Wurlitzer 6420 to audio amplifiers - 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 16th June 2010, 08:48 PM   #1
baddog is offline baddog  United States
diyAudio Member
 
Join Date: Nov 2008
Default Wurlitzer 6420 to audio amplifiers

I have 2 very nice 6420 ampos and would like to turn them into audio ampifiers. I want to be able to run my IPOD and Phonograph on them . I need a good 6l6 push pull desighn and I want to utilize the 6sn7 phase inverter. I have built a few guitar amps over the years but never audio amps. Need some help here...........I cant seem to find a good schematic on line .....
Thanks Baddog
Attached Files
File Type: pdf Wurlitzer 6420 amp schematic.pdf (67.6 KB, 157 views)
  Reply With Quote
Old 16th June 2010, 11:47 PM   #2
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
The O/P trafos can certainly be used. Triode wired 6L6GCs operating in Class "AB2" should produce all the power they can handle.

Those plugs and sockets are somewhat confusing. Does the 5U4 supply B+ power to the oscillator/keyboard section? No way are you going to get enough gain from a 6SN7. An additional tube is needed. I'd look into working up a variation on the H/K Cit. 5 circuit, which used the electrically equivalent 6CG7 in the phase splitter role. The issue is whether or not the OEM power trafo has sufficient "stones".

You will need a preamp. Have you given thought to the phono section?
__________________
Eli D.
  Reply With Quote
Old 17th June 2010, 01:07 AM   #3
baddog is offline baddog  United States
diyAudio Member
 
Join Date: Nov 2008
Quote:
Originally Posted by Eli Duttman View Post
The O/P trafos can certainly be used. Triode wired 6L6GCs operating in Class "AB2" should produce all the power they can handle.

Those plugs and sockets are somewhat confusing. Does the 5U4 supply B+ power to the oscillator/keyboard section? No way are you going to get enough gain from a 6SN7. An additional tube is needed. I'd look into working up a variation on the H/K Cit. 5 circuit, which used the electrically equivalent 6CG7 in the phase splitter role. The issue is whether or not the OEM power trafo has sufficient "stones".

I would like to keep the octal socket setup because of the cool factor. I could also use 6SL7 tubes which are close to 12ax7 as far as gain goes. I have extra room for another octal socker or two if I need it. Not sure how much the transformer can handle but the ones I converted to fender deluxes work great and the transformers dont seem to get warm

You will need a preamp. Have you given thought to the phono section?
I havent thought about it much thats why im asking the seasone pros here. What do you think. Any schematics out there I could use for refference.

Thanks for the reply.....
  Reply With Quote
Old 17th June 2010, 01:56 AM   #4
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
The H/K Cit. 5 uses Mullard style circuitry, with a 12BY7 voltage amplifier and a 6CG7 LTP. You could emulate that pattern, in Octal, by using a 6AC7 voltage amplifier and a 6SN7 LTP. If you want a Class "AB2" O/P stage, Tubelab's PowerDrive between splitter and "finals" is necessary.

As for a phono preamp, the attached tweaked version of RCA's "classic" passive EQ design is fairly easy to execute and delivers respectable results. Given its clean and quiet nature, the tube I recommend is the Sovtek 12AX7LPS.
Attached Images
File Type: jpg Full Tweaked RCA Phono Stage.jpg (45.4 KB, 186 views)
__________________
Eli D.
  Reply With Quote
Old 17th June 2010, 08:08 PM   #5
baddog is offline baddog  United States
diyAudio Member
 
Join Date: Nov 2008
Quote:
Originally Posted by Eli Duttman View Post
The H/K Cit. 5 uses Mullard style circuitry, with a 12BY7 voltage amplifier and a 6CG7 LTP. You could emulate that pattern, in Octal, by using a 6AC7 voltage amplifier and a 6SN7 LTP. If you want a Class "AB2" O/P stage, Tubelab's PowerDrive between splitter and "finals" is necessary.

As for a phono preamp, the attached tweaked version of RCA's "classic" passive EQ design is fairly easy to execute and delivers respectable results. Given its clean and quiet nature, the tube I recommend is the Sovtek 12AX7LPS.
Im not sure about the hole class AB/ AB2 thing.
The phono amp setup looks pretty straight forward and doable . What is the purpose of the Transistor? Im not much of a transistor uy so please enlighten me.....
  Reply With Quote
Old 18th June 2010, 12:05 AM   #6
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
Whenever you see Class "xy2" it means that at least part of the time positive control grid current is present. Your O/P trafos are for 6L6s, not 6L6GCs. You can't run 6L6GCs in pentode mode, but triode mode and AB2 would get a good amount of power out of the "iron".

The MOSFET source follower in the phono preamp circuit deals with the poor drive capability of the 12AX7. RCA's original needs to work into a 250 KOhm load. The hybrid version drives the IHF 10 KOhm load, without incident. While it's an oversimplification, think of a FET as a heaterless pentode.
__________________
Eli D.
  Reply With Quote
Old 21st June 2010, 11:01 AM   #7
diyAudio Member
 
Join Date: Nov 2002
If memory is correct I got 22 watts of output power into an 8 ohm dummy load with this amp. They actually sound good for what they are. I have 4) of them sitting on my shelf. I plan to use some 6Bg6ga's in them and modify the bias circuit for individual tube bias.
  Reply With Quote
Old 18th November 2010, 09:19 PM   #8
diyAudio Member
 
Join Date: Nov 2010
Thumbs up Wurlitzer 6420

I HAVE GOT Wurlitzer 6420 IN REALLY GOOD CONDITION in Japan.
Thank god I also have got schematics through DIYAUDIO forum where I have been coming often to see what other tube freaks are doing, now I will post as my project is taking shape.

Abhi
  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
Wurlitzer amplifier needs help Original Burnedfingers Tubes / Valves 28 16th June 2010 08:34 PM
Wurlitzer speakers Sonny ReVerb Multi-Way 1 3rd June 2008 08:49 AM
pro amplifiers vs. home audio amplifiers bonsai171 Solid State 26 25th February 2004 08:24 PM
Wurlitzer schematic needed for a 6420 amp Original Burnedfingers Tubes / Valves 2 15th November 2003 11:31 PM


New To Site? Need Help?

All times are GMT. The time now is 07:21 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