New Host, Founding Father of Marshall!!!!

Hosted by Marshall Founding Father G3SDW. Discuss JTM45, JTM50, JTM100, Bluesbreaker, Super Lead, Super Bass, 200W, 100W, 50W, 20W, Plexi Panels, Metal Panels, 4x12 straight, 4x12 slant, Pinstripe, Basketweave, Checkerboard, Park, Kitchen-Marshall and Narb

Re: New Host, Founding Father of Marshall!!!!

Postby G3SDW on Thu Nov 12, 2009 3:55 pm

Hi Phil i do agree about only using mean power when used with a guitar, it still amazes me that people that use amp`s for music do not appreciate the difference.

Ken
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Re: New Host, Founding Father of Marshall!!!!

Postby cerrem on Sun Nov 15, 2009 8:12 pm

zaphod_phil wrote:
VikingOne wrote: How was the 45 watt rating of the early Marshalls determined? I know you said your test equipment was lacking but even at todays high line voltages that seems closer to a peak rating than RMS.
G3SDW wrote:The first tubes used were 6L6`s and the data was taken from the tech sheets available at the time.

That makes sense. In fact, from the summary on http://tdsl.duncanamps.com/show.php?des=6L6GC we can see that a pair of 6L6s at 450V should be capable of producing 55W mean square power. For KT66s http://tdsl.duncanamps.com/show.php?des=KT66 shows 50W at 475V. So 45W even sounds a touch on the conservative side. I've read various places that these amps actually only put out 35W, but I'm somewhat skeptical. IMHO measuring clean power output is of limited value with guitar amps.


Keep in mind that when you use data sheets for tubes....In most cases these voltages that are listed are the FULL POWER OUTPUT voltages, not the IDLE voltages you measure when the amp has no audio signal.... The idle voltages will be higher..
These Marshall power supplies are not regulated, therefore you will see a substantial drop in the B+ and especially the screen voltage at full power output with respect to idle voltage... When a power amp stage is designed, it is designed at full loading from the power transformer at full power output.... This full power output is the maximum clean sine wave signal in RMS, not the distorted square wave power... So the designer is not really concerned with the idle voltages, they mean nothing, just as long as they are within safe operating range of tube is what matters....
For example... 100W Marshall sitting at 485V on the plates and 480V on the screens at IDLE..... AT full clean power output you will se 430V on the plates and 400V on the screens.....When the amp is fully cranked on 10, these voltages dip below 400V....of course your mileage will vary.....

Chris
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1964 JTM-45 (GEC KT66)
1965 JTM-45/100 Super-Amp100W(GEC KT66)
1965 JTM-45/100 100W SuperPA (GEC KT66)
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1968 Super Bass 100W (Mullard EL34)
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Re: New Host, Founding Father of Marshall!!!!

Postby G3SDW on Mon Nov 16, 2009 11:40 am

Yes Chris you are right of course but just remember that we are talking about 46 years ago and that detail like that you have just described where not appreciated like they are today, and as i am sure you will know the first amp` was a copy of a Fender Bassman so basic design was taken for granted.

I hope that this puts things into perspective.

73

Ken
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Re: New Host, Founding Father of Marshall!!!!

Postby zaphod_phil on Thu Nov 19, 2009 3:28 pm

cerrem wrote:Keep in mind that when you use data sheets for tubes.... These Marshall power supplies are not regulated, therefore you will see a substantial drop in the B+ and especially the screen voltage at full power output with respect to idle voltage... When a power amp stage is designed, it is designed at full loading from the power transformer at full power output....

Yes, I've seen that. Testing power output even with SS-rectified, heavily-filtered amps like Hiwatts, I see a lot of sag. With vacuum-state rectification in amps like the JTM45 the sage is even more. And that's where a problem lies. We inject a pure sine wave into an amp's input jack and leave that running with the amp's output going into a dummy load, while we tweak the controls to get the maximum clean sine wave showing on the output. So we run the amplifier under continuous conditions which are very different from those when it's being used with a guitar. The problem is compounded by the fact that most guitar preamp stages and PIs are asymmetrically biased, so that we prematurely see clipped waveforms at the output, when the power amp is in fact still operating within its clean power range. So a more meaningful figure for the guitarist probably lies somewhere in between the tube spec figure and the lab measured power output.

BTW just as piece of useless trivia, it's incorrect to talk about power in watts RMS. While AC voltage and current can be quantified in RMS units, when you multiply them together the square root goes away, and the correct measure of sine-equivalent power is in mean square (MS) watts. Naturally, the average guitarist won't care one bit, as long as it goes up to 11 :lol:
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Re: New Host, Founding Father of Marshall!!!!

Postby Grendyll on Thu Nov 19, 2009 8:50 pm

:popcorn:
ampeg aficionado,fender freak,marshall maven
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Re: New Host, Founding Father of Marshall!!!!

Postby bolero on Mon Nov 23, 2009 11:16 am

lets lighten this up a little bit...what kind of beer were you guys drinking when you went for pints @ the old marshall workshop?

:cheers:

I would bet some of the amps concept & design were first proposed over a pint of the sudsy stuff?
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Re: New Host, Founding Father of Marshall!!!!

Postby G3SDW on Mon Nov 23, 2009 5:54 pm

Well no i am sorry to say that was not the case,you may have read my post way back that it all started in a Wimpey Bar and the strongest that we had was coffee with the odd burger and of course Flap jacks with Maple syrup and fresh cream. You had to eat it before Keith Moon arrived as when he was in there always was a food fight and it was a shame to waste good Flap jacks lol.

So sorry to disappoint you but i can assure you that it is much better now days as things are better disgust over a good pint of English ale.

Ken
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Re: New Host, Founding Father of Marshall!!!!

Postby jcs on Tue Nov 24, 2009 7:53 am

Ahh, Keith Moon!!

Please keep the tidbits coming,what fun!

Over and out from North Missouri. :)
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Re: New Host, Founding Father of Marshall!!!!

Postby zaphod_phil on Tue Nov 24, 2009 8:45 pm

Sooner have Keith Moon throwing flapjacks at me than those sticks of dynamite he used to unblock the hotel toilets. :lol:

Ken, where was that Wimpey bar? I seem to remember one in Ealing Broadway, round the corner from the station, next to where the Nat West bank now is....
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Re: New Host, Founding Father of Marshall!!!!

Postby G3SDW on Tue Nov 24, 2009 10:47 pm

Yup spot on it was the only place that stayed open late that is why all the local bands used to meet there after there gigs,a birth place of what was to happen in the future in more ways than one and here we are 46 years later.

Ken
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Re: New Host, Founding Father of Marshall!!!!

Postby pseudonym goldtop0 on Wed Nov 25, 2009 9:05 am

Hi Ken, it's great that you're here and thanks for sharing all the interesting info.
I met and spent time with Ken and Pat Bran and Jim and his then wife Nancy when I got them to come to NZ for our national music trade show in '87.
Ken is a really gracious guy.He and Jim helped me set-up the sizable trade display we did that year for their 25th Silver Jubilee(but from what you have said it was the 24th year strictly speaking).
In those days there was little to no knowledge in NZ of Marshall vintage amps etc('60s amps and speaker cabs) as only a few examples ever made it here,generally sold at the end of a tour by visiting British bands so I'm told.In fact I've yet to hear of or see an example that is still around to this day.
I did however see one local musician using a stack in 70/71 which he told me he sold a long time ago,and he doesn't know where it is now unfortunately.
We stood in awe when we saw the pics and the odd film of Jimi and Eric standing in front of their stacks, extremely envious and drooling we were.
Thanks for helping to create one of the great amps of all time Ken 8)
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Re: New Host, Founding Father of Marshall!!!!

Postby pckpat on Sat Nov 28, 2009 6:09 pm

G3SDW wrote:Have used tube equipment all my life. At the moment at least hybrid, tube driver and output and all Kenwood and just like Marshall great audio quality.

Ken

hmmmm...ken underwood-using kenwood....makes sense :D -btw,my amp tech,who is a marshall fanatic,got started in electronics through ham radio,and getting his license as a teen.i'm sure he would be interested in hearing the connection with amateur radio and early marshall development.i'm not an operator myself,but have a couple of ww2 vintage pieces of communication gear.of course,the build quality of that era is very heavy-duty.
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Re: New Host, Founding Father of Marshall!!!!

Postby G3SDW on Sat Nov 28, 2009 11:11 pm

Great stuff give your guy my email address =g3sdw@mypostoffice.co.uk and get him drop us a line be good to talk.

Regards

Ken
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Re: New Host, Founding Father of Marshall!!!!

Postby pckpat on Mon Nov 30, 2009 7:28 pm

will do ken,i'm sure he'd be delighted.thnx. 8)
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Re: New Host, Founding Father of Marshall!!!!

Postby G3SDW on Mon Dec 21, 2009 6:44 pm

Just to say that i hope that all you guy`s have a great Christmas and a very Happy,Healthy and Prosperous New year in 2010.

It is a great pleasure to be of assistance to all followers of the name of Marshall and look forward to helping you all some way next year.

Hope all your gigs are great ones.

Kind Regards from the UK

Ken
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