The AM Forum

Hi Everybody,

As you know, I ordered up 4, 200V rated, 22 microfarad caps for my HP-23A power supply, from Digikey (along with the 120 microfarad caps) before I realized that Mouser sold 20 and 40 microfarad electrolytic caps I needed.  The cheapskate in me, hates to have ordered them for nothing, but if they'll be a problem in this supply, I won't use them (I can't revoke the order, because it shipped yesterday).  I guess my question is this:  I had planned to use the 22 microfarad caps to replace the 2, 20 microfarad caps in the supply, and (by wiring 2 in parallel) the 40 microfarad cap.  Will this cause any major issues?  Otherwise, before I leave work today, I'll place an order with Mouser for the proper value caps.  Also, what are your feelings on the HP-23 upgrade kits sold by The Heathkit Shop, and OldHeathkitParts.com?

73,
Ellen - AF9J

Ellen,
The only problem you may encounter is the physical size of  having 2 caps instead of one.  Hopefully they're small enough and there's enough room in the chassis.  Electrically, no problem.

Hi Ellen,

The problem is that the 40 in the low voltage supply needs to have a higher DC voltage rating than 200 as it will see the full low voltage output of either 275 or 350 so it should be a 450 volt unit.  The 20 uf units you ordered will be fine for the bias supply however.

73, Rodger WQ9E

      "Also, what are your feelings on the HP-23 upgrade kits sold by The Heathkit Shop, and OldHeathkitParts.com? "

The only thing I can think of is,  are the price of the parts, single lot,  cheeeper than the kit?

 klc

I have never had any problems using caps "near" to the original value. 22 uf should be fine for a 20 uf PS application. As others suggest, make sure the DCV rating is spec or greater.

OK.  To play it safe I bought 2, 450 V rated, the 20 microfard, and 1, 450V rated 40 microfarad cap.  I also bought 5, 2, metalfilm (you can't get carbon comp in 2W ratings anymore) 100K resisitors, since these sometimes go bad with time.  Thanks to everybody for the feedback.  I'm out of here, work is  done for the day.  I tell you, in some ways it might be almost as cheap to get the upgrade kit (it's about $55-$65, depending who you buy it from).  Some of these caps ran over $7 a piece (the 40 microfarad, in a 450V rating).

73,
Ellen - AF9J 

A new or a good cap will have a higher capacitance than what is stamped on it typically.   A few extra uF's won't make that much of a difference.

Uh huh.  That's what I decided to go with.  Also, Rodger, had a 47 microfarad, that he's sending me.  BTW, I took a look on eBay today, and what did I see?, an HP-20!!  Go figure!  BTW, hows your Poisin Ivy doing?

73,
Ellen - AF9J

PI is going A-way as we speak.

Great! :)

Ellen - AF9J

as a very general rule, the mo strap in your cap is betta. better to stay close to the rated value with a cap input supply, as the inrush when you turn it on can go over the cap's voltage limit. No so much on a choke input supply. I subbed up to +100% on choke input supplies and never had any problem. I like a lot of filter on my supplies. when presented with a 2 10uf, I'll sub a 10 before the choke and a 22 after. 

I'll just measure the voltage when turning the unit on, and add about 30% joltage rating to the highest level I see. If its already 450volt rated ( and it's got at least +400 on it) I stay tighter to the stock value. If I see any voltage over 425, I'll buy a 500 volt cap.

and never, ever, buy chinese made caps. Buy USA or Japan, like rubycons. Chinese caps are all junk. Google motherboard caps and looksee. They may have fixed them but I would not trust them.

Hi Derb,

I went with 500V for the HV part of the supply, for a safety margin.  I'm busy with some other things today.  I have all of the caps & I'm replacing the 2W 100K resistors too.  I'll try to get things replaced this week.

No Chinese caps either huh? - somehow I"m not surprised.  Chinese 6146s are the same way. Those who have Kenwood hybrids (TS-520, 820, 530, 0r 830), have learned this the hard way, when we used them.  They arc over, when the filaments are fired up.  In my case, I won the opportunity to replace fried resistors on the HV board. Others have lost finals resistors.  My solution was a set of NOS, JAN PHillips milspec 6146Ws.

Time to listen to some more static on 6 & 2 (6 is being a teaser with weak almost non-existent openings to W1 & W2 land).

73,
Ellen - AF9J