Help with splitter design for 7591 PP - 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 27th April 2008, 10:55 PM   #1
diyAudio Member
 
Join Date: Jan 2008
Location: Southern California
Default Help with splitter design for 7591 PP

I am building my first amp with a pair of 7591 in PP and have hit a slowdown figuring out the preceding splitter stage. My initial thought was to use a 12ax7 amp stage followed by a 12au7 splitter. I am planning to use a -20 bias on the 7591 so I am looking at a max 40v pp to drive each 7591 tube.

The 12ax7 has to much gain. I am assuming an input of 2vpp on the 12ax7.

If I use two 12au7 then there is not enough gain.

Should I lower the gain stage of the 12ax7 with a lot of negative feedback from the secondary of the transformer? I don't know if there is a good sounding tube to replace the 12ax7 but with less gain.

I'd appreciate any suggestion. I already built the chassis and would have 2x 9 pin sockets for the splitter circuits, it will be a stereo amp. I have built the chassis myself, see attached picture. I think it will at least look good... There are a total of three 9 pin sockets, one of them is for an amplifier section before a tone control circuit. The output of the tone control circuit will have aprox 2Vpp.

Alfredo
Attached Images
File Type: jpg dsc01746.jpg (44.8 KB, 229 views)
  Reply With Quote
Old 27th April 2008, 11:55 PM   #2
diyAudio Member
 
tubewade's Avatar
 
Join Date: Jun 2007
7591s are easy to drive. The AX7-AU7 idea would work. One way to get this is to use a 12DW7. The high mu section is half a 12AX7 and the low mu section is half a 12AU7. Set it up as a conventional concertina. Probably better sound wise, though, would be 12AT7 for the input valve and 6FQ7/6CG7 for the concertina splitter but you would lose symmetry in the amplifiers appearance.

Wade
  Reply With Quote
Old 28th April 2008, 12:03 AM   #3
SHiFTY is offline SHiFTY  New Zealand
diyAudio Member
 
SHiFTY's Avatar
 
Join Date: Jul 2002
Location: New Zealand
I'm partial to Eli's El-cheapo 12AT7 differential splitter myself, uses a CCS to get perfect AC balance and it sounds very alive- it's a single stage so very little in the signal path. I use a pair of Telefunken ECC801S which I found in an attic to drive 6V6-type tubes wired in triode. There is enough gain and plenty of drive voltage for 6V6.

I'll wait for his more technical explanation...
  Reply With Quote
Old 28th April 2008, 01:27 AM   #4
diyAudio Member
 
Join Date: Jan 2008
Location: Southern California
Thanks for the quick response. I think I will give the 12at7 a try. I modeled it in LTSPICE with a 12AU7 concertina splitter and it appears to yield what I am looking for.

I revisited the 12ax7 combination and I could get it to work if I lower the Plate voltage to around 200V. I am new to this, but I have heard that the higher the voltage the better linearity I will get. I could run the 12at7 at 300v.

Alfredo
  Reply With Quote
Old 28th April 2008, 02:30 AM   #5
diyAudio Member
 
tubewade's Avatar
 
Join Date: Jun 2007
Alfredo,

As time permits, study the following thread...

up-to-date El Cheapo schematic

There are some great ideas presented here that may be helpful for your project.

Wade
  Reply With Quote
Old 28th April 2008, 04:25 AM   #6
diyAudio Member
 
zigzagflux's Avatar
 
Join Date: Oct 2006
Location: Charlotte, NC
avincenty:

That's a beautiful chassis you have there.

I am giving a try of a similar design with EL34's using a 12AT7 (mu 60) front end and 6n6p (mu 22) LTP. Gain should be enough to add in enough NFB for good damping factor.
  Reply With Quote
Old 28th April 2008, 04:52 AM   #7
diyAudio Member
 
Join Date: Jan 2008
Location: Southern California
thanks Wade,

Some of the links are not valid but I should be able to find the info.

Alfredo
  Reply With Quote
Old 28th April 2008, 05:05 AM   #8
diyAudio Member
 
Join Date: Jan 2008
Location: Southern California
zigzagflux,

Thanks for the compliment on the chassis. It took me a while to build, the woodworking was very time consuming.

were do you get a 6n6p? Is it a good sounding tube?

BTW I attached a back view of the chassis.

Alfredo
Attached Images
File Type: jpg dsc01747.jpg (41.2 KB, 182 views)
  Reply With Quote
Old 28th April 2008, 06:20 AM   #9
diyAudio Member
 
sorenj07's Avatar
 
Join Date: May 2006
If a CD player puts out 2V peak to peak, that likely means 2VRMS which means about 2.8VAC peak to peak on transients. You will want a gain of 14.2 at the very least in order to drive your outputs to full power.

If you have room for three tubes, my suggestion is to use a 12BH7 grounded cathode feeding into a 12BH7 long tail pair.

The LTP: Set for 10mA with a CCS (300VB+, 20K plate resistors), the LTP can swing a decently clean 116V pk-pk at maximum input. Gain is 6.7 and bias is at -8.5V or so. A grounded cathode 12BH7 stage with 270VB+, a 22K plate resistor, and an unbypassed 1.4K cathode resistor will give you a gain of 6. (5mA plate current)

Doing the math: Input 2.82Vpk-pk, multiply by 6 for 17V pk-pk or so, and by 6.7 again for 113V pk-pk. You have an extra 9dB or so of headroom, some of which you can "spend" on negative feedback.
  Reply With Quote
Old 28th April 2008, 11:56 AM   #10
diyAudio Member
 
zigzagflux's Avatar
 
Join Date: Oct 2006
Location: Charlotte, NC
Quote:
Originally posted by avincenty
were do you get a 6n6p? Is it a good sounding tube?
That evil auction place called ebay. My only option, really.

Tube is pretty similar to the ECC99, at a fraction of the price. My samples have been nonmicrophonic and exhibit decent balance triode to triode on about 1/3 to 1/2. Good driver (low Rp) tube. Sounds very pleasant.
  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
Using the 7591 or 7868 andyjevans Tubes / Valves 11 21st June 2010 04:53 AM
What splitter for this design ? Jaap Tubes / Valves 52 31st December 2008 02:40 PM
Feedback requested on 7591 PP design tikiroo Tubes / Valves 33 30th October 2008 01:03 PM
PP 7591 amp HugoR Tubes / Valves 0 11th October 2005 08:08 PM
Strange phase splitter design !?!? Glass_painter Tubes / Valves 6 22nd April 2003 01:19 PM


New To Site? Need Help?

All times are GMT. The time now is 08:19 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