Build Your Own Clone Message Board

A 6l6 needs 900mA of heater current. A 12ax7 needs 300ma. That adds up to 1.2A. Seems to be well within spec.
An el34 needs 1A5, so with the 12ax7 this adds up to 1A8. Pushing the envelope a bit.
Of course this generates more heat so keep on eye on things but if there's 2A there could be some octal experimenting.

This wouldn't allow for 6550 or kt88.

I sit corrected:
6550; 1A6

I think the OT's rating of 50mADC through the primary winding might be the limiting factor...?

Good question. Exceeds my knowledge.
From my readings from TUT3 as long as the PT has enough heater current then the amp should be OK. It won't produce more wattage or power just more heat and a different tone. I may be missing something though.

.01mfd is a good choice.

Yes, you certainly don't want to use a 63v or 100v. If you use the .01mfd version of the .022mfd Mallory (now Cornell Dublier) that comes with the kit, you will have to use 630v because that model doesn't come any smaller than. However, that point is only 200v, so you'd be ok with a 250v if it's all you can find. But if you have your choice, go for the larger voltage rating.

Yes. A definite posiblity. Maybe you will like the stock values better. Personally, I don't find the bass loss noticeable. And if there is, I guess it's compensated by the larger diameter speakers that I prefer. But I think more important is the fact that the whole point of the champ, for most people, is that you can dime (or would it be dozen in this case) it and not rip your face off.

I only play my Champlifier dozened!

Well...no. You can't do that. The heater windings are 6.3vac @ 2amps. So, yes, the heater is ok to use the big boys. But you cannot use something bigger because the OT is only rated for 6w. Maybe if you drastically changed the bias. I dunno. As it is in Class A, an EL34 would put out about 10 or 11 watts. So you'd need a bigger OT.

Oops. Double post. Right. What he said.

Yes, the PT is just fine. It's the OT that you need to change. Your options are pretty limited with single ended transformers. Magnetic Components makes a 15w single ended and Hammond makes one (see the AX84 project for a part #). I'm sure there's a couple others, but I'm not familiar with them.

The 15w transformer can handle 70ma.

+1 on moving the wire from pin 4 to pin 6 and then running your screen resistor across 4 and 6. This is how you see most screen resistors in point-to-point amps.

I haven't tried this mod to a champ, but looking at the screen resistor(s) on most fender amps, it's a 470/1watt resistor.

Did you read this Keith?

Had to satisfy my curiosity and checked the differences between the OT that O'Connor recommends in his builds (and the one that I used in mine) and the Classictone ones. The one I have is Hammonds 125c rated @ 8W and 60maDC. The BYOC is rated 5W @50maDC. Big difference? I don't know but why take a chance.


Also, correct me if I'm wrong, but there is another primary wire so I think you could connect this Ultralinear. Basically you'd connect the brown wire to the screen (pin 4)
This is very unverified as this is just a hunch by me but it is certainly something to look into.
It is said that if you take away NFB that connecting the screen UL will sound great. And you could always switch between the two.

That sounds really cool! I'd like to explore that more.

My 5E1 clone has a Hammond OT in it. I probably have about 100 hours running a 6L6 in it with no issues.

Edcor has 25W output transformers: http://www.edcorusa.com/category/68-xse ... wattage=40

Can't help smiling to myself here--traditionally, the key selling point to the Champ is it's low power output and the ability to generate output tube overdrive at volumes that don't make your ears bleed. So naturally, one of the first modifications we talk about is how to pump up the output power!

So how big of an OT am I gonna need to run a KT120 in this thing?

It's not to get more power it's more for tube tasting.


Also it's pretty easy to do a pentode triode switch (harder to do is make a hole in the chassis for it)
Pin 4 is your screen - normally wired it's in pentode - to wire it triode you'd have to share the plate wire (from pin 3)this changes the impedance of the tube and cuts output to half.

I have to say though that I did this to my "Champ" and it was really hummy and I was generally underwhelmed YMMV.

Yep. I like the way a 6L6 distorts better in a Champ. Sounds more like a 'grown up' amp, but at a non-grown up volume.

No. I missed that. Huh? Morgan says he's gonna try it, so I reckon we'll find out.

Oh. Looks like he did already!

Well...I've done it on my old clone with the Hammond OT. I'm going to try it with the BYOC one too just to see how the OT does.

Just to be scientific about it take plate and cathode voltages with both tube types.

Just throwing this out there. The new Fender EC Vibro-Champ is also based on the 5F1 circuit. Has an output tube bias tremolo, "attenuator" switch to reduce output, and a bias pot inside. Controls include On/Off Switch, Attenuator Switch, Volume, Tremolo Speed. Jewel light between power and attenuator switches. Tubes are 6V6, 5Y3, and a pair of 12AX7s. There's also a Tremolo Footswitch Jack.

How viable would it be to add features like these to this Champ clone as a series of mods?? It's understood that there are challenges with the control layout on the chassis, and also the need for another 12AX7 socket and other bits of hardware.

Cheers...
Erik

It's certainly possible. But like you said, the toughest part would be punching another 12ax7 hole into the chassis. You'd also have to use another turret board as you couldn't use the one provided. It would be cool to have an option of no chassis with purchase.