Vacuum Tube Pre O.C.L. - 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 13th February 2006, 06:35 PM   #1
diyAudio Member
 
Join Date: Dec 2004
Location: Roma
Default Vacuum Tube Pre O.C.L.

Hi everybody!

Anybody knows a schematic of an all Vacuum Tube Pre amplifier, with no capacitor on the signal path?

What kind of solution has been implemented?

Thanks in advance.
Gm
  Reply With Quote
Old 13th February 2006, 07:38 PM   #2
diyAudio Member
 
analog_sa's Avatar
 
Join Date: Aug 2002
Location: Sofia
SY's preamp described on this forum. Any transformer coupled design. It's easy to avoid coupling caps but not necessarily cheap.
  Reply With Quote
Old 13th February 2006, 08:46 PM   #3
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Actually, my preamp does have one coupling cap internal to it, though I eliminated the troublesome output cap. The input cap could be eliminated, too, by returning the servo output to the bottom of the transformer, but I think that's a cure worse than the disease; the input cap is pretty innocuous, but redoing the servo connection puts any servo errors and grunge right back to the input of the circuit.

One can do some level shifting to get direct coupling all the way through at the expense of complexity. I've played with it in the past and never thought is was even vaguely worthwhile.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 14th February 2006, 04:54 AM   #4
diyAudio Member
 
Join Date: Oct 2005
Default Warning: NewB question

Sy,

What happened to the little chef? All this time I thought you were a child prodigy or something... heretical preamp with a little Frim Fram Sauce on the side.

Seriously (Sy or anyone) if cost weren't an issue, which would be the better choice for a simple preamp: a really good coupling capacitor or a really good input/interstage transformer? And who makes really good input/interstage transformers?

Thanks everyone.
  Reply With Quote
Old 14th February 2006, 12:37 PM   #5
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
I think that an input transformer brings a lot of benefits to the table. I'm much less convinced that there's a similar benefit/cost ratio for output transformers. And I hate big output coupling caps.

So far, I've tested Jensen and Cinemag 1:1 input transformers; both seemed excellent. I'm trying to get my hands on some Magnequest 1:1+1 units to give 6dB of gian in response to some requests. My guess, from testing other Magnequest products, is that they'll be first rate.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 15th February 2006, 03:29 AM   #6
diyAudio Member
 
Join Date: Oct 2005
Thanks SY
  Reply With Quote
Old 15th February 2006, 07:06 AM   #7
diyAudio Member
 
Join Date: Dec 2004
Location: Roma
Thank you to everybody!

Sorry, maybe I didn't post the question very well.

I meant a preamplifier with NO coupling capacitor e NO coupling transformer on the line path.

So, analog_sa, you got the question: could you help me to find the schematic of the mentioned SY's preamp?

Where do I have to look for?

Thank you in advance, G.M.
  Reply With Quote
Old 15th February 2006, 10:05 AM   #8
diyAudio Moderator
 
pinkmouse's Avatar
 
Join Date: Apr 2002
Location: Chatham, England
Look here.

A pic of my slowly progressing version...
Attached Images
File Type: jpg dscf0056.jpg (62.7 KB, 360 views)
__________________
Rick: Oh Cliff / Sometimes it must be difficult not to feel as if / You really are a cliff / when fascists keep trying to push you over it! / Are they the lemmings / Or are you, Cliff? / Or are you Cliff?
  Reply With Quote
Old 15th February 2006, 10:16 AM   #9
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
GM, the only way you can avoid having any transformer or capacitor is to have some level shifting. For example, if you use an ECC88 cathode follower with the grid at DC ground, the output will always be riding on a volt or three of offset- under the conditions that I run my CF, the offset will be 1.7V. So you can add 1.7V worth of battery or interpose an LED between the cathode and CCS, then pick the signal off the junction of the two.

In either case, the cure is much worse than the disease.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 15th February 2006, 01:22 PM   #10
EC8010 is offline EC8010  United Kingdom
diyAudio Moderator Emeritus
 
EC8010's Avatar
 
Join Date: Jan 2003
Location: Near London. UK
One solution is to use a Russian 6XS7 double triode, as its unique cathode emissive material based on unobtainium allows complementary operation from inverted supplies. There is a problem in that the cathode is somewhat radioactive (Pu) and there would be a toxicity issue should the fragilium quartz envelope be compromised, but the minor hazard was considered acceptable by the designers. Besides, the problem is not appreciably worse than some of the Western Electric gas voltage references (cf 313C). Because of the complementary operation, the valve must be biased to stimulate electron emission and the lowest noise option is to do this is optically, using a GaAl laser with a wavelength of 465nm pointing directly into the cathode singularity. Obviously, optically stimulated emission requires that the valve (and laser) is enclosed in a light-proof box, and given the minor radioactivity noted earlier, it is advisable to make the box out of pure lead (999 purity minimum). The original application for the 6XS7 was in reactor control systems (cf Chernobyl).
__________________
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
  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
Homemade Vacuum Tube dhaen Tubes / Valves 50 13th July 2011 05:48 PM
WTB: Vacuum Tube Tester mrdon Swap Meet 0 22nd May 2009 04:01 AM
S3E Vacuum Tube angsuman Tubes / Valves 12 15th March 2008 05:12 AM
The Vacuum Tube Truth Serratoga Tubes / Valves 31 29th November 2007 09:25 PM
DIY Vacuum tube amp turbo_h4 Tubes / Valves 2 1st July 2004 01:48 AM


New To Site? Need Help?

All times are GMT. The time now is 09:23 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