Rockerverb 50 MK1 head.............noises (HELP!!!)

[orys]

Hi there!

Bought this off a guy from the UK and had it shipped with Fedex.
It seems to make a rumbling hum noise on a specific note. That is A string 11th fret.
I tried checking the tubes by tapping very lightly on top of the tubes with a chopstick. They seem ok.
If i tap from the sides, it appears that 3 of the 4 6V6 tubes reproduce the noise i am hearing.
Also the V2 12AX7 seemed to be acting like the 3 power tubes and i replaced it with a spare one but noise is still there.
Furthermore, to make things more complicated, probably to me, as i am an newbie in this area, when i tap the head there is noise coming from the speaker. Is this normal? My OR15 is solid when i tap the wood or the front display and does not put out any strange noises when i do this.
If i increase the volume while i tap the RV50 head and the noise is there, the noise will not increase in volume at all.
Same thing when playing the A string on the 11th fret! The noise won't increase but it's there! Not always but at least 60-70 percent of the time i strike that note it comes on!
It's driving me crazy. I opened the amp up to check grounds.
Only one ground point is evident on the right side of the chassis and is most probably ok.
I believed the PPC212 cab was vibrating, which i believe it does, so the head was vibrating, and thus the noise coming out of the speakers.
Most probably the note i'm playing causes the vibration of both the cab and the head and it makes the noise.
I placed towels, foam, pads on the legs here and there but still it is there.
Am I right or is it a bad or many bad tubes?
Where do i start here? Replacing all the tubes, check the ground better, cry? I really love the sound of this amp and i wanna keep it!
I am including a video i recorded as well as a few pics of the board and the tubes.
Another thing to mention is that if i touch the reverb cable coming from the reverb tank when the amp is on, there is a change in the hum pitch, or it starts humming, stops humming, etc.
I am pretty sure the box was probably banged up when in transit.
I don't mind replacing the tubes but i can't find them locally. Found no 6V6s at all.

Thanks in advance for your assistance guys!

Thanks
Tio

Images
http://s6.photobucket.com/user/tb303/library/RV50

Video
https://youtu.be/LPDV3oohP34

[FleshOnGear]

If the sound is constant even when you turn the volume up, that indicates the problem is in the power section of the amp. You probably need to change the 6V6 tubes, maybe also the phase inverter 12AX7. I think the phase inverter is the preamp tube on the right, closest to the 6V6s, if you are looking at the back of the amp.

[orys]

If the sound is constant even when you turn the volume up, that indicates the problem is in the power section of the amp. You probably need to change the 6V6 tubes, maybe also the phase inverter 12AX7. I think the phase inverter is the preamp tube on the right, closest to the 6V6s, if you are looking at the back of the amp.

Hi there!
I've replaced ALL the preamp tubes to no remedy of the problem.
I also found in all sockets just ECC83/12AX7 tubes.
No 12AT7 tubes in reverb and effect loop sockets!
I have therefore replaced them with some old Fender tubes i had and some GT tubes but the noise is still there.
Another question is, when tubes are cold and you shake them, in some you hear a springy sound. Most are dead silent. Would this indicate the ones with something loose inside them are bad?

[orys]

Ok!!!
An update!
IF i put the head on the floor and i play the same notes, now its the E low string fret 14 and/ or A string fret 9, the weird sound stops.
So now i'm thinking the tubes are good and there's vibration coming from the cab passed onto the head and then back through the speaker.
Hmm, how do i go about fixing this?
I am pretty sure that the floor is not straight at all.
It's got this laminate floor which you walk onto and you hear the cracks and your feet sink in.
Also the cab is not solidly sitting on the floor, i know that for sure. Because the floor is by no means flat.
I am thinking sponges on the feet of the head where it sits on the amp and a flat rectangular piece of polystyrene where i'll sink the feet of the cab, although this material is kinds hard and it will not bend on the uneven floor to cover the lower and upper areas effectively.
Any ideas?

[Stu Cazz]

Something similar happens to me when I play at higher volume.
But in my case it is something like sympathetic vibration of windows and furniture.
It disappears when I change the amps location.

[orys]

I personally play at very low volume.
I am sure the vibration is there.
If you watch the video you can understand what i mean.
The noise is like a very low voice growl.

[orys]

Are these tubes right? WTF???
I think most are fecked in there if this is a sign of failure........

https://youtu.be/58Ye_luXFu8

[Phlowen]

Yeah, that sounds like your power tubes have gone microphonic. They'll need to be replaced.

[orys]

Yeah, that sounds like your power tubes have gone microphonic. They'll need to be replaced.

Cool!
Better than dry solder or intermittent problems.
Gonna buy a set of JJs for start for a full retube and see how it goes.

[a.hun]

Ok!!!
An update!
IF i put the head on the floor and i play the same notes, now its the E low string fret 14 and/ or A string fret 9, the weird sound stops.
So now i'm thinking the tubes are good and there's vibration coming from the cab passed onto the head and then back through the speaker.
Hmm, how do i go about fixing this?
Any ideas?

Yep almost certainly microphonic valve(s). Can be pre or power ones, but since you've replaced all the preamp ones (without improvement, right?) I'd put them right back in and indeed replace the power valves.

All valves are at least a little bit microphonic, meaning they'll put out a signal when vibrated, can be rattles, or whiny feedback on certain notes. IMO it is only a problem if it's a problem, and one way of minimising the problem (as you've founr) is to isolate the amp from the vibrations. I play bass and when using a valve amp for bass I'll isolate it from the cab by slipping an Astroturf doormat between them. Works a treat and likely increases the useable valve life a lot too!


Andy.

[orys]

Hello guys!
I replaced the tubes with a full JJs set and it is spot on!
Maybe, and i say maybe, a little more hum but it's GREAT!!!

[Phlowen]

Glad to hear you got it sorted out!

[Les Paul Lover]

Fantastic news!!!!!

Yeah, slightly microphonic valves can be hard to trace at times.

Hope you enjoy it now!!! It's a great amp !

[a.hun]

Hello guys!
I replaced the tubes with a full JJs set and it is spot on!
Maybe, and i say maybe, a little more hum but it's GREAT!!!

So you replaced the 6V6 power valves too. Did you get the amp biasing checked / adjusted for the new ones? Were they a performance matched set? Biasing can have a big effect on sound / reliability / valve lifespan. Need to have a tech check that for all new power valve sets with this type of amp!
Hum can be from an imbalance in the 'push - pull' output circuitry ie the valves aren't all working efficiently together in balance.

Hum is not normal with these amps which are usually very well sorted that way...


Andy.