807pp + input phase splitter - 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 9th January 2013, 05:35 PM   #11
diyAudio Member
 
Shoog's Avatar
 
Join Date: Aug 2002
Location: Eire
I find the lowest value terminating resistor your preamp can still drive to produce the smoothest result. I often go as low as 1K (but I generally go with a step down ratio of at least 4:1+1 so thats not a bad load really).
Try something really low and see how it sounds.

Shoog
  Reply With Quote
Old 9th January 2013, 05:40 PM   #12
diyAudio Member
 
Osvaldo de Banfield's Avatar
 
Join Date: Dec 2011
Location: Barrio Garay,Almirante Brown, Buenos Aires, Argentina
Try a common unbypassed cathode resistor at driver stage, to improve arms balance.
__________________
LW1DSE
  Reply With Quote
Old 9th January 2013, 05:49 PM   #13
mwiebe is offline mwiebe  United States
diyAudio Member
 
Join Date: Apr 2004
Sorry I mislead you there. Solder one lead of a 100K resistor to the central "+" pin of your input jack, and the other end of the 100K resistor to the ground tag of the same jack. Another wire goes from the central pin to one EF80 grid. The central pin as one leg of the resistor and the grid wire connected.

From the jack's ground tag you need a wire to the circuit ground and directly to the grid of the other EF80. So the ground tag has the other end of the resistor and a wire(s) to the other EF80 grid and to circuit ground. You should get a zero reading from input jack ground tag to circuit ground.

Get rid of the 4K3 grid stoppers for now and go from the input jack directly to the grids. Sorry about the confusion.

I don't understand your dotted line in the drawing, you have zero resistance from the LED ground to the circuit ground correct?
Matt
  Reply With Quote
Old 9th January 2013, 05:54 PM   #14
GoatGuy is offline GoatGuy  United States
diyAudio Member
 
Join Date: Dec 2012
Location: SF Bay Area
You're edging toward dangerous territory 6J7... While a well behaved tube won't have voltage on the grid to speak of (especially with the 150K to ground connections), I'm nervous about not having a DC blocking cap. But ... let's keep moving, ... no cap.

OK - you're right - the bottom half is doing nothing. It should not be hooked up to the jack at all, actually, just ground. And the outer-ring of the jack SHOULD definitely be attached to ground, not the grid of the pentode in the lower half. That may be part of your signal-generator-and-oscilloscope problem.

ONTO oscilloscopes. Remember to attach the ground-alligator-clamp (of the probe) to ground. If you don't , you'll get all sorts of waveforms that look ... unsurprisingly ... like the ones you captured.

Does your signal generator have a triangle wave output? Its actually better for debugging things than the square wave.

FINALLY - I'm against counting on the "right bias" coming from the pair of LED diodes that are cathode connected. The variance of tubes is so great that it is entirely likely that the bias-point is way off. This alone could count for quite a bit of non-linearity in the runtime behavior of the circuit. The design ... is nice ... but please do try to substitute an appropriate resistor and simple cheap electrolytic bypass capacitor, yes? If you're expecting a bias-point of +1.97 volts (say), and 5.25 milliamps (which I found by dividing the voltage-difference between plate supply and plate voltage, by 24K)... then working backward from E=IR... R=E/I ... = 2v / 5.25ma = 380 ohms. You might want to make it adjustable (500 ohm adjustment pot), so that you can SET the plate-voltage points of each tube to be very close to each other.

After that, just test each section (upper, lower half) in turn, by connecting the grid to the jack pin, as you have shown in the above diagram. You'll likely find now that with all the above advice taken, that the output waveforms are much cleaner. Having done that, it can be reconfigured per your original design ... less the LED voltage-drops, and with the RC bias convention in place.

GoatGuy
  Reply With Quote
Old 9th January 2013, 08:35 PM   #15
Jaap is offline Jaap  Netherlands
diyAudio Member
 
Jaap's Avatar
 
Join Date: Dec 2002
Location: Netherlands
If I was you I would make the Tabor clone design of Shoog.
Proved concept, good reports, trusted designer(s)
Attached Images
File Type: jpg 807_tabor clone final.jpg (84.0 KB, 177 views)
  Reply With Quote
Old 9th January 2013, 10:24 PM   #16
diyAudio Member
 
Shoog's Avatar
 
Join Date: Aug 2002
Location: Eire
Quote:
Originally Posted by Jaap View Post
If I was you I would make the Tabor clone design of Shoog.
Proved concept, good reports, trusted designer(s)
Listening to that amp right this second. After a few teething troubles initially, it has become my standard amp for the bedroom. I had similar issues with the input transformer until I loaded it down with a 1K resistor. I believe the toroidal power transformer I utilized for the input has a step down ration of 9:1+1 (to much gain with 1:1+1) and tends to to ring out at 60khz. The only CCS I could get which were capable of coping with the switch on transients were the IXY 900V chips, since then I tend to use 125V versions of the LM317 protected with zeners.

Currently building a new version using EL86's with a few interesting twists. Has a few issues so far but will be testing again at the weekend.

All the credit must go to Gary Pimm who designed the original (and best) Tabor.

Shoog

Last edited by Shoog; 9th January 2013 at 10:31 PM.
  Reply With Quote
Old 9th January 2013, 10:26 PM   #17
6J7 is offline 6J7
diyAudio Member
 
6J7's Avatar
 
Join Date: Apr 2009
Quote:
I don't understand your dotted line in the drawing
The dotted line is the circuit ground.

Quote:
you have zero resistance from the LED ground to the circuit ground correct?
That's right.

I'll try first with the led's (as you can see on the schematic, EF80 plates voltage are the same, anyway I have no clue about transconductance, maybe the most important in this case ?). Then with unbypassed cathode resistors, then bypassed for more gain.

Pictures tomorrow when done, squares + triangles.

Thank you all for your help, very appreciated
Attached Images
File Type: png QS3.png (85.8 KB, 164 views)
  Reply With Quote
Old 9th January 2013, 10:38 PM   #18
diyAudio Member
 
Shoog's Avatar
 
Join Date: Aug 2002
Location: Eire
Just out of interest - because of the design of the 807, which was optimised for low screen current, it is not generally very efficient running them as triodes. i think they are only rated at 1-2Watts per tube in triode mode. The same tubes can give 10watts class A in pentode mode.
They are also prone to generating high order harmonics, which makes some form of feedback mandatory to get a clean presentation.

Shoog
  Reply With Quote
Old 10th January 2013, 01:50 AM   #19
mwiebe is offline mwiebe  United States
diyAudio Member
 
Join Date: Apr 2004
As many have noted, there is nothing wrong with your schematic, the amp should sound good. If you are still hearing problems try taking a photo of the wiring because someone may catch something you have over looked.

Enjoy the music for a while first if you get it sorted. Wait a bit until you start screwing with it, though that is a different kind of fun entirely and addictive.

There will be lots of suggestions of things you can try. Put the input trans back in and play around with no loading between secondary legs, resistor loading and network loading. Force AC balance of your driver cathodes by putting the drive cathodes over a constant current source or a choke or even a resistor w/o bypass cap. You might find a negative supply for the cathode “ground” helps keep driver tube plate current where it needs to be.

Increasing plate current in driver and outputs might change things to your liking, or not. Then once you have the signal circuit sorted you can start screwing with the power supply which can have surprisingly more impact on sound than you would think---even for Push Pull which is supposedly “immune” to power supply changes.
Matt
  Reply With Quote
Old 10th January 2013, 11:00 AM   #20
6J7 is offline 6J7
diyAudio Member
 
6J7's Avatar
 
Join Date: Apr 2009
Upper EF80 works, and as I can see on the scope, there is a big improvement.. but I can't listen how it sounds because lower EF80 still doesn't split anything ! tube seems to be good, led on, plate voltage ok. But no signal at all, tried to change the probe, same result.

Here is what I did.
Attached Images
File Type: jpg Screen shot 2013-01-10 at 11.51.29.jpg (41.0 KB, 132 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
Need help on phase splitter guwakzhai Power Supplies 7 23rd December 2010 06:51 PM
Phase splitter and balance input johnmarkp Tubes / Valves 2 30th July 2010 03:34 PM
Optimizing a 807 PP amplifiers input stage and phase splitter... pauldune Tubes / Valves 4 26th November 2009 11:24 PM
Possible group buy of Lundahl input/phase splitter transformers. Shoog Tubes / Valves 51 14th November 2008 12:45 PM
Phase Splitter as input stage Peter Menting Tubes / Valves 21 3rd January 2005 09:48 AM


New To Site? Need Help?

All times are GMT. The time now is 01:18 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