plate stoppers or cathode stoppers? - Page 2 - 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 12th December 2010, 09:13 PM   #11
diyAudio Member
 
Join Date: Jan 2002
Location: nowhere
Well, I finally got my 'shop-amp' done. I skipped the plate stoppers, only used the usual grid stoppers, and separate cathode resistors, which I suppose act as 'cathode stoppers'. Being a flea power amp, it makes just under 1watt, I havent bypassed the cathode resistors since I dont need the gain. That gives some local NFB, which I don't mind, and ensures each triode operates within estimate.
I used what I had laying around, which is how most of the amps I build for myself end up being built.
I paralleled 3 5687 triodes in the output and used some 5k:8 Edcors I had. Unfortunately the only PT I had only gives me 170volt for B+. But the work shop only needs a watt so no real worries. With this low B+ I really don't need 3 5687s, but I don't like V-6s.
As is it sounds pretty damn good. Measurementwise it has nice low distortion till I pass 2.5V rms where the higher Hs start popping in. Max swing is +-4V into 8ohms. The 5687s wont let the plate voltage swing lower than about 80V without higher harmonics showing up. With some grid drive I imagine I can swing them a little lower for half a watt more, but I'm not that desperate.
Either way, sounds really nice, highly recommended but if doing it again I'd buy a new PT with proper B+ voltages, somewhere around 250-300volts.
The Edcors are great for the price, they are the real cheap XSE-15 types, and I measure -3dB corners at 15Hz and 54kHz. Not bad for those OTs.
Attached Images
File Type: jpg testarossa_ckt.JPG (24.6 KB, 115 views)
File Type: jpg testarossa.JPG (79.8 KB, 112 views)
  Reply With Quote
Old 12th December 2010, 10:01 PM   #12
diyAudio Member
 
Join Date: Jan 2002
Location: nowhere
Btw. I forgot to thank all of those who answered this thread.
  Reply With Quote
Old 13th December 2010, 12:45 PM   #13
Cassiel is offline Cassiel  Libya
diyAudio Member
 
Cassiel's Avatar
 
Join Date: Sep 2004
Location: Madrid
It's nice to see something different. I also have a 6SN7 mini amp. Yes, 1 Watt is enough.
  Reply With Quote
Old 13th December 2010, 04:20 PM   #14
diyAudio Member
 
richwalters's Avatar
 
Join Date: Sep 2003
Location: Alps:Tube amp designs over 150W, SMPS guru.
I find the ECC88 Cathode follower config is particulary prone to self oscillations around 470Mhz..I use small ferrite beads and carbon res at the grid pins and if a CCS is used on the cathode, an "output resistor of 50ohms".
As SY suggests, the shortest decoupling route to reduce self inductance from valve tag to chassis.
Ironically, the wire lead inductance inside the tube is nearly longer than the external with components !

richy
  Reply With Quote
Old 13th December 2010, 06:22 PM   #15
diyAudio Member
 
Join Date: Jan 2002
Location: nowhere
Hmm, my 'go to' scope has max 166kHz BW (It's an old trusty 16bit Picoscope). I guess I should unpack the old Philips scope, but that thing is a monster.

Just to keep this incredible thread going, here is the FFT of a 1kHz testsignal.
Attached Images
File Type: jpg Lch0dB.jpg (31.9 KB, 66 views)
  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
Base Stoppers lumanauw Solid State 72 22nd September 2010 03:30 PM
Metal Oxide Screen Stoppers SpreadSpectrum Tubes / Valves 33 13th February 2009 12:49 AM
Please explain grid stoppers.. JandG Tubes / Valves 7 2nd November 2007 08:21 AM
Anode stoppers Shoog Tubes / Valves 4 12th June 2007 07:14 PM
Grid stoppers? Tim Wyatt Tubes / Valves 14 26th November 2004 01:56 AM


New To Site? Need Help?

All times are GMT. The time now is 04:31 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