Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jeff on January 08, 2011, 03:24:32 pm

Title: Marshall 18watt
Post by: jeff on January 08, 2011, 03:24:32 pm

 The schematic for a marshall 18watt shows a 6.3V tap for the heaters and a seperate 6.3V tap for the EZ81 rectifier tube. Do these need to be on seperate taps? If you have a tramsformer that can supply enough current to run the EZ81 and all other heaters can you use the same supply for both? I notice the EZ81 heater has no reference to ground.

Title: Re: Marshall 18watt
Post by: sluckey on January 08, 2011, 03:38:29 pm

The EZ81 is good for max. 500v between cathode and heater. If your B+ will be the typical 350V for an 18Watter you should be OK.

Title: Re: Marshall 18watt
Post by: heymymy on January 08, 2011, 10:39:53 pm

such a great amp! you're gonna love it when it's done! it's exactly like a bluesbreaker at half the volume! break up is amazing!
good luck!

Title: Re: Marshall 18watt
Post by: jeff on January 09, 2011, 10:13:58 am

But does the EZ81 need a seperate tap?

Can you run the EZ81's heater off the same supply as the other tubes heaters if you have a 6.3V tap with enough current.

Title: Re: Marshall 18watt
Post by: sluckey on January 09, 2011, 10:28:06 am

Quote

But does the EZ81 need a seperate tap?

no

Quote

Can you run the EZ81's heater off the same supply as the other tubes heaters if you have a 6.3V tap with enough current.

yes

Title: Re: Marshall 18watt
Post by: jeff on January 09, 2011, 11:15:30 am

 Thanks

    Jeff

Title: Re: Marshall 18watt
Post by: Shrapnel on January 12, 2011, 01:30:23 am

Quote from: sluckey on January 09, 2011, 10:28:06 am

Quote

But does the EZ81 need a seperate tap?

no

Quote

Can you run the EZ81's heater off the same supply as the other tubes heaters if you have a 6.3V tap with enough current.

yes

Agreed, There are commercial amps out there that just used one 6.3v heater supply. (Some Davis PA Amps, i.e the 201(a), that used EL84/6BQ5s and preamp/mixer tubes and PI off the same tap as the EZ81.)

Title: Re: Marshall 18watt
Post by: Rev D on February 19, 2011, 12:56:51 pm

 The 18 watter is my favorite amp. I've built three version, right now I'm converting my TMB to a 5879 front end cause I dig the chime. I was using ez81's until I finally just replaced it with the weber copper cap or whatever they call it. I had the top come off, its just a big ceramic resistor and a few diodes if I recall. I've logged 4 years of gigging the amp with it and never looked back. Its still in the amp, its not like the Ez81 contributes to sag or anything. Just an opinion. Good luck with your amp!  :smiley:

Regards,

Don