Advice on 6V6 push pull Parallel - 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 28th March 2006, 12:09 AM   #1
krzanik is offline krzanik  United States
diyAudio Member
 
Join Date: Jan 2005
Location: Austin, TX
Default Advice on 6V6 push pull Parallel

I need some advice on a push pull parallel 6V6GT amplifier that was origionally from a Hammond P-40 Tone Cabinet. The schematic is at:http://www.captain-foldback.com/Hamm...schematics.htm If you scroll down to the bottom of the page to Tone Cabinet and click on the P-40 (sorry it's a zipped file) you can see the schematic. This amp has seperate treble and base output transformers, when I hooked up a cd player and speakers I get: fairly quite music from 4 ohm speakers and very faint music from 8 ohm (95 decible per watt efficiency) speakers. Origionally a preamplifier would provide the input to this amplifier and I imagine the preamplifier had a good amount of gain because my computer can add 12 decible of preamplification and it was still pretty quit on the 8ohm speakers. I have also tried replacing the output transformers with Hammond 1650F output transformers but the amp is still quite. If someone can take a look at the schematic and offer advice for turning this into a usable amplifier I would be very pleased. I had no luck with posting the schematic (too big!) Sorry
  Reply With Quote
Old 28th March 2006, 07:30 AM   #2
diyAudio Member
 
Miles Prower's Avatar
 
Join Date: May 2005
Location: USA
Blog Entries: 6
The Front End of this is a differential amp, and ideally it should be driven by a preamp with balanced output. One potential problem is applying the signal in such a manner that it becomes a common mode voltage. This really isn't a good diff amp (no CCS and very small resistors in the tail) so that would cause low output, instead of no output (which a good diff amp with a decent CMRR would produce).

Also, did you make sure that the bias is correct? 6V6s usually run with Vgk= -19Vdc. If that back bias resistor has increased in value, you might be getting excessive bias. That, too, would cause low output.

I'd check these first and see what the results are.
__________________
There are no foxes in atheistholes
www.dolphin-hsl.com
  Reply With Quote
Old 28th March 2006, 05:18 PM   #3
krzanik is offline krzanik  United States
diyAudio Member
 
Join Date: Jan 2005
Location: Austin, TX
Default Differential amp

Thanks for the reply and thanks for posting part of the schematic. I'm going to ohm-out the resisters with my volt meter this evening and see if the values have changed (pretty likely as it's 50 years old). I'm thinking about just using the power supply and building a push pull 6V6 per some of the schematics posted on the forum (new resisters and caps). Which brings up a good question...I have not had any luck finding a 6V6GT push pull parallel schematic anywhere. I've been looking for close to a week now. I would really like to use all four 6V6GTs per channel. If any one has a schematic that fits the bill I'd love to take a ganders (look at it).
  Reply With Quote
Old 28th March 2006, 07:35 PM   #4
diyAudio Member
 
Miles Prower's Avatar
 
Join Date: May 2005
Location: USA
Blog Entries: 6
Default Re: Differential amp

Quote:
Originally posted by krzanik
Thanks for the reply and thanks for posting part of the schematic. I'm going to ohm-out the resisters with my volt meter this evening and see if the values have changed (pretty likely as it's 50 years old). I'm thinking about just using the power supply and building a push pull 6V6 per some of the schematics posted on the forum (new resisters and caps). Which brings up a good question...I have not had any luck finding a 6V6GT push pull parallel schematic anywhere. I've been looking for close to a week now. I would really like to use all four 6V6GTs per channel. If any one has a schematic that fits the bill I'd love to take a ganders (look at it).
There's no reason that you couldn't use an existing schematic for a good 6V6 amp already out there and make it a PPP. Paralleling the 6V6's will cut the Rl and Zo in half, double the Ip, Cmiller, and Ci. You may need to add cathode follower drivers to insure that the slew rate stays up there. That's NBD. For stability, add grid and screen stoppers to each of the four 6V6s (never share these).

If you're keeping the original power supply, I'd ditch that back bias scheme in favor of this (see attached). Just make certain that each 6V6 has its own bias pot, so that the Ip's can be balanced.
Attached Images
File Type: jpg p40-new-ps.jpg (15.1 KB, 322 views)
__________________
There are no foxes in atheistholes
www.dolphin-hsl.com
  Reply With Quote
Old 28th March 2006, 09:14 PM   #5
krzanik is offline krzanik  United States
diyAudio Member
 
Join Date: Jan 2005
Location: Austin, TX
Default 6V6 PP parallel

Wow, thanks for the info. The power supply diagram is greatly appreciated. I am not sure how much of your information I will be able to utilize imediately. I am a novice and have been trying to stick to schematics of proven disigns that I find. I imagine after reading up some more your suggestions will make more sense to me.
  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
Bevois Valley and parallel push pull pbholmen Tubes / Valves 11 3rd November 2007 02:44 PM
modify parallel push-pull EL84 to single push-pull chungtat Tubes / Valves 12 3rd November 2005 11:25 PM
Parallel Push Pull Drivers gingertube Tubes / Valves 14 13th May 2005 01:32 PM
parallel or push-pull vlljpior Tubes / Valves 1 6th December 2004 12:13 AM
EL 34 parallel push pull (quad) navin Tubes / Valves 33 21st December 2003 09:50 PM


New To Site? Need Help?

All times are GMT. The time now is 01:47 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