Substitutes for Mallory TC78 and TC75 in a Rocket?

[George61]

I hate to post a dumbass question but I have searched the forum, until I was blue in the face, and couldn't find a definitive answer to my question. The answer may be there but there is a lot of information to sift through.

What can I use instead of the Mallory electrolytics in a Rocket build? I'm guessing, that's guessing, that 33uF is a suitable substitute for 40uF. I found BC Components 33uF and 22uF 450V caps online. Mouser has 33uF 450V Kemet PEG 124 electrolytic capacitors. I have read some diparaging comments on new production Sprauge Atom and F&T capacitors. I have read some good comments on Illinois Capacitor, which are also pratically free. Nichicon axial lead caps are easy to come by.

I haven't eliminated radial lead caps. Some of the Cornell Dubilier snap-in's have a very high ripple current rating, in the same range as the Mallory TC series.

[xtian]

I have read some diparaging comments on new production Sprauge Atom and F&T capacitors. I have read some good comments on Illinois Capacitor, which are also pratically free.

Really? I thought just the opposite. Interested to hear what folks say.

[Koop]

According to Gerald Weber the Illinois capacitors are Chinese junk.

[George61]

OK, Illinois is off of the list. It's back to BC Components, the only caps that I have any experience with. I replaced the 'Holy Grail' axials in my Ceriatone with BC Components and it was a marked improvement.

[George61]

I have the 'official' Mallory capacitors so I quess I will use them. I don't like the glued up stack but I think I have a work around for that. My problem is that using my Fluke 189 to measure the TC78's I am getting 50uF to 51uF each. That's 100uF on the output of the GZ34 which is 40uF over the data sheet limit. Seems to me that's a problem?

[Colossal]

I have the 'official' Mallory capacitors so I quess I will use them. I don't like the glued up stack but I think I have a work around for that. My problem is that using my Fluke 189 to measure the TC78's I am getting 50uF to 51uF each. That's 100uF on the output of the GZ34 which is 40uF over the data sheet limit. Seems to me that's a problem?

George61, you might already know this but electrolytic capacitors have poor precision and you will often see +20% of the nominal value printed on the cap. So it is not at all uncommon for a cap to read significantly higher than the printed value. Best to measure, as you have done, to select those parts which best fit your needs.

IRC, I believe RJ did some research (and maybe others so I don't want to leave anyone out) and found that the much vaunted Mallorys were the worst offenders of a group of caps he tested for precision. I cannot tell you what the other caps in the test group were however. There has been some discussion about exceeding the printed limit for a GZ34 in that the rectifier can see higher than specified limits so long as the current demand is not super high and also approaching the limit of the tube.

Hope that helps allay some of your concerns. Oh, and a lot of us don't care all that much for the stack o' caps approach and have devised workarounds, some by building dedicated cap boards, others going to cap cans in place of the six caps the design calls for.

[George61]

Thanks to Colossal for the reply. I will build this amp per the layout and schematic in the Trainwreck files section. It's not an experimental design, it's a tried and true designed. Maybe I will learn something new; like what flashover is.

Thanks again,
George

[George61]

I've started my Rocket build and me and the stack-o-mallory weren't getting along so I tried something I've done several times in solid state amps. I used a milling machine to make a cheesy circuit board and used radial capacitors. Does anyone think it has a snowball's chance in hell of working good? I think it should work because the main capacitors are the correct shade of blue. The whole board cost me 13 dollars and change to build. Can't beat the price.

[xtian]

That is AWESOME, George! I love how you casually toss off, "I used a milling machine" and "cheesy" in the same sentence, as if everyone had one in their kitchen. Dang.

[rock_mumbles]

Nice cap board!

There shouldn't be any reason it wouldn't work.

[Dr-Joned]

It look better than what Ken used! )

[Decko]

Hi George,

How did your power board turn out with in the whole scheme of your project?

Decko

[George61]

Hi George,

How did your power board turn out with in the whole scheme of your project?

Decko

I don't have very much amp building experience so I can't say for sure. The board seems to work fine to me. All of the voltages are correct. The amp doesn't make any strange sounds. The tone of the amp is very good. The bass is very tight, which surprises me. On my only other build (36W Ceriatone) the bass was mush.

I still have the Mallory's. If I get bored I may replace my cap board with the official Stack-O-Mallory to see if it makes a difference.

Solder on,
George

[cbass]

According to Gerald Weber the Illinois capacitors are Chinese junk.

I wouldn't let what ol gerald thinks sway my opinion one way or another

[M Fowler]

I use Illinois caps no problem but not all dealers are stocking them like they used to.

Actually finding 500v ecaps can be exhausting without going to large vendors like Mouser.

Mark