Resurrecting a 5F1 kit after 20+ years

[twtkid]

Recently unearthed this catastrophe from my mom's garage, a 5F1 kit I put together as a school project more than 20 years ago! (I promise the soldering skills have improved somewhat...)

Figured since I was going to order some parts from Mouser to flesh out my Father's day gift to myself - a Revibe kit from Weber - thought I would see if there was anything I should update on this beast before it's resurrection!

I built it according to the schematic provided, with the handwritten mods. I want to say that I ordered the kit from Triode but I can't say for sure. I'm just a tinkerer and have long forgotten any tube theory I used to know, would love to hear your thoughts!

 

[Lowerleftcoast]

Consider a bypass cap on the 12AX7. The original schematics did not show the cap but many of the amplifiers came with the cap. The original and typical Fender value was 25uF. Some bass reduction can be had by using a smaller value. I suggest a 2.2uF. Before you solder in a cap, use alligator clips to parallel different values across the cathode resistor to hear the differences. There are only a couple of volts here so a 10 to 50 volt rating is fine. 25uF is not critical, 22uF will not make an audible difference. This cap will increase gain/volume. At 25uF, all frequencies are increased. Smaller values keep the bass frequencies from being increased. Fender standard was 25uF. Marshall reduced bass a lot with a .68uF.

On the 6V6 you show a 1k screen resistor. Again, use alligator clips to have a listen. Clip in another 1k 1W resistor to hear an equivalent of 500R. Clip in a wire to hear what the original design sounded like. (If you cannot hear a preferred difference, a 6V6 does not need 1k here for tube operation. Install a 470R 3W to 5W. Usually this resistor hangs on the tube (pins4&6), you have it on the board. It gets hot and heat rises onto your filter caps.)

 

[Lowerleftcoast]

Sometimes a larger reservoir cap will reduce hum on a 5F1. A 5Y3 rectifier can take 40uF so you might consider changing out that 22uF.

 

[twtkid]

Thanks so much! I will be completely rewiring and installing everything into a Hammond chassis so these tweaks should be easily accomplished.

 

[King Fan]

Good for you. Smart. Actually, after 20+ years, all new filter caps might be a good idea. Even if it hasn’t mostly sat, which is bad for electrolyrics, you’ll be 20+ years further from them failing.

And I dont know about you, but part of the charm of a Champ is letting it be a Champ. A bypass cap (25uF) on V1a is actually more vintage correct; the great majority seem to have got it despite the schematic.

I like the idea of smallifying the screen resistor or eliminating it back to stock if your ear likes that. LLC has good points throughout.

For my money, don't mod the little guy too much. Nice project.

 

[Gunny]

while you're in there, you should put more air space between the 6V6 cathode resistor and the 22uf cap. Because they're currently touching each other, heat from that resistor will cook the capacitor and shorten its life. Just unsolder one or the other component and elevate it above where it is by at least 1/4".

 

[twtkid]

Thank you! Yes, I figured that would be a good idea from a longevity standpoint, and was planning on keeping the Champ a Champ, so to speak!

 

[twtkid]

heat from that resistor will cook the capacitor and shorten its life

Yes in my reading of Champ posts here that sounds familiar, will do!