Unwanted noise in Mark IV mode

[sheehanje]

While in the studio I wanted to do a track with Mark IV mode cranked up. I couldn't do it because of a high pitched whistling as both the Output and Channel Master went up. It happens with Output at about 2 o'clock and as the channel master gets to about 1 - 2. Really wanted to saturate the tubes. It's not happening in either of the other modes on Channel 3. I figured it was a preamp tube. I finished the track with Mark IIC+ mode with no issues.

I decided this past week to switch out to EL34's and ordered a complete Mesa Tube set figuring I would retube the whole amp. The merchant offered SPAX7's for $28 more - I went for it seeing it was just $4 more tube and I like to eliminate noise.

Amp sounds great - and the new tubes seemed to clean up a low volume issue I was having on Channels 1+2. But the whistle on Mark IV is not only still there - but if I go even a little higher with the channel master then 1 o'clock it degrades into an awful static/hissing/breaking glass kind of sound. Of course I didn't keep it there long. Maybe this added noise is due to the EL34's?

I did one more test and switched from Pentode to Triode - and I was nervous about going too high (I don't want to damage the amp) - but it seemed to not have the issues in Triode mode. Is this normal?

I've been mostly playing on Extreme Mode - but I'm finding that Mark IV mode seems more fluid to me . Should I just keep it in Triode and call it a day or is there something else lurking that may be wrong with the amp?

 

[Nicklotsaguitars]

A couple of weeks ago, Authorised Boogie told me, on these boards. Use EL34's in variac mode only. So you're not pushing the plate voltages too much I assume.
EL34's generally deal with plate voltage up to 450V. Which is what the MKV is set to. However of the many many Marshalls I've owned and worked on, I haven't seen one with a plate voltage below 465V.
The MKV also biasses EL34 valves quite hot.
Maybe A+B= squeal.
Definitely try variac, if you haven't already. Taking half the equation out of the problem may be the answer.

 

[sheehanje]

I would blame the EL34's but the high pitched whistle was happening with the 6L6's too.

I will try Variac and see if it makes a difference tomorrow.

 

[sheehanje]

A couple of weeks ago, Authorised Boogie told me, on these boards. Use EL34's in variac mode only. So you're not pushing the plate voltages too much I assume.

I tried it in Variac Mode and I don't get the squeal. I also don't get it on full power in Triode mode - I assume because according to the Mark V manual Triode produces less overall power output.

In any case, I've only had the amp 6 months and definitely don't want to damage it - I'm still searching for tones on it.

I really got the EL34's because I thought it would bring out AC/DC type tones in channel 2. I didn't have much luck achieving that tone with the 6L6's. Not that they sounded bad at all, they do sound quite good, but it wasn't giving me that tone.

In any case, I'm still curious to why the squeal is happening with the 6L6's. I'm very new to the world of tube amps. I played solid state for 20+ years. Bought a Blackstar 2 years ago (which even though it's a tube amp it is a world of simplicity compared to the Mark V). It's a totally different world to me. I'm perplexed yet drawn to it...

One last question - running the EL34's in Variac mode - am I losing out on what EL34's should sound like?

 

[Nicklotsaguitars]

No mate, I don't think you're losing the inherent EL34 sound in Variac mode.

I have quite a problem with the sound of kinkless tetrode valve types (KT66,77,88, 6L6,) I find them too shrill in the high end and too unfocused in the lows. It's exactly the problem I hear with my Mark V, exactly the same problem I heard with my 2203KK. I modded that for EL34 and it's a dream amp for me now.
Where EL34's tend to punch and lack the massive low end and icepick highs. I find they bolster the mids enough that those things become easy work rounds. To the point that I'm tempted to say they don't have less of those attributes. But that they're tempered somewhat by a flatter eq curve than KT type valves have.

I'm not ragging on 6L6's at all. They're a wonderful valve. I still haven't swapped to them in my MkV yet. I want them for the clean channel, which is what I bought the amp for. And where they are unbeatable. I just think that when it comes to a percussive, punching driven sound, EL34's are unbeatable.

Using Variac mode strangles the powersupply a little bit, allowing the amp to go into power amp distortion with less volume. Eddie Vanhalen made using an actual Variac power conditioner famous. On his Marshall amp. At live shows, so he could get that fabled 'brown sound' without destroying his audiences ears. Dunno about you but I like loud bands. However I've walked out of a few gigs because things are too loud.
So no, I think the Variac mode thing is a good way to help achieve that Marshall sound. I like the amp on Edge mode with 6L6's, Variac mode. 10watt and the volumes and mids way up. Gives a nice faux Vox sound.

I'm pleased that Variac cured the problem for you in EL34 mode. I've no idea why you are now getting that in 6L6 mode. With how cautious you appear to be about looking after the amp, I can't suppose that you haven't flipped the 6L6/EL34 switch on the back of the amp. But please waylay my fears and tell me that you have. Also that the shielding cans are still on the pre-amp valves.
Aside from that, all I can think is that running amps at max, no matter how good they are, who makes em. Stresses components, There's no getting round that. It's why bands like ACDC have loads of amps on rotation, some on tour, some in storage, some back at the manufacturer getting serviced.
All I can suggest now is that you switch the amp on and do a chopstick test on it. Tap all the valves with a chopstick. Rings pings, pops and zings. You've got a microphonic valve.
Should that produce nothing, get the amp in to be looked at.
I dunno where you are, I'm in the UK. When my footswitch broke I was expecting a month or 6 weeks before I saw it again. Took 3 days to get it sorted. I was utterly amazed at that turnround. It was a fix too, not a replacement.

 

[sheehanje]

I'm pleased that Variac cured the problem for you in EL34 mode. I've no idea why you are now getting that in 6L6 mode. With how cautious you appear to be about looking after the amp, I can't suppose that you haven't flipped the 6L6/EL34 switch on the back of the amp. But please waylay my fears and tell me that you have. Also that the shielding cans are still on the pre-amp valves.
Tap all the valves with a chopstick. Rings pings, pops and zings. You've got a microphonic valve.
Should that produce nothing, get the amp in to be looked at.

I am really liking the Mark V in Variac Mode with the EL34's. Channel 2 is absolutely coming alive and Channel 3 has some really good tone. This weekend I will get to tweak the amp a lot more while I'm off - but it already sounds as good as I thought it should. The SPAX7's seem to have cut down on the noise considerably.

As far as the tubes - I replaced every single one with SPAX7's - so if it happens to be a preamp tube I would have to be really unlucky to replace a bad one with another brand new band one. But it's always a possibility. In any case, I bought the amp in September - so very low mileage on it. A few gigs, some rehearsals, 3 days in the studio. Other than that mostly bedroom playing.

Speaking of backup amps - I need to get another one. I wish I didn't sell the Blackstar - it's no Mesa but it sounded pretty good considering the price. I may look at the Mark 5:35 or possible another Blackstar head.

I live across the pond in New York. Thanks for your responses!

 

[Nicklotsaguitars]

I had a Blackstar HT100. I didn't like it much and managed to straight swap it for a JVM, 2 channel. Were I choosing an amp to compliment my MkV. I think I'd be looking for something the MkV can't do. Which ain't an easy thing to find. Maybe a Mini Rectifier or a Marshall Class 5. Though it can easily get in those ballpark sounds. If you're new'ish to valve amps, take it from someone that has played them for decades. You hit on the absolute real deal with the MkV. I've modern and vintage Marshalls in my cupboard that don't see the light of day these days. Even a 1958 Watkins that was the British equivalent of the Fender Champ back then. All seem a bit redundant to me these days. I'm close on a year owning my MkV. Which is my first Mesa.

If you still have the original valves, it could be worth digging them out. Pre-amp valves rarely break down. They don't wear out anywhere near as quickly as power amp valves do.
You could try swapping individual valves. So you start at V1, swap that for one of the old valves, no change in noise levels. Swap it back to the spax7. And work your way through each valve to v7.

Funny thing about ecc83/12ax7 type valves. If you look in the manual at the valve roles. Where it tells you which valves do what. You'll see V7A and V7B or V3A and V3B. It's because each 12ax7 is actually two valves in one bottle.
One of my favourite amps is an old record player amplifier from the 60's that I converted to run a guitar signal.
It uses two ECL86 valves that are each half 12ax7 and half EL84.

 

[sheehanje]

If you still have the original valves, it could be worth digging them out. Pre-amp valves rarely break down. They don't wear out anywhere near as quickly as power amp valves do.
You could try swapping individual valves. So you start at V1, swap that for one of the old valves, no change in noise levels. Swap it back to the spax7. And work your way through each valve to v7.

I may have found my problem and it was in the manual (on page 8) all along. It says to avoid setting the treble too high when the gain is set high. I backed it off a bit and no problems at all in Mark IV mode.

I still have a lot to learn - but it's sounding really good now. Much to my wife's dismay.

 

[BrownieD2W]

If you still have the original valves, it could be worth digging them out. Pre-amp valves rarely break down. They don't wear out anywhere near as quickly as power amp valves do.
You could try swapping individual valves. So you start at V1, swap that for one of the old valves, no change in noise levels. Swap it back to the spax7. And work your way through each valve to v7.

I may have found my problem and it was in the manual (on page 8) all along. It says to avoid setting the treble too high when the gain is set high. I backed it off a bit and no problems at all in Mark IV mode.

I still have a lot to learn - but it's sounding really good now. Much to my wife's dismay.

It sounded like that was the problem, but since you went straight to swapping tubes I wasn't going to weigh in until I saw this last comment. Setting the Presence, Treble, and Gain to high will almost always force the Mark V into microphonics, and especially on the Mark IV setting with the Bright Switch engaged, something about that is just too much high-end for the preamp to deal with I guess. Also, watch out with the 6600 KHZ slider on the far right of the Graphic EQ, thats Microphonic territory as well is you set it to high. If you need more cut/crunch on the Crunch mode, try boosting the 2khz slider first instead of the 6600khz slider.