Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Mehfuzhoss on August 20, 2020, 08:44:43 pm

Title: marshall lite 2 preamp / 6sn7gtb power tube
Post by: Mehfuzhoss on August 20, 2020, 08:44:43 pm: Hello,

I am back to this forum for a build that I am planning. I built a ax84.com 4 4 0 (3x 12ax7 and 1x 6sn7gtb) and not liking the amp. I want to reuse the PT OT and the power tube 6SN7GTB and build a marshall preamp based amp if possible. I really like the lite ii circuit.

The PT is 269JX - 500VCT with 69ma
OT is 125C 8 watt output; Primary Impedance: 1.2 kOhms to 25 kOhms; Secondary Impedance: 1.5 Ohms to 15 Ohms

any idea or direction is appreciated
Title: Re: marshall lite 2 preamp / 6sn7gtb power tube
Post by: EL34 on August 21, 2020, 07:10:33 am: Posted in wrong board.... moving
Title: Re: marshall lite 2 preamp / 6sn7gtb power tube
Post by: tubenit on August 21, 2020, 07:40:28 am: This mini-bassman and marshall idea may prove useful to you. There is a schematic and layout. I have NOT built one.

https://el34world.com/Forum/index.php?topic=18481.0

With respect, Tubenit
Title: Re: marshall lite 2 preamp / 6sn7gtb power tube
Post by: Mehfuzhoss on August 21, 2020, 03:05:32 pm: Thanks a lot.
Title: Re: marshall lite 2 preamp / 6sn7gtb power tube
Post by: Mehfuzhoss on August 22, 2020, 04:44:41 pm: The 269JX PT doesnt have a center tap. (The green yellow wire to the 180k resistor in the attached image is the CT. )

Will i leave this connection? Will it cause him or buzzing? If so how can i create an artificial tap.

Help!
Title: Re: marshall lite 2 preamp / 6sn7gtb power tube
Post by: sluckey on August 22, 2020, 04:56:00 pm: Connect a 100Ω 1/2w resistor to a 6.3VAC filament pin of the closest (or most convenient) tube socket. Connect another 100Ω 1/2w resistor to the other filament pin of the same socket Connect the free ends of those two resistors together and then connect a wire from the junction of those resistors to that point on the board where the green/yellow wire is connected. I suggest using a terminal strip to secure the ends of those resistors and wire.
Title: Re: marshall lite 2 preamp / 6sn7gtb power tube
Post by: Mehfuzhoss on August 23, 2020, 04:41:26 am: PT spec: 269JX 50VA 115AC 60hz, 500V C.T. @ 69ma. 6.3V @ 2.5A . can I run the rectifier tube with the same 6.3V winding?

I need to power 3 12axy7, 1 12au7 and rectifier ez81. can the PT handle these load with same 6.3V tap?

thanks
Title: Re: marshall lite 2 preamp / 6sn7gtb power tube
Post by: Mehfuzhoss on August 23, 2020, 04:50:59 am: is the choke 5 Henry 50 milliamp a must for the JTM45 2 watt build? Will a resistor do the trick? if so, what size resistor would you recommend and where should i wire it in the layout!

Thanks.
Title: Re: marshall lite 2 preamp / 6sn7gtb power tube
Post by: sluckey on August 23, 2020, 06:03:56 am: Quote from: Mehfuzhoss on August 23, 2020, 04:41:26 am
PT spec: 269JX 50VA 115AC 60hz, 500V C.T. @ 69ma. 6.3V @ 2.5A . can I run the rectifier tube with the same 6.3V winding?
yes

Quote
I need to power 3 12axy7, 1 12au7 and rectifier ez81. can the PT handle these load with same 6.3V tap?
Very easy to do this yourself. Look up each tube. Write down the filament current requirement. Add 'em up. Start here...

http://tdsl.duncanamps.com/tubesearch.php

Quote
is the choke 5 Henry 50 milliamp a must for the JTM45 2 watt build? Will a resistor do the trick? if so, what size resistor would you recommend and where should i wire it in the layout!
The choke is very important to the sound of a JTM45. Probably not so much to your project. I'd start with a 1K/3W and experiment until you have the B+ voltages like you want.
Title: Re: marshall lite 2 preamp / 6sn7gtb power tube
Post by: Mehfuzhoss on August 23, 2020, 06:48:10 am: Is this choke will work?

https://tubedepot.com/products/filter-choke-for-fender-6l6-amps
Title: Re: marshall lite 2 preamp / 6sn7gtb power tube
Post by: sluckey on August 23, 2020, 06:54:30 am: yes
Title: Re: marshall lite 2 preamp / 6sn7gtb power tube
Post by: Mehfuzhoss on August 23, 2020, 05:29:32 pm: I have a F & T 100uf 500V cap, the build calls for two 47uf. Is there a way I can use the 100uf ?
Title: Re: marshall lite 2 preamp / 6sn7gtb power tube
Post by: shooter on August 23, 2020, 05:47:14 pm: post 4 shows a 40/20/20/20 :dontknow:

if you're doing the PS, 2 47uf will have a resistor between 'em, a single 100 won't
Title: Re: marshall lite 2 preamp / 6sn7gtb power tube
Post by: sluckey on August 23, 2020, 07:48:31 pm: Quote from: Mehfuzhoss on August 23, 2020, 05:29:32 pm
I have a F & T 100uf 500V cap, the build calls for two 47uf. Is there a way I can use the 100uf ?
No. You must follow the plans exactly.