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 Tue Sep 08, 2009 6:16 pm

Have been looking at various posts and thought i would try to put some facts down on three tubes that are mentioned quite a lot.

They are KT66 which is a direct equivalent to a 6L6G.
EL34 which is a direct equivalent to a 6CA7 or a KT77.
6550 which is a direct equivalent to a KT88.
Finally most valve spec`s give output power as xxxW this is called RMS this is mean power(Average) but in fact the max` (Peak) power is much more and this can be calculated by multiplying the RMS power by 1.414 to get the peak power.

Hope this helps and does not confuse matters.

Regards.

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

Postby T.G.3-55 on Wed Sep 09, 2009 10:02 pm

Welcome Ken - It's a real honor to have you with us. The folks here really are the keepers of the flame...you helped light it.

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

Postby Derrick on Thu Sep 10, 2009 9:45 pm

Ken, its rare enough to have someone who helped design the Marshall amplifier on available to a forum like this, let alone the lost art of tube technology (specifically with respect to guitar). I would like to bring up the subject of output tube bias and what your practice was at the time that the JTM-45 was conceived... Can you elaborate on:

* What was your method for biasing output tubes? (Shunt method? Scope? Other?)

* At what current did you typically set the bias of these tubes, or was it some arbitrary number you all chose?

* How did you determine what the bias point should be?

* was biasing simply looked at as a matter of "good enough" or did you consider the sound characteristic that different bias points would give you?

* What were the main problems encountered with output tubes/bias?

* Generally, it doesn't seem like there was nearly the importance placed on carefully and properly biasing one's output tubes back then as there is today. Is that true from your perspective?

Thank you so much!
Derrick
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Re: New Host, Founding Father of Marshall!!!!

Postby plexi on Fri Sep 11, 2009 2:35 am

I'm floored at how many of you have responded and read this posting. Great stuff. Lets follow our protocol, Use the search, If not found, Post your question, Please keep PMs and Emails to a minimum. I think we owe it to our new friend to treat him with courtesy.

Sorry to sound like the school teacher here. Just a reminder.

Now you can go nuts again. Yaaay!
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Re: New Host, Founding Father of Marshall!!!!

Postby G3SDW on Fri Sep 11, 2009 2:08 pm

Now we are digging very deep now but of course the working conditions of any valve circuit are important whether it be then or now.

From what i can remember we used a data sheet to play around with the biasing of the output tubes which would have been something like this.

http://www.retrovox.com.au/STC6L6G.pdf

Negative feed back was also tweaked to get the right sort of sound also so all in all we arrived at the sound that is custom to Marshall.

They way that Dudley arrived at the right bias for the right sound was purely by trial and error as in lots of cases in those days, a data sheet and an Avo meter and possibly a scope was all that was available.

Don`t forget that we were all short of money so that expensive test gear was out of the question. After JM took over i am sure that it became a little more professional.

Output tubes would some times take off, ie parasitic oscillations,too much distortion and not enough gain, ie output power.

So i hope that answers your points as i had to dig very deep on this one but i have done my best.

Regards.

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

Postby oh7hhi on Fri Sep 11, 2009 3:55 pm

Hello Ken!

I assume we have same hobby, according to your nickname "G3SDW" :D .

I have a question. Who developed the "Marshall Major"? It's so different compared to rest of the Marshall line.
I just build a new amp which includes Major 1978 preamp and JTM45 poweramp (2xKT66) and it sounds so massive, like regular plexi but much..hmmmm...BIGGER!

Best Regards!

OH7HHI
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Re: New Host, Founding Father of Marshall!!!!

Postby G3SDW on Fri Sep 11, 2009 4:50 pm

Hi Antti yes had my ticket since 1963 the year Marshall was born still active on all HF bands.

As for the Major that came after my time with the start of Marshall but i do suspect that it was a guy called Ken Flegg along with Dudley Craven who was G3PUN sadly now SK but that is as much as i know.

So as for Marshall you now know that it became what it is today because of Amateur Radio,myself, Ken Bran G3UDC and Dudley Craven G3PUN.

Hope to talk to you some day on the bands.

73

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

Postby Derrick on Fri Sep 11, 2009 6:25 pm

Ken, kindest regards for your answers. I had no Idea you all were ameteur radio operators as well. I have to look for you guys in the HF bands. Cheers :P
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Re: New Host, Founding Father of Marshall!!!!

Postby G3SDW on Fri Sep 11, 2009 7:03 pm

Yes Derrick started in the same year as these amps did still active after all this time mainly on CW but yes you can now see how much ham radio played in the making of Marshall. Perhaps you could let me know your call sign and i will keep an eye for you and give you a call.

73

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

Postby Emerson Biggins on Sat Sep 12, 2009 3:28 am

Hey Ken, Collins KWS-1 and 75 A-4 guy here! :cheers:
"Yesterday is history, and tomorrow is a mystery,, today is a gift - thats why they call it the present".
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Re: New Host, Founding Father of Marshall!!!!

Postby JeffWest on Sat Sep 12, 2009 3:55 am

Ken- While you were on the scene, if you know was there an effort to match pairs of tubes for the JTM45s? Thanks-

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

Postby bmi on Sat Sep 12, 2009 2:14 pm

Hi ken,
thanks a lot to being here. it's an honor but more a chance for me to get you there. I really appreciate that people that have been in the heart of rock history come and share their stories on the net before they RIP. As someone says they are so many rumors and myths in the books.
I should be not politicaly correct to ask you some questions and perhaps more but i'm french and you know we are not politicaly correct at all. :wink:
I hope that you didn't get offensed by that this is with all respect and a big pleasure to see someone like you here.

My question :
_ I have bought a JTM45/100 40th anniversary and i would like to know how exact replica you judge it is. Of course there are no mustards caps in there but what about the 2 outputs. I have not found a pictures of an old version with 2 outputs.
Marshall company says that the selectors were initialy on the OTs and that they can't do it today so there are now on the back plate. I have found a pictures on a japanese forum of an old JTM45 super pa amplifier with 2 OTs and it seems that there are knobs so selectors on the OTs, but there is only one output and i'm wondering what did you have to select on the OTs with only one input. By the way did you make during the 65 year a specific version for a customer with 2 OTs and 2 outputs???


And more...I have a big hum issue on my anniversary, and i'm afraid it comes from the amp. I have made a lot of basic tests..then i'm always wondering where it can comes...sounds like a ground issue or perhaps a big can/cap failure...if you have time it's here : :)
viewtopic.php?f=1&t=86617&p=855583#p855583

Best regards,
bmi.
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Re: New Host, Founding Father of Marshall!!!!

Postby G3SDW on Sat Sep 12, 2009 2:57 pm

Hi BMI thanks for the questions, well from what i can remember and i have said this before i am having the think back 46 years but from recolection there was only 1 output and 1 OT.

I was involved at the very start (`63 to late`63) before the name of Marshall was used and you will need to look at my previous posts for the fine details.

As for the hum what you need to do to isolate where it is coming from, do not have anything connected to the inputs, then turn down the Vol` 1&2 and see if the hum as gone, if it has not gone then you will know that the hum is being generated from the output stages and this will no doubt be caused by the main smoothing capacitors (big cap`s). If the hum goes when you turn down the Vol` 1&2 then it will be coming from the pre amp stages, then you must investigate all your input connections on the jack sockets. If of course if it only happens when you plug your guitar into the inputs then you know where the problem lies.

Biasing or unmatched pairs of output tubes will not cause hum.

I hope that this has been of some help.

Regards

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

Postby G3SDW on Sat Sep 12, 2009 3:01 pm

This is for Jeff West, sorry Jeff for not answering your question but the answer is no we did not match tubes in the very start but i became plainly obvious that we needed to buy in matched pairs as this made setting the amps up much easier.

Thanks for the question.

Regards

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

Postby JeffWest on Sat Sep 12, 2009 4:13 pm

And thanks for the answer-
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