Noob works on U-45B

[Jonathan]

Hi all. I've been doing a ton of homework in preparation for replacing the electrolytic caps on my Lafayette-branded U-45B. It looks like I can get Atoms for C5 and C9, which are both 10uF @ 50V. I intend to go with the Atoms rated at 10uF @ 150V. It also looks like I can get Atoms for C10 and C11, which are both 10uF @ 300V. That Atoms are rated at 10uF @ 500V. I'm stumped on C4, which is rated at 3uF @ 300V. I'm also stumped by what appears to be an unnumbered cap in the tremelo circuit. So I have three questions, and I really appreciate any guidance/flaming/hazing/support/responses you can offer:

1) Am I in the right direction as for the Atoms replacing C5, C9, C10, and C11?
2) What should I use to replace C4?
3) What's the story on the 10uF @ 50V cap in the tremelo circuit with no number (just left of R21)?

I've attached the schematic and a picture of my board for your reference.

Again, thanks for any info you can offer. What I've read on the site so far has been extremely informative.

Best regards,
Jonathan

[Bruce / Mission Amps]

Save some money and use inexpensive, generic Xicon or Illinois 50v caps instead of the over priced Sprague caps.
For that matter the high voltage Sprague caps are too big and not needed either... stick with the smaller and inexpensive Asian ones.
C-4: You should be able to find a 4.7uF-350v cap somewhere but, you can use two 10uF-150v in series (for 5uF @ 300v) or frankly, just use another 10v-450v there too and forget it.
The 10uF-50v cap in the vibrato section is an electrolytic cap too... it is a cathode bypass cap. The footswitch shorts the bottom of the biasing resistor to ground, turning the circuit ON.

Added:
By the way those Atlas oil caps are notorious for going leaky... (electrically speaking not leaking oil)... when re-furbishing these old gronks, I pull the Atlas caps out and use inexpensive Xicon high voltage MPP caps or any other modern plastic cap rated at 400v to 630v.

[Gtr_tech]

Paper/oil caps are just bad news. I've seen fairly new ones get leaky and melt down output sections. I don't care if they "sound vintage". If they destroy a set of real Mullard EL34s, that is just plain unacceptable. Film caps for me thanks.....

[Jonathan]

Thank you both very much for the guidance. Parts are on the way. Should be fun.

[dinglehopper]

I'm also cleaning up a u45b and have 2 questions:

There's a resistor at the top middle of the board in the photo which has one leg soldered to the board and the other off the board. it appears to connect to a terminal strip which subsequently goes to one of the 6bm8 tubes, as well as connecting to the output transformer in what appears to be a negative feedback circuit. I don't see negative feedback on any schematics. Was this a later addition to the circuit? any thoughts on keeping vs. removing it?

Also, the 0.01mfd coupling capacitors are box type 0.0047mfd capacitors wired in parallel pairs. would any of you advise keeping these?

thanks for any and all advice.