Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Zedman on July 02, 2016, 04:54:32 pm

Title: Wrong caps ordered
Post by: Zedman on July 02, 2016, 04:54:32 pm

Hello Forum! I'm still on the path of doing a JCM900- JCM800 conversion and last week my order of parts arrived.

It seems that some idiot (me) has ordered the wrong power supply filter caps. :BangHead:

I have received 3 * dual 100uf 500vdc caps where I should have ordered 3 * dual 50uf 500vdc caps.

I think I know the answer to this question but I will ask anyway. Should I use the larger incorrect value caps or should I get the correct value?

I expect that I would be best off returning the caps and staying true to the intentions of the circuit designer. Extra filtering may be a good thing but it also may change the filtering of low f ripple in the power supply.

thanks for your help
Z

Title: Re: Wrong caps ordered
Post by: jjasilli on July 02, 2016, 06:47:03 pm

SNAFU - ordering errors are the 3rd surest thing, after death & taxes.     :icon_biggrin:  Why incur more shipping fees to return them?  But where to put them?   :think1: Build another amp around them!

Title: Re: Wrong caps ordered
Post by: PRR on July 02, 2016, 08:28:59 pm

> staying true to the intentions of the circuit designer.

My suspicion is that The Designer wanted solid bones, the Cost Control Dept hammered the cost down. This is especially true on older electronics from days when large caps were expensive. I have "improved" a lot of gear by up-sizing the main caps.

Title: Re: Wrong caps ordered
Post by: Zedman on July 02, 2016, 11:22:45 pm

thanks Mr jjassilli and PRR. I got a good laugh with the idea of building another amp around them!

I will have a shot with what Ive got and order more carefully next time.

Today, I was hoping to get a couple of hours to get into this conversion.............and then the phone rang with repairs turning up this arvo. So much for Sunday being a days of rest.  :l2:

I get the feeling this project may take me longer than it should.

Z

Title: Re: Wrong caps ordered
Post by: sluckey on July 03, 2016, 07:10:57 am

Just a thought... The first two dual 50 cap cans on the B+ string for a JCM800 2204 are wired parallel to yield a total capacitance of 100µF at each node. You could use a single can to do the function of those two cans. Or you could just use two cans but not parallel the caps. That would leave one unused cap in each can. Either way, you only have to buy one additional dual 50 for the preamp.
 

Title: Re: Wrong caps ordered
Post by: Zedman on July 04, 2016, 04:13:24 am

thanks Sluckey, that would also negate the need for me to make another filter cap hole!

Z