Marshalls...

[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.

[Sam Spoons]

My old MusicMan RP65/100 produced 100 watts before clipping from a pair of EL34s, the only difference between the two versions was the transformers, the tranny in the 65 watt supplied 250V HT and the one in the 100 watt, 350V. I swapped the trannies* as I wanted the power but didn't like the speaker in the more powerful version.

* I worked in MI retail, the importers were kind enough to send me a pair of the bigger trannies and take the originals back into spares stock for, IIRC, £25.

[ef37a]

My old MusicMan RP65/100 produced 100 watts before clipping from a pair of EL34s, the only difference between the two versions was the transformers, the tranny in the 65 watt supplied 250V HT and the one in the 100 watt, 350V. I swapped the trannies* as I wanted the power but didn't like the speaker in the more powerful version.

* I worked in MI retail, the importers were kind enough to send me a pair of the bigger trannies and take the originals back into spares stock for, IIRC, £25.

Yes Sam 'The Book' says you can get 100W from a pair of EL34s but I don't know of any amplifier manufacturer that has ever marketed such an amp? 100 watters are usually 4 25W bottles.

In fact I was once asked to test a couple of amp to see what they could put out for 10% THD?
An Artisan 100 easily gave 120 watts and the HT-60 stage topped 80W for just two EL34s. So, it would be quite in order to market those models as "Artisan 120" and "Stage 80" because 10% THD is the rating point in most valve data specifications. (in these days of 3 or 4 decimal places for converter distortion, 10% sounds horrendous but in fact, for a single source it is on the verge of detectability and a modest 'rock edge' is much higher)

Note as well, the tests were fairly done at the rated 230V input. Most of us get 240V and so you could probably stick at least another 5W atop those figures.

Dave.

[Sam Spoons]

MusicMan did market the RP/RD100 as a 100 watt amp with only two EL34's, we didn't believe it so that was why we went to the trouble of measuring it.

We got a fraction over 100 watts measured for a 1kHz sine wave into an 8 ohm dummy load. We wound it up until the scope showed the top of the waveform flattening and then backed it off a touch. We didn't have the facilities to measure the THD but our method was accurate enough for me.

[Hewesy]

Interestingly some Marshall users did fit the KT88 - or 6550 which I think is interchangeable with the KT?

Zakk Wylde uses them in his Marshall's, i think possibly Randy Rhodes did too and a few others (Billy Corgan?).

Hewesy

[ef37a]

Interestingly some Marshall users did fit the KT88 - or 6550 which I think is interchangeable with the KT?

Zakk Wylde uses them in his Marshall's, i think possibly Randy Rhodes did too and a few others (Billy Corgan?).

Hewesy

GREAT debate found in the audiophool community as to whether or not they are exact equivalents. In the 'Ball of chalk and String' design world of guitar amps? They are the same but like any power valve change, bias must be checked.

Sam, in my opinion 'watts (well V across R) at a specified distortion level is the only fair way to specify amplifiers. You said yourself "observed clipping then backed it off a bit" !! That is a subjective judgement. Of course, 100 watts or 95 (at X%THD) matters not at all to player or punter, both too B loud but some people get sniffy when an amp does not meet a published (or assumed ) power specification.

No distortion meter? Wine into water to make for this application. J L Hood published a design based on a parallel T filter and SINGLE transistor! Today we would use an op amp.
Reading THD at 1% and higher is easy especially when you have tens of volts of signal. It is measuring to 3 decimal places where you need the Docs AP rig!

BTW anyone here still using tape seriously would do well to knock up the JLH meter circuit.

Dave.

[Kwackman]

anyone here still using tape seriously would do well to knock up the JLH meter circuit.

But in that situation it wouldn't be measuring distortion, but "Analogue Warmth"...

[ef37a]

anyone here still using tape seriously would do well to knock up the JLH meter circuit.

But in that situation it wouldn't be measuring distortion, but "Analogue Warmth"...

Yup, THREE parts in a hundred of the bugger!

Oh and, I got it wrongly, the JLH distortion meter is a somewhat more elaborate beast based on Wein networks. I shall try to find the simple 'bootstrapped' Pll T circuit, it worked well. Maybe it was in Studio Sound? (all a very long time ago........)

Dave

[Sam Spoons]

All that was a very long time ago, and the amp was sold long ago (something I went on to regret) but yes, it was loud.

[Hewesy]

So, as a small closer to the thread, last weekend I bought the DSL20 head.

All the reviews I read/watched which compared the DSL20 and Origin 20 heads reached the same two conclusions, one: that the DSL could do what the Origin could do but not vice versa, and two: that the Origin had to be wound up full to sound decent. Even on the 0.5w setting this would be way to loud for home use even with an attenuator.

First few plays and I'm really happy. Classic Gain channel, gain near max and volume around 11 o'clock (I have a 12db attenuator in line) through my Laney cab with a Celestion 25w Greenback and it's exactly what I wanted. Think Angus Young, Paul Weller (solo career) and even a little Gilmour (his HiWatt DR's were EL34 based I think).
Clarity on open chords but responds to pick dynamics for digging in.

The Ultra Gain channel gets more fizzy as you'd expect, quite a nice option for the odd heavy riff but not really my thing.

The Included pedal switches channels and switches the FX Loop on/off. Never used a loop up to now (I know, I know but my Laney had a mix control on the loop and I could never get it right for my rig...) but running the guitar in direct and adding delay, chorus and Phase 90 in the loop is the happiest I've heard them.

I'm impressed, for the money if you want to scratch the Marshall itch but can't decide on whether a Plexi, JTM/JMP or JCM 8/9/2000 fits your needs then this might be up your street.

Hewesy

[al_diablo]

I thought I would bring this thread back because I too decided I needed a Marshall and I wanted a small versatile combo

I bought a SC20C which is the JCM800 in a 20W (switchable to 5W) combo with a celestion V type 10”

There’s a low sensitivity input capable of glassy cleans and loads of headroom (but my word it’s bright) and a high sensitivity input that gives all the lovely Marshall growl and grind. Absolutely addictive.

With the gain up high it’s still very loud, even at 5W. I will probably end up buying an attenuator just to reduce the need to run the master volume at 1 or 2 when I’m at playing home.

But for anyone searching for Marshall tone in a small box I recommend this small box. It’s also pleasingly light to carry around!

[Hewesy]

Thanks for the addition, I have looked at these and wondered what they were like.

As with the Origin the 5w is a loud 5w, a good power soak is a must for these amps where you want to use the natural drive.

Hewesy

[edtheconfessor]

I have two Marshall’s, an AVT 20
Now sadly sick and a 2525c jubilee model. The jubilee model has a 5watt power at mode which is great for home practice/recording.
It has a single 12” Celestion Greenback, and sounds amazing. It lacks Reverb unfortunately.
I have had the ATV20 for about 20 years and loved it especially the clean chanel strangely. Unfortunately, it started to make a loud booming noise, it is not worth repairing.
The jubilee amp has a variety of usable tones even clean jazz style tones are possible. My favourite sound is the just starting to break up that works best with vintage humbuckers.

[Guest]

for me the Marshall branch is a must, not only for the speakers that for sure is great, but for other many good products like headphones, cameras, etc, and cool to discover as I always thought it was only speakers.

(spam link removed — HR)

[Hugh Robjohns]

Marshall, the well-known British guitar amp/speaker company is a completely different entity to Marshall Electronics, the American AV industry supplier, or the Swedish Marshall Group AB (Marshall Headphones), formerly known as Zound Industries.