New DHT heater - Page 52 - 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 27th July 2012, 07:33 AM   #511
Desmo is offline Desmo  Denmark
diyAudio Member
 
Join Date: Jan 2007
Location: Aarhus
OK... I have now done two listening sessions with the new Rod Coleman regulators installed.

The much lower noise floor than before is a big relief actually, listening is so much better, when there is no noise in the quite passages and between tracks.

But the lower noise floor is actually just a bonus because the major advantage is the sound that improves quite a lot with these Rod Coleman regulators..! I guess many does not know the DIY HIFI SUPPLY Tram II preamp, but it's a DHT using 2A3 triodes, and it has a very, very natural and dynamic sound. I have always considered the Tram II to be on of the most natural sounding preamps I have ever tried, but when listening with these regulators installed I now realize that a thin ''electronic sounding haze'' has been removed. It was natural sounding before, and even more natural sounding now.

Furthermore ''images float in space'', these words (the Danish version ;-)) just kept popping up in my head when listening with these installed. There is a flow to the music and the images float in a 3 dimensional space in a totally different way than before. It's not that the soundstage is bigger as such, but it's more real, more there, more open, more natural and the music has better flow and a focus that it did not have before. With this thin haze lifted away I also here more details, especially the ones that usually hides deep in the mix. For instance I listened to a jazz LP and during a guitar solo I could hear the guitar player humming his tunes while he was playing them. I have not heard that before on this record..!

These are my first impressions, and a big THANK YOU to you Rod for these regulators and your help

After reading the thread I see that even better sound can be had by a few updates of a resistor and a cap. Components are ordered
  Reply With Quote
Old 27th July 2012, 08:00 AM   #512
работник
diyAudio Member
 
Rod Coleman's Avatar
 
Join Date: Jul 2004
Location: Warwickshire UK
Thank you, Morten, for letting us know! I am pleased that the Regulators have worked well.

It is interesting to note that the TRAM II is 2A3-powered. Many DIYers still believe that the low filament-voltage of the 2A3 means that ac-heating is fine.

In fact, the 2A3 always needs careful filament heating, even in PP power amps, because the real consideration is the anode/plate current. At 60mA dc, and the signal current of 1 .. 10mA (for quiet listening) - you have to take very great care with the design of a 2500mA heating supply or regulator, if the errors/overshoots/noise of the 2500mA is to avoid stamping all over the 10mA! And since the heating current and the anode current flow in the same metal wire, this is what will happen.
  Reply With Quote
Old 27th July 2012, 08:31 AM   #513
Desmo is offline Desmo  Denmark
diyAudio Member
 
Join Date: Jan 2007
Location: Aarhus
Your welcome Rod..! And your explanation of errors/overshoot/noise from the 2500mA regulator stamping all over the tiny signal currents makes sense in relation to the improvements I hear with your regulators.
  Reply With Quote
Old 28th July 2012, 06:26 PM   #514
Desmo is offline Desmo  Denmark
diyAudio Member
 
Join Date: Jan 2007
Location: Aarhus
I have now updated C3 and R1. For C3 I have choosen Amtrans AMCH mylar caps... Good sound, decent price, not that big so they can actually fit, finally they are spec'ed for high temperatures. For R1 I have choosen 12W Mills wirewound, they sound great and have a big surface area to dissipate the heat from so they don't run so hot.

When not using R2 there is actually decent space for the caps, so the installation can be quite clean as seen here I agree with the previous posters: Upgrading these gives a clear sonic improvement..!

Click the image to open in full size.

Last edited by Desmo; 28th July 2012 at 06:42 PM.
  Reply With Quote
Old 31st July 2012, 02:48 AM   #515
Bigun is offline Bigun  Canada
diyAudio Member
 
Bigun's Avatar
 
Join Date: Jan 2009
Blog Entries: 2
you've done a very nice job of fitting that all neatly inside the existing chassis. Glad it turned out well from a sound point too.
__________________
"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.
  Reply With Quote
Old 31st July 2012, 07:07 AM   #516
Desmo is offline Desmo  Denmark
diyAudio Member
 
Join Date: Jan 2007
Location: Aarhus
Thanks Bigun..! It has been quite a lot of work to implement the heaters because the chassis is so small, but I'm really glad that I did the effort because the sound is so much better with these heaters (and noise so much lower).

BTW, I know that carbon resistors is ''the new crome'' these days, but if anyone is interested then give the Mills wirewound a chance, they sound really good..!
  Reply With Quote
Old 4th August 2012, 09:33 AM   #517
Desmo is offline Desmo  Denmark
diyAudio Member
 
Join Date: Jan 2007
Location: Aarhus
Tram II preamp owners calling Rod Coleman

Since your DHT regulators starts slower than the voltage regulators originally installed in the Tram II preamp we are bit worried about stressing the DHT's, so we consider a delayed start of the anode voltage. The Tram II has one of these ''electronic choke'' supplies that both sends out the +B and the -C supplies as you can see in this schematic. Looking at the best place to have the relays for the delayed start I think this position might be the best solution? (see red markings, upper right hand corner).

Let's say we delay for one minute, then the heater voltage will be strong on the DHT's and also on the rectifier tube when the +B and -C kicks in. The question is, if it's a problem that the +B will then ramp up faster than normal due to the heater voltage on the rectifier tube being on from the beginning..!?

Another option could be to insert the relay directly on the +B at the output of the power supply module, then everything except +B will start up as usual.

Any advise would be appreciated - thanks

Morten

Click the image to open in full size.

Last edited by Desmo; 4th August 2012 at 09:47 AM.
  Reply With Quote
Old 4th August 2012, 10:28 AM   #518
работник
diyAudio Member
 
Rod Coleman's Avatar
 
Join Date: Jul 2004
Location: Warwickshire UK
Hi Morten,

With any heating method, it is best to switch the HV on, after the filaments have warmed up. The Rise time of the B+ should be a slow ramp. You can put a switch or relay in the Centre-Tap-to-GND wire of the power trafo.


The alternative method: Bias the 2A3s and other fixed-bias tubes to cut-off level (eg -90V).


However, looking at the schematic you posted, the DIYHFS autobias module appears to be present. This module (If I have read correctly) applies a very high negative bias to the 2A3 grid when power is applied, and gradually decreases the bias level until the programmed anode current is achieved.

If this is so, the high negative bias will reduce the electric field around the filament to almost zero. So far as the filament knows, there is no HT applied!

You can check the value of negative bias at switch-ON, and if it is large enough to cut-off the anode current, it is safe.

This solution is better than switching the B+, and so for your preamp, no further action is required.
  Reply With Quote
Old 4th August 2012, 10:41 AM   #519
Desmo is offline Desmo  Denmark
diyAudio Member
 
Join Date: Jan 2007
Location: Aarhus
Hi Rod,

Yes, you are right: The DIYHFS autobias modules is part of the Tram II preamp (it's the circuit board between the DHT's in the pics I have show inside the Tram II), I will try to measure the time it takes for the autobias to decrease negative bias level, compared to the time it takes for your regulator to get up to 2,3 - 2,5V. Based on your comments I suppose all is good even if the +B is applied faster than the heater voltage from your regulator, as long as the autobias decreases the bias even slower than the voltage comes on from your regulator. Correct?

Last edited by Desmo; 4th August 2012 at 10:46 AM.
  Reply With Quote
Old 4th August 2012, 10:58 AM   #520
работник
diyAudio Member
 
Rod Coleman's Avatar
 
Join Date: Jul 2004
Location: Warwickshire UK
Yes, that's right.

Slow warming of the filaments is safer anyway, as the temperature will be more uniform.
  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
how to wire 6.3VDC heater on a heater with center tap (12.6V series, 6.3V parallel)? jarthel Tubes / Valves 9 14th April 2012 06:36 PM


New To Site? Need Help?

All times are GMT. The time now is 03:21 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