5F1 Champ build diary.

[matman14]

Getting set up to start a little champ build over the holiday.

I've drawn out my layout make sure I have it well ingrained in my head:

There are a couple of things I may add. I may need to do a virtual tap on the 6.3v. It'll depend on what the PT looks like on arrival. Mojotone says the PT has a CT of the 6.3v in the spec, but the Kit they offer, which is specced as using this PT, has setting up a virtual CT in the instructions. Since I'm not buying the kit, just some individual pieces, I'll have to wait and see if it will have the CT.

I'm also thinking about adding filtering ahead of the OT. I have a 330ohm 5W resistor and an 8uF 400v cap in my drawer of stuff from other projects. I'm not sure if hum is going to be a real issue with an 8" speaker, and the other stuff I'm doing, but I have the parts so why not?

I might even do shielded wires from the input jacks and move the resistors to the tube lug.

And parts are starting to show up

I have to wait until Christmas to start the build. The kids wrapped up the chassis, circuit boards and cab, and they are under the tree

 

[Lowerleftcoast]

A cursory look. I'd change a few things.

If there is no heater CT on the PT. Place the 100 ohm resistors directly on the 6V6 socket from pin7 to pin8 and from pin2 to pin8. (Neater and less wire running around.)

Swap the positions of the 6V6 Bias resistor and cap. The bias resistor gets hot and all of the caps can be next to each other without a hot resistor between them.

You forgot running the power to V1 plate resistors.

Run the heater wire directly across the V1 socket to pin9, keeping the heater wires twisted all the way to the socket.

Extra points for running the red OT wire directly to the rectifier pin8. (less wire).

 

[Lowerleftcoast]

If you decide to use the 8uF cap, go 20-10-10-8.

 

[matman14]

...
Swap the positions of the 6V6 Bias resistor and cap. The bias resistor gets hot and all of the caps can be next to each other without a hot resistor between them

Thanks, I'll wrap the resistor onto the cap lead and float it with an air gap to allow for better heat dissipation.

You forgot running the power to V1 plate resistors.

D'oh

 

[mjcyates]

I like your speaker choice!

 

[matman14]

I like your speaker choice!

I actually picked it because it had the most attractive sticker on the back, of all of the 8" speakers i could find.
Since then, I read the reviews, and am expecting great things.

 

[Lowerleftcoast]

I actually picked it because it had the most attractive sticker on the back, of all of the 8" speakers i could find.
Since then, I read the reviews, and am expecting great things.

Hah. Maybe I should try the *attractive sticker* method of choosing a speaker. The *listening to sound clips* method has not worked out too well for me.

 

[King Fan]

That's a well-planned amp. I admire your drawing skills. For sure I agree with @Lowerleftcoast. Well spotted sir!

I've never looked at an actual Champ chassis to see if there's space to mount a separate power switch and keep that 120V away from the pot. It'd be smart, noise-wise, if it could fit. And, detail, don't know what type resistors you plan to use -- IME the one place it *really* matters in the signal chain is the input resistor and 68Ks -- carbon comp there contributes a ton of hiss *that gets amplified* and I found MF (or at least CF) were clearly, audibly much quieter.

For sure I'm no eagle-eye like LLC. But without going point by point on yours, I always compare mine for spacing and routing to my personal gold standard, Rob's layout.

 

[Lowerleftcoast]

^^^^
Agree with King Fan. A separate power switch would help to keep the 5F1 quiet. Maybe put the fuse somewhere else and put the power switch in the fuse hole?

 

[matman14]

Hah. Maybe I should try the *attractive sticker* method of choosing a speaker. The *listening to sound clips* method has not worked out too well for me.

I have an alnico gold 10 in my Princeton Reissue, based solely on how cool it looks, that worked out great! Perception is reality

 

[jchabalk]

Compare your ground bus to the one in the layout posted by @King Fan - it's worth it to separate the ground for the 3rd filter cap and make it part of your pre-amp ground bus.

In your picture it looks like you've got the poweramp and preamp grounds connected.

 

[matman14]

Compare your ground bus to the one in the layout posted by @King Fan - it's worth it to separate the ground for the 3rd filter cap and make it part of your pre-amp ground bus.

In your picture it looks like you've got the poweramp and preamp grounds connected.

They are separated, thanks!
I am just not an experienced layout drawer and it gets pretty busy, pretty fast, even on a very simple circuit.

 

[matman14]

I am going to keep the pot/switch combo at least for now.
This is my first foray into putting an amp together and so don't want to start obsessing about drilling and trying to get perfect alignment and etching on the faceplate. If I fall into that rabbit hole, I'm going to end up with a laser etching rig in the garage, and divorce papers on the kitchen table

 

[Lowerleftcoast]

Consider this common mod to take some stress off of the rectifier tube (longer life). You will find an explanation in the Rob Robinette site *5E3 mods*.

If you will be purchasing a few extra parts, like these diodes, a 470k (any wattage) 6V6 screen resistor is sometimes desired to get rid of blocking distortion which is common for the 5F1. (You don't have to install it but it is nice to have it on hand.)

 

[matman14]

Stress relief on the rectifier looks interesting. A quick mod for the new year perhaps.

And how many LEDs would you need in series to get the same result and have a wierd green glow emanating from the amp

 

[King Fan]

I am going to keep the pot/switch combo at least for now.
This is my first foray into putting an amp together and so don't want to start obsessing about drilling and trying to get perfect alignment and etching on the faceplate. If I fall into that rabbit hole, I'm going to end up with a laser etching rig in the garage, and divorce papers on the kitchen table

LOL, good idea. This is a Champ, so 'KISS' and 'the perfect is the enemy of the good' both apply. If ever there was an amp that didn't even need a faceplate, this is it. And your layout is already way ahead of most kit-company layouts. Carry on, and enjoy.

 

[Lowerleftcoast]

If I fall into that rabbit hole, I'm going to end up with a laser etching rig in the garage, and divorce papers on the kitchen table

Looking forward to your Laser etched face plates. Do you think you will venture into pedal box etching?
Sorry to hear about the divorce.

 

[2L man]

When 5Y3 is used without choke there should be 50 ohm current limiting resistors on both anode circuits for voltages up to 400VAC and 140 ohm when AC voltage is higher. Some NOS datasheet also has max 10uF limit for the capacitor. Some new 5Y3 datasheet allow 20uF but they also recommend current limiting resistors. When choke is used resistors are not needed when choke lengthens the time the current flows and it also makes DC voltage more stable for different currents than resistive circuit but choke also decrease the voltage.

Also those already earlier mentioned silicon diodes are good protection!

Current limiter resistors increase the time the current flows to capacitor(s) and the rest of the amplifier when it "flatten" sine vave peaks and then they increase rectifier tube servise life but they also reculate DC when there comes RC circuit with the first capacitor although there is rectifier tube between Resistor and Capacitor

 

[matman14]

Stuff trickles in. I guess there are still some ClassicTone transformers out there

 

[King Fan]

Stuff trickles in. I guess there are still some ClassicTone transformers out there

Aha, nice score -- what I believe is vintage-correct 17K:4ohm 5W, and AFAIK worth getting from ClassicTone.