#26 pre amp - Page 201 - 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 2012, 12:41 PM   #2001
CSlee is offline CSlee  United Kingdom
diyAudio Member
 
CSlee's Avatar
 
Join Date: Mar 2009
Location: London
It's a beautiful day in London, probably the last of the year and also the first free time ive had in a long time, so alas I am in the workshop trying to get this #26 up and running.

Ive been following Rod's guide setting the regs and everything seems to be in order. I am running filiament bias 10R, so 10V across filiament resistor. Current is about 0.8A with about 1V across filiament.

Problem I am having at the moment is that the trimmer on the reg board is not making any difference to the current supplied. And looking closely it seems that my #26 isnt lighting up at all. I tried the other 26 and that doesn't light up either. And certainly not drawing any HT current as my HT reading is high, as if unloaded.

What steps do you think I should take now? Is it likely that I have 2 bad valves, or maybe it is something else? I am assuming that these things glow right?

The sunshine and pub is calling me outside, but I am keen to get this working... for now.

Charlie
__________________
Broke solderer with delusions of grandeur
  Reply With Quote
Old 8th September 2012, 03:01 PM   #2002
diyAudio Member
 
Join Date: Sep 2003
Location: London
Those new with filament bias can connect it up the wrong way without thinking. Make sure your supply negative goes to ground and positive goes to one side of the 26 filament. The other side of the filament goes via the 10 ohm resistor to ground. Your natural tendency is to connect the supply to each side of the filament. Just stating the obvious here! So measure the voltages
a) Across the filament
b) Cathode to ground on the resistor.

If these voltages are correct, the 26 should be working and the problem looks like the HT.
26 glows very faintly, but it should be visible. Also it doesn't get very hot. Can you measure the current the 26 is drawing across the plate choke or anode resistor or whatever by measuring its resistance and using Ohms law?

Andy
  Reply With Quote
Old 8th September 2012, 03:01 PM   #2003
CSlee is offline CSlee  United Kingdom
diyAudio Member
 
CSlee's Avatar
 
Join Date: Mar 2009
Location: London
Pub wins
__________________
Broke solderer with delusions of grandeur
  Reply With Quote
Old 8th September 2012, 03:06 PM   #2004
CSlee is offline CSlee  United Kingdom
diyAudio Member
 
CSlee's Avatar
 
Join Date: Mar 2009
Location: London
Hi Andy,

I was measuring no current at all through the valve, so I am assuming my heater wiring was incorrect. Thanks for the tips, I will come back to it later... there are more pressing things to get done first...

Interesting that the trim pot didn't work but the board did, I will go over it again.

Cheers

Charlie
__________________
Broke solderer with delusions of grandeur
  Reply With Quote
Old 8th September 2012, 03:15 PM   #2005
CSlee is offline CSlee  United Kingdom
diyAudio Member
 
CSlee's Avatar
 
Join Date: Mar 2009
Location: London
I'm not actually at my bench so unfortunately can't work on this at the same time as typing here. But I am 'pretty sure' that my wiring was OK as I was reading 10v across the filament resistor, and about 0.9v across heater pins.

Charlie
__________________
Broke solderer with delusions of grandeur
  Reply With Quote
Old 8th September 2012, 04:23 PM   #2006
mogliaa is offline mogliaa  United Kingdom
diyAudio Member
 
mogliaa's Avatar
 
Join Date: Dec 2009
Location: London
I worked fast today to finish the new preamp using the LL2745 that Thomas Mayer send me. The starved filaments at 760mA make the 26 filaments not to glow (use 01a if you are keen to get the nice shine out the valve glass )

Improved bass and overall sound compared to the LL1660 version.

26 Preamp Gen2 completed | Bartola Valves

Very happy so far with the results, for now will listen to it.

I'm going out to enjoy this lovely afternoon in London as well!!
Cheers,
Ale
__________________
"A mistake is always forgivable, rarely excusable and always unacceptable. " (Robert Fripp)
http://www.bartola.co.uk/valves/
  Reply With Quote
Old 8th September 2012, 07:03 PM   #2007
diyAudio Member
 
Join Date: Sep 2003
Location: London
Are those four glow tubes? Orange glow so thinking 75v. Straight sides - don't know those?

Andy
  Reply With Quote
Old 8th September 2012, 08:00 PM   #2008
diyAudio Member
 
Vinylsavor's Avatar
 
Join Date: Feb 2002
Location: Lindau
Hi Ale,

congrats for the completion of the new preamp!
Glad you like the LL2745!

Thomas
__________________
http://vinylsavor.blogspot.com/
  Reply With Quote
Old 8th September 2012, 08:57 PM   #2009
mogliaa is offline mogliaa  United Kingdom
diyAudio Member
 
mogliaa's Avatar
 
Join Date: Dec 2009
Location: London
Quote:
Originally Posted by andyjevans View Post
Are those four glow tubes? Orange glow so thinking 75v. Straight sides - don't know those?

Andy
Andy,
Yes, Russian 75v ones with CCS "a la Gary Pimm". Superb HT filtering using the glow tubes as shunt.

They look really cool in the dark!!
__________________
"A mistake is always forgivable, rarely excusable and always unacceptable. " (Robert Fripp)
http://www.bartola.co.uk/valves/
  Reply With Quote
Old 8th September 2012, 09:04 PM   #2010
mogliaa is offline mogliaa  United Kingdom
diyAudio Member
 
mogliaa's Avatar
 
Join Date: Dec 2009
Location: London
Quote:
Originally Posted by Vinylsavor View Post
Hi Ale,

congrats for the completion of the new preamp!
Glad you like the LL2745!

Thomas
Hi Thomas,
Yes, LL2745 is much better for the 26 clearly. I did not follow your advise in the end after some tests ended up wiring up it on 5.6:1 so sacrificed output impedance a bit.
Either way, bass is fuller than before and overall tone is very nice. I need to run this version for a while and then connect back older 26 preamp to contrast properly....
Thanks for the help!
Ale
__________________
"A mistake is always forgivable, rarely excusable and always unacceptable. " (Robert Fripp)
http://www.bartola.co.uk/valves/
  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 02:31 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