Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Dynaco VTA-inspired KT88 PP AMP project
Dynaco VTA-inspired KT88 PP AMP project
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 March 2019, 04:41 PM   #31
6A3sUMMER is offline 6A3sUMMER  United States
diyAudio Member
 
Join Date: Jun 2016
Troy Madden,

Good! You checked the phase splitter balance. With a (very good) CCS in the coupled cathodes (and no balance pot), and balanced plate resistors, and balanced grid circuits of the next stage, the balance is essentially intrinsic. And that is what is in this amp.

The same could be said of a Concertina phase splitter.

But a 'serial' phase splitter where the output of the first stage drives a series resistive divider of the two plates, and the 'center' of the resistive divider drives the grid of the second stage . . . does not have intrinsic balance. This is where the scope channels and probes must be carefully adjusted and checked.

Differential probes are expensive; especially if they have very good balance of amplitude and phase, and especially at high frequencies. That means most scope users have to use 2 probes, 2 channels, and then set up with Invert, and Math (no-invert and Math minus (-), Or Invert one channel and Math plus (+). This is a Pseudo Differential test.

It is good to increase the accuracy of a Pseudo Differential test. There is an Oscilloscope and Probe trick, that many scope users are not aware of:

1. Adjust the probe compensation of channel 1 and its probe on the scopes calibration signal.
2. Adjust the probe compensation of channel 2 and its probe on the scopes calibration signal.
3. With both probes on the scopes calibration signal, invert One of the channels (i.e. channel 2 invert).
4. Use the Math 'Add' function and look at the Error signal (mismatch between Ch 1 / probe 1, versus Ch 2 / probe 2. Or do not invert, and use Math Minus (-). If the match is good, the Math trace will be zero signal. Any signal is the Error signal (imperfect match).
5. Now you can accurately check the tube phase invertor amplitude balance and phase balance of the invertor's 2 signals.

If you fail to perform steps 1 - 4 above, then the accuracy of step 5 is totally unknown.

Note: there is an additional in-accuracy, it is when you change the Volts / Division on the two channels. The Amplitude and / or Phase may no longer match . . .

Therefore, it is better to put a square wave into the amplifier and put both probes on one phase of the invertor signal at the same time. Turn Math off, and Adjust the Volts / Division according to the signal amplitude, Then compensate each channel probe on its channel trace. Now turn Math on and check the channels/probes balance. There should be no signal on the math trace (any signal is the error signal). Once the balance on that (single) signal is verified, put one of the probes on the opposite phase. Now check the tube phase inverter balance of the amplitude and phase on the math trace.

If you want to do this without a square wave, you can use sine waves. I sometimes do spot frequency testing: I use a test CD that has 21.5 Hz, 1,000 Hz, and 19,999 Hz. Check the scope and probe balance at each frequency with both probes on one phase; and then move one probe to the opposite phase to see any un-balance. You may see more un-balance at 21.5 Hz and 19,999 Hz than at 1,000 Hz.

Happy Measuring! Happy Listening!

Last edited by 6A3sUMMER; 8th March 2019 at 05:06 PM.
  Reply With Quote
Old 9th March 2019, 03:03 PM   #32
Troy Madden is offline Troy Madden  United States
diyAudio Member
 
Join Date: Oct 2004
Looks like pretty the same driver circuit here, but with noval tubes....http://www.diytube.com/unidriver/poseidon.pdf
  Reply With Quote
Old 10th March 2019, 07:53 PM   #33
AnatolyAA is offline AnatolyAA  Russian Federation
diyAudio Member
 
Join Date: Jan 2018
Indeed it does! But I have read that 6SN7 have better characteristics, so we came up with this scheme. What types of caps you use? Anything preferred?
  Reply With Quote
Old 10th March 2019, 09:28 PM   #34
Troy Madden is offline Troy Madden  United States
diyAudio Member
 
Join Date: Oct 2004
I agree the 6SN7 is preferable. I used Nichicon poly film for audio coupling, a couple of .47uf poly Orange Drops across the main power supply caps, Nichicon 47uf low ESR for filtering on the driver board, silver mica in the feedback loop. Nothing too fancy, just good quality caps. I had my fling with boutique caps in the past, don't get too carried away theses days!
  Reply With Quote
Old 15th March 2019, 03:34 AM   #35
THIAGO LIMA is offline THIAGO LIMA  Brazil
diyAudio Member
 
Join Date: Feb 2019
Has there been any progress in the scheme or assembly?
  Reply With Quote
Old 16th March 2019, 12:48 PM   #36
AnatolyAA is offline AnatolyAA  Russian Federation
diyAudio Member
 
Join Date: Jan 2018
Quote:
Originally Posted by THIAGO LIMA View Post
Has there been any progress in the scheme or assembly?
Not yet. I am searching for the best places to buy the parts
  Reply With Quote

Reply


Dynaco VTA-inspired KT88 PP AMP projectHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
I need help with a Dynaco SCA 35 project, please 45scratches Tubes / Valves 1 5th June 2017 01:45 AM
New project inspired by 'beyond Ariel' jimluu Multi-Way 7 3rd May 2008 06:30 AM
My KT88 SE project JesseG Tubes / Valves 8 20th April 2008 04:26 AM
My new project, 2 x KT88 60W amp zafira1981 Tubes / Valves 31 27th January 2007 09:37 PM


New To Site? Need Help?

All times are GMT. The time now is 02:05 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 66.67% / PHP 37.64%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki