RV50 Hum / Servicing

[voycie]

Hi, I have a RV50 Head I'm running into a Marshall AV1960 Cab. I've owned it about 3 years and bought it secondhand, and although its in lovely condition, Ive never serviced it.

A few questions I have that I hope you guys can help with:

1. The amp hums a bit when powered up. Its not a hugely noisy hum but is a constant background noise. Is a certain amount of hum to be expected or should it be quiet?
2. The amp hums progressively when the gain is dialled in
3. Turning on the reverb also causes hum.

I'm thinking that it probably is in need of a service and replacement valves. What kind of costs would be involved for the valves, or a service by an amp tech? Is replacing the power valves and the biasing something that can be tackled at home?

I also have some issues with noise through my fx pedals, but it makes sense to start off with cleaning up the amp then adding the effects gradually afterwards so thats the plan!


Any thoughts appreciated!
By the way im in Aylesbury Bucks if anyone knows a good local tech

[a.hun]

Hi, I have a RV50 Head I'm running into a Marshall AV1960 Cab. I've owned it about 3 years and bought it secondhand, and although its in lovely condition, Ive never serviced it.

A few questions I have that I hope you guys can help with:

1. The amp hums a bit when powered up. Its not a hugely noisy hum but is a constant background noise. Is a certain amount of hum to be expected or should it be quiet?
2. The amp hums progressively when the gain is dialled in
3. Turning on the reverb also causes hum.

I'm thinking that it probably is in need of a service and replacement valves. What kind of costs would be involved for the valves, or a service by an amp tech? Is replacing the power valves and the biasing something that can be tackled at home?

I also have some issues with noise through my fx pedals, but it makes sense to start off with cleaning up the amp then adding the effects gradually afterwards so thats the plan!


Any thoughts appreciated!
By the way im in Aylesbury Bucks if anyone knows a good local tech

Hi voycie.
Well, the amp shouldn't really hum noticably. A very small amount may be normal, but basically the amp should be pretty quiet.
Causes of hum:
http://www.geofex.com/ampdbug/hum.htm" onclick="window.open(this.href);return false;

Divide and conquer: You say that it increases as you turn the gain up. Does the amp hum equally on both channels or is one noticably worse? And dialling in reverb also increases hum?

It may be that swapping valves will help, especially if one channel is more of a problem. But it could equally be that the power valves are getting hummy too. If so then I'd have to say that having the amp biasing checked really isn't a DIY thing, not unless you are totally familiar with working on high voltage circuitry safely. Youd want to have a tech do that.

Preamp valves you can safely swap out yourself. I'd start there, hopefully improving things as much as possible. So I'd suggest first try buying in a few spare preamp valves and doing some swapping out. Note that the FX and reverb valves are a different type from the other preamp valves.

Valve layout for the RV.50 here:
viewtopic.php?t=14949" onclick="window.open(this.href);return false;.

If that doesn't really improve things then replace the good sounding old preamp valves (you now have tested spares too!) and see about new power valves and calling in a tech. Since you will need new power valves at some point anyway (generally they don't last nearly as long as preamp valves) it is probably worth buying a new matched set at the same time. Check out the online valve suppliers such as Euro Tubes (http://www.eurotubes.com/index.htm" onclick="window.open(this.href);return false;) (JJ specialists), Watford valves (http://www.watfordvalves.com/home.asp" onclick="window.open(this.href);return false;), Groove Tubes (http://www.groovetubes.com/main.html" onclick="window.open(this.href);return false;), TAD (http://www.tubeampdoctor.com/index.php?language=en" onclick="window.open(this.href);return false;), and whatever else a search finds you.

The JJ 6V6 is probably about the most robust power valve choice and well liked by a lot of RV.50 users. Preamp valves are largely a matter of taste. Trying a small selection of different ones in the different slots will help you find your own preferences.

Good luck!


Andy.

[voycie]

Thanks Andy, I had checked out Watford Valves already so maybe I'll go for a preamp kit first, install that then see what its like. My amp was new 2005 and had a look last night and the valves are all stamped Orange so assume they're the originals - so 5 years of use - orange seem to recommend changes at 18 months so its probably easiest to just replace the lot. Meantime I'll have a play with swapping out the existing preamp valves to see if certain ones are the cause. What does the Phase one do?

[a.hun]

Thanks Andy, I had checked out Watford Valves already so maybe I'll go for a preamp kit first, install that then see what its like. My amp was new 2005 and had a look last night and the valves are all stamped Orange so assume they're the originals - so 5 years of use - orange seem to recommend changes at 18 months so its probably easiest to just replace the lot. Meantime I'll have a play with swapping out the existing preamp valves to see if certain ones are the cause. What does the Phase one do?

Well, blanket '18 month' recommendations are a bit daft IMO, especially for preamp valves whcih should last longer. But if they are the originals it is probably worth swapping them all out. Back then Orange used Chinese valves which weren't as good as they are now. They are probably well past their best now...

The phase inverter stage is between the pre and power amp sections. Explained it here:
viewtopic.php?f=2&t=14949&p=498663&hilit=+inverter" onclick="window.open(this.href);return false;


Andy.

[voycie]

The reverb gets progressively noisy with the hum as you dial it in. I tried swapping the tube for the preamp one, and it didnt make much difference. With a pedal in the effects loop, there is also a hum which is worsened by switching on the pedal. So it looks like both of the 12AT7s are past their best.

one the clean channel, past 1 o'clock on the volume it hums progressively noisily (and worse with the reverb on)

on the dirty channel, with the vol on full and no gain theres no noise, though dialling in gain creates hiss. With the vol on half way, the gain gets hissy from 12 o clock onwards. To bes expected on a high gain circuit? Adding reverb adds the hum again.

interested if this explaination helps at all before I go out and buy new valves!

[a.hun]

The reverb gets progressively noisy with the hum as you dial it in. I tried swapping the tube for the preamp one, and it didnt make much difference. With a pedal in the effects loop, there is also a hum which is worsened by switching on the pedal. So it looks like both of the 12AT7s are past their best.

one the clean channel, past 1 o'clock on the volume it hums progressively noisily (and worse with the reverb on)

on the dirty channel, with the vol on full and no gain theres no noise, though dialling in gain creates hiss. With the vol on half way, the gain gets hissy from 12 o clock onwards. To bes expected on a high gain circuit? Adding reverb adds the hum again.

interested if this explaination helps at all before I go out and buy new valves!

I'm not guaranteeing that it is just down to valves, but that is the most likely explaination, and the easiest to check.

Sounds like the preamp valves have indeed got noisy (hummy). Yes a bit of hiss is normal with high gain channels when the gain is set high, but even that may improve a bit with better valves. Normally I don't suggest swapping all the preamp valves at once but in this case I'd definitely try it. And as I say buying in spare 6V6s is probably a good move too. You'll need them sooner or later anyway.


Andy.

[cmscss]

Hi there,

Not sure if this will help but my Rockerverb 100 had an issue where a wire connected to the reverb pot that goes around the board was touching stuff - this caused a constant hum on both channels.

This was a Mark II head though.

Cheers

Ben

[voycie]

Thanks Chaps for advice so far.

I think the problem might actually be due to external sources...

I plugged my guitar into my Roland Microcube and the hum persists there as well. So, I tried a different guitar/leads, no change. I then tried swapping the PSU to battery power... the hum went (but strangely was present if I left the PSU in the socket, even if it was not connected to the microcube). Tried isolating all other power circuits in the house, turning everything including appliances off. Hum still persisted.

So, it looks like the problem is not due to the amp but the electrics in the house. Come to think of it. I dont recall even noticing the hum at rehearsals so I think it is related to the house electrics. Not sure if its 'dirty power' or an external problem like the overhead power cable, or maybe the PME earthing in the house.

Reading around the 'Net, it looks like a power conditioner might be the way to cure things. If I got one I would imagine a multiple-gang one with surge protection might be a good move and then can take it to gigs.
Anyone have any experience of one?

I have a pedal-board with a number of pedals that seem to raise the hum, these are connected with a diago power supply, so would be looking to run that through a conditioner too.

Interrested if anyone thinks I'm shooting in the right direction?

[Eddie Famine]

I get a hum at practice when the lights with the dimmer control are on.
Turn them off, no hum.