Everything We Know So Far

The man, the band, and everything else

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Ralle
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Re: Everything We Know So Far

Post by Ralle » Tue Jul 31, 2018 9:57 am

That's true, but I would lift the mixer bright cap even so, cause the lead 470k with the cap is connected to ground in this scenario... but other than that this would work fine. The buty of the real PA head is the tonecontroll on the gain... that is VERY usefull... not to mention the location of the master volume...

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Re: Everything We Know So Far

Post by jnew » Tue Jul 31, 2018 10:14 am

Good point. I have 3 plexi heads and am thinking maybe I could just convert one over to the full PA Head spec. I'm pretty sure finding an original PA Head will not be easy. Or cheap. :shock:

:lol:
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Re: Everything We Know So Far

Post by jnew » Tue Jul 31, 2018 10:19 am

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Ralle
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Re: Everything We Know So Far

Post by Ralle » Tue Jul 31, 2018 11:24 am

Close, but not the exact model Ed had... Ed's was a 4 channel with a tonecorntroll per channel. If you convert one of your head, you will only need one channel, really... that's what I did. Do you have the schems for it? It's on Marshalls Archive site... 2003 Master PA. There's a number of different circuts for that model, but it's that 4 channel circut you should be going for

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Ralle
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Re: Everything We Know So Far

Post by Ralle » Tue Jul 31, 2018 11:29 am

Here's a link;
file:///D:/Pictures/Master%20PA%20head.htm
This is the one I belive Ed had

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Re: Everything We Know So Far

Post by jnew » Tue Jul 31, 2018 11:35 am

Hmm, no link there. What's the name of the Marshall Archive site?
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Ralle
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Re: Everything We Know So Far

Post by Ralle » Tue Jul 31, 2018 12:36 pm

If you copy/paste you'll get there... I just did that, and it works... you'll have to copy the whole link inc. "file..."

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Re: Everything We Know So Far

Post by Tazin » Tue Jul 31, 2018 2:53 pm

Ralle, how exactly do you have your line out (0.68 ohm) setup?

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Re: Everything We Know So Far

Post by jnew » Tue Jul 31, 2018 3:10 pm

I still don't understand the link. I get nowhere with any of it. Help me out here.

www.???
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Re: Everything We Know So Far

Post by Tazin » Tue Jul 31, 2018 3:26 pm

jnew wrote:
Tue Jul 31, 2018 3:10 pm
I still don't understand the link. I get nowhere with any of it. Help me out here.

www.???
That link can't be correct... The D:/ refers to a local hard drive. Amparchives site is setup with folders "/folder" for each amp entry.

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Ralle
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Re: Everything We Know So Far

Post by Ralle » Tue Jul 31, 2018 4:56 pm

Sorry about that... here's the correct link:
http://www.marshallforum.com/threads/20 ... date.6855/
The marshall archives is fro the schems only, I think...

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Re: Everything We Know So Far

Post by jnew » Tue Jul 31, 2018 5:36 pm

That's more like it. I saw and read it all but I couldn't find a schematic. Do you have a schematic for that PA Head?
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Re: Everything We Know So Far

Post by Tazin » Tue Jul 31, 2018 6:14 pm

jnew wrote:
Tue Jul 31, 2018 5:36 pm
That's more like it. I saw and read it all but I couldn't find a schematic. Do you have a schematic for that PA Head?
Just do a search for Marshall Master PA 2002 and you should be able to find the 1970 schematic for the 50w version. The pre-amp and phase inverter section should be the same for the 50w & 100w versions. The power amp sections are "typical" for the PA amps of that time frame.
The only mistake; on the schematic, I believe is the way the input(s) jacks are shown...The high sensitivity jacks should not be present.

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Ralle
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Re: Everything We Know So Far

Post by Ralle » Wed Aug 01, 2018 5:49 am

That is correct... If you look at the pics in the link, the inputs only have one 68k ( instead of two 68k )... in other words; no low sensitive inputs, but other than that, it's just the same as any other input. The powerstage is the same as any other 100w marshall bass head with the big cans. The only thing that I could find different there, is the feedback resistor of 100k... I have 47k in there... I guess that's very opptional.
It's very easy to see that you you don't have to do much to convert a bass head into this PA head ( alltough with only one channel, but that's all it takes ). I use the lead channel volumepot for the master volume, since there's the most logic place to put it, fysically. The gain and tone pots goes into the normall channel and into one of the remaining holes were the normal input was. I guess one can do it differently but that's the way I did it, most important is to get it right circutwise.
DON'T FOTGET the tonecontroll... can't stress enough how important that one is...

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Re: Everything We Know So Far

Post by jnew » Wed Aug 01, 2018 8:09 am

I'm following you on how you converted your plexi. Makes sense to use input jacks for gain and tone pots, so as not to have to drill more holes and butcher a stock amp/chassis. That's what I'll do as well. Only question left for me, because I cannot see the input jacks from the dark photo's in the link, is whether or not there are 1Meg resistors like the high sensitivity inputs would have. I know there is only on 68K like low sensitivity would be but you and Tazin are saying opposite things. He says no high sensitivity inputs, which to me would mean no 1Megs, and you say no low sensitivity, which would suggest the 1Meg's would be there.

On another note, I have a pretty convincing RWTD clip I did with my 50 running flat out into a variac between the head and cab, and into a 4X12 loaded with 55hz 25W greenbacks. Probably my best tone yet but I'm having trouble getting it from my iTunes to Soundclick. Haven't had trouble in the past with this. Has something changed about uploading lately?
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http://www.soundclick.com/bands/default ... ID=1214336" onclick="window.open(this.href);return false;

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