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Unread 03-05-2012, 02:08 PM   #1 (permalink)
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Marshall JMP 50 watt lead '72, now this thing rocks!

Got a new baby to my collection, a 50-watt large box Lead 1987 from '72. I also found a relatively rare Marshall 2x12" cabinet model 2045 from '74(ish). I bought it empty and loaded it with a Celestion G12-65 and a Weber C1265 so now it can handle a total of 130 watts - should be enough even for a JCM800 2203. This mini-stack just screams.

Here's a picture of them together with my '60 relic Stratocaster (Cunetto neck and Sheptone pickups):


There's a little story about the amp on my web page, which I guote here:
A metal panel point-to-point Marshall JMP 50W Lead (model 1987) from 1972. This amp came to me with the most suspicious power tube configuration I've ever seen: a near-dead RCA 6L6G and a very strong Tungsram EL34. Also the bias resistor had drifted from 68k to 89k so the tubes couldn't be biased warm enough. Luckily I found a nice 56k carbon composition resistor as a replacement and now the bias trimmer has a usable range again. A nice pair of Telefunken EL34s really does justice to this baby.
The power transformer is an upright one. In 1972 Marshall used both laydown and upright power transformers and even though the laydown power transformers were more common in the early years of Marshall amps, some of the later '72 models have laydown transformers as well. Wonder why they put upright ones on some of the early '72 ones. My guess is that they put in whatever they had in stock at any given time.
There are six rare Wima "chicklet" capacitors on the board as opposed to the all-mustard set you'd expect from most amps of the era. Marshall only used these capacitors in '72 and only in a handful of amps. Some say these capacitors sound a bit more aggressive than the "mustard" capacitors. I'm definitely not going to swap them out, to me they sound great! On top of all this: the grid wires are orange as opposed to the usual green, but the solder joints seem untouched, so I think they are original. All those facts combined it's no wonder that even though most old Marshalls sound great, they all sound a bit different!

Here's a link to more detailed pictures:
https://www.dropbox.com/gallery/4302...01972?h=674fa3

I'm going to get this thing recapped as it has a slight buzz - nothing dramatic though. I think I'll get the fuse holders replaced as well and install a pair of screen grid resistors just to be sure. Strange that my '71 already has those and this baby doesn't. I'm using Telefunken EL34s that should be able to handle all the voltages this amp has to offer. Did I mention the amp came with three original Mullard BVA ECC83 preamp tubes and the weakest of them tested at 100% - the rest were stronger.

Now a couple of questions:
1) I read on the other forum that the white bias voltage wire should be moved from the rectifier lug to the standby switch, because otherwise there's a risk of damaging the PT or the rectifier. Do you agree? On my '71 the wire is already connected to one of the standby switch lugs.
2) Have you seen a lot of Marshalls with orange grid wires instead of green?
3) Anybody else here with a '72 Marshall loaded partially with those yellow chicklet capacitors?

If I had to describe this amp with one word, it would be "Van Halen". Not that it would be exactly the legendary brown sound, but I'm very happy to play the early VH stuff with this baby - no need for pedals or anything, there's exactly the right amount of gain and punch. I love it.

Feel free to comment!
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Unread 03-06-2012, 02:54 PM   #2 (permalink)
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Re: Marshall JMP 50 watt lead '72, now this thing rocks!

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Originally Posted by Jucciz View Post
1) I read on the other forum that the white bias voltage wire should be moved from the rectifier lug to the standby switch.
Yes. The bias supply should be wired up to the hot side of the standby switch.
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Unread 03-06-2012, 03:37 PM   #3 (permalink)
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Re: Marshall JMP 50 watt lead '72, now this thing rocks!

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Yes. The bias supply should be wired up to the hot side of the standby switch.
Yeah, I'll get that sorted out immediately. Wonder why they put it on the rectifier in the first place. Any advantages or just disadvantages?

The snubber caps have also been removed - which isn't that uncommon I guess. Do they actually even serve a purpose nowadays? I mean, I've heard some techs even say that they're more dangerous than useful and they simply should be gotten rid of. I've understood that they can eliminate popping and other noise while switching from/to standby - but I can't hear a single pop even without them so I'm not particularly missing them.
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Unread 03-28-2012, 01:02 AM   #4 (permalink)
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Re: good work

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there are was good work !
Another strange newb post. What's with these things?
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Unread 03-28-2012, 01:53 AM   #5 (permalink)
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Re: good work

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Another strange newb post. What's with these things?
Newb in what sense? The OP seems to have way more knowledge of what counts and whatnot.

Additionally, he got himself an older amp - and a good one too, have the same but with both 1986/1987 circuits inside - which is not a common newb thing.
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Unread 03-28-2012, 01:54 PM   #6 (permalink)
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Re: good work

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Newb in what sense? The OP seems to have way more knowledge of what counts and whatnot.

Additionally, he got himself an older amp - and a good one too, have the same but with both 1986/1987 circuits inside - which is not a common newb thing.
I'm referring to Nightwishh's bizarre response I quoted in my post, not the OP.

There some kind of spammery going on - similar replies have appeared on other threads.
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Unread 03-31-2012, 02:31 PM   #7 (permalink)
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Re: Marshall JMP 50 watt lead '72, now this thing rocks!

They dont are about spam here... just member count

Nice amp btw
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Unread 03-31-2012, 07:09 PM   #8 (permalink)
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Re: Marshall JMP 50 watt lead '72, now this thing rocks!

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They dont are about spam here... just member count

Nice amp btw
shit man you sound like someones forcin you to be here, or you just tryin to drum up some work? whinge a lot?
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Unread 04-01-2012, 12:31 PM   #9 (permalink)
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Re: Marshall JMP 50 watt lead '72, now this thing rocks!

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They dont are about spam here... just member count

Nice amp btw
1- You're wrong, any spam that comes to my attention is deleted immediately. I guess you missed the countless times that it happened?

2- I don't see any spam in the newb's post. Strange, yes, but no spam. What's even more strange is that you felt the need to comment. Irony, perhaps?

3- Thanks for the attitude. So you stopped contributing here but you come back to complain?

4- I also find it ironic that you claim we only care about member count, when you and a bunch of your cohorts left because you didn't like the way things were run around here.

Sorry to hijack the thread.
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Unread 04-02-2012, 05:19 AM   #10 (permalink)
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Re: Marshall JMP 50 watt lead '72, now this thing rocks!

Thanks for the bump.

Now that we're at it, I have some news to share. The amp has now been serviced. It was recapped and screen grid resistors were installed. Also the fuse holders were replaced - and I'm glad we did that: one of the "fuses" was actually just a piece of aluminum foil crammed inside the holder. Talk about electrical safety!

In addition, the white bias wire was moved from the rectifier to the standby switch as advised. Now the bias voltage is there immediately after flicking the standby switch - this way the amp is not so hard on the power tubes. Also the bias circuit series resistor is now a 47k. It may not be a Piher but still old stock (probably Vishay or similar) and it looks very good and period-correct-ish. I also installed new captive nuts to the chassis since the original ones had been long gone.

The V1A had a 320uF cap that measured 560uF (!) and it had been paired with a non-stock 2,2k resistor. The 2,2k got replaced with a correct 820ohm resistor (the same type as the 47k series resistor in the bias circuit) and the drifted 320uF cap got replaced with a 220uF Philips.

To summarize, the new electrolytics are:
TAD Gold Cap 50+50uF filter caps
Sprague Atom 8uF/150V bias supply caps
Philips 220uF/63V V1A bypass cap

Here are the latest pictures after the service:
https://www.dropbox.com/gallery/4302...23new?h=cdc36f

I'd be glad to hear your comments!
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Unread 04-03-2012, 01:45 PM   #11 (permalink)
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Red face Re: Marshall JMP 50 watt lead '72, now this thing rocks!

And here she is with a '73 angled cabinet and a '72 straight cabinet:


So... it's ALMOST a '72 fullstack. Not quite, but pretty close. Sounds pretty OK'ish though.
Blokkadeleider and 2210Rocker like this.
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Unread 04-03-2012, 01:57 PM   #12 (permalink)
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Re: Marshall JMP 50 watt lead '72, now this thing rocks!

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And here she is with a '73 angled cabinet and a '72 straight cabinet:


So... it's ALMOST a '72 fullstack. Not quite, but pretty close. Sounds pretty OK'ish though.

Nice!


Gr,

Gerrit.
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Unread 04-06-2012, 11:04 AM   #13 (permalink)
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Re: Marshall JMP 50 watt lead '72, now this thing rocks!

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I also found a relatively rare Marshall 2x12" cabinet model 2045 from '74(ish). I bought it empty and loaded it with a Celestion G12-65 and a Weber C1265 so now it can handle a total of 130 watts - should be enough even for a JCM800 2203.
Are the speakers sharing the power evenly? I've tried mixing speakers up before, and even with the same impedance one of them always seemed to be dominant.
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Unread 04-07-2012, 03:12 AM   #14 (permalink)
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Re: Marshall JMP 50 watt lead '72, now this thing rocks!

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Are the speakers sharing the power evenly? I've tried mixing speakers up before, and even with the same impedance one of them always seemed to be dominant.
I've hadn't had problems so far. The trick is to match the sensitivity as well. On the other hand: if you have a 8ohm 97dB speaker combined with a 16ohm 100dB speaker, they should theoretically be equally loud hooked up together as the 16ohm speaker gets 1/3 of the power and the 8ohm speaker gets 2/3. The 3db difference is compensated with the double power the 8ohm speaker gets. Of course in this scenario you'll end up with a bit awkward total impedance, but it won't necessarily be a problem.
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Unread 04-13-2012, 01:23 PM   #15 (permalink)
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Re: Marshall JMP 50 watt lead '72, now this thing rocks!

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Yes. The bias supply should be wired up to the hot side of the standby switch.
Would my 71 have this same circuit error???
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Unread 04-13-2012, 06:08 PM   #16 (permalink)
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Re: Marshall JMP 50 watt lead '72, now this thing rocks!

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Would my 71 have this same circuit error???
Mine didn't. The '72 has been so far the only one that had the wrong kind of wiring.
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Unread 04-14-2012, 10:19 AM   #17 (permalink)
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Re: Marshall JMP 50 watt lead '72, now this thing rocks!

Thanks!
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Unread 04-18-2012, 01:34 PM   #18 (permalink)
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Re: Marshall JMP 50 watt lead '72, now this thing rocks!

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And here she is with a '73 angled cabinet and a '72 straight cabinet:
http://dl.dropbox.com/u/4302688/olkkarikioski.jpg

So... it's ALMOST a '72 fullstack. Not quite, but pretty close. Sounds pretty OK'ish though.

SWEET Stack man and glad you were able to bring the JMP 50watt back to life, did you shake any pictures off the walls yet? Looks like you'll be having many years of rockin power now.

Rock it,
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Unread 04-18-2012, 01:36 PM   #19 (permalink)
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Re: Marshall JMP 50 watt lead '72, now this thing rocks!

I just want that in my living room - it's like ART..!!!
put little spot lights on it
a velvet rope around it
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Unread 04-18-2012, 03:32 PM   #20 (permalink)
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Re: Marshall JMP 50 watt lead '72, now this thing rocks!

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I just want that in my living room - it's like ART..!!!
put little spot lights on it
a velvet rope around it
An old Marshall IS a work of art.

By the way: did anyone notice the two cabinets have differend kind of chequeboard front cloth? Marshall has used both larger and smaller figured chequerboard around '72-73 and it seems that these cabinets are from the transition period - from different sides of the fence, so to speak.

I have the Doyle book but it doesn't seem to discuss this matter much, if at all.
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Unread 04-18-2012, 04:57 PM   #21 (permalink)
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Re: Marshall JMP 50 watt lead '72, now this thing rocks!

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I've hadn't had problems so far. The trick is to match the sensitivity as well. On the other hand: if you have a 8ohm 97dB speaker combined with a 16ohm 100dB speaker, they should theoretically be equally loud hooked up together as the 16ohm speaker gets 1/3 of the power and the 8ohm speaker gets 2/3. The 3db difference is compensated with the double power the 8ohm speaker gets. Of course in this scenario you'll end up with a bit awkward total impedance, but it won't necessarily be a problem.

First off I want to say, really nice amp! And you Strat is a real beauty, too...

But I must say to not mismatch impedances with speakers and use them with Marshalls. It sounds like you know a bunch more than me, but I've always used a rule that Marshalls don't like mismatches. Sure some have no apparent problems, but why mess with perfection!
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Unread 04-18-2012, 05:16 PM   #22 (permalink)
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Re: Marshall JMP 50 watt lead '72, now this thing rocks!

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First off I want to say, really nice amp! And you Strat is a real beauty, too...

But I must say to not mismatch impedances with speakers and use them with Marshalls. It sounds like you know a bunch more than me, but I've always used a rule that Marshalls don't like mismatches. Sure some have no apparent problems, but why mess with perfection!
Thanks for the compliments. Sure it's always safer not to mismatch at all - but in case that needs to be done, it can't hurt to know how to do it the safest way. I personally never have the need to mismatch speakers or speaker cabinets though. Generally output transformers aren't that picky about the speaker load: if you can successfully use an 8-ohm load with a 4-ohm tap (which usually is the case), a 5.33-ohm load (as a result of a mismatch) can't hurt since it's actually much closer to the optimum load than an 8-ohm load, which probably works just fine.
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Unread 04-18-2012, 06:41 PM   #23 (permalink)
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Re: Marshall JMP 50 watt lead '72, now this thing rocks!

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An old Marshall IS a work of art.

By the way: did anyone notice the two cabinets have differend kind of chequeboard front cloth? Marshall has used both larger and smaller figured chequerboard around '72-73 and it seems that these cabinets are from the transition period - from different sides of the fence, so to speak.

I have the Doyle book but it doesn't seem to discuss this matter much, if at all.
Yeah, I also noticed the slant has the plastic corner guards and the straight is without like the 60s cabs. Michael Doyle is a great guy, he was our Marshall rep for the music gear store in the 90s, his book is very informative.
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Unread 04-19-2012, 08:14 AM   #24 (permalink)
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Re: Marshall JMP 50 watt lead '72, now this thing rocks!

I bought a 16 ohm speaker for my combo, but it actually turned out to be an 8 ohm speaker, I blew a couple of diodes, a power tube , and socket...that was my first trip to a tech ever! Just play it safe with your Marshalls...
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Unread 04-19-2012, 10:43 PM   #25 (permalink)
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Re: Marshall JMP 50 watt lead '72, now this thing rocks!

Ha!

I've just noticed the MI Audio Neo fuzz in the background.
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Unread 04-25-2012, 04:56 PM   #26 (permalink)
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Re: Marshall JMP 50 watt lead '72, now this thing rocks!

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Ha!

I've just noticed the MI Audio Neo fuzz in the background.
Well spotted, sir!

Here's my gigging pedal board in its entirety:
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Unread 04-25-2012, 07:55 PM   #27 (permalink)
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Re: Marshall JMP 50 watt lead '72, now this thing rocks!

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There are six rare Wima "chicklet" capacitors on the board as opposed to the all-mustard set you'd expect from most amps of the era. Marshall only used these capacitors in '72 and only in a handful of amps. Some say these capacitors sound a bit more aggressive than the "mustard" capacitors. I'm definitely not going to swap them out, to me they sound great! On top of all this: the grid wires are orange as opposed to the usual green, but the solder joints seem untouched, so I think they are original. All those facts combined it's no wonder that even though most old Marshalls sound great, they all sound a bit different!

3) Anybody else here with a '72 Marshall loaded partially with those yellow chicklet capacitors?

If I had to describe this amp with one word, it would be "Van Halen". Not that it would be exactly the legendary brown sound, but I'm very happy to play the early VH stuff with this baby - no need for pedals or anything, there's exactly the right amount of gain and punch. I love it.

Feel free to comment!

Are these the yellow "Chicklets" you're referring to? This is my former 72' 100 watter. Sold it last month but as far as I know the board is all original.



Nice Set up BTW! Down to 2 amp a 77' JMP 50 and a 74' 50 watter that I just love. the 74' 50 has more growl than the 72' 100 watter for sure!
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Unread 04-26-2012, 02:34 AM   #28 (permalink)
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Re: Marshall JMP 50 watt lead '72, now this thing rocks!

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Are these the yellow "Chicklets" you're referring to? This is my former 72' 100 watter. Sold it last month but as far as I know the board is all original.

http://www.marshallforum.com/members...4-img-6001.jpg

Nice Set up BTW! Down to 2 amp a 77' JMP 50 and a 74' 50 watter that I just love. the 74' 50 has more growl than the 72' 100 watter for sure!
Hi!

Yes, exactly those yellow square-ish capacitors.

My '72 looks like this on the inside:


Seems that the locations for the chicklet capacitors were chosen pretty much randomly.
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Unread 04-26-2012, 03:53 AM   #29 (permalink)
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Re: Marshall JMP 50 watt lead '72, now this thing rocks!

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And here she is with a '73 angled cabinet and a '72 straight cabinet:
http://dl.dropbox.com/u/4302688/olkkarikioski.jpg

So... it's ALMOST a '72 fullstack. Not quite, but pretty close. Sounds pretty OK'ish though.
I think I wet myself...
Beautiful stack, congrats!
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Unread 04-29-2012, 02:53 PM   #30 (permalink)
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Re: Marshall JMP 50 watt lead '72, now this thing rocks!

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I think I wet myself...
Beautiful stack, congrats!
Thanks! It's nice and loud - exactly as it ought to be.
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