Capacitor Voltage ever too high?

[timmyjoe]

I'm getting ready to replace all the capacitors in a Bell & Howell 385. I'm wondering if it is OK to use capacitors of a higher voltage rating when shopping for parts.

My overall plan is to use the transformers from the original, use the resistors after testing them, and replace all capacitors. I'm making a new housing for it and also putting in new tube sockets.

[acheld]

I'm wondering if it is OK to use capacitors of a higher voltage rating when shopping for parts.

Yes, perfectly fine to do so.  Only reason not to is that the higher the voltage rating, the higher the cost and the larger the size.  Neither of those should really factor in much for the project you're describing unless you go way overboard.

LOL, I recently experimented with film caps in a power section, and saw a 40uF film cap rated at 1.1kV, and had to buy it.  Yup, way too big!   But it looks cool . . . in my drawer.   

[PRR]

Off-off-off topic drift about projector and husband moved:

https://el34world.com/Forum/index.php?topic=28053.0

[timmyjoe]

But how is this for under the hood for the 385?

Any thoughts on layout so far in terms of placement of capacitors and such? Tried to group the filter caps together like other amps do.

[Willabe]

You should separate the power amp ground from the preamp ground. And since your gutting the chassis you can distribute the B+ filter caps so their close to the circuitry they feed.   

Read this on grounding;

http://www.valvewizard.co.uk/Grounding.pdf

And this on lead dress;

http://www.geofex.com/Article_Folders/lead_dress/lead_dress_in_tube_amps.htm

[timmyjoe]

thanks for material!

[Willabe]

Most guys here use 2 chassis grounds, 1. Power amp. 2. Preamp.  If your amp has a -FB loop around the power amp, then you ground the phase inverter (PI) with the power amp chassis ground. (You do this because the -FB loop is tapped off the OT secondary.) If it doesn't have a -FB loop then you ground the PI with the preamp ground.

Merlin uses only 1 chassis ground, but using the 2 chassis grounds like above is fine.

See below; The 1st B+ filter cap should have the PT B+ CT going directly to that filter caps ground lead, red arrow, then you run a wire over to the 2nd filter cap, screen cap, purple arrow. That way the heavy current, ripple/charging, won't modulate any other caps and what they feed. So keep that 1st filter cap close to the PT.

[timmyjoe]

Willabe,

Started to read the materials you linked to......... but got a ways to go before digesting it all.

Here's my fast read on what you are saying to do though in terms of the schematic. I labeled it G2 for preamp ground and rectifier power amp as G1.

[Willabe]

Yes.

That's the idea. You have to break the ground between the PI and preamp, and run the B+ preamp filter caps to the preamp ground, C4, C5. Most guitar amps would not use the 3 caps I circled in blue. 

Now figure out what tube grounds go to which B+ filter cap grounds as ground stars.

I'd probably get rid of R1, 440ohm/10w, I don't think you need it.

[Willabe]

Started to read the materials you linked to......... but got a ways to go before digesting it all.

Yes, it took me a while to understand it too. Just keep reading it over and over again and keep looking at the drawings. It will sink in. 

Your making ground stars for each B+ filter cap and stringing them together with a ground buss.