Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: bigdaddy on April 08, 2010, 01:28:10 pm
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Since it seems so many people are into these small low wattage SE amps I figured I would start a thread about them.
I was wondering as I am guessing so many others are too what y'alls favorite champ mod is or are. I'm sure everybody has something special they do. I thought that having an open thread would condense so many of the ideas from people here. Also answer any questions about them.
This would include those Epiphone and Blackheart amps too since they are just champ amps.
I would also love to see anything from other amps like this new Marshall 5 watter. Also the Hi Watt Custom 7 and some other amps from bootek companies. If anybody has a schematic for any of them that would be great too. I am hoping for a good response to this thread........
I have visited some other places like AX84 and SEwatt web sites and for the most part this forum is superior in every way. I will list any of mine also as space to write here is limited.
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Negative feedback switch
I've got a 5E3 tone stack that switchable/off to the original Champ raw sound.
I put a standby switch in everything
I've got a little hotter PT where I can use a 6L6
I recently took out my triode switch and converted it to another preamp cathode bypas cap option.
I also got a plug in SS rectifier.
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I've got the early 70's silverface model.
I use it in my shop a lot so I added a loop (between the volume and the second gain stage).
And a line out.
The amp is stock (minus the repaired parts).
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I built mine so I don't suppose you'd call it mods, but...
I wanted mine for practice. It's loud enough but I can't get quite enough clean volume to compete with the drummer, bass, other guitar. It has an SS rectifier and a 6L6. Volume, treble, mid bass, and master. Sometime in the next couple weeks, I'm going to use the empty socket that originally held a 5AR4 to add a second 6L6 in parallel. Since it actually has a 15 watt OT (my original design was a 6V6 and EL84 in paralllel), it should be fine... and hopefully just a bit louder.
Dave
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Since it actually has a 15 watt OT (my original design was a 6V6 and EL84 in paralllel), it should be fine... and hopefully just a bit louder.
I'm using a Hammond 125ESE (15w) in one of my 2x5881 builds & it works great. The extra power of the parallel power tube should get you where you want to be.
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Here's an idea I've been tinkering with. I'm sure the gain on the stages would have to be tweaked, and I'd be tempted to add a master volume as well, but other than that... should be good to go. I was thinking that it would be a good fit for a Deluxe style cab with a 12" speaker.
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My favourite Champ mod is to make it into a Tweed Princeton and use two power tubes in parallel with bigger transformers.
I built one a while back in a Bandmaster three ten tweed cabinet and it sounded absolutely stellar.
I used a Hammond 272HX PT and a 125FSE OT.
It sounds best with a pair or KT66's.Three alnico Weber 10's.
You can hear sound clips on my website in the 'custom builds' section.It was recorded using a Les Paul with 490T humbuckers.
It sounds like a much bigger amp and the transition from it's considerable clean headroom(compared to a champ) to fluid overdrive is seamless.The guy I sold it to uses it as his main amp.All the clips are on the neck pickup.It sounded so fat,we recorded it that way.
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Well for me it depends on whether you're building from scratch, it's a hacked up champ amp from the 70's or a pristine blackface.
I'll go with the hacked up 70's because I see more of them, this I guess would go for those musicmaster bass amps too to some degree. Those are cool.
The first thing I would do is take out the second input, replace the grid resistor with a 33k. Remove the 15K resistor on the bass control and add a 25KL pot into the empty hole with a small knob like the early 60's fender ones. David Allen has some nice black ones for $2. This makes a world of difference with tone and the ability to have some flexibility, much better. Next I would either remove or add a switch to defeat the NFB. That for me was a big change since I do crank these things. Next is the cathode bypass cap and resistor there. For me I use anything from an 820 ohm to a 2.7K and a .68 to the 25mfd cap, that's to taste and whether or not you have retained the NFB. In my opinion for a BF/SF Champ the voltages on the plates should be somewhere between 180-200. But that really depends on whether it's a Fender champ or a clone of some kind. On some of my clones I go higher depending on many factors. As for the first stage I keep the 1.5K/25mfd combination because I have found with some preamp tubes lowering the cap value creates noise, this was substantiated by a well known Fender amp guy.
My next post I will go into tubes and the power supply. There's really no more room to post anything here.