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

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

4P1L DHT Line Stage
4P1L DHT Line Stage
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 17th April 2019, 01:57 AM   #1631
mr ed is offline mr ed  United States
diyAudio Member
 
Join Date: Jan 2009
Location: Willis Tx
I just move to Willis in 2014.
Austin area since 1982. I like San Marcos, have other family in thearea.

Cheers
__________________
currently watching electrons party under glass
  Reply With Quote
Old 19th April 2019, 08:26 AM   #1632
andyjevans is offline andyjevans  United Kingdom
diyAudio Member
 
Join Date: Sep 2003
Location: London
Thanks to the suggestions here I left out the resistor at the top of the SIC diodes - turned out it wasn't doing anything useful and the sound was better with just the diodes. I A-B'd the 4P1L with my large NP Acoustics plate choke against the 26, and I'm slightly preferring the 26. It has more "life" and makes the 4P1L, which is otherwise very detailed and neutral, sound just a touch two-dimensional. I've been running the 26 at 7mA without any obvious ill effects.
Attached Images
File Type: png SIC:R bias 26 7mA Plus.png (33.2 KB, 349 views)

Last edited by andyjevans; 19th April 2019 at 08:29 AM.
  Reply With Quote
Old 19th April 2019, 01:33 PM   #1633
vcoustics is offline vcoustics  United States
diyAudio Member
 
Join Date: Jan 2017
Location: Atlanta, GA
I have a 4P1L using the K & K audio board (great build quality) and Rod Coleman Regs for each tube.
Issue I am having: the f- and f+ is always rising to 2.7 V which it too high and not the 2.1 the data sheet dictates. Anyone incountered this? I dropped the supply voltage down to 13.5V in a attempt to lover the f voltage and still 2.7.


Should the tubes also be making a chime noise during warmup?
Might be the way too high f voltage. I only ran them a few min because of the high voltage.
  Reply With Quote
Old 19th April 2019, 07:19 PM   #1634
andyjevans is offline andyjevans  United Kingdom
diyAudio Member
 
Join Date: Sep 2003
Location: London
I'm sure Rod will come in here, but 13.5v seems far too high as a supply voltage. I think it depends which vintage of Coleman regs you have. Around V4 you needed approx 7v headroom which puts the supply voltage at around 9v. We're now on V7 and I think the ideal headroom is a bit below that. So I'd try 9v supply just to start with, not more. You also need to use the onboard trimmer to set the voltage correctly once the supply voltage is in the right range, with your voltmeter between pin 7 and pin 1+8. I assume that's how it's connected for 2.1v. If you have a bench voltage supply you can bring the voltage up gradually and you should come to an area (probably around 7-9v supply) where the filament voltage stabilises and goes up more slowly. This is the area where the reg should be working correctly. The voltage continues to rise, but more slowly.

Have you fully read Rod's instructions for use of the reg? His instructions are a model of completeness and clarity.

Last edited by andyjevans; 19th April 2019 at 07:22 PM.
  Reply With Quote
Old 19th April 2019, 09:13 PM   #1635
Rod Coleman is offline Rod Coleman  United Kingdom
работник
diyAudio Member
 
Rod Coleman's Avatar
 
Join Date: Jul 2004
Location: Warwickshire UK
4P1L DHT Line Stage
Quote:
Originally Posted by vcoustics View Post
I have a 4P1L using the K & K audio board (great build quality) and Rod Coleman Regs for each tube.
Issue I am having: the f- and f+ is always rising to 2.7 V which it too high and not the 2.1 the data sheet dictates. Anyone incountered this? I dropped the supply voltage down to 13.5V in a attempt to lover the f voltage and still 2.7.


Should the tubes also be making a chime noise during warmup?
Might be the way too high f voltage. I only ran them a few min because of the high voltage.
Yes, 13.5V supply is very high - unless you have a filament bias resistor.

Is the filament connected in parallel mode for 2.1V?

If you send me some email, I can send the debug test points - if there is anything wrong, it will show up there.

When a DHT filament warms up, it slackens its tension, and this can chime on the supports.
  Reply With Quote
Old 19th April 2019, 11:12 PM   #1636
andyjevans is offline andyjevans  United Kingdom
diyAudio Member
 
Join Date: Sep 2003
Location: London
Quote:
Originally Posted by andyjevans View Post
You also need to use the onboard trimmer to set the voltage correctly once the supply voltage is in the right range, with your voltmeter between pin 7 and pin 1+8. I assume that's how it's connected for 2.1v.
Silly mistake - connection in parallel is between pin 8 and pin 7+1. Sorry!
  Reply With Quote
Old 20th April 2019, 11:45 AM   #1637
vcoustics is offline vcoustics  United States
diyAudio Member
 
Join Date: Jan 2017
Location: Atlanta, GA
I do use a Fill bias resistor at 12R.
I Use the V7 version.
I use the 8,1 and 7 to get the 2.7V

Even as I adjust the trim pot on the Regs it still floats at 2.7. Could the pots screw mechanics be broken? Or melted? I have large heat sinks on them and they get luke warm at best.
  Reply With Quote
Old 20th April 2019, 07:24 PM   #1638
Rod Coleman is offline Rod Coleman  United Kingdom
работник
diyAudio Member
 
Rod Coleman's Avatar
 
Join Date: Jul 2004
Location: Warwickshire UK
4P1L DHT Line Stage
Please send me some email - I can send a guide to taking a handful of voltage measurements, that will show what is wrong.
  Reply With Quote
Old 22nd April 2019, 11:57 AM   #1639
Frank40 is offline Frank40  Denmark
diyAudio Member
 
Frank40's Avatar
 
Join Date: May 2004
Location: My workshop :-)
I can see that some of you uses diodes as bias for your tubes, it seems to me that the reason must be to get a low value of cathode impedance in the absent of an cap.

But you lose the ability to adjust to a precise current. I was thinking of another solution, se schematics below. Please tell me if you think it will work.

The dynamic resistant is roughly R (in ohm) = 25/I cathode (in mA)
Attached Images
File Type: jpg catode_voltages.JPG (50.0 KB, 231 views)
  Reply With Quote
Old 23rd April 2019, 12:54 PM   #1640
mogliaa is offline mogliaa  United Kingdom
diyAudio Member
 
mogliaa's Avatar
 
Join Date: Dec 2009
Location: London
4P1L DHT Line Stage
The use of SiC diodes or some specific wirewound resistors has to do solely on their sound clarity. There are multiple ways to bias a stage (like there are to skin cats as they say) but not all sound equal

You can build and compare the one you show above.

Ale
__________________
"A mistake is always forgivable, rarely excusable and always unacceptable. " (Robert Fripp)
http://www.bartola.co.uk/valves/
  Reply With Quote

Reply


4P1L DHT Line StageHide 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
All DHT Phono Stage Steve Cresswell Tubes / Valves 32 2nd April 2013 06:24 PM
one stage DHT amp Jaime Tubes / Valves 2 18th October 2010 12:31 PM
Which DHT for Line stage? andyjevans Tubes / Valves 15 26th March 2009 01:10 PM
Aikido line stage - plus phono line stage cjkpkg Tubes / Valves 1 22nd November 2008 09:50 PM
Line stage preamp, based on SY's "Heretical Unity gain line stage" Danko Tubes / Valves 23 18th July 2005 04:07 AM


New To Site? Need Help?

All times are GMT. The time now is 07:43 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki