Chassis / headshell question

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JMMP

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Hi everyone,

About a year ago, I bought a headshell off of eBay for a short chassis mark series (I have a short mark IV). After getting everything installed, I noticed the fan that came with it bumps into one of the power tubes. Just recently I swapped the mark IV back into my rack kit.

Question: is there a difference in length in different mark designs (II, III, IV) from the front of a chassis to the front of the power tubes? I'm wondering if the headshell I bought was made for a II or III, as it doesn't have a reverb cutout either.
For the record, it is supposedly imbuya wood.
Thanks in advance for any answers!
 
Kind of surprised to hear the tubes were hitting the fan.
Short head cabs for a II, III, IV should be the same size/ work the same for each amp.

Post some pics of yours.
 
Thanks for the replies

Markedman: everything is for sale! But I am considering selling it. The Imbuya is a gorgeous wood (I'm attaching pictures), but anything further will be posted in the classifieds.

GTS: I was hoping you would respond. It would make sense that all of the chassis' would have the output tubes in a similar place. I have attached pics below, but just using a tape measure, the rack mount keeps the fan 2" away from the power tubes. The headshell is touching the left two power tubes completely. I think the seller I bought it from said this was a factory B-stock, because someone ordered it, then decided they didn't want it.

On to the pics:

Mark IV in headshell

20141105_224628.jpg


47xRz5TLbCcB7io3G1KTbwtdxa1ArF1wsoQwQNSnDDg=w115-h203-p-no


Mark IV in rackmount

MYtHEROgy8izEmRUItB63DOw1TRuXcferrGRuhJdjZA=w114-h203-p-no


Ec9n14aS5YcM0A9yW56v7IqHeu7s6ovHMgoIbQKclj8=w114-h203-p-no


The following link has every photo I took. Not all of them are the most clear, but it's the best I can do tonight.

https://www.dropbox.com/sh/1n2csxb0y5g3kem/AACC4prMvBy3VuvdCHOl0YDTa?dl=0
 
It's not unusual in a head shell to have the fan close to the power tubes.
The fan is typically very close, ~1/8" to 1/4" away but it shouldn't be touching the tubes.

In your pics a couple of things look odd to me.
The width of the "baffle" (the plywood part of the head cab that the fan bracket is attached to)
and the location of the mounting screws on top of the cab.

If you think you can do it accurately Measure from the back edge of the cab to the center of the rear mounting screws.
Also measure the thickness of the plywood baffle.

Let me know what you find.
 
Below is a pic of the front baffle. It is ~1/8" thick, and offset from the front grill by 1/2".
Also of interest, the top and bottom wood is 1" thick, whilst the sides are 3/4".

The depth from back of the shell to the center of the rear screw is 3 and 1/8"

Markedman, it may not be original boogie, but it came with a boogie box (which quite excited me, as it also came with fitted foam corners) and is consistent with how I would expect a boogie headshell to appear.

I'm going to try flipping the fan 90 degrees. Right now, it is 90 degrees off from the one in the rackmouny, and if it's just a fraction of an inch, that could fix the problem.


QaH6qRix6K6G3TPFRvz4sgMjCmWD9iBfo-iLdVlj6q4=w116-h207-p-no
 
JMMP said:
Below is a pic of the front baffle. It is ~1/8" thick, and offset from the front grill by 1/2".

Pretty sure 1/8" a typo. Looking at the pic(s) I'm guessing you meant 3/8".

Also of interest, the top and bottom wood is 1" thick, whilst the sides are 3/4".

Definitely not standard. In a short head all should be 3/4".
And if an old school long head the sides would be wider not the top and bottom.

The depth from back of the shell to the center of the rear screw is 3 and 1/8"

That there is an issue. Should be 2-1/2". At 3-1/8" the chassis is pushed farther forward thus putting the power tubes closer to the fan.
Also looking at the pics the reveal (aka the area in front) of the grill looks shallow.
Considering it's a 1/2" grill (they are usually 3/4") that means the baffle could be pushed forward too.
Then again you say there is 1/2" space between the baffle and grille. This is odd but may mean one side (front or back) of the baffle is in a 'normal position'.

In any case some of, if not all of these things are issues.
Whether they were done to make up for the chassis being pushed forward or just a bad design for a headshell is anybodies guess.
Even if the chassis is mounted farther forward than standard, whoever made it didn't compensate the design enough to avoid having the fan hit the power tubes.

Fwiw I bet the whole thing is off what the standard measurements would be for short head shell.

Markedman, it may not be original boogie, but it came with a boogie box (which quite excited me, as it also came with fitted foam corners) and is consistent with how I would expect a boogie headshell to appear.

I agree with Markedman that it's not a Mesa headshell.

What's a Boogie Box? Did you mean the box it was shipped in?
If so maybe the seller bought a head shell from Mesa. Then shipped this head shell to you in the box his Mesa head shell came in.

I'm going to try flipping the fan 90 degrees. Right now, it is 90 degrees off from the one in the rackmouny, and if it's just a fraction of an inch, that could fix the problem.

Won't make a difference because those fans are square; same dimensions all the way around.
Click to expand...
 
Thanks for the response GTS.

I likely did mean 3/8". I was typing on my phone, and sometimes that gets a little dicey.

The distance from the back of the headship being off does make sense, but the overhang on the front of the amp is also, shall we say, excessive? All the controls are not inhibited, but there seems to be more there than other headshells I have seen. I am even more curious who made it, now that it obviously wasn't boogie. The wood work seems good, and the wood has nice figuring and such, but the dimensions are off. I wonder who would have made such a thing.

And yes, I mean the box it was shipped in. I am weird in that I like having original boxes for my stuff, which is why i asked the store i bought my roadster from to include the shipping box. Makes it easier if I ever need to send it to mesa for service.

I realize the fan is a square, but sometimes manufacturing tolerances can be off. But that didn't help.

I wonder if this headshell would work for any mesa amp (without hitting the power tubes)? I am putting the mark IV back in the rack case, so I don't know what good the headshell could do for anyone with a mesa head.
Maybe I need to build an amp to go inside the shell!
 
I decided if I'm going to try to be a DIY guy (been modding and making pedals about a year and a half now) then I should be able to solve this. Bought a 120V computer fan off of eBay for 14$. It spins faster, is about half the size, and moves ~20% more air per minute than the stock fan. It is a little louder, but that doesn't bother me. Redrilled the metal fan mount plate for this smaller fan, and voila, I have an excellent headshell. Now just to make my wicker front panel....
 

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