Recent content by wagdog

That’s the one of the beautiful things about music; soundscapes that don’t do much for one person can make amazing music in the hands of another. In my case those single ended tones just don’t do much for me, hence I don’t use them. I’ve built single ended amps, and while they sound like...

@rolandibus - those are some interesting values your seeing on the cathodes as well as some very different idle bias values as a result. I agree that separate thread might get you some input on it. I’m sorry I’m not more help!

I’m admittedly not 100% certain of the SE operation going on in the express, but it would appear that none to very little current is going through the disconnected tube. This would result in abnormal wear on a pair of tubes as the operational tube would wear out faster over time. Both tubes have...

When you switch to 5w mode, the power amp circuit is changed from being a push-pull fixed bias configuration, into a single-ended (SE) cathode biased configuration (sort of, as I would have expected the B+ to start at the opposite end of the OT in SE configuration and it looks like it still...

I’m very happy with it. I ended up running the current set of EL84s a bit over 70%, but well under where they were at. I generally run my 6L6 amps a bit cold, but have found el84s do sound best a touch over 70%. Nowhere near where MESA had them set though. Good luck - be safe!

Here is the last video in the series in which the bias pot is installed. It's long. This is a schematic of the final version of the mod as well:

I went back in and added a wire between the unused bottom leg of the pot and wiper as suggested above. Although I’m still editing the video (coming soon!), in it, I biased the tubes a little cold. I played it that way for a bit and decided to bring them up a hair hotter. Not nearly as much as...

Gotcha. FWIW, I’m not engineer by any stretch either. I have been working on amps for quite a few years though (20?), and haven’t catastrophically modded anything, yet. My take on the reference to ground for the 55v secondary (bias supply) is that it is through the red/ylw wire, which is the...

Thanks for that, I may do just that. My thought is if the pot fails (wiper disconnects for example), the bias will receive max negative bias voltage as there won’t be any current going to ground through the pot and 7.5k resistor This would effectively shutdown the output tubes, but I don’t...

Hey all, In the video below, I explain the bias mod I'm going to do. The next video will have the mod as I performed it.

I uploaded a video demonstrating how overbiased my MESA Express 5.25 is. In the video, I use a set of unopened MESA EL84s I purchased last week. I got a bit long-winded in the video - the actual measurement of the tubes starts about 8:30. I'm going to shoot a video of installing the mod at some...

@wildschwein - I haven’t modded the amp yet. I confirmed the values of the three resistors in the bias circuit and they are spot on. What I haven’t done is check the voltages in the bias circuit while the amp is running. I’ll do that before I change anything. When I spoke with MESA back in 2013...

Greetings all, I've been using my Express 5:25 for just over 10 years. It was a floor model at guitar center when I bought it (they were blowing them out), so after a few months of use, I ordered new MESA brand power tubes from Sweetwater. The first set redplated fairly quickly, and Sweetwater...