EVH 5150 III 50W: Microphonic Tubes

[programci_84]

Hi all.

First post! Searched the forum of course, but couldn't find anything.

I also e-mailed to H. Kaplan but you guys may help me as well.

I've an EVH 5150 III 50W head and it's approx 1 month old. I've two questions about it:

1) I accidentally plugged a 16 ohm speaker in while the amp's impedance selector was at 4 ohm. I played it about 30-40 mins at very low volume (approx %5-%8). Then I switched the amp off. Plugged an 8 ohm speaker in while the impedance selector at the same position and the volume at the same level. Switched the amp on. Played about 30 mins. The day after I've learned that plugging higher impedance loads in can damage output transformer (OT). Now I'm using my amp with matched impedances, sounds good but I still worry about the OT. How can I determine a damaged OT? How does it sound like or how does the problem show itself?

2) The most important question, about microphonic V1 and V2 tubes: You know what is a microphonic tube
I removed the front grill, removed all the preamps' shields, powered the amp on /w cabinet connected, waited for the tubes to warm up, plugged my headphones in.
- Activated ch2 with full gain and volume. Tapped on V1 and V2 with a pencil, then I heard a sound from my headphones. But I didn't hear any sound with the other tubes.
- Activated ch3 with full gain and volume. Tapped on V1 and V2 with a pencil.. Same thing, same glass-like sound. And the others didn't make any sound again.
- Exchanged V1 with V4, but no go. Exchanged other tubes with V1 but all the ones plugged in V1's socket produced the same microphonic effect even if they were not microphonic on their original positions. V2 does the same thing as well.
- I asked my friend to try the same thing. He tried and saw the same microphonic effect.
- Spec sheet says that all the 12AX7s are JJ. But I couldn't see any logo, print etc. on the tubes.


Is this normal about the tubes? Should I replace 'em?

Thanks in advance.

 

[Viesczy]

The build quality on the 5150 III 50 is pretty robust, I wouldn't imagine plugging in a 16 ohm cab while the selector was on 4 ohm or 8 ohm will be a worry as that typically is a safe mismatch. If it is, I'm sending mine back to Sweetwater. You'd be more apt to fry your amp if you had the selector on 16 ohm and plugged 4 ohm in.

What you should've noticed was that when you had your 16 ohm cab with the mismatched loads it didn't sound nearly as good as when you had all matched up.

As far as your tubes and the noise, all my amps'll have a reaction to the pre getting attention like that. Nature of them really, I've always seen, well heard, microphonic tubes manifest themselves as whistling/whining & not the tap test.

I had a Peavey Ultra Gain Triumph 60 watt combo (heavy as an anchor & loud as a nuclear explosion) that devoured pre-amp tubes, within 6 months they'd be whistling/whining. I still have that boat achor too, she like 25 years old now! She has a fuse or a power tube going as I get light but no sound & the footswitch in is toast. I should get that fixed, despite how loud she was, there were some quality tones to be had in that girl.

Derek

 

[nwright]

I had 4 stock microphonic jj's in my 100 watt when I bought it, but all of my 50 watts per tubes are fine. The microphonic effect was always most exaggerated in v1. Mine were so bad I could tap the input jack and make it ring.