b+ Delay Arrangement for Power Amp - 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 28th June 2012, 12:33 PM   #1
diyAudio Member
 
Join Date: Oct 2002
Location: SINGAPORE
Default b+ Delay Arrangement for Power Amp

I have individual filament transformers for my pair power output DHTs, and a separate power transformer for the high voltage. Rectification for HV is by means of SS diodes.

I am planning to have the powering up sequence in such a manner :-
Upon turning on the amp, the filament transformers will be powered up and light up the filaments of the output DHTs. 20 seconds later, the AC input to the primary of the HV transformer will be turned on by means of a delay relay and thus giving the HV. And since this is SS diode rectified, full high tension DC will immediately hit the anode of the DHTs and also channels to supply the driver section of the amp, without the slow start benefit of tube rectifiers.

Will there be any potential problems with this kind of arrangement? Eg. any noise or pops when the maximum HV dc hits the tubes?
  Reply With Quote
Old 28th June 2012, 12:46 PM   #2
oshifis is offline oshifis  Hungary
diyAudio Member
 
Join Date: Mar 2004
Location: Budapest, Hungary
Quote:
Originally Posted by commstech View Post
I have individual filament transformers for my pair power output DHTs, and a separate power transformer for the high voltage. Rectification for HV is by means of SS diodes.

I am planning to have the powering up sequence in such a manner :-
Upon turning on the amp, the filament transformers will be powered up and light up the filaments of the output DHTs. 20 seconds later, the AC input to the primary of the HV transformer will be turned on by means of a delay relay and thus giving the HV. And since this is SS diode rectified, full high tension DC will immediately hit the anode of the DHTs and also channels to supply the driver section of the amp, without the slow start benefit of tube rectifiers.

Will there be any potential problems with this kind of arrangement? Eg. any noise or pops when the maximum HV dc hits the tubes?
I use a similar arrangement, but separate manual switches for the filament and for the HV. Actually the filament is permanently on, except being away from home for several days. When I turn on the HV, there is no any pops heard. Take into account that the mains transformer has some stray inductance, and together with the filter capacitor it makes a low-pass filter, so reaching the full HV takes some (however little) time. At least the capacitors do not charge with infinite speed. The HV switch should pass high surge current, and should withstand at least 2x the amount of HV. I switch the AC at the secondary of the transformer before the rectifier diodes, not the filtered HV after the capacitor.
  Reply With Quote
Old 28th June 2012, 02:52 PM   #3
diyAudio Member
 
Osvaldo de Banfield's Avatar
 
Join Date: Dec 2011
Location: Barrio Garay,Almirante Brown, Buenos Aires, Argentina
I think that would be better to add a NTC surge protector at each AC line of the rectifier, to protect them from inrush currents, and reduce surges in the power line.
__________________
LW1DSE
  Reply With Quote
Old 29th June 2012, 03:09 AM   #4
garbage is offline garbage  Singapore
diyAudio Member
 
garbage's Avatar
 
Join Date: Apr 2004
Location: Singapore
i use something similar, but it is because of the MV rectifiers (ok, taboo; i know). the amps are mono blocks and when b+ kicks in on the first mono, no pop or clicks. but at the second one, i get a pop on the speaker.

the speakers are coral beta 8 in BR box. ~100db sensitivity.

i tried various NTC values, but they did not help.
  Reply With Quote
Old 29th June 2012, 05:41 AM   #5
diyAudio Member
 
Join Date: Oct 2002
Location: SINGAPORE
strange that it only happens for one channel. could be due to other reasons besides the turn on surge. Have u managed to solve the problem?
  Reply With Quote
Old 29th June 2012, 06:56 AM   #6
garbage is offline garbage  Singapore
diyAudio Member
 
garbage's Avatar
 
Join Date: Apr 2004
Location: Singapore
i did not manage to solve the problem. the pop occurs at the speaker with the mono that is already turned on. i think it is because the b+ in rush on the 2nd mono caused some spike in the electrical outlet. both monos are connected to the same electrical circuit.

the circuit to my audio room is a dedicated ring that comes from my main circuit breaker.

i guess the only way to really solve this is to build a soft start circuit like the one at ESP, or implement some muting at the output transformer secondary (but i was told that output transformers should ideally not be unloaded for too long).
  Reply With Quote
Old 29th June 2012, 07:11 AM   #7
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
Here is DIY delay relay that can be more effective:

Click the image to open in full size.

But if to speak seriously, all depends on which tubes you use, on which voltages, and how is bias organized.
__________________
The Devil is not so terrible as his math model is!
  Reply With Quote
Old 29th June 2012, 08:16 AM   #8
12E1 is offline 12E1  United Kingdom
diyAudio Member
 
12E1's Avatar
 
Join Date: May 2012
Location: Near Huntingdon, Cambridgeshire, UK
Quote:
Originally Posted by garbage View Post
i guess the only way to really solve this is to build a soft start circuit like the one at ESP, or implement some muting at the output transformer secondary (but i was told that output transformers should ideally not be unloaded for too long).
You should not mute by removing the load from an output transformer, since large current transients on the primary side while the secondary is unconnected can induce very high voltages across the primary which can result in arcing and insulation breakdown. Bye-bye transformer.

In my view, if you really need to disconnect the speaker, then you should first switch an alternative dummy load across the secondary and then remove the speaker from the circuit. It's more complex but safer. An alternative would be to simply place an additional temporary load across the speaker terminals with a relay contact which will absorb most of the unwanted noise (this could be less than one ohm, possibly almost a short circuit). If there is no real signal going through the amplifier at this time then that should be a pretty safe option.
  Reply With Quote
Old 29th June 2012, 03:34 PM   #9
diyAudio Member
 
Join Date: Oct 2002
Location: SINGAPORE
Quote:
Originally Posted by Wavebourn View Post

But if to speak seriously, all depends on which tubes you use, on which voltages, and how is bias organized.
Let's just say large transmitter tubes in general working in the 1kV range, in self-bias design. Any disastrous effect on the powering up arrangement mentioned?
  Reply With Quote
Old 29th June 2012, 10:38 PM   #10
diyAudio Member
 
Join Date: Mar 2011
Location: Jarna
Should work fine.

Always keep the relays on the AC side if possible.

Preferable on primary low voltage.

If trying to switch DC the chance of arcing is high.

Only thing i found working on the HV DC (>1kV) is high vakuum reed relays and they cost an arm and a leg !
  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
Simple B+ delay circuit for tube power amp? rongon Tubes / Valves 31 29th August 2011 09:40 AM
Delay Amp power up using a relay. HAUDIO Solid State 3 21st June 2011 02:36 AM
Delay time through power amp? sumaudioguy Solid State 2 6th March 2010 01:12 PM
Janszen Model 1 (New ESL & Woofer Arrangement) bolserst Planars & Exotics 22 12th November 2009 09:42 PM
Question on capacitor arrangement for aleph 2 amp BrianGT Pass Labs 11 12th March 2002 09:51 PM


New To Site? Need Help?

All times are GMT. The time now is 12:40 PM.


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