Marshalls...

[SecretSam]

Hendrix, Gallagher, Trower on the one hand.

Some geezer on the internet on the other.

Hm.

[ef37a]

EC used one in the Bluesbreakers so there can't be much wrong with them.....

That's the amp he spent years finding according to the documentary on recently.

Clapton was also said to have convinced recording engineers to mic his amp from several mtrs away. Said, " The ****g audience is out THERE not with their ****g ears stuck against the speaker!"

But, how does 'everyone' still do it these days? Mind you, Clapton was a bit loud.

Head-on-block time... Marshalls, the valve jobs, are really just variants of Fender designs and Fenders just built from the valve data sheets. So in practice the only real variable is the 'voicing' in the pre amp. You can distort a bit then EQ or EQ then distort. Then do either or both again and the frequencies at which you do so are infinitely variable.

People bang on about output transformers but in my, admittedly small, experience they all sound much the same. (some are however a bit feeble)

Dave.

[Sam Spoons]

For practical reasons I close mic my guitar cab in the studio but going from 1" from the grill to 4-6" back makes a huge difference to the sound.

[CS70]

But, how does 'everyone' still do it these days? Mind you, Clapton was a bit loud.

This is quite nice:

https://www.loudersound.com/features/jo ... -the-beano

[SecretSam]

I am also coming to the conclusion that I am looking for a Marshall, and not a Vox.

A local company hand builds valve amps at reasonable prices. Would the spec below sound Marshally in your collective opinion?

"18 watts of cathode biased British tone
12AX7 (ECC83) preamp tubes
EL84 power tubes
6CA7 rectifier
Aluminium chassis with perspex faceplates.
one channel features plexie style tone controls with gain, treble, bass, mids and master volume"

The company is Mars Tube Audio, and they do clones of a few classic designs:

http://www.marsamps.co.za/product/18-watt/

They can provide them as kits, fully built amps, or just the fully built electrical bit - so you can design your own arty case. Which could be fun.

Shipping to the UK might cost a bit, but locally the fully built electrical bit costs about 10% less than a Chinese-built Origin 20 head.

[ef37a]

I am ABSOLUTELY no kind of expert on Marshalls but I would say that THE marsh' tone is EL34s and fixed biased?

That kit is EL84s and cathode bias and that is a Vox AC15 line up. Can you get a schematic out of them before you buy? I seem to recall Marshalls used a bit of negative feedback? Vox did not.

Dave.

[SecretSam]

Thanks very much Dave. I'll see if they will part with one.

[Sam Inglis]

I have an old Marshall PA20 head. Despite being EL84 rather than EL34 based it sounds pretty Marshall-y to me. And it's only 20W so perfect volume for rehearsals, pub gigs, etc. If those things ever happen again.

[ef37a]

I have an old Marshall PA20 head. Despite being EL84 rather than EL34 based it sounds pretty Marshall-y to me. And it's only 20W so perfect volume for rehearsals, pub gigs, etc. If those things ever happen again.

Hi Sam (there's always one!) Ok! As I said, I know nowt but schematics. "Sounds" are ephemeral things that defy scrutiny! But thinking about it, 20 watts* is a lot to get out of 84s in cathode bias and so it might be a fixed biased amp? Rare for 12W pentodes but would give that extra 'punch' and headroom.

*FYI there was a hospital headphone diss' amp that used EL81s, a TV line output valve that could stand a kV or more. I think that could put out around 25-30 watts from a 12W valve. Not in any way hi fidelity but I bet one would make a killer rock gitamp!

Dave.

[Sam Spoons]

Not quite the same spec* but this would be well worth considering if you are up for a bit of self build (I did,** and it was not difficult, just take heed of the warnings about working on valve amps and the high voltages they use). Quite a bit cheaper*** and UK based so you'll save on shipping, duty and 20% VAT which will be added to the Mars kit/amp.

That said, the difference between the kit and the amp chassis built up is only about £40 which seems ridiculously cheap. Even though a pro build would probably be a fair bit quicker it'd probably still cost you at least £120 for somebody to assemble it for you in the UK.

I love mine, it's been the only guitar amp I use since I built it about 4 or 5 years ago

https://www.ampmaker.com/shop/p1800-18w-vintage-plexi-amplifier/

* The mapmaker kit lacks the valve rectifier.

** I actually built the PP-18 which is slightly less complex, it took about 10-12 hours and worked first time.

*** £308 including UK shipping, no VAT as he is no longer VAT registered.

[Sam Spoons]

Just to add these 18 watt amps are all based on the WEM Dominator design.

[ef37a]

Just to add these 18 watt amps are all based on the WEM Dominator design.

Ah! Something I know, I have a Dominator looky-likely, actually a Mersey Super 15 and it is cathode biased with no NFB.

Not that hard to add a negative bias supply and get the anode current down to 20mA* or so. Runs the valves a lot cooler and as said before, beefs up output. NFB is a trickier matter. Get it dead wrong and the amp takes off. Mind you, being valves they will survive the few seconds it takes to kill the power...transistors? POOF! in mu seconds. Even if stable you only want the merest whiff of NFB or you can get squegging on heavy drive.

*Can't remember what 84s bias to, EL34 'we' always set to 25mA per valve. Will look it up.

Dave.

[Hewesy]

I am ABSOLUTELY no kind of expert on Marshalls but I would say that THE marsh' tone is EL34s and fixed biased?

That kit is EL84s and cathode bias and that is a Vox AC15 line up. Can you get a schematic out of them before you buy? I seem to recall Marshalls used a bit of negative feedback? Vox did not.

Dave.

It'll be an 1958X clone Dave, supposedly "half" a Bluebreaker but running EL84's not 5881like the BB (which was JTM45 based?).

Essentially the 1958X is Watkins/WEM Dominator circuit/copy but modded, it has come across my radar being more accessible than a BB or even the heads (and it have valve trem for the win) but the EL84'S put me off to as that's basically my Laney.

Hewesy

[ef37a]

Never been a fan of the EL84. They run blinking hot and although they seem to last (well, GOOD ones!) much longer than you would think I would much rather a pair of 6V6s. The latter were used in radios and Bell&Howell projectors and seemed last forever!

You could even use a pair of 'detuned' El34s in one of those kits. Strictly speaking the anode loading would be wrong but since when did guitar amp manufacturers fuss about such niceties?

Life is throwing me some strange curves at the moment but in a year or so I MIGHT be able to get back into messing with valve amps at home. Just hope the eye and other 'bits' hold up!

Dave.

[SecretSam]

OK that was me misleading you all by misinterpreting 'British invasion' in the marketing blurb.

Their Marshally thing costs about 30% more, is 30w and harder to build:

"A classic Plexi Amplifier. More than 30watts of power from two KT66’s
GZ34 rectifier tube
This amp kit is virtually a clone of the famous 1960’s amplifier that was widely used by Brit rockers.
This build is more complex than the other kits listed above. If you are uncertain if you’ll manage, book a seat at our next DIY workshop, and we’ll show you how."

[SecretSam]

Not quite the same spec* but this would be well worth considering if you are up for a bit of self build (I did,** and it was not difficult, just take heed of the warnings about working on valve amps and the high voltages they use). Quite a bit cheaper*** and UK based so you'll save on shipping, duty and 20% VAT which will be added to the Mars kit/amp.

That said, the difference between the kit and the amp chassis built up is only about £40 which seems ridiculously cheap. Even though a pro build would probably be a fair bit quicker it'd probably still cost you at least £120 for somebody to assemble it for you in the UK.

I love mine, it's been the only guitar amp I use since I built it about 4 or 5 years ago

https://www.ampmaker.com/shop/p1800-18w-vintage-plexi-amplifier/

* The mapmaker kit lacks the valve rectifier.

** I actually built the PP-18 which is slightly less complex, it took about 10-12 hours and worked first time.

*** £308 including UK shipping, no VAT as he is no longer VAT registered.

Thanks Lord Spoons. That's a good recommendation.

[ef37a]

Found some data on fixed biasing 84 and, Ooo! Interesting
https://frank.pocnet.net/sheets/084/e/EL84.pdf

It seems two valves will deliver 17W for 300V on anodes at 4% THD which is naff all for guitar amps and you should be able to push that well over 20W.
The very good news is that -14.7V on the grids gives an Ia of just 7.5mA and thus a Pa of around 2.5W meaning even the minging modern valves should last a long time.

I wonder why more amp makers have not done this (they don't do it for 6V6 either and they should deliver similar results) ? Maybe fixed B 84s sound BAAAAD!

Hmm? I have read that there are a few guitar amps that produce a decent and loud overdrive sound but cannot do 'clean' at any volume. A very coldly biased amp mayhap?

Dave.

[Hewesy]

Interesting, I've a 5w Kustom head which cannot do clean at all.

1x 12AX7 and 1x EL84 IIRC, nice amp but not a "daily" for me.

I did fit a 12AT7 which calmed the drive but still not actually clean.

Hewesy

[Sam Spoons]

My 18 watt doesn't really do 'clean' in the Fender Twin sense but it does do a decent 'clean with just a little edge' which works well enough for my needs and is reasonably loud driving a V30.

[ef37a]

Interesting, I've a 5w Kustom head which cannot do clean at all.

1x 12AX7 and 1x EL84 IIRC, nice amp but not a "daily" for me.

I did fit a 12AT7 which calmed the drive but still not actually clean.

Hewesy

Well it orta! I suspect they designed it to give a distorted sound because, 1) that is what they think everyone wants and 2) distorted sound always give the impression of greater volume.
OR! Maybe they just don't know how to design a linear valve amp.

Not hard. There was a very famous Mullard design, the 3-3 that produced 3 watts at hi fi distortion levels(ok yes, it used an EF86 not an AX7 but could be done) The EL84 and ones section of the triode could be given a bit of NFB and the result deliver 4 or 5 watts at lowish distortion* and that would easily be loud enough through a 100dB/w/mtr speaker in a pub sans drummer.

After all, there have been millions of radios and TV sound stages made with a single 12W valve output and these were quite clean and loud enough to cause social rifts! Even though the speakers were at least 10dB less sensitive.

*And for guitar you are not trying to deliver clean tones at 40Hz which is where transformers show their problems unless VERY expensive.

[Folderol]

ECL86 comes to mind. A pair make a complete amp with push-pull output.

[ef37a]

ECL86 comes to mind. A pair make a complete amp with push-pull output.

Cracking valve Will! The ECL82 was good as well, slightly less power. The other numbers, the 83s and 84 not so reliable. The ECL83 in particular was very compact and ran very hot.

I cannot understand the present rave for single ended amps? Ok, if you want to market something really cheap and bit nasty, a double T and 12W pentode, VC and top cut pot and you have a 'practice' amp but for more than 5 watts or so, go push pull. Cost? Nah, the OP traff can be much smaller and cheaper. Standing current is lower so the power transformer can be a tad smaller. Smoothing caps can have lower values because the OP stage 'hum bucks' I dare say also that a pair of 6V6s cost about the same as a single EL34 and less than a 6L6 or KT66, and MUCH less than a KT88!

But then I came late to the industry and found it is waist deep in snake oil, hype and marketing bllx.

Dave.

[SecretSam]

Hm. How's this for a lockdown project, Dave: design a circuit for the amp you think should be out there, (double-ended valves etc etc) and sell the drawings plus idiot-proof instructions as a Kindle book on the interweb for twenty quid a time.

Would it sell ? Well, Wampler's book on modding pedals is currently US$ 69.95 in paperback.

I always thought a KT88 was a Japanese motorcycle, so am always slightly awed by your posts.

[ef37a]

Heh! Oh if only I had the energy!

I assume as well that if you SELL detailed designs you need to submit a prototype for safety and RF testing? That is a long and expensive process. I have also written 'Working Instructions' for VERY simple assemblies to 9001 specc' and BELIEVE me! NO such thing as idiot proof instructions!

And Oh! The KT88 is a lovely valve (well, was) Two of them can produce an easy 30 watts at what was state of art distortion levels and even pushing to 50W the sound quality can be very good. Get serious and 4 can deliver 200W but you need about 700V on the anodes anf the modern ones are not up to the job...Well, maybe selected, high grade/hi fi types are but they are just not cost effective for the guitar amp market.

If'n I Was to do anything I think I would dabble with some of the techniques in Merlin Blencowes Tube pre amps book? There are many ways to have very versatile biasing circuits that could produce a variety of harmonic effects that I don't think any major amp maker has explored? Very little has been done with Pentodes for example such as the EF86 and cheaper ones such as the EF80, EF812, ECF80.

Dave.