New member...Hi everybody.

[tubeydude]

Hi all,

I've had my Boogies now for about 10 years. I bought them used from guy that just didn't use them. I've taken good care of them and have gigged quite a bit with my Mk IV. It is a bit modded. I got it as a combo but got a head shell from boogie. I still have all the orig stuff in case...

I'm running KT77 from eurotubes in my MKIV. I only use two of them as I don't need the full power of the amp. I also put some of those tube dampers on. It got rid of some microphonic issues I was having. I made the new front grill to promote tube cooling. I also raised the fan up a bit and added some holes on the front bottom to allow cool air to come in from the front. I added a bias pot in line with a resistor in place of the stock resistor only setup. I mounted the pot to the top of the power XFMR and placed it such that all I have to do is remove the right handle screw and I can get a skinny screwdriver in there to adjust bias...no need to pull the chassis.

I also added a little box with a volume pot in it. I run it into the FX loop and turn it down a bit. I'll normally run with the FX loop on and turn it off for solos. This way I get a volume "boost" when I want it. So I have 3 channels with a switchable volume boost on each. It works quite well.

The last pic is of my rack setup. Fairly standard except I mounted an input jack on the lower left. I also put a hardwired switch for 1/2 power on the lower right. I usually don't tweak this from patch to patch. I'll set it depending on what we are doing at the show.

Enjoy.

I had no idea this forum was here. I hope to learn much from everybody and participate often.

Thanks,

Erik

 

[Schmoog]

welcome!

trade you an 88 Mark III blue stripe and a 1x12 thiele for your mark IV.....

 

[tubeydude]

While I appreciate the offer...I just don't know what I would do without my "Feather" Yup, that's it's name. I'm sure any MkIV owner will realize why.

Erik

 

[Schmoog]

yeah. I had one of my buddy's mark IV's for a month while he was away. hence the frantic search for a mark IV

 

[Schmoog]

PS: is that a framus 4x12?

 

[tubeydude]

No it is actually a home brew 2 x 12. A buddy of mine made a couple of 2 x 12 cabinets and he ended up not using them. I picked them up. They were just raw wood. (13 ply void free baltic birch) I covered one of them in black vinyl...stained and tung oiled the other. The black one has a baffle/grill cloth made from some crazy fabric I found at a yard sale. I also put some weber beam blockers on that one. The other cab has the expanded metal grill.
The black/red cab has one eminence wizard and one governor. It's got a huge and fat sound
The stained/expanded metal cab has a boogie black shadow 90 and a carvin BR-12 (eminence made) This one has a sharper, crisper, more focused sound.

I don't always use them together, although it is quite nice.

Enjoy,

Erik

 

[Schmoog]

that grill cloth looked freakishly close to the cloth on the framus dragon bottom.

 

[Russ]

Would you mind sharing more information on the little volume box in the loop and your bias mod? I am very curious.

 

[Russ]

Also, what do you use as your settings to use only the KT-77's in the outer sockets? I have a pair that I might want to try in mine.

 

[Russ]

How thoughtless of me.... :roll:


Welcome to the board man....

 

[tubeydude]

Thanks all,

Russ, there is a closeup of the volume box on my first post. It is just a small project box from radio shack. I installed a volume pot on one side (I believe it was a 250k linear) I also installed two 1/4 inch jacks on another side. These were then ran to the send and return of the FX loop. When the FX loop is on the volume pot is in the signal path and can lower the level. I typically turn this down a bit to my desired rhythm level. When I turn the FX loop off, I take the volume pot out of the signal path and it reverts back to normal full volume (solo level). It's sort of a volume "boost" although the correct way to explain it would be a volume attenuation when the FX loop is on.

If you find a schematic for your amp you'll find that there is a circuit that sets the voltage for the grids of the power tubes. Our MK IV's are fixed bias; this means that that resistor is set at the factory to force the amp to bias tubes to a certain value. Replacing this resistor with a resistor and pot (important not to just use a pot or you can red-plate your tubes) will give you adjustability high or low from the resistance that was set by our good people in petaluma. I should say that if anyone is not familiar with working on tube amps, the potentially lethal voltages inside or the architecture of a bias circuit, then stay away! As far as the pot location goes...I just noticed that there was a free spot on top of the power transformer that happened to be directly underneath one of the handle screws. I just place the pot there and now can adjust bias for different tubes without having to take the chassis out. (after I take that handle screw out)

I usually run the KT77's in the outside sockets in pentode mode and full power. Although I have run them in all possible configurations.

I hope that helps.

Erik

 

[tubeydude]

rabies,

I really dig the KT77's. I have only used them in the outer sockets as a pair.
I only bought a pair and it is PLENTY loud with just two tubes. The 77's give me a more reactive feel and a more lively clean tone. Feels and sounds a lot like a nicely sorted blackface when you dial up the gain on the clean channel.
The lead channel also sounds really creamy and dynamic. EL34's were good for crunch, but the clean suffered. 6L6's were good for the clean, and the leads were very focused. I also used to run 6L6's in the center and E34L's in the outer sockets. It sounded great, but it was too loud for me and the band situation. The KT77's seem to a be a compromise, but also better than either. I can also push the power section a bit and let the tubes breathe.

I had a guy over that had a Dumble and he was just gushing about how great is sounded. It did sound great, no doubt about it, but it is a one trick pony (and an expensive one at that). I plugged my MKIV with the KT77's in to my red Eminence 2X12 cab, dialed up a mild gain setting one RH2 and got almost EXACTLY the same tone. He was quite surprised. He said he'd never heard a MKIV sound like that. Of course I still had two more channels to go, but I didn't want to go there.

Man this makes want to go play...

(edit: I should also say that adjusting the bias to run the tubes a bit hotter than factory really made a difference. The feel and the tone changed. More dynamic and string feel was more...juicy. I'm not sure how else to describe it...)

Erik

 

[turmoil]

hey man! welcome to the board

i really dig your gear a lot! that Mark IV looks really nice!!

im just curious though, where did you get that expanded metal grill cover for your one 2x12 cab?
thanks!!

 

[tubeydude]

Turmoil,

Thanks! I took the measurements of the inside space and took a drawing to a local sheet metal/welding shop. He cut out the expanded metal and bent the sides over (about 3/8 to 1/2 inch to add structural rigidity). I Think it cost me something like 20 bucks. I then sand blasted the grill, primed it and painted it. It was a fun garage project. The same guy also bent up the grill for the bottom cabinet. I cleaned, primed and painted it. Just killz primer and ACE hardware black enamel spray.

Erik

 

[disassembled]

hey man! welcome to the board

i really dig your gear a lot! that Mark IV looks really nice!!

im just curious though, where did you get that expanded metal grill cover for your one 2x12 cab?
thanks!!

You can go to a hardware store or to a metal fab shop to pick up some. I don't know how much it costs but i don't imagine something that size being more than $10.


Greg

 

[Russ]

So would you say that your loop gadget is comparable to having a volume pedal in the loop or is it still different? From your description it sounds like a volume pedal minus the treadle/pedal, the rack and pinion gears to adjust the pot.

 

[tubeydude]

Russ,
That is correct. It is acting just like a volume pedal that I can set and leave attached to the amp. The only footswitch I have on the floor in front of me is the MKIV's footswitch. The FX loop switch on the MKIV's pedal board gives me control of it. (on/off)

Erik

 

[Russ]

Ok, that's cool. I had originally thought maybe it was something really really trick you had going on there that was giving you something different. I may have ot invest in a volume pedal.

The little bias thing is definitely trick. I like the fact that the way that you have described it is stealthy. Would you mind showing pics of the mod? I would like to adjust my bias some but I really don't want to make any changes that would affect the outside of the amp as far as a lame potentiometer or anything. The stick the screwdriver through the handle screw hole sounds so intriguing to me. It would be like bomb diffusal or something. It sounds really trick.

 

[tubeydude]

I don't have any pictures of it. I didn't think to do that when I made the mod. If you take your chassis out though and look at it from the top front, the lower left corner of the top of the power XFMR is right under the right side handle screw hole. I mounted the pot there with 3M VHB tape. The stuff is crazy strong and gets stronger with time and heat. Just locate the center of the handle hole on the top of the XFMR while it is in the cabinet. Push something skinny and NON-CONDUCTIVE like a bamboo skewer through the hole to mark the center spot. Take the chassis out and put the new bias adjust pot on center with that mark and there you have it.

Next time I take the chassis out I'll snap some pics.

Just in case: Make sure the amp is off and fully discharged before doing any of this and if not comfortable with working with tube amps and lethal voltages...don't do it.

Erik

 

[Russ]

I think I will wait for pics before I go and pull my chassis again.