6J7 preamp - Page 2 - 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 31st August 2012, 08:11 PM   #11
diyAudio Member
 
Osvaldo de Banfield's Avatar
 
Join Date: Dec 2011
Location: Barrio Garay,Almirante Brown, Buenos Aires, Argentina
Pin 1 MUST be to ground, not to the cathode!!!
__________________
LW1DSE
  Reply With Quote
Old 31st August 2012, 08:14 PM   #12
diyAudio Member
 
Joe Roberts's Avatar
 
Join Date: Feb 2006
Location: VA
Quote:
Originally Posted by Osvaldo de Banfield View Post
Pin 1 MUST be to ground, not to the cathode!!!
That is for sure.
  Reply With Quote
Old 31st August 2012, 08:28 PM   #13
disco is offline disco  Netherlands
diyAudio Member
 
disco's Avatar
 
Join Date: Apr 2006
Location: Holland
for starters....
__________________
jaap
  Reply With Quote
Old 31st August 2012, 08:28 PM   #14
diyAudio Member
 
Osvaldo de Banfield's Avatar
 
Join Date: Dec 2011
Location: Barrio Garay,Almirante Brown, Buenos Aires, Argentina
Quote:
Originally Posted by Joe Roberts View Post
That is for sure.
Appears for the guy, not to be so.
__________________
LW1DSE
  Reply With Quote
Old 31st August 2012, 08:34 PM   #15
6J7 is offline 6J7
diyAudio Member
 
6J7's Avatar
 
Join Date: Apr 2009
Thank you all for your answers, tomorrow I'll take a photo and try what you said.

About pin 1, when looking at the datasheet:

"with shell and internal shield connected to cathode"

I tought it was the way to connect it..
  Reply With Quote
Old 31st August 2012, 08:35 PM   #16
diyAudio Member
 
Joe Roberts's Avatar
 
Join Date: Feb 2006
Location: VA
Quote:
Appears for the guy, not to be so.
But he is off to a great start. Nice looking project!

Time to learn a few basic tube DIY lessons the hard way, the best way to learn.
  Reply With Quote
Old 1st September 2012, 09:23 AM   #17
6J7 is offline 6J7
diyAudio Member
 
6J7's Avatar
 
Join Date: Apr 2009
Hi,

This morning I connected the grid wire shield to ground, connected the 6J7 pin 1 to ground and completely disconnected the pot (maybe easier to find the problem)

Not yet connected to my system to see if there is an improvement but I tried this:

- input shorted
- preamp output to line-in computer (playthrough option + headphones), laptop on battery only.

As soon as I switch on the main preamp switch (not the B+), there is HUM.. even when the 6J7 are removed from the sockets..

Here is a pic:

https://dl.dropbox.com/u/425350/6J7%...p/IMG_1631.jpg

- C1 si common to L & R
- chassis connected to earth (also green/yellow wire of the transformer)
- C1 ground connected to earth through a 100R (test without earth connection, it does not really change something)

Transformer is a toroidal..

Do you see some things totally wrong on the pic ? ( Yes, I am a beginner..)

Thank you

  Reply With Quote
Old 1st September 2012, 11:09 AM   #18
6J7 is offline 6J7
diyAudio Member
 
6J7's Avatar
 
Join Date: Apr 2009
Following the same procedure (laptop + headphones), I moved the preamplifier to the living room on its table, I clearly hear a hum even when it's not plugged in the mains..

When switching off the 1KVA isolation transformer who is just under the table, hum disappears.

When moving the preamplifier 1 meter away from the 1KVA transformer, hum disappears.

When connecting the preamp to the mains (but switched off) while it's away, no hum.

When I switch it on (no B+), hum appears...

  Reply With Quote
Old 1st September 2012, 12:01 PM   #19
diyAudio Member
 
Shoog's Avatar
 
Join Date: Aug 2002
Location: Eire
Single star ground for all grounding points has never failed to kill hum for me. Bus type grounds often produce issues with hum. Pick a central point on your case and run earth leads with tags to that point. Run a bolt through the case, attach all tags and bolt down.

PS - The connection between signal earth and safety earth has been cut, reinstate it heavy gauge wire without the resistor. Think of current as water flowing down hill with the safety earth as a sink hole. It encourages the high currents in the power supply section to bleed off to earth rather than up to the small signal ground. If you try this it may allow you to avoid using star grounding.

Shoog

Last edited by Shoog; 1st September 2012 at 12:12 PM.
  Reply With Quote
Old 1st September 2012, 08:32 PM   #20
6J7 is offline 6J7
diyAudio Member
 
6J7's Avatar
 
Join Date: Apr 2009
I removed the resistor and installed a big wire, there is definitively a big improvement ! hum not completely gone but far better than before, thanks.

This preamplifier has too much gain, time to try again with the stepdown transformers.

I have to reinstall the volume pot, is it a bad idea to connect it to output instead of input ? it's a 10K.
  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
6J7 driver in WE91 like amplifier bobluis Tubes / Valves 9 10th February 2011 07:09 PM
Tube Preamp Popping on Source Input Change (?) / 6DJ8 Preamp On Chip Amps MartyM Tubes / Valves 3 16th October 2008 05:52 AM
Guitar Preamp = MIC Preamp = other preamp ,,are they all same? Paswa Solid State 1 12th March 2008 06:16 PM
twisted pear Preamp/other suggestions for Preamp kit LukeDuke Chip Amps 1 1st February 2008 10:57 PM
Electret mic preamp - will phono preamp work? darthmullet Analogue Source 6 12th October 2007 08:32 AM


New To Site? Need Help?

All times are GMT. The time now is 07:30 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2