Marshall Amplifiers FAQ

paul_ · Post by **paul_** » Thu Apr 05, 2007 12:08 am

Doog wrote:How is that build going, Paul?

whenever i'm not working on that amp i'm thinking "doog's gonna laugh when i post this on the web in 10 years and go 'finished,' he always asks about it."

well here you are, sir. sorry bout the blurry pic, the amp was rocking too much.

euan wrote:Were Super Basses the 200watt monsters?

nah that's the Major. beastly things! my super bass is 100w and has been modded with an optional master volume in a push/pull pot. so it's basically the best tones i've ever heard without going deaf, nice and thick and bassy for all you garys out there, but someone put a 4700k bright cap on volume I so it's pretty far-out for all sorts of guitar sounds.

Post by **Doog** » Thu Apr 05, 2007 12:30 am

That looks fuckin' great, man. How much in parts do you reckon it cost you?

How does it stand up to "the real thing", presuming you've played one?

paul_ · Post by **paul_** » Thu Apr 05, 2007 1:57 am

Doog wrote:That looks fuckin' great, man. How much in parts do you reckon it cost you?

How does it stand up to "the real thing", presuming you've played one?

i'd say by now its been at least 800 dollars, but the headcase was given to me for my last birthday so i didn't pay for that bit. the guy from metroamp sells a fully loaded kit with everything you need for a grand... we managed to do a bit cheaper by just snagging the bare essentials and getting the components ourselves. but it stands up REAL well to my plexi and to the superleads i've played in shops (not very loud obviously), which makes it a good deal as the 1959HW re-issue goes for around 3 grand over here... we went mega-authentic with the capacitors and resistors, and used heyboer transformers, and went from schematics of the real thing coupled with instructions by a guy who's reverse-engineered a billion of these things. building it ourselves has put it in the price-range of a modern marshall and not into ker-azy vintage RI or boutique territory, which is what a pre-built version of the same amp would run.

overall, it's not like getting a plexi for super-cheap, but you're certainly saving MOST of the money usually involved in getting one, and having an experience, and an amp with a story behind it. also, because we put it together ourselves, it's always in the back of my mind that if i want to change SO-AND-SO i'll just open 'er up and switch out THIS'n'THAT, etc... looking forward to experimenting with different bright caps on input I and maybe trying out a different value negative feedback resistor.

i also learned how to bias all of my amps through the course of this, so that's always good.

euan · Post by **euan** » Thu Apr 05, 2007 7:51 am

No scrimping on a decent OT is a good thing.

Thom · Post by **Thom** » Thu Apr 05, 2007 8:04 am

Looks great - looking forward to hearing samples!

Post by **Mike** » Thu Apr 05, 2007 8:44 am

As I said i nthe other thread - Awesome.

euan · Post by **euan** » Thu Apr 05, 2007 8:57 am

I gotta start saving up for my Champ.

luke · Post by **luke** » Thu Apr 05, 2007 8:59 am

euan wrote:I gotta start saving up for my Champ.

I gotta start saving up for my Tiny Terror. Stupid weekend only job.

euan · Post by **euan** » Thu Apr 05, 2007 9:14 am

Malik wrote:
euan wrote:I gotta start saving up for my Champ.
I gotta start saving up for my Tiny Terror. Stupid weekend only job.

Enjoy being young. I'm planning on making it sometime in the summer when I can work with my father to make the combo cabinet.

gary · Post by **gary** » Thu Apr 05, 2007 12:28 pm

paul_ wrote:i also learned how to bias all of my amps through the course of this, so that's always good.

Damn right it is! A proper bias can take a valve amp from good to fucking outstanding. I was lucky that my LC50 was biased perfectly when I bought it... with feedback and at a decent volume I can get about four harmonic overtones simultaneously. Best amp I've ever owned, cheapest too - Â£210 for a 50 watt valve amp.

What valves (tubes) are you running in your handmade beast?

Post by **Mike** » Thu Apr 05, 2007 12:32 pm

Paul wrote that, not Doog.

Post by **Doog** » Thu Apr 05, 2007 12:41 pm

For real- my amp has a super convenient bias point, an idiot with a multimeter could do it. And he has.

paul_ · Post by **paul_** » Fri Apr 06, 2007 9:17 am

gary wrote:
What valves (tubes) are you running in your handmade beast?

preamp: three ecc83's
output: four el34's

the handwired circuits aren't all that different from biasing a modern marshall, really. i just never knew how to bias amps, where to put the multimeter, what to read for, etc...
here's the old-school vertical trimmer for you though:

gary · Post by **gary** » Fri Apr 06, 2007 11:09 am

Mike wrote:Paul wrote that, not Doog.

fix'd

paul_ wrote:
gary wrote:
What valves (tubes) are you running in your handmade beast?
preamp: three ecc83's
output: four el34's

the handwired circuits aren't all that different from biasing a modern marshall, really. i just never knew how to bias amps, where to put the multimeter, what to read for, etc...
here's the old-school vertical trimmer for you though:

I really should learn to bias myself, for the price of a good multimeter I can save myself beer money by not paying a tech with an oscilloscope to do it. EL34s are what, 25mA a side?

Post by **Mike** » Fri Apr 06, 2007 11:28 am

gary wrote:I really should learn to bias myself, for the price of a good multimeter I can save myself beer money by not paying a tech with an oscilloscope to do it. EL34s are what, 25mA a side?

It's nowhere near that simple. You have to calculate the bias from the Plate Voltage and what percentage of the dissapation current you want to bias the idling Power tubes at. It's completely tied to the individual amplifier design, not the tube - and not something you should mess with unless you understand what you're doing - which you clearly don't seem to.

euan · Post by **euan** » Fri Apr 06, 2007 11:44 am

Mike laying it down Easter style

Post by **Mike** » Fri Apr 06, 2007 11:47 am

I'm only just getting started

Also some amplifiers don't have 1 ohm shunt resistors to probe points for you to conveniently measure the bias voltage (and therefore current due to the 1 ohm resistor), or equally simple locations to measure the plate voltage (unless you want to probe a tube socket), so sometimes you have to use teh Transformer method (dangerous), install your own 1 ohm shunts (tricky + dangerous + voids warranty) or use Bias probes (costly and potentially inaccurate).

Post by **Doog** » Fri Apr 06, 2007 12:11 pm

euan wrote:Mike laying it down Easter style

He passed out for 3 days, then was reborn and laid down the 10 commandmentz

Bacchus · Post by **Bacchus** » Fri Apr 06, 2007 4:38 pm

There's no need for any biasing on my Epiphone Valve Junior, is there, what with there only being on valve in each section?

I know fuck all about this.

Post by **Mike** » Fri Apr 06, 2007 4:42 pm

BacchusPaul wrote:There's no need for any biasing on my Epiphone Valve Junior, is there, what with there only being on valve in each section?

I know fuck all about this.

You can design multitube amps to self bias (or be biased to a set point). Fender Twins have a non adjustable cathode bias.

It's a design choice.