My personal cab is actually not a Marshall, as I don't like quad boxes, and the Marshall 2X12 cabs are way overpriced.
It's actually a Traynor YCX212 that I've installed old Celestion 75W in them.
The kicker? It was actually a 4 ohms cab that I rewired to 16 ohms!
Why did I do this? So I can play with two cabs if need be (happens once in a while).

Problem is there are occasions where I may have to use a provided cabinet, and 2 times out of 3, it's a 16 ohm Marshall with no impedance switch. I can't rewire all my friend's cabs.

However, I may have changed my plans... I'll most likely build a combo amp, as it will also make an easy amp to carry to rehearsals, and will provide a spare speaker at the same time.
I'm thinking a single LM3875 into a single 8 ohm Celestion V30 or similar. It's rated at 56W RMS and the V30 has a very high sensitivity, so it will be equivalent to 100W into a single Celestion G12T-75 (what I'm using right now).
I'll leave it sealed to get the maximum output (I hate open back cabs), something that's easier to do with SS as you can still have the heat dissipating part (the heat sink) on the outside without building the amp in a separate part (and end up with a big and heavy combo).

Still undecided about the preamp, and I may experiment a bit. A Thor/Thunderchief sort of circuit with a full tone stack would make for an easy transition from my main amp (a JCM800/Plexi hybrid), but I'm curious about using an LM386 as a preamp. Worst case I'll just use my Marshall Guv'nor pedal to drive the power amp until I settle!

When you say "those LM3886 kits being offered here". Are you referring to Brian's kit?
I've been trying to access his website for the last week and it's offline.
On another board, he keeps saying it should be back within a day or two. I may very much order from him.

Hi, thanks for jumping in!

Thr bridged 4780 solution was appealing because of an inexpensive PCB available on the internet that would make the project a breeze.
But as you say, thermal management would be much more complicated, as confirmed by the calculator provided by National.

So, a pair of bridged 3886 is a better idea considering the higher temperatures that the amp could be subjected to.

I've noticed the TDA7293/94 too, but further reading here and other sites seem to imply the LM serie is a better contender. Also, a pair of 3886 is just the right power point I'm looking for. And there are plenty of sample circuits circulating around, including a ready to print PCB design on GGG.

I've thought about rewiring the cab too, but laws of electricity being what they are, I can only choose between 4 and 16 ohms (2 8ohms driver in parallel or serie). And at 4 ohms, that means paralleling 2 chips, which is not much different from bridging them (except for the lack of a "phase inverter").
If I keep it optimized for 16 ohms, that means I can also use my bandmate's cab if need be. And most Marshall cabs are 16 ohms, so it's a pretty common load.

It would be great though to have the option to run an 8 ohms cab. I understand this is possible but would be safer with a lower voltage (which would make for a less power at 16 ohms).

Seems like I answer my own question
Used the XL sheet provided by National to do the math. With 35W on a bridged 4870 driving a 16ohm load, it works with a 25C ambient temperature (albeit with a huge heatsink), but anything hotter (which is to be expected on stage) and it's beyond the limit of the chip package.

So how easy is it to configure chipamp.com's stereo kit to bridged operation?
I understand that I'll have to provide an inverted signal to one of the amps since it's not exactly possible to configured one as inverting, being fixed in the PCB design.

Could I use a pair of JFET to simulate a tube amp's phase inverter? Sounds like fun...

Sure I can use an op-amp to do it, but where's the fun?

Hello everyone,

First a little background, I've built a few tube amps and my main gigging amp is a 50W Marshall style amp.
I'm currently carrying around a smaller 8W (6K6 power tubes) backup amp, which sounds really fine but it's far from being powerful enough for my needs. Monitoring is often deficient and I need my amp to be loud enough to get a nice stage balance with the drums pounding, not to mention the occasionnal gig where the PA can only provide vocal support.

So my plan is to build (cause i love building!) a SS amp that can rival with the 50W tube amp (which is really about 75W clean!) volume-wise (note that I rarely get to go into power amp overdrive territory). The 2nd part of the problem is that the cabinet is 16 ohm. This is not a problem with a tube amp, but it is with a SS amp.

Now, I discovered this forum and I fell in love with it! After much reading, it seems that cascading a pair of LM3886 with a 35V+/- supply would get me about 100W RMS (200W peak) into 16ohms. To be fair, I used to have a Line6 Flextone XL which had 2 LM3886 (stereo) and found it rather weak, but I'll be using a closed-back cabinet, which helps a lot.

I notice tech-diy.com sells a bridged LM4780 PCB, this would make the power amp build a piece of cake! But extracting this much power from a single chip seems maybe a bit risky. We're talking an amp could be running at full tilt for hours at a time (once played a 4h30 straight gig!). We're talking a big heatsink and probably a fan.

Another option is a stereo LM3886 kit from chipamp.com, then I run them bridged by feeding one an inverted signal and hooking up their outputs appropriately. By having the chips farther appart, or even on separate heatsinks, seems it could run cooler. But I still have the same power to dissipate.

There are also a couple discrete circuits circulating on the internet, but a chip amp seems like a safe birst SS build.

For the PSU, I like Hammond cause they are cheap to me being in Canada, they have a 225VA toro PT that would do a good job. Big fat bridge rectifiers and caps are cheap and plentiful at the local surplus store.

Does that seems like a good plan? Double 3886 or single 4780?

Thanks