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Then I would try a 12AY7. I have a read (somebody please correct me if I'm wrong, I'm not an expert on this), that a 12AU7 is a high current tube and may not always be a good choice. I have used 12AY7s in place of 12AX7s and they work fine. Just lower output.

The reverb driver for that amp should be a 12AT7 in V4, and 12AX7 in V6. Check and see if that is what is installed in your amp. See page 28 of the manual... https://mesa-boogie.imgix.net/070653-CaliforniaTweed220_241024.pdf

Video!

Welcome to the forum. What a great find! Congrats!

Physicist here. When someone says "this effect exists!", the question to ask is not only "is the effect real?" but also "under what conditions is the effect size large enough for us to care?" Yes, humidity affects sound. High humidity air conducts sound better than lower humidity air, contrary...

It's not that hard. Here we'd start from the reverb return jack and look for the J175 next to the 5532 op amp. They're probably all right next to each other. In other words, you'd be looking for the sticky-upy black thing with three legs next to a lying down flat black rectangle with 8 legs...

I'd first look at replacing the J175 transistor at the end of the reverb circuit. If that's faulty the circuit is permanently muted.

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"Although these are not frequency response curves, which I can't say I've seen for a discrete electronic device" That's what I said. If there was any meaningful fundamental difference in frequency response between types or brands of tubes, it would have been published. That has never been the case.

I agree. Example from personal experience: I changed a JJ ECC83S in V1 for a Mesa Branded 12AY7. That's both different brand and different type of tube. Should be a clear difference, right? If I set the gain on the amp to get the same total output and distortion, nobody can tell the difference...

Facing the back of the amplifier, it's the one on the LEFT. Thanks for reminding me to change them around. (I like to make sure that one tube doesn't get all the 5 W workload. Will it make any real difference to tube life? Maybe not, but it makes me feel better).

V2a/b -> Gain -> Tone -> V1b/a -> V3a -> master - contour - loop -> V3b -> V4 (PI) -> Power amp V5 is reverb drive and recovery. Google search will find schematic quickly

Yes. See first post. HoF has the worst spring reverb sound of any pedal in its price range, IMHO. Starting with v3 of the toneprint app each subsequent update of theapps got worse and worse, by v4 it was sometimes unusable and then (in 2020) it refused to recognise my Alter Ego pedal (they...

Impossible to say without the amp in front of me. It could be caused by one tube or two or four, or it could be no tubes. Tubes (that are working correctly) don't change the basic character of the amp. That's the circuit and the speaker. When were the tubes last changed?

Guitar magazines are all but dead in the water (except to a few die hard boomers and gen Xers) and they have been replaced by YouTube for quite some time now as people's primary means of learning about new gear.

The J175s are prone to crapping out in Mesa's. They are often used for muting parts of the circuit, e.g. the reverb and contour, and for fast temporary muting when switching channels. The contour on my amps wasn't working when I got it initially and replacing the J175s solved the problem. As I...

No, it's not the tubes, and the tanks tests fine, the cable is fine, and I've replaced the switching transistors, I'm really deep diving the circuit now here but without another Express amp to test against I still have a nagging doubt that maybe it's actually working as designed! :D I have an...

Thank you all for your thoughts. I really appreciate it. If there are any more, please keep them coming! Thanks for this, it seems to confirm that I have a fault somewhere to chase down? Dialing in "just a touch" is not possible, here because the lowest settings destroy the base tone of the...

A question for owners of other Mesa amps in addition to the Express: How does the Express series compare sonically to other Mesa models? Or even any other well-known benchmark amplifiers? What are the Express series unique characters? Personally (having little experience with other Mesa amps)...

Not normal. Possibly a microphonic tube.