Filter Cap Replacement - 1984 Mark II C+

[DrewV]

I had an idea that they were in circuit. I'm going to leave them alone..I buy my 6L6's from Boogie anyway. 14 amps! that"s gotta be close to being in HEAVEN!!! The FedX man just dropped off the caps I ordered from Mouser YESTERDAY! Time to heat up the iron. thanks...Boogie On...dv

 

[DrewV]

UhOh...The 2- 47uf63V caps on the psb are high temp capsrated at 105*. the replacements I got are rated at 85*. should I stick with what I've got or order the high temp caps? thanks ... dv

 

[stokes]

Dont sweat it the 85 deg.-its 85deg celsius-like 200deg farenheit.They'll never get that hot anyway,theres no appreciable current in the bias supply.You do have a variac to form the new caps,right?If not I can tell you another way to do it.Email me if you need the info.

 

[Tuna141]

Stokes,

Sorry to jump in...I have a variac, but have never "formed" electrolytic caps - can you explain how this is done? (for future reference)

Thanks.

 

[stokes]

Let me start by saying this is the way I learned to do it.There are others who do it differently and I am sure they will jump in with their techniques,which I am sure work fine also.I take all the tubes out first, if you have a tube rectifier you will have to sub a SS rectifier here.If you dont have a plug in sub,simply wire in two 1N4007 diodes across the tube socket.Plug the amp with the new caps installed into the variac,start with the variac at 40.Leave it for an hour or more and slowly turn the variac up to 50.Raise the variac by 10 every hour or or so till you reach the point where the DC voltage on your caps get close to the rated voltage. If the caps are rated for 450vdc stop at about 400v and leave it for a couple of hours.Keep a close watch on the volts going to the caps because with no load the voltage could pass the dc rating of the cap.Should take 8-10 hours to complete but you will have nicely formed caps.I use the same technique before firing up old amps that havent been used in a long time to reform the old caps before putting full voltage on them.Always drain the old caps before trying to remove them.I made that mistake many years ago and will never forget again-it hurts!

 

[DrewV]

Stokes, please don't think that I am dissing you,.You are totally knowledgeable on the subject of guitar amps and have way more knowledge than I do. I truly appreciate the info you have presented in this forum. Regarding the question of forming the filter caps, here is what Jon from thetubestore.com had to say when I emailed him about forming the caps I was buying from him: "They are ready to go. Simply install" . After doing some net research, it seems that the idea of forming caps is valid in 2 circumstances: 1) to paraphrase Stokes, ' when the amp is old and hasn't been fired up for a while' and 2) when the caps you are installing are VOS caps. That's my 2 cents!! Anyone else want to chime in? and thanks again Stokes for the latest info re high temp caps....Boogie On...dv

 

[stokes]

By VOS I assume you mean very old stock.Do you know when the caps you are buying were manufactured?How long they were sitting on the sellers shelf?I dont take chances,having seen what they do when they explode,if you are lucky they only make a mess of the inside of the chassis which is no fun to clean up,if you can clean it all.Before they explode they draw major current,which is no good for every component in the amp.Some suppliers do sell pre-formed caps,Kendrick is one I know of.Dont know if the tubestore does,I would ask before assuming.As for VOS caps,if I know they are old I dont use them,I dont buy caps from ebay or flea markets if I have any doubt about a cap I would throw it out,before I even think about putting it in my or someone elses amp.Your amp is worth over $2,000-if you want to take that chance... I am sure 9 out of 10 times you can get away with not forming the caps,odds may even be better but I dont want to be the one who fries someones equipment.The "damage" may not be imediate,but caps that are properly formed will outlast ones that are put in and fired up cold.I am sure there are alot of people who will disagree,and I aint saying I am 100% right,but it is the way I was taught and it is a good insurance policy.Like I said before, I change filter caps after 10 yrs.,usually sooner,thats just me.I dont like when they pop.Even if the caps seem okay I still notice an improvement after a cap job.

 

[DrewV]

Yeah, once again your points, "Do you know when the caps you are buying were manufactured?How long they were sitting on the sellers shelf?" are TOTALLY VALID. Your method is failsafe. I don't have a vari-ac, tho I could probably take the amp into one of several music/repair shops here in Austin and have them do it. Does the other method you mentioned involve putting a 100watt light bulb in series with the ac? Boogie on..dv

 

[DrewV]

Here's a link that supports Stokes' position: http://www.harpamps.com/micKcaps/Forming-Capacitors.html
Boogie On...dv

 

[stokes]

Drew,
Yes the other method involves the light bulb in series,but you have to leave it on this way for a day or two.I have never done it this way but there are some who swear by it.I would think it is better than not doing anything.Even fresh,brand new caps have to be formed to function efficiently.I read about the light bulb/series procedure somewhere.I believe you have to monitor either the current across one of the power resistors in the supply rail or the voltage as it rises.I am not sure offhand but I can dig out some books and look it up for you.The light bulb in series apperatus is easy and cheap to make,and is very handy if you ever have a problem with fuses blowing.If there is a short in the amp the bulb will glow bright but not blow the fuse so you can pull power tubes and such till the bulb dims.....getting off topic here.Let me know if you need the info on the bulb/series procedure.

 

[DrewV]

I've got a diagram of the light bulb current limiter that I got off the net a couple days ago. I think you monitor the voltage, but I am not sure. I was reading it today, but haven't found "that" webpage again. If you want to send the info to my email address it's: [email protected]. Boogie On...dv

 

[DrewV]

The cap job was successful! I used the light bulb current limiter for an hour. When I fired the amp up, it sounded as good or better than new (if that's possible). I reccommend to anyone that's got a tube amp 10 or more years old to have it recapped. you won't be disappointed! Boogie On...dv

 

[psychodave]

The cap job was successful! I used the light bulb current limiter for an hour. When I fired the amp up, it sounded as good or better than new (if that's possible). I reccommend to anyone that's got a tube amp 10 or more years old to have it recapped. you won't be disappointed! Boogie On...dv

Did the amp get "tighter" ? I am thinking about re-capping my Mark III which was made in 1989.

 

[DrewV]

pyscodave,
Tighter & Brighter!! The improvement in the sound coming out of the amp can only be described as "glorious". When I fired it up I was instantly reminded of the first time I turned the new from the factory amp on (and up ) back in '84, ...better than that new car smell by a mile. Everything is tighter...the clean channel jumps out at you and the lead channel just spanks! Overall volume is increased....I had forgotten how loud this 60 watter was...now I remember...just do it or have someone do it for you... you will not regret it! Boogie On...dv

 

[psychodave]

pyscodave,
Tighter & Brighter!! The improvement in the sound coming out of the amp can only be described as "glorious". When I fired it up I was instantly reminded of the first time I turned the new from the factory amp on (and up ) back in '84, ...better than that new car smell by a mile. Everything is tighter...the clean channel jumps out at you and the lead channel just spanks! Overall volume is increased....I had forgotten how loud this 60 watter was...now I remember...just do it or have someone do it for you... you will not regret it! Boogie On...dv

Now I just need to get the parts... I will post my results 8)

 

[Dasein]

I'd love to see pics of these --- both before and after.

 

[DrewV]

psychodave.. thetubestore.com has the main filter supply caps ( 220uf/ 300V & 30uf /500V) mouser.com has all the rest. The big caps were about $45 and mouser was under $20... Boogie On...dv

 

[DrewV]

Daein..I've got some piks of the Boogie at www.armadillospeakers.com
Boogie On...dv

 

[Henz]

Greetings> I hope that this isn't a ghost topic. If I get thru, Drew, I have the exact amp and year ( except mine is Simul Class). Im happy your amp turned out great. I want to re cap mine.They all have original caps in it. My question is what value of the two bias caps did you put in? my schematic is hard to read. I think it says 80uf 75v. I'll have to remove them first to be sure because they are installed with the values hidden. You used 47uf 63v ? Man , i hope to hear from you. Thanks for your time, Jim

 

[jrb32]

The bias caps are 2x 47uF 63V. Don't trust the schematic it has errors. You can use 100V rated ones though too if you want. Get a decent brand like Kemet. https://www.mouser.com/ProductDetail/80-PEG124MB247VQL1 are the ones I used in mine (I think I bought both 100V and 63V and used whichever size fitted - higher rated voltage the better)

All other filter caps get from Boogie directly! They use BMI ones (same as originals) at a lower price than anyone else.

There's also 680 Ohm resistor that should be replaced with a wirewound 3W or higher should be fine.

Check the values for your 470 Ohm and 2.7K resistors for the output valves as well using a multimeter (or 4 x 470 Ohm for 100W, 2 x 470 Ohm for 60W) They tend to go out of spec after a while and can also be replaced with wirewound resistors (again 3W or higher should be fine)

Hope that helps!