Marshalls...

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Re: Marshalls...

Post by 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.
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Re: Marshalls...

Post by ef37a »

Sam Spoons wrote: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.

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Re: Marshalls...

Post by 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.
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Re: Marshalls...

Post by 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?).

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Re: Marshalls...

Post by ef37a »

Hewesy wrote: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.

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Re: Marshalls...

Post by Kwackman »

ef37a wrote: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"... ;):mrgreen:
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Re: Marshalls...

Post by ef37a »

Kwackman wrote:
ef37a wrote: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"... ;):mrgreen:


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........)

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Re: Marshalls...

Post by 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.
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Re: Marshalls...

Post by 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.

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Re: Marshalls...

Post by 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!
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Re: Marshalls...

Post by 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.

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Re: Marshalls...

Post by 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.
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