when do filament supplies need to be floated - Page 4 - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 16th August 2012, 04:33 PM   #31
ChrisA is offline ChrisA  United States
diyAudio Member
 
Join Date: Jan 2008
Quote:
Originally Posted by puginfo View Post
i use DC filament supply for both the input - AX7 and invertor - AU7 stages but AC for the output stage - 6550. so do i need to ground or reference the DC filament supply cct? its floating right now as it has its own line transfo and the whole thing does not tie to any part of the main HT supply cct.

cheers
Yes floating is not good. It can chrage up to any un-known voltage. 'd at least use a high value resistor to ground. But if being extra carful why bias it it up? It only takes one more resistor
  Reply With Quote
Old 17th August 2012, 08:04 AM   #32
puginfo is offline puginfo  Malaysia
diyAudio Member
 
Join Date: Apr 2007
think i will try a 20k resistor on the -ve leg of this 12.5vdc heater supply to the amp star ground and see what happens. did not think of biasing up to the HT line (via voltage divider of course) because this is still 12vdc biasing on another dc HT voltage of a totally different transfo.
  Reply With Quote
Old 19th August 2012, 12:24 AM   #33
diyAudio Member
 
PlasticIsGood's Avatar
 
Join Date: Mar 2012
Location: Bradford
Thanks, all. Just been peering into my amps for the first time in years.


When I made them, some years ago, I agonised for some time over heater grounding. Small valve heater supply is current source, and heaters are in series. Eventually I decided to ground the middle of the chain, probably on the basis that any fluctuation in current would cause least common mode voltage variation. Actually current is as constant as I've ever seen a constant thing be.


When I get round to it, I'll ground the negative end of the chain, so the valves with greatest gain are least positive, and the elevated drivers will see 20-odd volts. I guess the ultimate would be to connect the centre of the chain to an elevated ground, but I don't care enough.


The amps have been happy for years as they are. Heaters are left at half power when not in use, so they've been on for years. There is no apparent difference in the condition of the valves with negative heaters.

I've been a bit lazy about bias I notice...
  Reply With Quote
Old 21st August 2012, 04:06 AM   #34
jt1 is offline jt1  United States
diyAudio Member
 
Join Date: Feb 2010
While I am still on a pretty steep learing curve about all this it occurs to me that some confusion may come from the way this technique is
explained, as I recall I read that referencing a DC voltage allowed the AC componet to "Float" on top of the DC stablizing the leakage current from heater to cathode...or something close to that. I do know it helped to reduce hum in my 12au7 preamp.
  Reply With Quote
Old 21st August 2012, 04:15 AM   #35
AJT is offline AJT  Philippines
diyAudio Moderator
 
AJT's Avatar
 
Join Date: May 2003
Location: Palatiw, Pasig City
yes, that's the thing....
__________________
the best advertisement for a good audio design is the number of diy'ers wanting to build it after all the years....never the say so of so called gurus....
  Reply With Quote
Old 7th July 2015, 06:02 PM   #36
yero is offline yero  United States
diyAudio Member
 
Join Date: Mar 2010
Location: Medina, N.Y. near Rochester N.Y.
Is it possible to see A schematic diagram of franks cathode follower preamp circuit showing how to elevate the heater supply? I have a NOS Chicago Standard PC8406 which has a center tapped 6.3V heater winding. I understand the artificial center tapped methodology using the 100ohm resistors and the hum dinger concept which is not needed because I have a center tap. The elevation of the heater's is what I am having difficulty implementing. Also, why is the recommended transformer for this preamp 100ma. I have single ended power amps that utilize transformers less than 100ma.
  Reply With Quote
Old 7th July 2015, 07:13 PM   #37
diyAudio Member
 
Join Date: Dec 2010
Location: Amesbury, MA
A potential divider coming from the power supply works. Use large values so you don't pull too much current and set the divider to around 50V.

For a B+ of 300V

Two resistors from B+ to ground in series. A 220k on the B+ side and 47k on the ground side. Tie your your heater center tap to the junction of these two resistors and decouple with a cap. Should only draw a milliamp and give you 52V.
  Reply With Quote
Old 8th July 2015, 12:08 AM   #38
yero is offline yero  United States
diyAudio Member
 
Join Date: Mar 2010
Location: Medina, N.Y. near Rochester N.Y.
famousmockingbird, THANK YOU!! just to be certain that I fully understand, use two resistors tied from my 300v B+ to ground. At the junction of the 220K and 47K to ground resistors, solder a capacitor to that junction. Solder the 6.3 v heater center tap to the other end of the capacitor. Is the connection placement to the B+ at the power supply output?

Could you please help me to understand why the rating of the transformer is recommended at 100 ma.
I have a Magnavox AM/FM STEREO console That utilizes 2 EL-84 output tubes and additional tubes for the tuner and the transformer rating is 80ma.
The Stancor transformer rating I would like to use is 650v c.t. at 50ma and I am not using the 5v 2A winding, can' that drive two 6sn7? Thanks to all responses.
  Reply With Quote
Old 8th July 2015, 12:12 AM   #39
AJT is offline AJT  Philippines
diyAudio Moderator
 
AJT's Avatar
 
Join Date: May 2003
Location: Palatiw, Pasig City
1/4 of B+ is typical...the thing is not the exceed the heater cathode rating of the tube when using dc coupling...

Click the image to open in full size.

Click the image to open in full size.
__________________
the best advertisement for a good audio design is the number of diy'ers wanting to build it after all the years....never the say so of so called gurus....
  Reply With Quote
Old 8th July 2015, 12:39 AM   #40
yero is offline yero  United States
diyAudio Member
 
Join Date: Mar 2010
Location: Medina, N.Y. near Rochester N.Y.
AJT, thank you. You clarified my understanding of the decoupling cap also !! I mistakenly thought the cap was used as a coupling cap. Your drawing states Fil. Ref. Just to be sure what you mean is filament center tap?
The 6sn7 DC cathode current draws 20ma. so two tubes would draw 40ma. Won't the stancor 50ma transformer handle the load of two preamp tubes?
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Coleman filament supplies for 300b tubes renton1 Swap Meet 1 2nd January 2012 04:10 PM
Tentlab Filament Supplies on Ebay and Black Gate caps wanted Carrier Bag Man Swap Meet 2 5th April 2011 02:31 PM
FS: Tentlabs DHT Filament Supplies damohpi Swap Meet 0 14th April 2010 10:53 AM
Alpine MRV-1507 - RCA Ground Floated - Need help silversweden Car Audio 41 5th June 2008 06:20 PM
Tentlabs DHT Filament Supplies damohpi Swap Meet 1 12th March 2008 05:27 AM


New To Site? Need Help?

All times are GMT. The time now is 11:39 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2015 DragonByte Technologies Ltd.
Copyright ©1999-2015 diyAudio

Content Relevant URLs by vBSEO 3.3.2