#26 pre amp - Page 119 - 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 8th September 2011, 04:25 PM   #1181
diyAudio Member
 
Vinylsavor's Avatar
 
Join Date: Feb 2002
Location: Lindau
Hi!

I never had to apply any such screening to DHTs in linestages. never had an issue with hum or other noise pick up. I have used 26, UX201A, UX112, 801, 10Y and others.

I keep the PSU separate with power transformers with electrstatic shields.

Only in an experimental all-DHT phonostage I had to shield the tubes in the very first stage.

Best regards

Thomas
__________________
http://vinylsavor.blogspot.com/
  Reply With Quote
Old 8th September 2011, 04:33 PM   #1182
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Quote:
Originally Posted by Vinylsavor View Post
Hi!

I never had to apply any such screening to DHTs in linestages. never had an issue with hum or other noise pick up. I have used 26, UX201A, UX112, 801, 10Y and others.

I keep the PSU separate with power transformers with electrstatic shields.

Only in an experimental all-DHT phonostage I had to shield the tubes in the very first stage.

Best regards

Thomas
I do much the same in my own projects, but found that close proximity to other ungrounded, but powered metalic objects (like my tuner and SACD player) resulted in electro-static coupling. My environment is quite possibly much less benign than yours, and using HE speakers that roll off well below 40Hz probably doesn't help me much either..
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 8th September 2011, 04:38 PM   #1183
diyAudio Member
 
Vinylsavor's Avatar
 
Join Date: Feb 2002
Location: Lindau
Hi!

Ok, in such a case I believe that it helps.

I have built several DHT linestages for customers in the meantime. Nobody had any noise issues so far. They woudn't have accepted that these beauties are hidden anyways

Best regards

Thomas
__________________
http://vinylsavor.blogspot.com/
  Reply With Quote
Old 9th September 2011, 07:24 AM   #1184
FRUGIVO is offline FRUGIVO  Spain
diyAudio Member
 
Join Date: Feb 2010
Location: Burgos
what I've found is that
the 26 is a real pickup
in my opinion needs to be screened
but the sound achieved with this tube is super

Last edited by FRUGIVO; 9th September 2011 at 07:30 AM.
  Reply With Quote
Old 9th September 2011, 08:01 AM   #1185
diyAudio Member
 
Vinylsavor's Avatar
 
Join Date: Feb 2002
Location: Lindau
Hi!

Quote:
Originally Posted by FRUGIVO View Post
the 26 is a real pickup

As I wrote: not in my experience. For example this preamp is totally quiet. Some people who use such preamps from me said that it has much less noise than their previous ones using indirectly heated tubes.

VinylSavor: 801A / 26 linestage with output transformer and TVC

No screening on the tubes. All metal parts and capacitor enclosures are properly grounded. Also the subplates which hold the tube sockets are grounded.

Power supply is external and well filtered (passive multiple LC stages). Filament is LCL. More photos with external PSU here:

VinylSavor: 801A / 26 linestage with output transformer and TVC

I suspect it has more to do with the surroundings of the tube if there is noise pickup. Especially plate chokes can pick up noise.

Best regards

Thomas
__________________
http://vinylsavor.blogspot.com/
  Reply With Quote
Old 9th September 2011, 09:46 AM   #1186
FRUGIVO is offline FRUGIVO  Spain
diyAudio Member
 
Join Date: Feb 2010
Location: Burgos
Default #27-#26-6c33

this is my project now
source-DAC pcm58- nos--resistor- i/v converter
gain-#27
driver-#26
output-6c33 1w SE OTL cathode follower
Speaker Lowther EX4 in Hedlund horn
Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.

Last edited by FRUGIVO; 9th September 2011 at 09:53 AM.
  Reply With Quote
Old 9th September 2011, 10:51 AM   #1187
diyAudio Member
 
Vinylsavor's Avatar
 
Join Date: Feb 2002
Location: Lindau
Hi!

I bet you are the first one who drives an indirectly heated tube with a DHT

Careful with globe 27s. I have measured a lot on a curve tracer and found that especially the mesh 27s are prone to electrode misalignment which leads to distorted plate curves.

Best regards

Thomas
__________________
http://vinylsavor.blogspot.com/
  Reply With Quote
Old 9th September 2011, 12:01 PM   #1188
regal is offline regal  United States
diyAudio Member
 
Join Date: Jan 2004
Location: MD
Frugivo, I can tell you are a speaker guy. I am willing to chip in to buy you some copper foil, Reynolds wrap has no place covering an antique classic tube

I love that you are driving the 6c33's at 1W with the #26, I can't think of a harder tube to drive than the 6c33 and you are doing it with a #26! I had another thread veiled in disguise touching on this topic, I believe your sucess is dependant on the <1W output cause you aren't swinging many volts into the 6c33 grid and hence don't need a lot of driver current, your post gives me encouragement for my plans with the #26. You wouldn't happen to have a freq response plot you could post ?

Fascinating that you chose the PCM58, I bought one of mouser's last pair of PCM56K thinking of a similar route, just combine the DAC to the amp, I mean with a DAC gain stage why the hard target of 2vRMS? Causes more trouble than it is worth. My concern with an NOS dac like this in combo with the #26 driver is the potential for the #26 to get dragged down by pushing all the unfiltered ultrasonics from the NOS DAC, if you do the math the #26 is seeing a nasty load above the sampling freq and my concern is this could hurt the #26's exemplary linearity. Miller effect must take care of it in the gain stage? You may want to consider a small cap between the plate and grid of the #27 to reduce the ultrasonic content heading to the #26, but only if you want to experiement, your design is creative and a real inspiration. Thanks for the post.

Last edited by regal; 9th September 2011 at 12:04 PM.
  Reply With Quote
Old 9th September 2011, 12:43 PM   #1189
iko is offline iko  Canada
diyAudio Moderator
 
iko's Avatar
 
Join Date: May 2008
Location: Toronto
I would expect the 26 doesn't work so well in the second stage. I was looking myself at a small power amp, 26 choke loaded followed by a 47 (triode connected), gyrator (dn2540) loaded, possibly with a third stage which I've yet to decide, perhaps two paralleled 4P1L. The first two stages look promising so far.
  Reply With Quote
Old 9th September 2011, 01:31 PM   #1190
regal is offline regal  United States
diyAudio Member
 
Join Date: Jan 2004
Location: MD
Quote:
Originally Posted by ikoflexer View Post
I would expect the 26 doesn't work so well in the second stage. I was looking myself at a small power amp, 26 choke loaded followed by a 47 (triode connected), gyrator (dn2540) loaded, possibly with a third stage which I've yet to decide, perhaps two paralleled 4P1L. The first two stages look promising so far.
Yes 1W may be pushing it, I'm still determined to try a #26-45 headamp, would only need to drive the 45 with a 20v volt swing or less, milliwatt output, thinking slew rate wouldn't be much of a factor at such a low output. My fabrication skills to build a vibration dampening platform as vinylsailor innovated has been holding me back, don't want it to look like a hack job, his work sets a high bar!

On paper it would really seem that if the #26 is amplifying any ultrasonics from a filterless DAC that it would be pushed out of linearity. But this is fairly uncharted territory, and I admire this PCM58-#27-#26-6c33 design, its unique, a bit ground breaking with the whole integration.
  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



New To Site? Need Help?

All times are GMT. The time now is 11:05 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