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 3rd December 2008, 09:24 PM   #1
diyAudio Member
 
Join Date: Jun 2007
Location: Lubbock, TX
Default 6V6 Push Pull

So, this is my second time to post something. I have built this small 6V6 push pull amplifier out of some spare parts. I have included my schematic of the amplifier section. This includes some numbers and values. Just fyi I dont know much about the output transformer, I stole it off a Bogen Amplifier that had a pentode power tube and triode in the same glass tube El86 or something? At any rate I beleive it to be rated from 6-10K Ohms on the primary, it also has a 70volt line isolated secondary tap. That aside;

First: I would like to add a feedback loop which I have not done yet; i would like suggestions.

Second: Also I would like to see some math for the feedback if someone could do so?

Thirdly: I have indicated in red a grid stopper resistor, is there a reasonable value for what I have drawn? Also being as there should theoreticaly be no input current I coud pick this to be 100K as well?

Lastly: Any suggestions on the circuit would be much appriciated.

Any information or suggestions would be much appriciated. Thanks again,
Jonathan
  Reply With Quote
Old 3rd December 2008, 09:26 PM   #2
diyAudio Member
 
Join Date: Jun 2007
Location: Lubbock, TX
Here is the schematic
Attached Files
File Type: pdf jlh6v6.pdf (19.1 KB, 374 views)
  Reply With Quote
Old 3rd December 2008, 09:46 PM   #3
chrish is offline chrish  Australia
diyAudio Member
 
chrish's Avatar
 
Join Date: Oct 2003
Location: Sydney
Sorry I am not qualified to comment on the circuit, but I am interested to know what program you used to draw the schematic.

Thanks,

Chris
  Reply With Quote
Old 3rd December 2008, 09:56 PM   #4
diyAudio Member
 
Join Date: Jun 2007
Location: Lubbock, TX
I just used Power Point, somewhat painstakingly but it worked. I do not have a good schematic program so I just found a way around it. Hope it helps.
Jonathan
  Reply With Quote
Old 3rd December 2008, 10:14 PM   #5
mach1 is offline mach1  Australia
diyAudio Member
 
mach1's Avatar
 
Join Date: Sep 2004
Location: Brisvegas
Unecessarily complex. You can drive a 6V6pp with a single 12AT7 long tailed pair. Type in 'el cheapo' and do a search of the forum. Also do a search under 'musical machine' for a slightly different approach.
__________________
Au rutti wop-bop-a-loom-bop-a-boom-bam-boom - Richard Penniman
  Reply With Quote
Old 3rd December 2008, 11:26 PM   #6
diyAudio Member
 
Join Date: Sep 2003
Location: London
As above. Except I'd use the ECC40 which is a terrific sounding tube, very popular in European equipment. Three stages of 12AU7 is out to lunch and then some.

Actually I'd use a 1J6G as driver. Just discovered this little jewel of a double DHT and can't get enough of it - have it in my linestage. You'd need a preamp since mu is about 15. And a DC filament supply since it's directly heated, but that's simple enough and the tube is cheap.

andy
  Reply With Quote
Old 4th December 2008, 12:24 AM   #7
diyAudio Member
 
jerluwoo's Avatar
 
Join Date: Feb 2006
Location: Ashland,Ky U.S
Your circuit will not work. Here is a scheme to give you a starting point that should work correctly.
Attached Images
File Type: gif pp6v6.gif (31.0 KB, 703 views)
  Reply With Quote
Old 4th December 2008, 01:48 AM   #8
diyAudio Member
 
Join Date: Jun 2007
Location: Lubbock, TX
Quote:
Originally posted by jerluwoo
Your circuit will not work.
I dissagree, I have it built currently and it operates. It could be debated how well it works but that aside it works.

Thanks for the input that it is overly complicated, now that I step back it does look a little excessive all for just a little output. A simpler solution could be had. I will take a look at a simpler circuit.

Again to repeat however, if I wanted to put a global feedback network is there some mathmatical solution to go about this? Local feedback I somewhat understand; however, once I need to take the tansformer into account I get a bit lost. Do I just make a voltage divider based on what I expect at one of the secondary taps? Then just assume that voltage divider to feed back an overall % compared to the input?
  Reply With Quote
Old 4th December 2008, 02:15 AM   #9
diyAudio Member
 
Join Date: Oct 2004
Location: Maui, Hawai'i, USA
I mainly agree with those above; the main problem with your circuit is that it has way too much front end gain, so the noise level will be a little higher than optimum. You could remove that third front end stage and drive directly off the split load inverter, it would improve the sound, I bet.

If your outputs are operating in triode, as shown, I think it would be a mistake to apply global feedback around the circuit.  You would probably be disappointed in the reduction of space, image, and inner resolution.  Feedback was used in the pentode amps of the Bogen period because the output impedance of the amp would be unacceptably high without it, thus the inclusion of extra gain stages to supply Av that would be subsequently lost in the NFB.

If you wish to try NFB, take a wire from the top tap of the output transformer secondary, through a resistor of about 15K - 18K (try different values experimentally), but not to the top of that 10K cathode resistor; you gonna put that voltage on your output secondary winding.  Split that resistor into 8.2K on top and 1.8K on the bottom, and attach the NFB loop to the junction.

This will give you 6-8dB of NFB to listen to, and not send the amp into oscillation.

Spearmint on!

Poinz
  Reply With Quote
Old 4th December 2008, 03:52 AM   #10
diyAudio Member
 
jerluwoo's Avatar
 
Join Date: Feb 2006
Location: Ashland,Ky U.S
I say that it doesnt work because of your phase splitter. As it is the tube is biased well into cutoff. Since you have the grid referenced to ground then you have that 56k resistor from cathode to ground biasing the tube. It would work like that if you were using a negative voltage supply, but not as is. Also the input tube is biased very close to cuttoff as well. It should only need a cathode resistor of 560 to 620 at most with the 100k plate resistor. Take some voltage measurements at the plate of the input tube and the cathode of the phase splitter tube and you'll see what i mean.
  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
Push pull BPA warriorcookie Chip Amps 6 4th October 2008 05:41 PM
12V push pull PSU. Need help. darw82 Power Supplies 4 3rd June 2007 02:42 AM
modify parallel push-pull EL84 to single push-pull chungtat Tubes / Valves 12 3rd November 2005 11:25 PM
Push-pull amp with OP piney Solid State 1 28th March 2005 02:34 AM
Double push-pull versus single push-pull jraraujo Tubes / Valves 19 19th October 2002 12:23 AM


New To Site? Need Help?

All times are GMT. The time now is 10:24 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