Filter Cap Replacement - 1984 Mark II C+

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

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DrewV
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Post by DrewV » Wed Jul 26, 2006 5:55 pm

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: drew@drewswebsite.com. Boogie On...dv

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DrewV
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Post by DrewV » Fri Jul 28, 2006 9:24 pm

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

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Post by psychodave » Sat Jul 29, 2006 5:44 pm

DrewV wrote: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.

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DrewV
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Post by DrewV » Sat Jul 29, 2006 7:29 pm

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

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Post by psychodave » Sun Jul 30, 2006 4:45 pm

DrewV wrote: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
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Post by Dasein » Sun Jul 30, 2006 6:18 pm

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

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DrewV
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Post by DrewV » Mon Jul 31, 2006 1:59 am

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

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DrewV
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Post by DrewV » Mon Jul 31, 2006 2:03 am

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

Henz
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Re: Filter Cap Replacement - 1984 Mark II C+

Post by Henz » Sat Jan 05, 2019 3:36 pm

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
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jrb32
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Re: Filter Cap Replacement - 1984 Mark II C+

Post by jrb32 » Mon Jan 07, 2019 4:37 am

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!

Henz
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Re: Filter Cap Replacement - 1984 Mark II C+

Post by Henz » Mon Jan 07, 2019 2:19 pm

Thanks for the reply! And the link. I'll do the same, get both and probably use the higher voltage. I think higher is better. The 680 was replaced by MB at Mesa. He rebuilt the ldr supply which that goes to. Now, my amp uses 4 470ohm for the plates of all four power tubes. I have replaced them.(I may get new ones anyway. Wire wound like you suggested. I've always used 2 watt but would 3 be better?) I always measure them. They are within specs. My outer two tubes have 220k resistors going to the grids and the inner tubes have 2.2k resistors going the those grids. In circuit, the 2.2k's measure fine. The 220's measure 188, all of them, even the two at the bias input( E ) feeding the two bias rails on pcb. The issue that I have is the plate voltages were always around 470v in the past which is in specs rite? Recently the voltages have been 504v. I have no idea what caused that unless OT is going bad. The tubes do run a little hot. I just did a complete recap on my 2:90. Those voltages have increased too inside (prior to recap). Maybe it's my electric coming to house. My C+ doesn't have lots of noise but over the yrs I may not be noticing it, but it's there. Follow? Since I re capped 2:90 I thought I would do C+( they are all original). Did you notice a huge improvement in tone? Sorry for the long reply. I love talking shop. Hope to hear from you, thanks, Jim
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Henz
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Re: Filter Cap Replacement - 1984 Mark II C+

Post by Henz » Mon Jan 07, 2019 2:32 pm

Just went to Mouser. Those caps are a lot shorter and fatter than the ones that are in there now. Does that matter? Also, forgot to mention bias voltages above. Voltages on pin 5 on outer tubes are - 48. Inner tube especially is - 60. In the past they were always -39 and - 50. Don't know why the jump. While I'm at it, I'm gonna get new power tube sockets too. Thanks, Jim
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woodbutcher65
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Re: Filter Cap Replacement - 1984 Mark II C+

Post by woodbutcher65 » Thu Jan 10, 2019 6:52 pm

I recommend you get your electrolytics from Mesa. I don't have a particularly high opinion of IC brand caps. They're decent but you can get better.

The major caps (the 220s and 30s) found in the power supply are now made by BMI, Barker Microfarads Inc, which means they're Sprague Atoms in everything but name alone. BMI is the former Sprague Atom factory with Sprague tooling run by former Sprague employees. They're top quality.

So you've got a 15 year old cap that's already failed. And some people think that my recommendation to replace caps any time after 10 years is too conservative. Well, a 10 year replacement cycle is certainly conservative but it's highly unlikely that you'll ever find a failed cap on that replacement time frame. If you do, it was defective or the amp took a power surge that took it out.

I change tires BEFORE they are running on the cords, too. Same reason. Safety margin.

Definitely change out the bias electrolytics as well. I also recommend replacing the .1 uF coupling caps between the phase inverter and power tubes as well, because they're the single part that I've seen fail most often after recapping an amp. Recapping restores power supply voltages to their designed values and that increase in voltage is enough to push some old, worn caps over the edge.

The symptom of this is that you get one or more red plating tubes right after a recap job. So change those coupling caps when you recap the amp. Use CDE (formerly Sprague) 600 volt 0.1 uF series 715P caps. Don't get the knockoffs offered by some vendors. Get genuine CDE branded parts. There are other orange caps that look like orange drops but if they don't say Sprague or CDE on them, they are not to be trusted.


As for alternative cap brands, if I can't get CDE then I want Vishay or Nichicon electrolytics if I can get them. And I'll spring for long life/high temperature types.

I just recapped a Kendrick amp and because I could get them, I put in 100v/100uF Vishay electrolytics for the bias caps, which are rated 10,000 hours at 125c. I think they should last.

Henz
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Re: Filter Cap Replacement - 1984 Mark II C+

Post by Henz » Thu Jan 10, 2019 11:55 pm

Thank you for your reply. And input. I'll get those two .1 caps as well. On the schematic, they are the ones going to the plates of PI correct? Should i replace the electrolytics on my EQ board? They are original as well. I'm gonna put new plate resistors and new power tube sockets too. I just don't understand why my plate voltages increased . And my bias voltages as well. Is there a way that I can drain my old caps with a volt meter? I re capped my 2:90 and didn't drain anything. I didn't get bit but I was careful , or lucky?I sincerely thank you for your advice. Jim
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woodbutcher65
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Re: Filter Cap Replacement - 1984 Mark II C+

Post by woodbutcher65 » Fri Jan 11, 2019 11:54 pm

If there's no voltage bleed resistor in the power supply, add a 330K 1 watt resistor from the highest voltage node to ground. That'll bleed it down quickly enough and not draw appreciable current. (About 1 milliamp, total max dissipation on the resistor will be barely half a watt at most. No problem.) This can be a permanent addition to the circuit but there should already be a bleed resistor.

Why voltages increase when you replace old caps: Because the old caps have degraded and their capacitance has dropped, their leakage current has increased, and their ESR has increased. All factors of ageing.

The bias caps on a Mark IIC+ should be 50uF 75V if original. They'll be the two smaller axial lead caps right next to the big 220 uF 450/500 volt caps on the supply board.

Since those take the heat (literally) if a tube should short and red plate, I do recommend putting in the best caps you can in this application and adding capacitance would do no harm.

Thus, I would not hesitate to put these beauties in: 4258PHBK-ND (Digikey part number) 100 volt 100 uF Vishay axial lead capacitor, rated for 10,000 hours at 105c. That'll do it!

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