Re: Marshall Amps
 

In case anyone's wondering what all the fuss is about, here's a nice original one that arrived this week with me, dating from the mid 1970's.

All the transformers are made by Dagnall.

Re: Marshall Amps
 

When comparing different (for example) ECC83 valves in a guitar amp, you only really notice the difference when the amp is being driven into distortion, the clean sounds will sound similar. Also, if you're comparing a load of different modern valves, then they may well sound similar. The strong point I'm making is, a modern 'Chinese' valve just will not hold up to a Mullard when overdriven. See my earlier descriptions.

Re: Marshall Amps
 

If people are still puzzled as to what "harp" is being talked about, the blues harp is actually a harmonica/mouth-organ and Marine Band relates to a set of seven pitched in different keys. I think Marine Band was an early and very good manufacturer of these sets.

I think I have a soft-bound copy of a publication on the history of Marshall amplification, but I can't locate it at present. It may have been co-written by Ken Bran and someone else and had no mention of anyone called Dudley Craven. Jim Marshall was a drummer and owned a music-shop. I think Ken Bran was working full-time somewhere else before the event of copying the Fender Bassman 5F6-A came about. To suggest that Ken Bran was only there to populate the tag-boards is, I think, a bit of an insult. After all, when Jim Marshall got into a bad business deal later on and couldn't sell amps bearing his own name, he got Ken to make copies which were called "Narb". That's Bran backwards, get it? Certainly not "Nevarc".

Just my tuppence-worth, Colin.

Re: Marshall Amps
 

Kevin,
The rust does suggest 1970-something, but I think that circuit board doesn't. The early amps would have had tag-strips or turret-boards. Has someone been doing some "improvements" to yours?
Colin.

Re: Marshall Amps
 

I still haven't found my copy of the book I mentioned, but I have found a reference to it on the web:

https://books.google.co.uk/books?id=...page&q&f=false

It is called "The History of Marshall: The Illustrated Story of "The Sound of Rock" and was written by Michael Doyle. On page 12, there is a reference that I hadn't really noticed before, of "Ken and his long-time friend and assistant Dudley Craven".

I really must locate this book amongst my others.....

Colin.

Re: Marshall Amps
 

I dated it as it's written on it, and it was inspected by Carole ;D

Re: Marshall Amps
 

Here are the two books that I have about Marshall amps. The story (relatively short as it is) about how the amp was 'developed' is on page 39 of 'The The father of Loud' book.

Re: Marshall Amps
 

Marshall changed to PCB's in 1973, prior to that they would have been turret boards. As far as I know no Marshall amps were ever built with tag strips.

Re: Marshall Amps
 

I stand corrected. My mistake was in assuming that when McMurdo described his amp as "original", that he meant one of the early ones, which were of course built in the early 1960s. I should have checked the decades.

With regard to my mention of tag-strips, I really meant tag-boards similar to those used in Vox guitar amps and recalled that Barbara Craven claimed that Ken Bran populated "the component tag boards", even though he was Jim Marshall's Chief Service Engineer.

My excuse is that I was tired, which is a better one than some that I have heard recently.

Colin.

Re: Marshall Amps
 

Here are some pictures of an early Super Lead Plexi 100w I once owned. The amplifier components are mounted on a turret board and the power supply caps on a (thick) matrix board. The electrolytic caps are 32uF RS Components and there is an RS bridge rectifier mounted on the end of the chassis.

Re: Marshall Amps
 

Yes, turret-board. I notice that your amp has those knobs that looked nice in the clear light of day, but were just about impossible to work out where they were set on a dark stage. I've been there and done that myself on a home-brew guitar amp :shrug:.
Colin.

Re: Marshall Amps
 

"Those knobs" are what are used on current Marshall amps and have been for decades now - as you know Colin, I'm sure. But anyway, aren't Marshall users supposed to turn everything up to 11?

Re: Marshall Amps
 

Dave Simpson guitar on youtube has an interesting video on why he prefers transistor amps, worth a look, great guitarist as well, really infectious watching,
Regards, Alan.

Re: Marshall Amps
 

I haven't worked on a lot of Marshall amps, but I was sure that there were some that had the early metal nameplates with the red lettering and had bigger knobs with rather more obvious index lines. I understand that those small knobs are typical of Marshall, but I would have thought that once people saw that the other knobs were more convenient, Marshall would have at least used them on some of the later amps, but maybe not the "re-issue" models. Perhaps by then all the performers had fried their brains with the loudness and didn't really care where the knobs were adjusted to.
Colin.

Re: Marshall Amps
 

The very early JTM45's did have a different type of control knob but these were only produced for a very short period (1963-1965 I think). Pretty much every Marshall amp produced since then has used the current style of knob.

Re: Marshall Amps
 

Fortunately, audio is much easier than whisky flavour because it's measurable.

Time I think to get the scope on to a Marshall and find out something about its gain structure. For example, as volume is increased, one would expect the output stage to overload first. Overload behaviour of different EL34 samples may well be different, accounting for some of the audible differences.

But we then have to look at the earlier stages to account for sensitivity to different sample of ECC83.

As a start, a relevant question is: once the output stage is clipping, at what volume point does an ECC83 section also begin to clip? If the 'magic' ECC83 isn't clipping, it's difficult to understand the reported variation between samples.

On the other hand, maybe an ECC83 operating in normal linear mode is at some volume point being asked to drive grid current into a clipping EL34. Again, different samples may exhibit different behaviour. Either way, I suspect that we're looking at valve characteristics outside the normal data sheet parameters and it would be interesting to know the relevant drive conditions.

Then we could begin an actual technical discussion on the 'Mullard magic'.

It's what we normally do with 'magic'!

Martin

Re: Marshall Amps
 

Hmmm, try telling some of the cork sniffing "tube rollers" that... They will assure you their ears are far more sensitive than any oscilloscope and they can hear things that can't be measured! :)

The gain structure will depend a lot on which Marshall amp you are looking at. Older versions with no master volume control will behave a lot like you describe with power amp distortion starting first but a lot of the more recent models will have higher gain preamp stages with most of the distortion coming from the preamp valves. A word of advice if you are going to start driving a non master volume Marshall into distortion I would recommend getting some good ear defenders! Once you turn that volume knob much above about 2 they start to get pretty loud pretty quickly!

Re: Marshall Amps
 

There were in fact four if not five different styles of knobs used on Marshall amps - see photos. My current build project that I referred to earlier is a 64 style amp. I made one about 15 years ago, and you can see the metal 'coffin' logo on the photo attached. Called a coffin logo because that's exactly what they are made out of, a coffin nameplate. My new build will be much more accurate than the photo you see, that one has long gone.

Re the photo with text, where it refers to "the bottom photo", due to the way I've cropped images, it is the photo above that text itself.

Re: Marshall Amps
 

Quite so, in the early 80's I had a 1968 100W plexi, I started noticing the audience wincing at my kerangs - was my playing that bad, no I was told "it's so ******* loud" :o

Re: Marshall Amps
 

So.....the Marshall pre-amp is also a volume limiter. The overload characteristic of the ECC83 is all important to the sound of the end result. Unexplored audio territory I guess.

Martin