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Messages - CraftyZA

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1
Tubes and Hybrids / Re: Rebuilding Marshal Amp
« on: May 08, 2015, 02:00:38 AM »
This Alemic circuit that was posted a few weeks ago.

I still need the parts the build the psu, and voltage doubler. Will get to that end of the month

2
Tubes and Hybrids / Re: Rebuilding Marshal Amp
« on: May 06, 2015, 07:25:19 AM »
What should the voltage be on on the rest of the caps?
They only show the one on the b+ rail which is 350v

My components was delivered, but supplier gave little tiny ceramic caps for everything, and not the polly types. They are not waisted at least, i can use them on other projects as filters over diodes etc...
 I need to re-order the caps, but need to double check the voltages. The polorized caps in die diagram is obviously electrolytic alu caps. Trying to find radial versins for them. The main concern is over all those poly caps.

 

3
Tubes and Hybrids / Re: Rebuilding Marshal Amp
« on: April 14, 2015, 09:52:44 AM »
I stay in Centurion. Pretty sure I can source something like that.
Looking at the diagram in a bit more detail I discovered there is no R6, and C6 is used twice :-)

C6 is not a problem. I just labeled one C7 which seems to missing. So just a mislable issue
Am I missing something with R6?

4
Tubes and Hybrids / Re: Rebuilding Marshal Amp
« on: April 13, 2015, 09:23:56 AM »
@J M Fahey, You don't by any chance have a pcb layout for that alembic? I've ordered the parts, And the Etching bath is ready. Or is it better to solder the components directly to each other?
Alternativly I can just do it on some G10, or even masonite board and use wires like the diagram I posted.

5
Tubes and Hybrids / Re: Rebuilding Marshal Amp
« on: April 08, 2015, 08:06:38 AM »
But the multiplier runs from the nominal 60VAC coming out of your transformer secondary (a transformer you already have?).

If you have the existing transformer, just use it as JMF mentioned.  It has a 200VAC winding for the tube HV, as well as a heater winding.

Schematic attached:

Personally I prefer not to ground power supply to ground. Unless it's really necessary. It introduces all sorts of noise from the fridge and aircons from other rooms. The biggest culprit is a fridge. I've added a snubber to the plug on the fridge and that reduced noise by halve! It generates vast amounts of noise which becomes audible when grounding on the same plane where you central tap your power supply and audio grounds.
In my SRPP I have 2 grounding planes, linked with ceramic cap, and 2 diodes in opposite directions. Between the snubber on the fridge and this, very little interference gets through. Actually All I hear is valve humm i think.
 

6
Tubes and Hybrids / Re: Rebuilding Marshal Amp
« on: April 04, 2015, 07:49:01 AM »
Thanks. Will do that tripler. Just a question. In south africa we have between 240 and 250v mains. Mine is sitting at about 251. So i need to aim for almost 1:1 ratio.


Sent from my iPad using Tapatalk

7
Tubes and Hybrids / Rebuilding Marshal Amp
« on: April 04, 2015, 01:46:35 AM »
This looks so simple





Do you want an amp that has some character, a range of voicing, or do you just want a grunge engine?

A bit of both. You can have both, if you don't overdo the overdrive bits.

Jack white
Pixies
The who
Clapton

Otherwise one can simply hook up a boss mt2 and crank it all the open, but that sounds crappy.. That MT2 must be worst peddle ever. I like warm tones, with a touch of crunch.
But as you said in one of your earlier replies,  one can achieve that with a peddle.

8
Tubes and Hybrids / Re: Rebuilding Marshal Amp
« on: April 03, 2015, 05:34:33 PM »
This seems fantastic!!
http://www.alembic.com/prod/f2b.html
Thanks for the input. I think this alembic is the one :)

9
Tubes and Hybrids / Re: Rebuilding Marshal Amp
« on: April 02, 2015, 08:19:05 AM »





Am I right in saying that if I increase the gain on the left I can create a stronger distortion, and the output from the valve on the right will stay relative static. Thus I can have a 2v output signal, and by really overdriving it, that signal should still stay close to 2v? I'm going to order parts for this now, and pick it up on saturday. Should make for a nice weekend project :-)

10
Tubes and Hybrids / Re: Rebuilding Marshal Amp
« on: March 31, 2015, 09:31:28 AM »
Sorry, did not take pics. I had the amp with somebody I really trust. Even he said to not spend more money. Everything is fried inside the power stages. It has 2 power stages. I think the one is used for chorus. All circuits in the line of the first stage was blown.  So not the chorus channel.
After salvaging some parts I discarded the board. Got enough 30% - 70% projects floating around. Time to clean up.
Towards the end of the year, I'm going to build a Twead like clapton used. But that is a project for later.

Roly, Thanks for that explanation. Strange to think that there are even 12v circuits on the net. Valve Caster 2.0 runs on 9 volt batteries  :duh

I will do some more searching. I've got 2 x 12x7 tubes (not matched), and have not bought components yet. They are all in an online basket. Still researching.
However, I have ordered a 60v transformer vir 6v seconadry. Can use voltage doubler on that 6v and try to regulate it to 12.6 for the filaments. However, seems like that 60v will not be enough.
I'm sure I can use it in another project somewhere.





11
Tubes and Hybrids / Re: Rebuilding Marshal Amp
« on: March 31, 2015, 06:36:56 AM »
Hi CraftyZA, welcome.


Quote from: CraftyZA
I'm rebuilding a marshal valvestate S80 amp.

Why?

It is fried! Replaced the 2 chips, and a bunch of zeners, then some resistors blew up, and some tracks melted.
I rescued the valve, and some other parts. Will Use the chassis and drivers in this hybrid project.

12
Tubes and Hybrids / Re: Rebuilding Marshal Amp
« on: March 30, 2015, 09:30:31 AM »
So I've decided on this:

www.instructables.com/id/Guitar-Tube-Pre-Amp/?ALLSTEPS

Seems like this will do the trick. Do you guys know this design? know what it will sound like?

13
Tubes and Hybrids / Rebuilding Marshal Amp
« on: March 25, 2015, 02:39:11 AM »
I'm rebuilding a marshal valvestate S80 amp. The one with the 2 x 12" drivers.
I'm going to rip out the current amp portions and only use the chassis and drivers.
I've got the new power stage sourced. I can decide between a veloman kit amp, or lm3886 based amp designed by a friend of mine.
However...
The preamp and overdrive is still a headache. I need to understand the dynamics before i can design it.
The idea is to use an 12ax7 valve for that. possibly 2.
The input signal on the power stage is set to max 2v. This i quite high. I can adjust to about 1v
Do i need 2 stages before that? IE normal preamp, that will be overdriven by a 2nd preamp? Or do i just give one preamp a very large gain range from clean to crunchy?
Any one got simple circuit diagrams for it?
I've bought an extra 12ax7 tube. Plus I have the one that can be salvaged from the original valvestate amp.

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