Filter Cap Replacement - 1984 Mark II C+

Pre Recto days. Boogie modified Fenders, Mark I-IV, Dual Calibers, etc

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Henz
Mark II
Posts: 102
Joined: Wed May 18, 2016 11:05 pm

Re: Filter Cap Replacement - 1984 Mark II C+

Post by Henz » Sun Jan 13, 2019 12:01 am

Thank you for your reply. Instead of what the C+ calls for ( 50uf 75v) , 100uf 100v is better? Ya know from what i heard from you, you are very intelligent. I;m gonna order the bias caps that you suggested. I do get red plated tubes at times. I do not know if there is a bleed resister in power supply, so im just goin to remove and solder. I don't care at this point in my life. If I get electrocuted, at least I died trying! Blessings to you. you are a great help. Sincerely, Jim
MKIIC+
2:90
4x12 Recto Cab w/ Eminence and V30's
Home made 2x12 half open cab w/ Eminence and V30's
Rocktron Patchmate, Rocktron Intellifex, TS10 Tubescreamer

woodbutcher65
Mark III
Posts: 183
Joined: Fri May 04, 2018 10:36 pm

Re: Filter Cap Replacement - 1984 Mark II C+

Post by woodbutcher65 » Sun Jan 13, 2019 12:17 pm

Stiffening up the bias supply with 100/100s is something I'd do on my own amps. There's no down side to it. While you should not be too aggressive in increasing capacitor values in the power supply, going to a bigger bias supply cap will just help keep the bias even more stable. Since 75 volt ratings on caps are comparatively rare, you go up a voltage rating. No harm in uprating a cap, but don't downrate one.

You COULD stick with 47 uf if you want. No harm in that either. So there's a wide range of possible caps that fit in the box defined between 47/75 and 100/100 ratings.

Pick any caps you like within those limits. I recommend 105c temperature rating, OR HIGHER, and a long rated life. Your standard capacitors are going to be rated for 1000 hours use at the design rated temperature of 65c, 85c, or 105c. 105c is a premium grade. But going with longer rated lifespan is even better. I picked the Vishay 105c/10,000 hour caps because I'm pretty sure those will be lifetime parts. I'd expect them to still be good 20 or 30 years from now.

If a tube does red plate, the bias cap is going to be where the current draw comes from. So it's going to run warmer. If it's rated for that, then it means that the shorted tube isn't going to blow up the caps. If the cap blows, it'll usually short out. And THAT is bad for the power transformer.

It's not great for the power transformer to have to feed current to a red plating tube, either. But a shorted cap is much worse.

Henz
Mark II
Posts: 102
Joined: Wed May 18, 2016 11:05 pm

Re: Filter Cap Replacement - 1984 Mark II C+

Post by Henz » Thu Jan 17, 2019 2:51 pm

Thanks for the reply. You are very helpful. Drew, did you change the caps on your eq circuit board? And was it hard to remove from the side of the chassis? Thanks, Jim
MKIIC+
2:90
4x12 Recto Cab w/ Eminence and V30's
Home made 2x12 half open cab w/ Eminence and V30's
Rocktron Patchmate, Rocktron Intellifex, TS10 Tubescreamer

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