Results 1 to 7 of 7

Thread: Resistor size artificial center tap

  1. #1
    Senior Member
    Join Date
    Dec 2009
    Posts
    1,188
    Thumbs Up/Down
    Received: 4/0
    Given: 2/1
    Rep Power
    12

    Resistor size artificial center tap

    Are there any cons in having bigger center tap resistors? I have a 2kOhm multi turned pot i would like to use for this.

    0 Not allowed! Not allowed!
    In this forum everyone is entitled to my opinion.

  2. #2
    "Thermionic Apocalypse" -JT nickb's Avatar
    Join Date
    Dec 2009
    Location
    Devon, UK
    Posts
    3,815
    Thumbs Up/Down
    Received: 947/1
    Given: 693/1
    Rep Power
    14
    Quote Originally Posted by überfuzz View Post
    Are there any cons in having bigger center tap resistors? I have a 2kOhm multi turned pot i would like to use for this.

    The problem comes if you get a short inside the tube from plate to heater. Then a high current can flow which will blow too your resistor and then feed that high volatge to all the other tubes vias the heater circuit and damage them too.

    So you need something that will not blow and then, when the current flows, does not have a high volatge drop. The usual two 100 ohms resistors, I use 2W ones, fits the bill.

    0 Not allowed! Not allowed!
    Experience is something you get, just after you really needed it.

  3. #3
    Senior Member
    Join Date
    Dec 2009
    Posts
    1,188
    Thumbs Up/Down
    Received: 4/0
    Given: 2/1
    Rep Power
    12
    Okay, thanks!

    I have an additional question. In order to set the level of a voltage drop in my circuit I use this artificial center tap as an voltage divider, see the attached picture. I hook up the 6Vac taps from the PT.

    Click image for larger version. 

Name:	Low supply.png 
Views:	33 
Size:	6.5 KB 
ID:	57968

    Is this kosher or should I do it some other way?

    Thanks!

    0 Not allowed! Not allowed!
    In this forum everyone is entitled to my opinion.

  4. #4
    Supporting Member
    Join Date
    May 2006
    Location
    Staffordshire UK
    Posts
    3,880
    Thumbs Up/Down
    Received: 599/1
    Given: 556/2
    Rep Power
    19
    R1-4 are tube heaters? If do what tube type, do the 21 and 10 indicate heater resistance?

    0 Not allowed! Not allowed!

  5. #5
    Senior Member
    Join Date
    Dec 2009
    Posts
    1,188
    Thumbs Up/Down
    Received: 4/0
    Given: 2/1
    Rep Power
    12
    R1, R2, R3 are tube filament resistance. The 10 is mock load.

    0 Not allowed! Not allowed!
    In this forum everyone is entitled to my opinion.

  6. #6
    "Thermionic Apocalypse" -JT nickb's Avatar
    Join Date
    Dec 2009
    Location
    Devon, UK
    Posts
    3,815
    Thumbs Up/Down
    Received: 947/1
    Given: 693/1
    Rep Power
    14
    It's better to put the balancing resistors on the AC side. 1N914's will not handle the current. I suggest schottky diodes so you can use a resistor, something like half an ohm, in series with the rectifiers to control the final output DC voltage and (probably) lower the ripple.

    Click image for larger version. 

Name:	Htr bal + DC.JPG 
Views:	20 
Size:	29.5 KB 
ID:	57969

    2 Not allowed! Not allowed!
    Experience is something you get, just after you really needed it.

  7. #7
    Senior Member trobbins's Avatar
    Join Date
    Jun 2010
    Location
    Australia
    Posts
    756
    Thumbs Up/Down
    Received: 123/0
    Given: 3/0
    Rep Power
    11
    That short can also be from pin 2 to pin 3 arcing on the tube socket, which is an increasing risk for amps with higher B+, and why I've seen some vintage amps with a plastic sleeve over each plate terminal and glued to the socket.

    Then comes the choice of how to protect the output transformer and power transformer secondary from any such heater-plate fault current flow. One option is to use humdinger parts that will 'fuse' (such as the suggested 2k trimpot), and that then also needs an extra resistor from heater to ground to continue to conduct the fault current but limit heater voltage rise to something like 150-180Vdc or whatever won't cause collateral damage to all the tubes - I recall something like an 82k may achieve that.

    1 Not allowed! Not allowed!

Thread Information

Users Browsing this Thread

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

Similar Threads

  1. Artificial center tap for elevated heater question
    By tubedood in forum Theory & Design
    Replies: 23
    Last Post: 07-16-2018, 05:10 AM
  2. Sovtek Mig 60 artificial center tap?
    By evil79 in forum Maintenance, Troubleshooting & Repair
    Replies: 8
    Last Post: 06-01-2018, 08:18 AM
  3. Replies: 14
    Last Post: 08-07-2017, 10:20 AM
  4. DC Heaters and artificial center tap
    By JacksonRR in forum Theory & Design
    Replies: 14
    Last Post: 12-05-2011, 11:19 AM
  5. Replies: 9
    Last Post: 04-14-2009, 06:07 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
  •