Mark IIC Standard Question

[Jisais]

Hello Knowledgeable Boogie-philes!
I am a new member to the board, inspired by the wisdom and enlightenment of the "Mark II-C+ Guide for Dummies" post which I recently read.

I have a standard Mark II-C (as far as I know) which I bought second hand in 1986 at Guitar Center in San Jose Ca. (No Boogie hang tags were included)
It is a 60 watt, non-EQ, non-Reverb, non-export model with a walnut cabinet and wicker grille, and came with the soft cover.
As you will note in the photos, it is serial number 11323.

I have played this amp off and on (mostly off for the last several years due to family, work, etc...) and it has never had an issue. Somewhere long ago, I used the "spare" tube that used to live in the little plastic retainer in the back cabinet to replace one that was damaged. It is otherwise in nearly new condition.

My question is this.
I notice the front panel version is silk-screened with the "Pull Deep" nomenclature on the Master 1 knob, rather than the "Gain Boost" that should correspond with this serial number range normally. (If I read the "Mark II-C+ Guide for Dummies" correctly) I swear it has not been out of my sight long enough for evil gremlins to switch the front plate.
Seriously, if any modifications were performed by Boogie to this unit, it would have been in the first year or two that the original owner still had possession, and it seems unlikely to me.

Also, for the avoidance of doubt, I have done the loop test and it failed miserably. It is definitely NOT a C+.

So if anyone has any thoughts or experience as to why this may be labeled in this way, or speculation on the history of this unit, I would greatly appreciate the insight.
Pictures follow below.

Thanks in advance!

Jay



Mark IIC Front by jisais1, on Flickr


Mark IIC Back by jisais1, on Flickr


Mark IIC Sig by jisais1, on Flickr

 

[gts]

Welcome Jay.
Nice looking amp, very clean.
Good to see the original STR-415's power tubes in there too. They are the best in these amps!

The labeling on the front, as you have found out, is not a sure thing toward indicating a C+.
Why it has a "Pull Deep" versus a "Gain Boost" faceplate is anybodies guess. But I have seen IIC's with "Pull Deep" and original IIC+'s with a "Gain Boost".
The one thing that we all know is Mesa wasted nothing. So if during production of a C+ an old faceplate with "Gain Boost was on hand they used it.

Going the other way, meaning a "Pull Deep" face plate being used on a IIC when supposedly these faceplates didn't get made until after IIC+ production started...
Perhaps Mesa had started building the IIC and after getting the serial number got stamped on the chassis the order got put on hold, or the customer canceled the order.
It could be that months went by before Mesa used the chassis to build an amp.
And by then IIC+ production may have just started (and use of the "Pull Deep" faceplates).
But the customer ordering it this time wanted it to be a IIC and not the "newer upgrade" aka IIC+.

Pull the chassis and see what, if any, dates are written in magic marker on it.
There probably will be one near the pre-amp tubes which you might be able to see without pulling the chassis.

 

[Big Block]

Mesa is notorious for mix matching their faceplates.

I've owned two C's and three C+'s. One C had a "Gain Boost" faceplate and the other had a "Pull Deep" faceplate. The C+'s all had the "Pull Deep" faceplates, but all have different labeling on the "Full Power/Half Power" switch.

 

[boola]

I'm wondering, what does the pull pot do? Does it give a gain boost or the bass boost of a normal pull deep?

 

[tony777]

I have seen mark III's with gain boost faceplate as well as IIC's with pull deep, so there is exception to the rule a long way. There is nothing strange with your amps' faceplate.
The pull deep does enhance the low frequenzies a lot, IE pull deep ;-)

 

[chipaudette]

The "Pull Deep" and "Gain Boost" on the Mark II's are all the same function...they merely changed the name written on the face plate. IMO, "Pull Deep" is definitely a better name for it.

In the circuit, what it's doing is attaching a bigger capacitor to the cathode of the gain stage immediately following the effects loop. The size of the cap affects how much bass gets amplified by that gain stage. The amp normally has a medium sized cap in there all the time, which means that that stage boosts the upper mids and treble, while down-playing some of the bass. When you engage the "Pull Deep" (or "Gain Boost"), another cap is added in, thereby increasing the total capacitance. The added capacitance extends the amplification to apply to all the frequencies -- high and low. Because you had already been amplifying the higher frequencies, all that you notice is the added boost to the bass frequencies. So, while both names are correct, the "pull deep" name gives a better indication of the change in sound.

On the original Mark I amps, there was also a pull knob labeled "gain boost". It caused a completely different type of change to amp's circuitry. When you pulled that knob, it disabled the tone stack, which means that the massive signal attenuation that naturally occurs in the tone stack went away. All of a sudden, the amp had way more gain. It was kind of tubby and flubby (because there was no tone stack to cut the low mids and bass) but it certainly had more gain.

The Mark II "Gain Boost" / "Pull Deep" was completely different. "Pull Deep" was a better name, but they had this history calling it "Gain Boost", so it took them a while to change.

Chip