Wurlitzer 6420 to audio amplifiers

[baddog]

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

[Eli Duttman]

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?

[baddog]

Originally Posted by Eli Duttman

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.....

[Eli Duttman]

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.

[baddog]

Originally Posted by Eli Duttman

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.....

[Eli Duttman]

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.

[Original Burnedfingers]

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.

[abhivandansuzuki]

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