Results 1 to 17 of 17

Thread: Silvertone 1451: death cap and more

  1. #1
    Member
    Join Date
    Nov 2009
    Posts
    65
    Thumbs Up/Down
    Received: 0/0
    Given: 0/0

    Silvertone 1451: death cap and more

    I have an old Silvertone 1451, which is essentially the same as the 1430 whose schematic is attached here.

    As you'll see, there's no power transformer, and the ground side of the power supply is connected directly to one side of the power cord. Then theres a 68k resistor and a .05 cap from there to the chassis.

    I have installed a grounded power cord. Any suggestions as to how to make this atrocity as safe as possible?
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	silvertone1430.gif 
Views:	1346 
Size:	73.9 KB 
ID:	7171  

    0 Not allowed! Not allowed!

  2. #2
    Senior Member JHow's Avatar
    Join Date
    Oct 2009
    Location
    St Johns, FL
    Posts
    510
    Thumbs Up/Down
    Received: 0/0
    Given: 0/0
    I think people have made these circuits safer by re-doing the power supply using 1:1 isolation transformers. Do a search on the forum for triad n68x. Ithink there is discussion of this somewhere.

    Edit: Here is a guy doing something similar:

    http://www.clarkhuckaby.com/AmpMods/Silvertn.html

    0 Not allowed! Not allowed!
    Last edited by JHow; 12-06-2009 at 06:09 PM.

  3. #3
    Old Timer olddawg's Avatar
    Join Date
    Dec 2007
    Location
    Carlsbad, CA and Kona, HI
    Posts
    2,690
    Thumbs Up/Down
    Received: 63/0
    Given: 1/0
    Personally, I have never found anything redeeming in the sound of these types of amplifiers and they are definitely a dangerous shock hazard. IMHO, if you must use it your best bet is to use an isolation transformer as mentioned previously. You can wire a couple of 12v transformers (or whatever same ratio pair you have laying around) back to back if they have a sufficient current rating. People usually mount the isolation transformer on the bottom of the cab and hard wire it. Otherwise, leave the circuit as is.

    0 Not allowed! Not allowed!

  4. #4
    Senior Member
    Join Date
    Jul 2009
    Location
    Phoenix, AZ
    Posts
    483
    Thumbs Up/Down
    Received: 0/0
    Given: 0/0
    You can replace the death cap with a new Y rated cap that is UL approved to open if it fails, like this:

    PME271Y547MR30 Kemet Film Suppression Capacitors

    0 Not allowed! Not allowed!
    ST in Phoenix

  5. #5
    Member
    Join Date
    Nov 2009
    Posts
    65
    Thumbs Up/Down
    Received: 0/0
    Given: 0/0

    Success

    I put an isolation transformer in this thing. It ended up giving me almost 140VAC to work with. (Should that happen?) I put in a huge cap to bring the hum down to a reasonable level, and I added a couple of resistors to balance the heater in the preamp tube. You'll notice a couple of other tweaks if you compare to the original schematic. Also, the 6" speaker was crap, so I put in an 8" Jensen C8R.

    Now she's louder and better sounding than she has any right to be!



    (Note to search engine: Silvertone 1451 and Silvertone 1430 are essentially the same.)

    0 Not allowed! Not allowed!
    Last edited by otto pärt; 01-04-2010 at 04:35 AM.

  6. #6
    Senior Member JHow's Avatar
    Join Date
    Oct 2009
    Location
    St Johns, FL
    Posts
    510
    Thumbs Up/Down
    Received: 0/0
    Given: 0/0
    Cool. Where did you locate the 1:1 xformer? Do you have pix to share?

    0 Not allowed! Not allowed!

  7. #7
    Member
    Join Date
    Nov 2009
    Posts
    65
    Thumbs Up/Down
    Received: 0/0
    Given: 0/0
    Quote Originally Posted by JHow View Post
    Cool. Where did you locate the 1:1 xformer? Do you have pix to share?
    The transformer came from Mouser. Click here.

    I'll try to post a couple of pictures ...

    0 Not allowed! Not allowed!

  8. #8
    Member
    Join Date
    Nov 2009
    Posts
    65
    Thumbs Up/Down
    Received: 0/0
    Given: 0/0
    A few pix:
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	1.jpg 
Views:	114 
Size:	277.4 KB 
ID:	7446   Click image for larger version. 

Name:	2.jpg 
Views:	136 
Size:	211.6 KB 
ID:	7447   Click image for larger version. 

Name:	3.jpg 
Views:	168 
Size:	210.6 KB 
ID:	7448   Click image for larger version. 

Name:	4.jpg 
Views:	139 
Size:	206.3 KB 
ID:	7449   Click image for larger version. 

Name:	5.jpg 
Views:	222 
Size:	236.3 KB 
ID:	7450  

    0 Not allowed! Not allowed!

  9. #9
    Senior Member JHow's Avatar
    Join Date
    Oct 2009
    Location
    St Johns, FL
    Posts
    510
    Thumbs Up/Down
    Received: 0/0
    Given: 0/0
    Oh, I see, the 1:1 is at lower right, n'est-ce pas?

    0 Not allowed! Not allowed!

  10. #10
    Member
    Join Date
    Nov 2009
    Posts
    65
    Thumbs Up/Down
    Received: 0/0
    Given: 0/0
    Quote Originally Posted by JHow View Post
    Oh, I see, the 1:1 is at lower right, n'est-ce pas?
    Yep.

    The output transformer is mounted on the outside of the chassis; it was previously mounted on the original speaker. The transformer inside the chassis is the 12v 1:1 transformer for the preamp tube heater.

    0 Not allowed! Not allowed!

  11. #11
    Senior Member
    Join Date
    Apr 2009
    Posts
    689
    Thumbs Up/Down
    Received: 1/0
    Given: 0/0
    Quote Originally Posted by olddawg View Post
    Personally, I have never found anything redeeming in the sound of these types of amplifiers and they are definitely a dangerous shock hazard. IMHO, if you must use it your best bet is to use an isolation transformer as mentioned previously. You can wire a couple of 12v transformers (or whatever same ratio pair you have laying around) back to back if they have a sufficient current rating. People usually mount the isolation transformer on the bottom of the cab and hard wire it. Otherwise, leave the circuit as is.
    Depends. I had a series string Danelectro Leader for a while that had 2x6SJ7, 2x25L6 in push pull, and a 25Z6 rectifier. Once I figured out what was wrong with it it was a nice sounding 5-7w amp. The things people did to avoid buying power transformers.

    0 Not allowed! Not allowed!

  12. #12
    New Member
    Join Date
    Jan 2014
    Location
    Altadena CA
    Posts
    1
    Thumbs Up/Down
    Received: 0/0
    Given: 0/0
    Quote Originally Posted by Prairie Dawg View Post
    Depends. I had a series string Danelectro Leader for a while that had 2x6SJ7, 2x25L6 in push pull, and a 25Z6 rectifier. Once I figured out what was wrong with it it was a nice sounding 5-7w amp. The things people did to avoid buying power transformers.
    Keep in mind, not all power mains in the US were AC until sometimes in the '70s, NYC still had Mr. Edison's DC (AND his original nickel-iron batteries!) in some neighborhoods, so AC/DC radios and other gear were (and still can be) quite useful. No sound? Reverse the plug. Now with all-AC, polarized plugs are practical, and even better/safer, three-wire with bonding ground.

    The back-to-back filament transformers to make an isolation depend on the wattage rating of the (best if identical) units, and you can tap the 12V for heaters. Figure Watts = Volts x Amps, and allow about 50% more for safety margin, cool running.

    Oh, and if you're adding or rewiring a fuseholder, make sure the 'hot' line-in goes to the back-end of the fuseholder, so with the fuse out, you can't touch the hot circuit. Obviously, open on the bench, you could, but remember, these voltages (line/mains AND B+) are *LETHAL*! One hand in the pocket if you HAVE to work live, dry floor, rubber-sole shoes, no metal stools etc. etc.

    0 Not allowed! Not allowed!

  13. #13
    Lifetime Member
    Join Date
    May 2006
    Posts
    4,298
    Thumbs Up/Down
    Received: 156/0
    Given: 0/0
    Quote Originally Posted by pbarnrob View Post
    Keep in mind, not all power mains in the US were AC until sometimes in the '70s, NYC still had Mr. Edison's DC (AND his original nickel-iron batteries!) in some neighborhoods,
    This fascinated me, so I went and looked it up.

    There is STILL a DC distribution network in San Franscisco! PG&E maintained a DC distribution grid up through ?2009? when a short in a faulty splice in DC cables started a fire in nearby oil-filled AC distribution stuff and shot flames out of a manhole cover, and interrupted power to a neighborhood. They then split the DC network into a large number of DC "islands", each serving several customers and not interconnected to limit collateral damage.

    They do this because of a large number of DC powered elevators in hotels; this was the only way to do good elevators until the 1940s/50s? and they're still there. Replacing them with modern motors is hugely expensive, apparently.

    I was wowed. But then I'm easily amused.

    0 Not allowed! Not allowed!
    Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!

    Oh, wait! That sounds familiar, somehow.

  14. #14
    Senior Member
    Join Date
    Mar 2018
    Location
    Germany
    Posts
    508
    Thumbs Up/Down
    Received: 244/1
    Given: 207/2
    Quote Originally Posted by otto pärt View Post
    I put an isolation transformer in this thing. It ended up giving me almost 140VAC to work with. (Should that happen?) I put in a huge cap to bring the hum down to a reasonable level, and I added a couple of resistors to balance the heater in the preamp tube. You'll notice a couple of other tweaks if you compare to the original schematic. Also, the 6" speaker was crap, so I put in an 8" Jensen C8R.

    Now she's louder and better sounding than she has any right to be!



    (Note to search engine: Silvertone 1451 and Silvertone 1430 are essentially the same.)
    Tube rectifier have limits on the C value of the first filter cap to limit peak currents. Have you checked with the tube's datasheet? 350µ seems extremely high.

    1 Not allowed! Not allowed!

  15. #15
    Lifetime Member Enzo's Avatar
    Join Date
    May 2006
    Location
    Lansing, Michigan, USA
    Posts
    30,806
    Thumbs Up/Down
    Received: 723/4
    Given: 0/0
    HI Helm, Otto has not logged onto this forum in about five years. He may not see your post.

    0 Not allowed! Not allowed!
    Education is what you're left with after you have forgotten what you have learned.

  16. #16
    Senior Member
    Join Date
    Mar 2018
    Location
    Germany
    Posts
    508
    Thumbs Up/Down
    Received: 244/1
    Given: 207/2
    Quote Originally Posted by Enzo View Post
    HI Helm, Otto has not logged onto this forum in about five years. He may not see your post.
    Oh yes, old thread. Thanks Enzo. Guess it was to late for me last night at 1am. Nevertheless I got a "Thumbs up "

    0 Not allowed! Not allowed!

  17. #17
    don't forget the joker g1's Avatar
    Join Date
    Feb 2010
    Location
    Canada, somewhere north of Fargo
    Posts
    10,312
    Thumbs Up/Down
    Received: 458/3
    Given: 982/2
    Because other might stumble across this thread like Randall did while searching for 'Silvertone 1451'.
    Your pointing out the error of putting such a large cap there may save somebody from toasting rectifier tubes.

    1 Not allowed! Not allowed!
    Quote Originally Posted by The Dude View Post
    But, I did learn something. There are protons, neutrons, electrons, ............ and morons.

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Replace Death Cap with Safety Cap?
    By Axtman in forum Maintenance, Troubleshooting & Repair
    Replies: 31
    Last Post: 03-04-2014, 05:54 PM
  2. When a Death Cap Commits Suicide...
    By Dave Curtis, dB AudioTech in forum Maintenance, Troubleshooting & Repair
    Replies: 9
    Last Post: 08-06-2009, 08:01 PM
  3. removing the "death cap" on a 72 JCM800
    By PRNDL in forum Vintage Amps
    Replies: 3
    Last Post: 01-17-2009, 07:36 AM
  4. Peavey Classic Dual Death Cap Question
    By rf7 in forum Maintenance, Troubleshooting & Repair
    Replies: 3
    Last Post: 04-16-2008, 11:37 AM
  5. Your take on the death cap issue
    By Mars Amp Repair in forum Maintenance, Troubleshooting & Repair
    Replies: 13
    Last Post: 01-09-2008, 03:23 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •