Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: fossilshark on October 23, 2016, 01:51:15 am

Title: 6v6 push pull circuit change
Post by: fossilshark on October 23, 2016, 01:51:15 am: In a push pull 6v6 power amp, using this circuit as an example, could i wire everything exactly the same except disconnect the screen taps or connect them somewhere else in the circuit if my transformer doesnt have the necessary 40% windings? How would this affect the circuit
Title: Re: 6v6 push pull circuit change
Post by: TIMBO on October 23, 2016, 02:55:02 am: Like this..........
http://el34world.com/charts/Schematics/files/fender/Fender_DELUXE_5E3.pdf (http://el34world.com/charts/Schematics/files/fender/Fender_DELUXE_5E3.pdf)
Title: Re: 6v6 push pull circuit change
Post by: fossilshark on October 23, 2016, 09:16:55 am: Like that except would i have to change the 12ax7 wiring too? It looks like the fender schematic has one tube amplifying the positive of the signal and the other is doing the negative. In the schematic i posted the 12ax7 is wired different i think. Im a little new to this sorry for the dumb questions :laugh:
Title: Re: 6v6 push pull circuit change
Post by: shooter on October 23, 2016, 10:12:58 am: Quote
except disconnect the screen taps or connect them somewhere else in the circuit
I think Timbo was showing an example of how to do a screen tap without UL connections, NOT how to re-do your PI
Title: Re: 6v6 push pull circuit change
Post by: kagliostro on October 23, 2016, 10:58:27 am: Which is your purpose ?

There are thousands of schematics that didn't use UL OT

Why your choice was that schematic that you can't build because of the missing UL connections ?

If you say more about your need, someone can give you councils about possibilities

Franco
Title: Re: 6v6 push pull circuit change
Post by: fossilshark on October 23, 2016, 11:36:43 am: Yes sorry. Im finishing up a build and i have everything on this schematic built in my power amp section, until i went to wire up the OT and realized that it did not (or at least was not specified by the ebay seller) have the windings for the screen taps, just the 8k center tapped primary. For $15 im not terribly worried if i have to but a new one, although to buy them new is very expensive for me. So could i just disconnect the screen taps? Or i should be asking, what is the purpose of the screen tap connections?
Title: Re: 6v6 push pull circuit change
Post by: sluckey on October 23, 2016, 12:30:16 pm: Quote
So could i just disconnect the screen taps?
No. The screens must be connected to a B+ supply, similar to what Timbo showed.
Title: Re: 6v6 push pull circuit change
Post by: fossilshark on October 23, 2016, 12:43:01 pm: So if i connect them to b+ instead of the transformer i should have no problem?
Title: Re: 6v6 push pull circuit change
Post by: PRR on October 23, 2016, 01:25:31 pm: .
Title: Re: 6v6 push pull circuit change
Post by: fossilshark on October 23, 2016, 01:46:42 pm: Thats great, thanks!
Title: Re: 6v6 push pull circuit change
Post by: 2deaf on October 23, 2016, 04:49:53 pm: What does your power supply look like?

That presence control isn't going to do much unless you hook up some negative feedback from the speaker output.
Title: Re: 6v6 push pull circuit change
Post by: jbrew73 on October 23, 2016, 07:23:48 pm: http://el34world.com/charts/Schematics/files/ampeg/Ampeg_j12b_jet.pdf (http://el34world.com/charts/Schematics/files/ampeg/Ampeg_j12b_jet.pdf)
Title: Re: 6v6 push pull circuit change
Post by: tubeswell on October 24, 2016, 02:24:51 am: Quote from: fossilshark on October 23, 2016, 01:51:15 am
In a push pull 6v6 power amp, using this circuit as an example, could i wire everything exactly the same except disconnect the screen taps or connect them somewhere else in the circuit if my transformer doesnt have the necessary 40% windings? How would this affect the circuit

What the others said already. Most guitar amps don't use ultra linear OTs. You only 'need' to hook up ultra linearly if you want to run in ultra linear mode. (UL is designed to make the screen voltage vary in synch with the plate voltage. This sacrifices a bit of gain in return for giving a more 'hi-fi' quality output signal. But it isn't necessary, or even strictly desirable, to run a guitar amp this way.)