to find what DL means in the upper left of this schematic. Using DL as a search term only brings up massive amounts of download links. Can anyone help? This is from a Silvertone 1335 tube amp.Thanks!Peter

author: TimFox
author_rank: Super Contributor
timestamp: January 25, 2021, 08:07:03 pm
content: It means “dial lamp”, a small 6.3 V incandescent light bulb indicating power on. The term refers to its use in radio receivers to illuminate the tuning dial.

author: pak
author_rank: Newbie
timestamp: January 25, 2021, 08:51:10 pm
content: Thanks so much! That's totally it.

author: floobydust
author_rank: Super Contributor
timestamp: January 25, 2021, 09:15:38 pm
content: Be careful- C14 is the "death capacitor" and you can do research on it, but changing over to a grounded three-wire power cord I would recommend. Others replace the cap with a modern Y2 capacitor, keeping the two-wire polarized power cord.

author: Benta
author_rank: Super Contributor
timestamp: January 25, 2021, 09:24:27 pm
content: Quote from: floobydust on January 25, 2021, 09:15:38 pmGood call!I'd just remove it and leave the secondary floating, but if earthing is possible, that's even better.

author: TimFox
author_rank: Super Contributor
timestamp: January 25, 2021, 10:03:10 pm
content: If C14 is the usual paper capacitor from that era, it has probably absorbed moisture and has a high leakage current, making it more dangerous.

author: pak
author_rank: Newbie
timestamp: January 26, 2021, 03:56:23 am
content: Thanks for the recommendations. I've done a fair amount of research on the death cap, and figured I'd just remove it and run a grounded 3 wire cord. What's in there now is a Micamold Tropicap 0.05uf 600V. I've seen varying assumptions about their composition, so I don't know. Wax paper? Polyester? Most of the caps, including the death cap, are at least outwardly fine, but with the age of this amp and lack of use, I'm assuming they're all bad and replacing all of them. I appreciate the concern!

author: TimFox
author_rank: Super Contributor
timestamp: January 26, 2021, 02:42:52 pm
content: In general, it is wise to replace all paper-dielectric capacitors from that era, except for the military units that are hermetically sealed in "bathtub" enclosures.Following that advice, I replaced all the plastic-cased capacitors from a Tektronix 130 L,C meter with modern polypropylenes. All of the pulled capacitors had lousy Q values on a bridge.

author: Benta
author_rank: Super Contributor
timestamp: January 26, 2021, 05:06:24 pm
content: pak says it's called Micamold, so I'd expect it to be ... mica.

author: drussell
author_rank: Super Contributor
timestamp: January 26, 2021, 05:30:29 pm
content: Quote from: Benta on January 26, 2021, 05:06:24 pmNoooo... Micamold was a capacitorbrand nameof the Micamold Radio Corporation.They made some mica capacitors, yes, but also made other kinds of capacitors, resistors, etc. Most Miscamold capacitors you will encounter will be paper types, and none of Micamold's stuff is regarded for its,erm, quality but rather a lack thereof...

author: drussell
author_rank: Super Contributor
timestamp: January 26, 2021, 05:48:59 pm
content: This is what the inside of one of the typical flat ones that from the outside looks like it might be mica, but is just a flattened paper/foil cap in the same kind of bakelite case. Anything above, say a few hundred pF tend to be paper models but it can be difficult to tell for sure from the exterior. (The leftmost photo in middle row below shows the "guts" of a typical paper/foil model.)This guy is "restuffing" some with modern plastic film to maintain the originalappearanceof a restored radio while actually containing a modern, stable part:

author: TimFox
author_rank: Super Contributor
timestamp: January 26, 2021, 06:06:03 pm
content: That package looks like a "postage-stamp mica" capacitor, but 50 nF would be a much larger physical size if mica.

author: BrokenYugo
author_rank: Super Contributor
timestamp: January 26, 2021, 08:57:51 pm
content: Quote from: Benta on January 26, 2021, 05:06:24 pmSilver mica caps in this sort of stuff were only really used where high stability was necessary and the high cost warranted. The position in circuit and the value being very high for a typical mica are both strong indicators it's a paper cap in a box.