Fender 600 champion reissue complete rebuild

[Mikante]

I am starting a new thread, here is the schematic with my mods.
I m going to rebuild this amp using the same power transformer and schematic design with a very few modification.
Cabinet will be bren new and hosting a 10 inch speaker.
Every step along the way i will be adding photos

C960E076-ABEF-45E6-AAC8-070A77C0ECC0.jpeg

I m just adding two switches and replacing r10 resistor with a 680r but here, i need your advice, there are many threads that i have read about the power tube bias, running crazy hot with the stock values.
I have no way to check that, the amp is dismounted right now, not to mention that it wasn’t working anymore.

[thetragichero]

first stage cathode bypass cap you'll get a lot more mileage from farther apart values.... something like 220-470nf, 1uf, 25uf. your values are a little close for much audible difference. attach the small value directly to the cathode resistor and have your switch short a larger value resistor (47k, 100k?) between the cap's negative end and ground for the 1uf and 25uf. this should avoid (or at least minimize) the switch making a loud pop when switching between cathode bypass caps

[thetragichero]

for your power tube bias, best thing to do is measure and do the maths (or enter into a calculator like on robinette's site) and see. 100% or so bias is okay here

if you don't mind throwing an extra couple of dollars into it (and if it will fit), adding a pi filter (cap + choke) before your first power supply node is the single best thing one can add to a single ended amp. MUCH cleaner power going to your output tube plate. the deluxe reverb-style chokes (50ma 4H) should work great here for about ten bucks (mojotone has them cheapest now that you can no longer get the magnetic components versions)

[martin manning]

Extra filtering was suggested a couple of times in the original thread. CLC is great, but there may be a need to reduce the voltage a bit, so adding some resistance might be an option. I notice that in the proposed schematic there is no reservoir capacitor (?).

[Mikante]

first stage cathode bypass cap you'll get a lot more mileage from farther apart values.... something like 220-470nf, 1uf, 25uf. your values are a little close for much audible difference. attach the small value directly to the cathode resistor and have your switch short a larger value resistor (47k, 100k?) between the cap's negative end and ground for the 1uf and 25uf. this should avoid (or at least minimize) the switch making a loud pop when switching between cathode bypass caps

I din t know that, thank you, i never had a switch there, i was just replacing caps one by one and hear the results.
About the values, it is just meant for fine tuning, my first mod was to replace the stock 22uf with a 10uf and i really could hear the difference. I din t like it very much to be honest, it sounded a lot like a fixed position on a wha wha pedal.
I can t immagine a 4.7uf to be any better. My first choice was 22, 4,7, 0,1uf but i need to work on that and the values i added on the schematic are just a number right now.
Anyway thank you for the advice, i didn t know it was going to pop when switching between values.

for your power tube bias, best thing to do is measure and do the maths (or enter into a calculator like on robinette's site) and see. 100% or so bias is okay here

if you don't mind throwing an extra couple of Euros into it (and if it will fit), adding a pi filter (cap + choke) before your first power supply node is the single best thing one can add to a single ended amp. MUCH cleaner power going to your output tube plate. the deluxe reverb-style chokes (50ma 4H) should work great here for about ten bucks (mojotone has them cheapest now that you can no longer get the magnetic components versions)

Many have already tested the plate current on the stock circuit, i still don t know enough to start testing the amp with the power on.
Anyway, the result are over 17watt of plate current, not ideal as far as i can tell.

Extra filtering was suggested a couple of times in the original thread. CLC is great, but there may be a need to reduce the voltage a bit, so adding some resistance might be an option. I notice that in the proposed schematic there is no reservoir capacitor (?).

Adding a choke is not a problem of money, more a problem for me because i need to understand how to make it a part of this circuit when i know so little and i am still trying to figure out the basic staff

[brewdude]

Do you have multi-meter?
You will need one.

[thetragichero]

Adding a choke is not a problem of money, more a problem for me because i need to understand how to make it a part of this circuit when i know so little and i am still trying to figure out the basic staff

so why a lot of guitar amps use a choke instead of a resistor is because it filters as well as a much larger resistor without dropping much voltage. in a push pull amp, this means the voltage on the screens is higher which generally results in more output. in a single-ended amp, which doesn't have the common mode rejection of a push pull amp, it provides much better filtered dc without significantly changing the operating point

[ChopSauce]

Extra filtering was suggested a couple of times in the original thread. CLC is great, but there may be a need to reduce the voltage a bit, so adding some resistance might be an option.

That ...

Also I do write that YOU sketch (the whole circuit, on your own, so that you're forced to consider every single part of it.)

I don't believe that you should start messing with an existing circuit if you don't already know what your doing.

(Almost) just forget about the 600 RI and acts as if you just already have transformers and tubes for building a 5F1 - roughly.

There are so many resources about this simple circuit that you shouldn't have much left to ask about it here.

[Mikante]

Extra filtering was suggested a couple of times in the original thread. CLC is great, but there may be a need to reduce the voltage a bit, so adding some resistance might be an option.

That ...

Also I do write that YOU sketch (the whole circuit, on your own, so that you're forced to consider every single part of it.)

I don't believe that you should start messing with an existing circuit if you don't already know what your doing.

(Almost) just forget about the 600 RI and acts as if you just already have transformers and tubes for building a 5F1 - roughly.

There are so many resources about this simple circuit that you shouldn't have much left to ask about it here.

I agree with you but i m not going to modify the design of the circuit,
I m just trying to improve it a little bit without as i just said, changing it.
I m considering every step of the build and circuit from my experience, and i am here to learn and fully understand each one of those steps.
That is the meaning of this thread and i would otherwise agree with you if this was merely about the 5f1 champ

Do you have multi-meter?
You will need one.

Course i do, a good one, i can test every thing except valves.

@thetragichero
About adding a Choke,
Would you palce it right after b+? Just the choke?
I have read opposite opinions about voltage dropping, some says that it is the opposite, apart from the benefit of a better dc signal.

[thetragichero]

so go power transformer -> rectifier -> electro cap -> choke -> electro cap. you'll connect this last electro cap to the output transformer, and then continue with your RC filter string for the rest of the power supply nodes

[Mikante]

Thank you, i ll try to edit the schematic with this choke if i decide to have it.
I have seen the deluxe reverb type of choke is ok for the task, i m saying this because is the only one i found on my supplier shop.
What elocrtolitic cap value would you use?

[Craig B]

Yup, I find that a CLC filter is necessary for all single ended amps when using a speaker with any bass response at all. Using only a capacitor for B+ filtering makes too much ripple (hum).
Some deluxe reverb chokes are only rated for 40ma. If I was going to drive this amp HARD I would opt for the larger Fender choke (90ma) that is used on the screens of the 6L6 amps.

[Mikante]

Yup, I find that a CLC filter is necessary for all single ended amps when using a speaker with any bass response at all. Using only a capacitor for B+ filtering makes too much ripple (hum).
Some deluxe reverb chokes are only rated for 40ma. If I was going to drive this amp HARD I would opt for the larger Fender choke (90ma) that is used on the screens of the 6L6 amps.

Hello, isn t that a little too much for a small 5 watt amp with only two tubes?
The one i m about to buy is rated 50ma.

[martin manning]

50 mA is plenty. The '57 Champ schematic shows HV supply current at less than 35 mA.

[Mikante]

The difference in price is minimal, but i also thought 50ma was enough.
It is the only upgrade apart from better components.