Filter Cap Replacement - 1984 Mark II C+

[DrewV]

Hi All, I have a Mark II C+ which I bought NEW from the factory in 1984. It's a Blond / wheat Super Sixty combo with graphic and 'verb with a 150w Black Shadow. I also bought the road casewhich has kept "The Amp" looking showroom clean, near mint condition! It's time to replace the filter caps. One of the 220uf 300v caps is spittin out tobacco juice! They were replaced about 15 years ago at a shop here in Austin. There are another 4/ 30uf 500v 'blue' caps that are original Mesa "Made in USA" caps, 3 on the power supply board and 1 on the preamp board. All the 30uf 500v caps look good, although the one on the preamp board has the letter "R" written on it with a felt tip pen as well as a 1/4" green stick-on dot on it (?). My questions: 1) Should I replace the 30uf 500v caps? 2) Is there a "better" or "best" cap to use for a replacement rather than the stock item? 3) Where do I buy the replacement capicitors? 4) While I'm in there should I replace anything else?
Thanks
DrewV
This amp has been my faithful gigging pal for 22+ years

 

[BPski]

Call Mesa and get the caps from them. I replaced all my Boogie's filter caps and got them right from Mesa. They are U.S.A. made and are exact replacements. While you are under the hood check all of the other electrolytic caps including the cathode bypass caps. Check yours out. Have fun!!!

 

[DrewV]

Thanks - will do Monday when they are back in the shop....... dv

 

[stokes]

I would also suggest changing all the electrolytics.I changed mine (same amp) in '96 and just ordered a new set from New Sensor.I dont know what Mesa charges,but I paid $66. for the 2-220mf/300v and 4-30mf/500v.These caps are not pre-formed,I think Mesa may be able to do that for you,if you cant do it yourself.You may pay a little more but if they are pre-formed it is worth it.I dont believe in leaving caps for more than ten years even if they look okay,when they blow they make quite a mess not to mention what they might take with them.By the way the 30mf's are Sprague and the 220mf are German made F&T's.I believe Mesa uses Illinois for the 220's and Sprague for the 30's.Dont use the Jap caps in that amp,they are cheaper for a reason.

 

[DrewV]

Thanks,
I did some checking yesterday and found a couple IC 220uf 300V's and 4 Atom 30uf 500V's at thetubestore.com for $44.85 with shipping. I count another 7 electrolytics in various places. I also want to change out the cathode bypass caps, but I am kind of having a hard time identifying them on the preamp board. I know they are 25uf 25V, but I can't find anything marked like that. What I am seeing is: '5' black 3/8" x 1/8" components that look like they could be capacitors marked as follows: "226K" underneath that is "6V with a "+" towards one end and underneath that the number: 8319. I would say this has to be them? This is my first cap job so I'm a little cautious!
dv

 

[BPski]

That'd be them. I don't think they are electrolytic though. They are probably tantalum. Leave them alone. Just replace the electrolytic caps. Have fun!!!

 

[DrewV]

That's what I'll do then! Thanks again for the info...dv

 

[stokes]

Thats a good price.I would get the F&T 220's.I think they are a better quality than the IC's.Just my opinion.I paid 2x what thetubestore is asking.The two small 75v caps on the power board are the bias supply caps you want to change those also.Dont mess with thos preamp cathodes on the board like BP said they arent eloctrolytics.Be careful-lots of volts there.Make sure you drain them caps.

 

[DrewV]

thetubestore.com doesn't have that great of a selection of caps, none of the smaller 7 caps, but apparently the price is good on what they do have. The caps on this power supply board are 47uf/63V if I'm not mistaken. They are the only other caps on the psb besides the 220's and 30's.. I've been checking the DC on the filter caps. They have been draining over the last few days and are down to + 10V on the 220's and +14V on the 30's. They should hit zero by the time the replacements get here. I won't be messing with the bypass caps..no signs of damage or discoloration. The circut boards looka little cruddyand could use a clean up. Boogie On...dv

 

[DrewV]

I went ahead and got the F&T 220's. About $3 more a cap. Mouser.com had the rest of the smaller caps & a high ohm power resistor for about $9 including shipping. I'll post when the amp is done. thanks dv

 

[stokes]

I assume the "7other electro's" you refer to are for the EQ,I dont have EQ in mine and dont have these smaller ones.But if they are on the preamp circuit board I would clip the old ones off close to the cap so you leave a nice length of lead from the board and you can solder the new ones right to the wire-its easier than trying to desolder and resolder directly to the PCB.Good idea for the larger caps as well.Hate those PCBs but love the amp.

 

[DrewV]

there are 2/ 47uf63v on the powersupplyboard, 1/ 470uf16v on the preamp board, 2 /220uf63v and 2 /10uf63v on what I think is the graphic eq board (it's mounted on the side of the chassis, near the input.

 

[stokes]

Yea thats the EQ board,so it looks like you have 4 more caps than mine,all on the eq board.

 

[DrewV]

I've found a sprague orange drop cap running parallel with a resistor that is next to the 4th preamp tube socket (called the gain boost footswitch circut on the schematic) that has turned brown but doesn't look disfigured and is not leaking. the value is sprague 715P .005-400V. As far as I can see, it's the only 715P in there.Should I replace it?

 

[stokes]

If it isnt leaky then I would leave it alone.I have a drawerful of orange drops that are brown and have never been used.Just discolored.

 

[DrewV]

Thanks Stokes.. There is a large 1 or 2 watt 680 ohm resistor that was almost touching the cap. Also the cap is darker brown on the end closest to the resistor. The boards are all cleaned up, I've checked most of the resistors, cailubed the pots, deoxited the jacks....Now it's time to relax a little and wait for delivery! Boogie On.........dv

 

[DrewV]

side note: 2 of the 3- 30uf/500 caps on the psb are seriously bulging on the + end... Boogie On... dv

 

[stokes]

Mine doesnt have that cap.I see the 680ohm resistor but I dont have a cap near mine except for the 470mf electro.Sounds like those 30mf's are about to blow.

 

[DrewV]

Let 'em blow, I pulled them out of the amp already! I'm not sure about a couple resistors: (1/4 0r 1/2 watt) on the psb. one is supposed to read 22k (red/red/orange). It's reads 5.17k. Also the 6.8k (blue/silver/red) resistor right next to it ( they are connected on one end) is reading the same 5.17k They look good and don't test to be shorted. Any ideas? ..Boogie...dv

 

[stokes]

Those are your bias supply resistors.Mine are different because I rewired mine to make it adjustable.As far as the values,when you try to read resistors "in circuit"your readings are not always right since they are connected to caps.If you want to read values you must lift one end of the component in question,or your results will not be accurate.I wouldnt worry about the bias resistors,chances of them goin south is very slim.I happen to have my amp on the variac right now cooking the new caps.A couple of hours more and I'll be done for another ten years-with this one.Between me and my 2 sons we have 14 amps in the basement,keeps me busy!