Champ Reverb Build

[Craig B]

The negative feedback plan needs more thought. Connecting it to V1b means that all of the reverb circuit is in the loop! V3b is a more logical connecting point but would require splitting the cathodes on V3 and adding a 47ohm tail like the Princeton Reverb has.

[bryankloos]

Thanks Craig.

That was going to be my next question, as I was looking last night and thought that the NFP may be better placed on the final stage before the output tube.
Thanks for the info. I'll look at the PR and then make some changes to the schematic accordingly.
I appreciate the help!

[JGK]

Finished mine love it will try to do some sound clips. But it is really a nice versatile amp. It came out a bit bigger than I planned but it has a full sized reverb tank, upgraded transformers and a 10" Celestion gold. I built the cab big enough for a 12 inch speaker also.

[bryankloos]

Very nice!!!

[bryankloos]

I've updated the schematic to account for NFB at V3b, and I've added in the SS rectification option.

I'm hopeful to get the layout hand drawn in the next few days.

Does anyone see any issue with the schematic before I proceed? I think it should make sound...

[Craig B]

https://el34world.com/Forum/index.php?topic=15254.0

The Kaligstro post in the above link shows the EC VibroChamp schematic which uses a 2.2k resistor with a 47 ohm tail resistor for the feedback circuit. The 27k value in the original circuit gives the proper amount of feedback when connecting directly to the cathode.

[bryankloos]

Good call. I wouldn't have noticed that change in NFB value.

What do you think about the filter cap values in the PS?
I"m trying to keep the first cap low enough for the valve rectifier, but want some reservoir capacity hence the second larger value at Node A.

Thanks!

Bryan

[Craig B]

My very unscientific opinion is that 22uf is sufficient.
I used the CLC that you have adopted and found it gave me great hum rejection and 22uf gave me sufficient reservoir for a 5881 power tube.

I have removed standby switches from my builds after reading assessments by real experts here.

You may find that your B+ voltage is higher than you wish. A 5R4GYB rectifier dropped mine by 23 volts compared to a 5AR4. 5Y3GT dropped it by 29 volts compared to 5AR4.

[telentubes]

JGK,
That's one fine looking cab. The one it's stacked on ain't bad either.

[bryankloos]

Hey Fellas,

Hope you are all well.

Would anyone care to suggest operating points for the 6CA7/EL34 and the 6L6?
I'll have switchable bias resistors for 6CA7/EL34 and the 6L6, but looking at the tube data it seems they don't like to operate at similar plate voltages.
The reason I ask is that I'm trying to "guestimate" dropping resistor values and wattages as my layout is going to be tight.
I need to play around some more with PSUD2 but figured I'd ask where people find the sweet-spot for these tubes..

Many Thanks

Bryan

[bryankloos]

Here is the most recent schematic and PSUD sim.

I've probably made a bunch of incorrect assumptions on PSUD...

Thoughts?

[JGK]

JGK,
That's one fine looking cab. The one it's stacked on ain't bad either.

Thanks. The one below is a started life as a 6V6 Plexi but I ended up running EL34 in it. Sounds fantastic. I have a switch to cascade the 2 channels and PPIMV to tame it. The smaller output tranny saturates nicely. Its pretty much my gigging amp.

[JGK]

Hey Fellas,

Hope you are all well.

Would anyone care to suggest operating points for the 6CA7/EL34 and the 6L6?
I'll have switchable bias resistors for 6CA7/EL34 and the 6L6, but looking at the tube data it seems they don't like to operate at similar plate voltages.
The reason I ask is that I'm trying to "guestimate" dropping resistor values and wattages as my layout is going to be tight.
I need to play around some more with PSUD2 but figured I'd ask where people find the sweet-spot for these tubes..

Many Thanks

Bryan

I ended up with a 10Watt 400ohm bias resistor with a 100uf/100 volt cap I have tried a 6L6 in it liked the EL34 sound better all a matter of taste. I am running a Copper Cap SS rectifier. It's biased fairly hot but I'm not seeing any problems.

[Craig B]

That 22k negative feedback resistor is to big to allow much negative feedback. You could get a cleaner sound (if you wish) bu using the 2.7k value from the vibrochamp or princeton reverb circuit.

[bryankloos]

Thanks Craig,

I made that adjustment to the schematic, as I was reminded the 22K is way too high.
I'm going to play with 2-5K and see what works best in the amp.

I appreciate the "eyes" on the design.

I'm hopeful it will work when I'm finished...???

BK