#26 pre amp - Page 112 - 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 5th July 2011, 05:33 PM   #1111
diyAudio Member
 
coolzero's Avatar
 
Join Date: Sep 2009
Location: UAE
Quote:
Originally Posted by Vinylsavor View Post
Hi!

I use LCLCLC filtering in my preamps. I use large inductances of 50-100Hy. Caps in the range 40-50uF. I want my preamps to be hum free.

The last LC section is separate for each channel.

Ultrapath requires much more ripple free B+ unless it is used in hum cancelling mode which I'm not doing. With conventional circuit you might get away with LCLC, but I'd use much bigger inductances. With the small currents needed by the 26, 100Hy is easily available

Thomas
This may be a dumb question but anyway I ask . I have two of 200H plate chokes. Is it possible to use those for this application?
  Reply With Quote
Old 5th July 2011, 05:39 PM   #1112
diyAudio Member
 
Vinylsavor's Avatar
 
Join Date: Feb 2002
Location: Lindau
Hi coolzero,

if their current rating is sufficient, yes.

Thomas
__________________
http://vinylsavor.blogspot.com/
  Reply With Quote
Old 6th July 2011, 04:41 PM   #1113
diyAudio Member
 
coolzero's Avatar
 
Join Date: Sep 2009
Location: UAE
Quote:
Originally Posted by Vinylsavor View Post
Hi coolzero,

if their current rating is sufficient, yes.

Thomas
It is rated 10ma.
  Reply With Quote
Old 10th July 2011, 03:33 PM   #1114
BenZene is offline BenZene  United States
diyAudio Member
 
Join Date: Feb 2007
Location: California
Default #26 pre amp

Hi!

Am new to this site and also a newbie to tube audio.

After reading the posts from start to the latest (from coolzero) , I was inspired to resurrect my 26 pre amp, which I had ask a friend to build 2 years ago. Thanks to the wealth of info I got from this site, my 26 is now making music and is quiet. (It hummed and buzzed and sounded thin in my system before, that's why I abandoned it). Now I'm immensely satisfied with the sound of my system!

There's something that puzzles me with regards to the B+ reading I get. My friend told me the easiest way to get the B+ reading is to connect the probes of my multimeter to the cathode and plate of the tube. BTW my settings are Va= 138v; Vg=-9v; Ia=6mA. With the multimeter set at VDC, I did just as I was told to. With the RCA tubes in I got B+ readings of 144v & 147.9v. I only have 5 pairs of 26 tubes of different brands i.e., RCA, Silvertone, Philco, Sylvannia & NU and took B+ readings for each pair. The difference in B+ readings per pair were from a low of 2 volts (132.2 & 134.2) to a high of 13 volts (154.1 & 141.1). The pair with the lowest B+ reading, which was the Philco and which sounded poor in the original iteration of my 26 preamp sounded the best now! ... Is this normal and did I do the correct procedure in getting the B+ reading?

Another thing that puzzles me is the filament reading I get. What I did was I took out the tubes from their sockets, turned on the preamp and stuck the probes of my digital meter to the pins assigned to the filaments. Both sockets gave me a reading of 4 VDC! ... When I placed back the tubes in the sockets, I get a reading of 1.4 VDC & 1.53 VDC. Just for curiosity sake, I added a 0.11R to the channel with the higher filament reading (hoping it would also bring down the B+ reading for that tube.) ... Turned on the preamp and took a reading of the filaments. I got 1.41 VDC & 1.45VDC, which I think is just fine. However, when I took the B+ reading for both tubes (same procedure as I did before), I got 144 VDC & 87 VDC! Before the addition of the 0.11R, the B+ readings were 144 & 147.9. I checked my solder connections and didn't find anything wrong with it. Turned on the preamp again and took a B+ reading ... same thing, 144 & 87! I took out the 0.11R and the reading is back to 1.40 & 1.53 (filaments) and 144 & 147.9 (B+). BTW these readings are for the RCA pair.

So sorry for the long post and newbie questions. Am still trying to learn more about tubes.

Please enlighten me on what's going on in my preamp. Why the difference in the voltages.

Humbly yours,
BenZene
  Reply With Quote
Old 17th July 2011, 05:37 PM   #1115
diyAudio Member
 
Join Date: Dec 2007
hi guys

i need help please. this is my 1st DHT preamp. i am using LOT for output and Rod's filamen

i just wired up my #26 and there is a loud hum. as loud as when we listen to music and maybe bit louder. i pass through the music tho. hence i dont wired it wrongly

my psu consist of 4 chokes. 2 for B+ and 2 for ground and 2 dropping resistor also one for ground and B+

the hum gets louder when i connect the inputs from the Dac which has output caps. while i dont have input caps for #26

when i float the ground from IEC earth, the hum is cut to half

im using 470K grid resistor to ground and 1K8 cathode resistor to ground

B+ is 170v
voltage at cathode is 13v
Plate voltage is 166v

any helps, pointers, suggestions are really appreciated
thanks in advance
erwin
  Reply With Quote
Old 17th July 2011, 06:01 PM   #1116
diyAudio Member
 
merlin el mago's Avatar
 
Join Date: Sep 2009
Location: Catalonia - Europe
Quote:
Originally Posted by merlin el mago View Post
For AZ1 tube hybrid rectification I only get 2 x 6VAC 12VA

MULTICOMP|MCF/N3506F|TRANSFORMADOR, 12VA, 2 X 6V | Farnell España

To drop 2V I will connect 1R 5W in each cathode, it's OK?
Quote:
Originally Posted by andyjevans View Post
Looks about right.
Wich kind of resistors are the best suitables? both 1% tol.:

| Pasivos | Resistencias | Pasantes, fijas | No inductivo - Encapsulado por orificio pasante
TCR +-50ppm/ºC
Wire Wound Silicon Coated
5W

NS0051R000FB12 Vishay/Dale Wirewound Resistors - Through Hole
TCR 20 → 80ppm/°C
Thick film
15W

Others suggestions will welcome.
  Reply With Quote
Old 17th July 2011, 06:15 PM   #1117
diyAudio Member
 
Join Date: Sep 2003
Location: London
Welwyn | Pasivos | Resistencias | Pasantes, fijas | Formato axial con esmalte vítreo - 2,5 a 14 W |W22-1R0JI

I use Welwyn wire wounds for most things.

Andy
  Reply With Quote
Old 17th July 2011, 06:19 PM   #1118
diyAudio Member
 
merlin el mago's Avatar
 
Join Date: Sep 2009
Location: Catalonia - Europe
I used Welwyn too, are great resistors, thanks Andy.
  Reply With Quote
Old 17th July 2011, 06:22 PM   #1119
diyAudio Member
 
Vinylsavor's Avatar
 
Join Date: Feb 2002
Location: Lindau
Hi!

Quote:
Originally Posted by milen007 View Post
my psu consist of 4 chokes. 2 for B+ and 2 for ground and 2 dropping resistor also one for ground and B+

In order to help, some more information is required. A schematic maybe? Did you measure the ripple present on B+ and filament?

Is the signal ground connected to chassis?

also a photo of the wiring would be helpful

Thomas
__________________
http://vinylsavor.blogspot.com/
  Reply With Quote
Old 18th July 2011, 08:52 AM   #1120
diyAudio Member
 
Join Date: Dec 2007
hi Thomas

i sketch up a schematic. hope they good enough
B+ is vary around 2v

hope the link i paste the pictures works

https://picasaweb.google.com/lh/phot...eat=directlink

https://picasaweb.google.com/lh/phot...eat=directlink


schematic
https://picasaweb.google.com/lh/phot...eat=directlink


ground wiring
https://picasaweb.google.com/lh/phot...eat=directlink
  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 10:28 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