When to replace filter caps?

[Russ]

I guess that is a project on the long list of things to get to. Thanks stokes.

 

[kdove]

These are pictures of my '78 Mark 1 filter caps. I'm comfortable that I could do this job. I also have no problem completely removing the blue mallorys and replacing with the F&Ts. It's only important that it sounds good & it's not going to "fry" or "explode" since I'm never selling this amp. But I have a few questions:

1-How do my caps look visually? They look pretty clean to me.

2-What are the values of the 5 blue cans on my Mark? There are set of 3 smaller caps ... then a set of 2 larger caps. The values are covered by the foam in the picture. I can remove the foam ... if there's any doubt. But I imagine the Marks all had the same 5 Mallorys.

3-How do I properly/safely off-load the cap "charge" before I begin?

4-Anything other than the 5 caps need replacing? The two small silver caps? Anything else?

 

[user 2126]

Notice small dimples starting to form on the second and third cap:

can go worst:

 

[Shep]

These are pictures of my '78 Mark 1 filter caps. I'm comfortable that I could do this job. I also have no problem completely removing the blue mallorys and replacing with the F&Ts. It's only important that it sounds good & it's not going to "fry" or "explode" since I'm never selling this amp. But I have a few questions:

1-How do my caps look visually? They look pretty clean to me.

2-What are the values of the 5 blue cans on my Mark? There are set of 3 smaller caps ... then a set of 2 larger caps. The values are covered by the foam in the picture. I can remove the foam ... if there's any doubt. But I imagine the Marks all had the same 5 Mallorys.

3-How do I properly/safely off-load the cap "charge" before I begin?

4-Anything other than the 5 caps need replacing? The two small silver caps? Anything else?

Can you see the blue/green stuff on those silver caps last pic ( change them too )

 

[stokes]

Kdove,its been a long time since I've been in an original MKI,but I believe the bigger caps were 60uf at 350v and the smaller blue ones are 30uf at500v.But just pull off the foam and check to be sure.I would change all the electrolytics in an amp that old.To discharge the old caps you could just take a screw driver and touch the + end to chassis,but that may give you a loud pop,I use a 1k 1 to 3 watt resistor wired to 2 alligator clips at each end of the resistor,one clip to the + lead of the cap the other to any ground or chassis.If you dont have a 1k almost any value will do to slow down the discharge.

 

[kdove]

Kdove,its been a long time since I've been in an original MKI,but I believe the bigger caps were 60uf at 350v and the smaller blue ones are 30uf at500v.But just pull off the foam and check to be sure.I would change all the electrolytics in an amp that old.

1-Confirmed the 3 smaller blue caps are 30 MFD 500V (match my original schematic)

2-My original schematic shows 60 MFD 350V ... the one on the right is in fact 220 MFD 285V ??? Can't tell about the other one ... it's underneath the cap. Is it likely that these are paired up and it is a 220 MFD 285V too? Can I put a meter on it while it's in the circuit after discharging and just measure it?

3-The smaller silver caps ... I took a digital picture with a mirror then reversed the image. You can tell its 50 MFD but I can't tell the voltage???

 

[stokes]

the schematic I found shows 2x 60uf@350v stacked,I have a feeling that is a typo,I think they should be 220uf's.If they were 60uf that would only give you 30uf total,but the one after the stdby is 60uf in parallel with the "stacked" pair which would give you 90uf total.I would have no problem using either 2x60uf's stacked or 2x220uf's stacked.As for the silver ones,I have a feeling these are your bias caps,you can verify this by checking if the + lead is connected to ground.The schem calls for one 50uf@70v's.If you have 2x50uf in parallel that would be 100uf total which leads me to believe someone replaced the originals or wired a second one with the first for some reason,some techs do just wire a good cap across a bad one,not a good idea,but I've seen it done.When re-capping you cant always get exact uf values so close is good eneough,for those main supply caps,the 2x60 or 220uf stacked you can use the 60uf or 220uf,using the 220uf would give you a little extra filtering,not a bad thing IMO.Okay,now this is probably getting confusing,so I'll tell you what I would do if it were up to me.Looking at the schem,I would use 2x220uf@350 volt F&T's for the stacked main cap before the standby.The cap after the standby I would use 30uf to 60uf@500v's Spragues.The other 3 are your preamp filters and there I use 30uf@500v Spragues.If you verify that the 2 silver are your bias caps,and are reverse polarity,in other words have the + lead to ground,any value from 50 to 100uf@100v's is good there.I dont see anything else on the schem that would indicate that these are not your bias caps.Looking at your photo again,I see a blue wire that goes to your neg.lead on that silver cap,tells me that this is most likely your bias cap.Use a 50-100uf @ 100v's here.

 

[kdove]

You are correct ... I am confused ... I usually get it ... but slowly:

1st - none of these caps have been touched since it was built ... I bought it new in '78 and it has never been in the shop. There is a blue wire to one side of the small silver caps. I'll check to see if + lead is to ground. Not sure why there are two ... but since it's original I should replace these "as is" with (2) 50 MFD 70V (if it's 70V).

2nd - (3) 30 MFD 500V Spragues makes sense

3rd - there are only two more large blue caps remaining - the 220 MFD 285V and the one I can't identify until I remove it. You mention 2x220 MFD 300V stacked before the standby ... I'm assuming that's these two large caps.

4th - when you say "The cap after the standby I would use 30uf to 60uf@500v's Spragues" ... which one is that ... I think I'm out of caps? Are you saying this is the remaining large blue Mallory that I can't identify?

Sorry I'm getting this slow but it is appreciated!

 

[kdove]

I've become convinced that my Mark 1 amp was right in the seam between Mark I and Mark II amps in 1978. I already made some adjustments to my amp for the fetron that appeared on Mark II schematics. If you take a look this section from an early Mark II drawing (that included the fetron by the way). You'll notice it has a pair of 220uf/285V, a trio of 30uf/500v and a pair of 50uf/70v capacitors. THAT'S WHAT I HAVE!!!!

I think I have a Mark I that was on the work table while the Mark II was being created. :idea: VERY INTERESTING! :idea: What do you guys think?

 

[stokes]

Okay,kDove,it seems the schematic I am looking at is what was causing the confusion,it doesnt match what you are describing and what I am seeing in the pictures,I've got it now,sorry for the confusion.Lets start again.You need 2x220uf@300v F&T's for that main filter arrangement,3x30uf@500v Spragues for the 3 preamp caps.As for the 2 silver caps,they appear to be so close together in the picture that they are connected together,but apparantly that is not the case.They are your bias caps.My schem has a totally different bias circuit.It may be hard to find an exact value replacement so I would suggest using any value between 50 and 100uf at 100volts,unless of course you can find exact replacements,but dont use anything under 50uf @ 70v's.These are main subjects of a re-cap,if you see any other electros,you can change them as well,but the 5 bigger ones and the 2 bias caps are the most important.

 

[kdove]

That's OK ... I just posted a theory that my Mark I has a lot of Mark II built into it. I'm really interested in everyone's opinion on this because the last two times I've tried to figure out this amp, the Mark II has been closer to what's in my amp.

That's why it's always so hard for me to figure out the right thing to do.

Take a look at my theory in the separate post!!

I think I know what to order now. One other question: I can get all F&T versions from Waterford (Europe). Obviously, it will cost more. Or I can get the F&T (large caps) and Sprague (smaller caps) from thetubestore. Is it worth it to go all F&T or are the Spragues good enough?

Thanks again for all the help. I was really confused but I think I'm on to something with this "partial" Mark II theory. All I know is, the next time I'm trying to figure something out on this amp ... the Mark II schematic is coming out.

 

[stokes]

I wouldnt order caps from Europe,you can find what you need here in the states.I use the F&T's for the first or main filters because Sprague doesnt make the 220uf's,or at least I havent seen them.I use the Sprague for the 30uf's.Your older MKI's are marked Mallory but I suspect they were made by Sprague.The later Mesa amps use Sprague for the 30uf's and have their own(Mesa) name on the plastic covering.The 220uf's that I have seen are Illinois brand with a Mesa labeled blue plastic cover.The power section on most of the Mark series amps are almost identical.I just looked again at my schem and it appears that I have the MKI reissue,it came in a Tech Support Pack I have from Mesa.But looking at the schematics on Schematic Heaven,it appears they have the original and the reissue schems crossed.There has always been a lot of controversy over Mesa schems anyway.I would order your replacements locally,no need to order from Europe,get the F&T's 220uf and the Sprague 30uf's.They are both good quality.The bias caps dont get high volts or current so anything you can find should be good eneough.

 

[kdove]

Great ... www.thetubestore.com has got all 7 caps for $43. Now I can do the job knowing how to handle the cap charge and knowing the caps are the right ones.

This forum is always a lot of help.

 

[stokes]

Looks like those resistors that are standing up,connected at one end to the board and connected on the end sticking up to a gray wire, replaced whatever burnt in the past.I assume you arent having any problem,or you would have said so,so I would say,dont worry about it,the repair was already done.

 

[Boogiebabies]

Looks like those resistors that are standing up,connected at one end to the board and connected on the end sticking up to a gray wire, replaced whatever burnt in the past.I assume you arent having any problem,or you would have said so,so I would say,dont worry about it,the repair was already done.

cool, thx bro. It's going back into the headshell now.

That's the rectifier bridge for the tube heaters. In some cases when a tube red plates or blows, it takes out the two resistors that give it ground reference.

 

[kdove]

New caps arrived yesterday ... new filter caps are now in the Boogie ...

Sounds good ... maybe a little "tighter"?

 

[6L6C]

New caps arrived yesterday ... new filter ca[s are now in the Boogie ...

Sounds good ... maybe a little "tighter"?

I changed my caps in my Mark IV this past year the amp was 13 years old, no bad signs just wanted them changed I also found my amp to be tighter sounding, but also found it more harmonically rich.
Keep in mind the amp sounded good before the cap job, I really wish I did a before and after recording of the amp.
Anyway after my experience every 7-8 years for all my amps for sure, it’s not that big of a investment and I noticed a night and day difference.
My cap job was also under the direction of Stokes

 

[kdove]

Yeah ... there's some great technical knowledge here ... Boogiebabies, Stokes and many others. I've been able to make some adjustments to keep my Boogie solid. To be honest, I didn't even know there were parts other than tubes that needed to be changed!

 

[stokes]

Glad to hear you are happy with the results,kdove.

 

[kdove]

Thanks to all ...

Now that I've successfully changed the fetron ... the power tubes (pre-amp tubes are checked and OK) ... and the filter caps:

Is there anything else that the owner of a 30 year old boogie amp needs to check? :roll: