Cracking noise on a Diezel VH4

maB

New member
Hi! First post on the forum!

Recently I bought a used Diezel VH4, it's my very first tube amp, before I was playing only a modelling combo.

When testing the amp beforehand I didn't really notice anything, but at home after a while I noticed that the amp is sometimes producing very loud and noticeable cracking sounds. So I started some troubleshooting and found out that:

  • The cracking sound is mostly appearing when there's a lot of bass in the tone
  • On some notes (around D#, E, F, especially E and A string) it's extremely jarring
  • It's happening on multiple guitars, so it's not the guitar
  • It's happening on both my Marshall 1960ax and my old modelling amp loudspeaker (I modified it with a 6.3mm jack so it can take external input), so it's not the cab
  • It's getting better when I lift the amp from the ground, but the cracking is still produced
  • It's completely gone when I use a 20m cable and put the cab in a completely different room
From these points I conclude that the root of the problem is something in the amp mechanically oscillating from the sound and thus producing the noise. But don't get me wrong, the noise itself is not something mechanic inside the amp but coming from the loudspeaker.

I tried repeating an E (which produces a lot of cracking) with a looper pedal, while carefully touching all the tubes (with a welding glove on, those are hot af :oops:) and trying to 'damp' any oscillation, but that didn't help at all.

Any hints what inside the amp could be producing the noise?

Regarding the tubes: The guy I bought the amp from said he had them replaced recently, but I don't know if there's any way to verify that.

Edit: One thing I forgot to mention, I have the feeling that it's getting less noticeable the longer the amp is turned on. Could it be that the tubes heat up, expand and sit more tightly in their sockets? I'm just completely poking in the dark here.
 
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DragonCrestPC

Well-known member
Most likely a pre-amp or power tube failure/failing. First try softly tapping the tubes with something plastic or wooden like a pencil when the amp is turned on and off stand by ( ready to play). If you hear a tapping sound when the tube is being tapped that's a microphonic tube ( bad tube ). If that doesn't work, replace the power tubes and bias it correctly. If you've never biased a tube amp, take it to a tech. Another thing i've ran into was a dirty tube socket that would cause popping and crackling, which would require using contact cleaner on the sockets when the amp is off obviously.
 

311splawndude

Well-known member
Most likely a pre-amp or power tube failure/failing. First try softly tapping the tubes with something plastic or wooden like a pencil when the amp is turned on and off stand by ( ready to play). If you hear a tapping sound when the tube is being tapped that's a microphonic tube ( bad tube ). If that doesn't work, replace the power tubes and bias it correctly. If you've never biased a tube amp, take it to a tech. Another thing i've ran into was a dirty tube socket that would cause popping and crackling, which would require using contact cleaner on the sockets when the amp is off obviously.
These are all things I would do too to trouble shoot with the follow caveats:

1.) Like DragonCrest said, do the tap test. The tapping you will be listening for would be coming through the speakers. For preamp tube in particular that can be a microphonic preamp tube, although I would suspect it would still do that even with the cab in the other room. Alsways have extra preamp tubes laying around :yes: For power tubes, you could rotate them around (while cleaning their sockets) and see if it changes the results.

2.) If you do get new power tubes and you've never biased an amp and this amp requires biasing I have a tutorial that can help you safely do it yourself if you want to learn.

3.) Using contact cleaner is great. Make sure it is the electronics cleaner version (like Dioxit). Also, I suggest spraying tube pins (or cable tips) vs sockets and jacks. In other words, spray it on the male part and work it in and out of the female part.


Welcome to Rig-Talk :cheers:
 

maB

New member
Okay, I'll try tapping to check for microphonic tubes and cleaning the sockets and will report back.

Another thing I forgot to mention is that the cracking scales with volume, so if I turn up the volume the cracking becomes louder with sound.
Welcome to Rig-Talk :cheers:
Thanks! And thanks for the help :cheers:

Edit:
I did the the tapping with a pencil and it turns out that most tubes (pre and power) give some noise, but one preamp tube (4th one starting from the side of the amp or the center one in the group of 5) gives a crystal clear bell sound when I tap it :(

So I should probably replace all tubes in that thing?

Next to the pre amp tubes there's handwriting saying "7 - 12AX7WB". The attached pic shows the tubes that are actually inside, 6x the left "China" and 1x the "Russia".

I found this set https://www.tubeampdoctor.com/roehrenset-fuer-diezel-vh4-vorstufe containing 6xECC83 and 1x7025 tubes. Are those the same?
Sorry if these are obvious things, it's just the first time me doing this so I have absolutely no clue. Is the Marshall ECC-83 / 55 the same tube?
 

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311splawndude

Well-known member
(NOTE: I am not an EE, Diezel owner, tube amp repair guy, etc etc)

Personally, I would not replace all tubes unless you just have money to burn. Find your culprits, and replace as needed. I'm not sure which one you are talking about specifically but certainly you can start with that one. Assuming you do not have any other preamp tubes to test or swap with I would personally get 3 or 4 preamp tubes for now.

ECC83 / 7025 / 12AX7 = same thing

From there, the letters will tell you a bit more. The combination that TAD laid out there should be fine. I also recommend Dougs Tubes.com. He can provide some recommendations as well. Unless you have money to burn, I wouldn't worry about NOS tubes at the moment. They are crazy expensive. The JAN 5751, that I recommend all the time, has jumped to $80. The TAD tubes seem very reasonable at roughly $23 a pop.

Also, I found this on a quick google search. Go to page 35-38. Also, the biasing method the show for power tubes on page 5 is pretty much for people that have electronics background. If you were to bias yourself, I highly recommend a bias probe (that goes in the socket underneath the actual tube).


Also - we have a Diezel Subforum you can ask in for more info and sure some smarter people than I will come in here and give you further/better info. There are several VH4 variants so I'm just going off a standard VH4 info I'm finding.

V1 will be closest to guitar input jack and V7 will be closest to power tubes (usually)

Tube layouts
VH4:
V1 = input stage for all channels
V2 = channel 4
V3 = channel 2,3,4
V4 = all channels
V5 = mixer and send buffer
V6 = return driver serial and parallel
V7 = phase inverter
 

sahlomonic

Active member
To piggyback on what was said above, I wouldn't necessarily replace all the tubes, but on the other hand it's great insurance to have a full spare set on hand.

Regarding the contact cleaner, you don't have to wait for it to dry. Quick spritz and you can literally plug them in immediately.
 

raiken

Active member
One thing to note: just because a tube is microphonic doesn't necessarily mean you have to throw it away. Microphonic tubes can sometimes live long and productive lives in other tube positions, most notably, in the phase inverter.

You can try swapping tubes around to find the worst and best of the ones you have, as long as they are all the same type. This can be done by swapping them one at a time into the first preamp tube position (usually the most sensitive to microphonics), tapping them, and noting whether it has better or worse microphonics than the one you swapped out.

Put the best one in the first preamp position, the worst one in the phase inverter position, and the others where they work best. If your amp has a tube-buffered effects loop, you will most likely want to use a relatively low microphonics tube to keep the return amplifier stage quiet.

Some amps use a different type of tube for the phase inverter, so you can't swap it. For example, most Fender amps use a 12at7 for the phase inverter. 12at7s are also commonly used in reverb driver circuits, so be sure to exclude them from the 12ax7 microphonics swapping test.
 
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rickenbacker198

Active member
It’s probably the serial effects jacks on the back of the head.
The cab being removed and the issue stopping likely confirms it.
It has some corrosion and is causing the signal to cut in and out.
Had the exact same problem, Exact same advice replace the tubes.
Try cleaning it first.

Save some money and frustration.
 

maB

New member
Thanks everyone for your replies, here's a short update.
  • In my local music store they had a single TAD 12AX7A-C. I tried it in different positions and switching it out for different pre-amp tubes → still there
  • I bought a new set of power tubes → still there
  • I tried to tighten the contact springs on the power tube plugs → still there
Here's a sound file how it sounds like: https://vocaroo.com/1cXIikl1OJEV

It’s probably the serial effects jacks on the back of the head.
The cab being removed and the issue stopping likely confirms it.
It has some corrosion and is causing the signal to cut in and out.
Had the exact same problem, Exact same advice replace the tubes.
Try cleaning it first.

Save some money and frustration.

I took the amp outside of the box, put a guitar loop on the input and carefully tapped (trying not to "ride the lightning") a few wires on and around the PCB and jacks with a wooden pencil. The serial effects jack produced nothing, but some wires of the power tube wiring (between power tubes and PCB) produced the same cracking sound when tapped. That was one reason why I decided to tighten the contact springs of the power tube plugs, I thought maybe they're too loose and there's a loose contact, but tightening did nothing. Another reason why I tried that is I have the feeling that the output volume of the amp is not really consistent and sometimes fluctuates a little, but I'm not sure yet whether that has something to do with the cracking.

What I'm still planning to do
  • Get at least two more new pre-amp tubes and switch a little more, since I know that a few of them are microphonic
  • Check the bias of the power tubes
  • Buy contact cleaner and clean all the tube plug contacts
 
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Wizard of Ozz

Well-known member
+1 on a bad preamp tube. Remember this amp has 7 of them... so that's 7 possible variables to go wrong.

Find one good tested, known to be good preamp tube... tested in another amp... and go thru swapping that known good tube in/out of all 7 spots on the VH4 until you find the offender.

Remember it could also be 1, 2, or 3 of the preamp tubes that are bad too.
 

maB

New member
After experimenting around with another two new preamp tubes and getting no results, I had another look at the wiring and I think I've found the culprit.

When I tap the yellow marked element I get the exact same cracking. In fact even if I tap around the element, e.g. just the PCB, it's also cracking, but it's loudest when I tap the element itself. I guess because it's sticking out so much it can vibrate quite easily. Anyone knows what type of element this is? Either it's broken or the soldering is loose somewhere.

Edit: Maybe it would also make sense to move this thread to the Diezel subforum.
20220514_121519.jpg
20220514_121551.jpg
 
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maB

New member
Hi everyone,

indeed, one of the contacts of this capacitor in the image of my last post was loose. After renewing the soldering the noise is gone! :m17:
Thanks for everyone who tried to help!
Maybe one last question: Can someone with a known stock Diezel VH4 tell me whether the soldering / the setup with the multiple resistors on this capacitor is stock or if some previous owner fiddled with it? Because it looks kind of wild.
 
Hi everyone,

indeed, one of the contacts of this capacitor in the image of my last post was loose. After renewing the soldering the noise is gone! :m17:
Thanks for everyone who tried to help!
Maybe one last question: Can someone with a known stock Diezel VH4 tell me whether the soldering / the setup with the multiple resistors on this capacitor is stock or if some previous owner fiddled with it? Because it looks kind of wild.
Looks stock to me. My VH4 has a very similar wiring like yours. But you can ask Papa Diezel to be sure. Send him an email to peterdiezel (at) diezelamplification (dot) com
 
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