Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: john_t on October 08, 2012, 10:23:02 am

Title: el84 schedule 40 to 6v6 ?
Post by: john_t on October 08, 2012, 10:23:02 am

I am considering changing my el 84 ga-5 build  to a 6v6 power tube. The el 84 has plenty of drive and crunch. After having the amp awhile Iam just not sure it's my taste. Can I just change out to the octal tube or would I need to swap out anything else.

john

Title: Re: el84 schedule 40 to 6v6 ?
Post by: Willabe on October 08, 2012, 03:12:07 pm

EL84=9 pin socket, 6V6=8 pin socket.


                Brad     :icon_biggrin:

Title: Re: el84 schedule 40 to 6v6 ?
Post by: shortfuse on October 08, 2012, 10:10:23 pm

I built the ga5 / sch 40 in a alum chassis.  I never could get the b+ down to bias correctly and change mine out to a 6V6.  Was not that difficult.  If you want I can send you the diagrams I used.  Had a few suggestions to use a zenier to drop the voltage but I felt changing to the 6V6 would be better.  After the swap I thought is sounded better.  I also installed the moonlight push pull tone stack from the Adams amps site.

Title: Re: el84 schedule 40 to 6v6 ?
Post by: PRR on October 08, 2012, 10:41:33 pm

6V6 will need different bias than EL84.

Title: Re: el84 schedule 40 to 6v6 ?
Post by: john_t on October 09, 2012, 12:01:22 am

Thanks for the help all. Shortfuse diagrams would be very helpful. Iam not sure how you get them to me. Or at least direct me to where I might find them.

Thanks John t

Title: Re: el84 schedule 40 to 6v6 ?
Post by: tubeswell on October 09, 2012, 04:13:57 am

Different socket with different pin out and different bias.

The 6V6 also likes its voltages a bit higher than an EL84. This may happen 'automatically' when you swap to a 6V6, as a 6V6 typically has lower tube current  than an EL84, so the load won't be as great.  Or this may be a matter of going to a more efficient rectifier tube (depending on what sort of windings your PT has). But if your power supply is already SS rectified, then you may just have to accept lower voltages for the 6V6 or change the PT.  If it were me I'd suck it and see with the existing PT first.

And you'll probably want a 470k grid load resistor for the 6V6

You should be able to get away with the same OT and speaker though.

Title: Re: el84 schedule 40 to 6v6 ?
Post by: kagliostro on October 09, 2012, 08:43:21 am

Looking in the web I've found this

hope this can be of some help

K

Title: Re: el84 schedule 40 to 6v6 ?
Post by: shortfuse on October 10, 2012, 12:43:35 am

kagliostro got hem.  I used all 3 as references but did it like in the last one by Joe Piazza.

Title: Re: el84 schedule 40 to 6v6 ?
Post by: john_t on October 10, 2012, 08:35:14 am

Shortfuse can you post the plans you used for your rebuild. Or I can shhot you My e address.

thanks John t