Go Back   Home > Forums > > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Tubelab Discussion and support of Tubelab products, prototypes and experiments

Reply
 
Thread Tools Search this Thread
Old 14th March 2017, 05:55 PM   #1
waltroman is offline waltroman  United States
diyAudio Member
 
Join Date: Jan 2008
Location: Near Gettysburg PA
Default Noise at output transformers

I am starting a new thread with new info. See thread Possible Transformer problems. Last night I verified I had 25mV of noise at output transformers. I had been suspecting the 6.3 volt tap on the Edcor power transformer had a problem. It was reading higher than it did when I built this amp two years ago.

It now reads 7.4 volts with no load and 6.8 with tubes in. With the 5842's out the heater voltage to the pins is 8 volts, OUCH!

My discovery is the noise at the output's does not change with all the tubes removed.

I need to get the 5842 heater voltage under control and eliminate the noise or buzz/hum.
  Reply With Quote
Old 14th March 2017, 06:21 PM   #2
Osvaldo de Banfield is offline Osvaldo de Banfield  Argentina
diyAudio Member
 
Osvaldo de Banfield's Avatar
 
Join Date: Dec 2011
Location: Barrio Garay,Almirante Brown, Buenos Aires, Argentina
I don't find any relation between two facts. Output transformers doesn't give any heaters supply. Noise is electrical or acoustic?

Also, 10% variation in heater's voltage is tolerable.
__________________
Osvaldo F. Zappacosta. Electronic Engineer UTN FRA from 2001.
Argentine Ham Radio LW1DSE since 1987.
  Reply With Quote
Old 14th March 2017, 07:15 PM   #3
goodlionaudio is offline goodlionaudio  United States
diyAudio Member
 
Join Date: Jul 2011
Location: Columbia, MD
Default two separate issues?

Agree, 7.4V heater voltage is too much when loaded. Do you have access to a variac? If so, adjust variac for 6.3V heater voltage, and then measure the primary AC. It should be lose to its specification; e.g. 115 or 120V.

With the information at hand, I do not see the connection with measured output noise. It seems these are two separate issues?
  Reply With Quote
Old 14th March 2017, 08:31 PM   #4
waltroman is offline waltroman  United States
diyAudio Member
 
Join Date: Jan 2008
Location: Near Gettysburg PA
OK so I guess what is being said I can rule out pwr transformer?

I do not have a variac.

The tech at Edcor suggested I pad down the 6.3 volt secondary to equal 6.3. If I do that would the best place be the center tap? I will need some heavy duty resistors to use. Any guess what value and wattage I should use?
  Reply With Quote
Old 14th March 2017, 08:55 PM   #5
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
Noise at output transformers
Hi waltroman,
Are your heaters DC or AC?
Quote:
My discovery is the noise at the output's does not change with all the tubes removed.
Your power transformer can magnetically couple to the output transformers and output the 60 Hz supply waveform. You can try rotating the transformers to where you get minimal hum, ideally this would be at 90 from the power transformer. There are times when you will be stuck with an odd angle too. Right now it's a bit late since you have built the chassis.

-Chris
__________________
"Just because you can, doesn't mean you should" my Wife
  Reply With Quote
Old 14th March 2017, 08:56 PM   #6
goodlionaudio is offline goodlionaudio  United States
diyAudio Member
 
Join Date: Jul 2011
Location: Columbia, MD
Default series resistor

You need to know the total heater current and the measured heater supply voltage.

Let's say you want to drop the heater supply voltage by 1.0 volt and the heater current is 3A. The you will need a series resistor of 1/3 = 0.33 ohm (R = V/I). The power dissipated by this resistor will be 3*3*0.33 = 3 Watt (P = I^2 * R). If you don't cool the resistor take one with at least a 10W rating. Ordinary wire wound ceramic is fine.

Because the heater current is non-linear with respect to heater voltage, you may have to go to through an additional iteration to get to the optimal value.

Still you need to be aware that the heater voltage is proportional to the momentary mains voltage; so, always make reference to it.
  Reply With Quote
Old 14th March 2017, 08:56 PM   #7
w5jag is offline w5jag  United States
diyAudio Member
 
Join Date: Feb 2007
Location: Arkansas
6.8 - 6.3 = 0.5 volt drop required

0.5 volt / .6 amp ( 2 x 300 ma 5842 heater current ) = 0.83 ohm ( Ohm's law R = E/I)

(0.6 amp )(0.5 volt) = 300 mW.

So, about 0.8 ohm or slightly more, at one watt ought to do it. If my arithmetic is correct.

Win W5JAG
  Reply With Quote
Old 14th March 2017, 09:05 PM   #8
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
Noise at output transformers
So 0.82R at 1 watt would be fine, but if you are using DC, the result might be different. You could also use a 2 watt part if you wanted, but it isn't necessary. A wirewound resistor would handle the power up surge better than any other type of resistor.

I'm just trying to make it easy for you to find parts by listing the closest available resistance value.

-Chris
__________________
"Just because you can, doesn't mean you should" my Wife
  Reply With Quote
Old 14th March 2017, 09:35 PM   #9
waltroman is offline waltroman  United States
diyAudio Member
 
Join Date: Jan 2008
Location: Near Gettysburg PA
Quote:
Originally Posted by w5jag View Post
6.8 - 6.3 = 0.5 volt drop required

0.5 volt / .6 amp ( 2 x 300 ma 5842 heater current ) = 0.83 ohm ( Ohm's law R = E/I)

(0.6 amp )(0.5 volt) = 300 mW.

So, about 0.8 ohm or slightly more, at one watt ought to do it. If my arithmetic is correct.

Win W5JAG
Thanks Win, I forgot about R3. I will increase proportionally to get the value down. Time for another Digikey order.

Now just need to address the noise/hum/buzz.
  Reply With Quote
Old 14th March 2017, 09:42 PM   #10
waltroman is offline waltroman  United States
diyAudio Member
 
Join Date: Jan 2008
Location: Near Gettysburg PA
Quote:
Originally Posted by anatech View Post
Hi waltroman,
Are your heaters DC or AC?

Your power transformer can magnetically couple to the output transformers and output the 60 Hz supply waveform. You can try rotating the transformers to where you get minimal hum, ideally this would be at 90 from the power transformer. There are times when you will be stuck with an odd angle too. Right now it's a bit late since you have built the chassis.

-Chris
\

This amp played for almost two years with zero noise/hum.
  Reply With Quote

Reply


Noise at output transformersHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
transformers and noise Bibio Power Supplies 3 28th March 2014 05:51 PM
Looking for a decent pair of 807(output tube) output transformers hatrack71 Swap Meet 4 5th April 2012 07:43 PM
Difference between SE output transformer and push-pull output transformers hilbert_mostert Tubes / Valves 12 8th March 2009 05:10 PM
Help identifying a pair of output transformers and power transformers mjk130 Parts 3 30th January 2009 10:44 AM
Noise floor rise on heathkit W4-AMs when power supply transformers were swapped terminatorx Tubes / Valves 4 8th October 2006 01:31 AM


New To Site? Need Help?

All times are GMT. The time now is 08:51 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio
Wiki