Build Your Own Clone Message Board

Since a few of us have one on the way, let's start throwing out some mods to this fine little circuit.

I've had a stock 5E1 homebuild for ages, so I plan on modding this one.

One simple mod off the top of my head is putting C1 on a switch. C1 is a cathode bypass cap and it adds gain. With C1 out of the circuit, you get more headroom, less gain, and it basically turns the circuit from a 5E1 to a 5F1. You put the switch between the positive side of C1 and the turret that connects C1, R4, and the brown wire.

Feedback mod - R10 is the negative feedback resistor. Changing the value or subbing it with a pot basically makes a presence control. Removing it with a switch turns the amp into an unstable little fire-breather!

Input cap - these things can be pretty bassy/woofy. Knocking down the first coupling cap (C2) helps filter out some of the lows.



Keep 'em coming!

I'm pretty sure you're going to need to add an additional resistor across the switch to keep the amp from popping when you switch this cap in/out. I would start with something about 10x the size of R4 (the V1 cathode resistor), so between 15k and 22k. The idea is to get a resistor that is large enough to not mess with biasing the triode but small enough to provide adequate pull-up of the cap.

Yep - done that one before and it popped like the dickens. Forgot about that. I think I killed it with a 100k pulldown.

Does the kit have a screen resistor? I play my champ at 10 with an overdrive pedal hitting the front with over 3V. I was killing nice JAN 6V6 tubes before I put in the screen resistor. Doesn't affect the tone (to me).

Nope. 470r?

I used 1k 5W. The best way to do it seems to be to move the wire from pin4 to the unused pin6 of the 6V6, then put the 1k 5W resistor from pin6 to pin4. This will really help your tube if you're overdriving it at all.

Shielded cable from input. Put a screen resistor on my homemade champ too. 3k 1w. I think at these currents 1w is about as high as you need (including bias resistor). I wouldn't quote myself on that but Kevin O'Connor seems to think so seeing as my build was based off his layout. I suppose it doesn't hurt to go with bigger wattage.

You mention taking the cathode cap out but you could also put it on an on/off/on switch and go between say 25uf - unbypassed and 470n. I have these on both triodes on my champ and it sounds awesome. Pops are fine by me. It's not like I'm switching it mid song.

+1

Yup I do the shielded input jack cable too. If it doesn't come in the kit you can just wrap/braid a solid core wire around the input jack wire and connect only one end to ground.

Replacing C2 and C3 is the 2nd most important mod for a Champ IMHO. The numbers on the volume go to 12. It starts to fart out at about 9 with C2 and C3 stock. It doesn't get any louder, just flubbier. More distortion, but not in a good way.

But the most important mod, IMHO, for a champ is to not use an 8" speaker. I suppose it's part of what makes a Champ a Champ, and running it through anything else doesn't really make it a Champ, but holy mackerel, it sounds so good through a 2 x 12! And if you mod C2 and C3, the improved bass response of the larger diameter speaker is nice too.

What values for C2 and C3? I've noticed this behavior on my other diy champ. That one runs through a single 10" and sounds really good.

I was thinking about exactly this, because I've never been too impressed with the 8" speaker in my Epi Valve Jr., even after upgrading to a Jensen from the stock cheapo speaker. Bottom-line is that you're just fighting physics with a speaker that small, and that's a fight you can't win. I'd rather have something that really sounded good than something that was "vintage-correct".

An option that I spotted on that Marsh Amps site that sells the Champ tweed cabinet is that they offer an upgrade to a 10" speaker baffle for an additional $40. Granted, you're up to $185 for the cab and you still need to buy a speaker for it, so you'd be looking at a total investment upwards of $575 for a finished 10" Champlifier combo by going this route. I'm guessing that it would sound pretty damned good, though!

C2 and C3 are the coupling caps after the preamp stages. Their stock value is 0.022uf, which is a pretty standard value for alot of amps. Having never played a Champ (not really my thing), I have not experienced what Keith is talking about, however, from an amp building background, "flabbier" means "too much bass", which means these values are too large. 0.015 or 0.01u would be moving in the right direction to reduce bass, but I do not have a good "scale" on where you would want to end up. In an amp forum I'm a mod at, the saying "season to taste" is commonly used for picking coupling cap sizes.

Note the voltage ratings on these caps! (for the uninitiated, I know you'll know this Marsh) They will be 400v parts at minimum (the original Fender schematic calls for 600v parts, 630v is a common modern equivalent). Do not take your standard stompbox fare film caps (generally rated at 63 to 100v) and substitute them out even for testing, you will blow them up.

That is a possibility. Having never played with these values on this amp, I defer any sonic evaluations to someone else. I have a feeling I'm going to be building one of these soon

An option would be to rig up a switchable cap setup with a pair of the stock 0.022uf's and a pair of 0.01's (or whatever the optimum value would be). This is obviously a lot more work and would be a true modification to the amp rather than a simple cap substitution. You'd basically end up with a "loose/tight" switch for the bass response and could switch to the "tight" setting when really cranking the amp. Whether or not it would really be all that useful, I don't know--would defer to Keith's judgment on that. His comments seem to indicate that the straight cap substitution is the preferred route, but I don't want to put words in the Boss's mouth!

It's always good to remind us about this stuff! Lots of folks at different levels of experience are reading so it's a good idea to take every occassion to educate.

And thanks for the info on the caps!

I think the handwired Fender champ is like $999. You can't compare these with the Champion 600. The Champion 600 sounds awesome, my friend has one, but it's all made in China inexpensive parts inside. My other friend has a Fender 65 reissue Twin reverb that has solder joints breaking multiple times per year it's ridiculous.

That's a very good suggestion. Depending on how you do it, the pop problem comes back (assuming it bugs you), and you have to be careful about which side of the cap you switch (one end of it is at several hundred volts DC). A thread popped up on another forum I frequent which gives some solutions to doing this: http://music-electronics-forum.com/t27476/#post238612

What's not noted on that post is the external connections; the plate of the preamp tube would be connected on the left, the output (gain knob, grid of next tube, whatever), is on the right. Basically the same signal flow as on most audio schematics (input on the left, output on the right).

One way to "subltely" improve bass response is upping the filter capacitance. 22uf across the board would be a good start.

Remember, they added a 10" to the champ line back in the day and called it a "SuperChamp". I believe a true superchamp also has a 2nd 6v6 in it though...
-P

If the heater current is high enough you can swap a bigger bottle tube in the power section. 6l6 el34, etc....

What is the heater amperage Keith?

I built a 5F2-A which isn't all that different and highly recommend a switch to toggle the negative feedback in or out. Goes from pretty tame to all wild and crazy.

According to the pics on the main page, the PT is a Magnetic Components 40-18019, which has 2 amps of 5v for the rectifier and 2 amps of 6.3v for everything else. Can the iron actually support a 6L6 in Class A at those voltages? Most of the stuff I'm finding online about putting 6L6s in a 5F1 start with "change the transformers"; data sheets and other Class A 6L6 designs seem to support this, but I've not personally sat down and done the load lines and don't have similar iron to experiment with.