Swindon Music

Finally got myself a valve amp (Peavey Road Master 160w head), but as it's apparently not been used in about five years I was thinking it would be a good idea to get it serviced (it works fine, but I'd like to make sure everything's ship-shape and Bristol fashion). Is there anyone locally that can do this?

If it works, then no point in getting it serviced right now. The parts they'd be replacing will have a life span of around 30 years (capacitors) and valves don't need to be replaced as often as people make out, you still find amps from the 60s & 70s with the Mullards they came with.

I haven't changed anything about my amp in over 6 years and the only problem I've had has been a blown fuse. If the amp starts blowing fuses regularly, then it needs a service.

Yep. And it may smell a bit fishy when you turn it on for the first few time - totally normal and down (usually) to dust heating up on caps and valves. Worry not! Only things to worry about are strange noises when idle, smoke or valves glowing blue

Yeah, it does smell a bit funny... but I figured that was dust. Probably need to take a duster to it at some point!

At anything other than low volume, however, it is noisy as a really noisy thing... lots of hiss and that's after fiddling with the hum cancelling knob at the back to reduce the noise levels (clever Mr Dreadful downloaded the manual). Is this something to be concerned about, or is it just a "valve amp thing"?

Is it just a steady hiss or humming sound that stays at the same level, gets louder as you turn volume up etc? Or intermittent bursts of noise?

If it's option A, then it may just be other things in your setup (pedal power supplies, cheap leads, bad shielding in your guitar etc). If it's option B, it's more likely the amp, and it can be quite a serious thing in older amps.

You could possibly try replacing the preamp valves as this *may* lower the noise floor of the amp, but I'd try and eliminate the other stuff first.

It goes up as I turn up the post-gain, even when the pre-gain is at low levels... effects power supply may be a factor but it happens even when I'm running the guitar alone into the amp with no effects at all. My cables are cheap, and old. I was intending to replace them anyway.

Try turning up the preamp gain rather than post, turning off reverb, don't go nuts with the presence. You can expect some noise though.

What valves are in it?

Reverb doesn't seem to affect the noise, will try fiddling with levels of pre/post-gain and presence... still learning how to use this thing really!

Not sure what valves are in it TBH, I could tell you what the stock valves were, but the guy I bought it off said he replaced them at some point in the past.

Edit: Just taken the back off and had a squint inside. (Damn, that's a lot of dust and cobwebs!) Seems the replacement valves were just the same as the stock ones; 3 12AX7s and a 12AT7 in the preamp and 6 6L6GCs in the power amp. All Peavey.

Interesting. 12AT7 is a lower gain preamp tube - could be that the previous owner installed to cut down on noise in place of the last 12AX7?? Have you checked that the 12AT7 is supposed to be there? As they are not interchangeable with 12AX7 due to plate voltage. Could be there as the phase splitter.

If it's louder than you deem appropriate, get an engineer to have a squizz at it. Simon Law (should be able to contact him through Kempsters) is the man you want.

The 12AT7 is supposed to be there... checked it against the specs in the manual.

I'll continue fiddling with it and see whether there's something I can do to make it all sound nice at higher volumes... I think I'll see about getting a service anyway, if nothing else it needs cleaning and I'm not sure the reverb is working properly.

The usual culprits causing hums and nasty noises in valve amps are:


The first step in older amps that have had some downtime is to sray some electrical switch cleaner inside all the control pots and turning them a few times from min to max in order to losen and clean any debris/dust.

Secondly, depending on where the amp has been stored, is a build up of corrosion (they will appear very dull) on the valve pins.
This is easily remedied by removing the valve and using some fine wire wool, clean the pins so they return to a clean and shiny condition, This is a job I have to do to mine, especially during winter as on occasions it's left in the band lockup between gigs and corrosion can build up on the pins in cold conditions.

The swapping of 12AX7 and 12AT7 is not a problem if they are being used as preamp valves, however if they are used as rectifier valves then the plate voltage issue will come into play.
I use 12AT7 and 12AX7's in a variety of different places on all of my amps (current and previous amps i've owned) is it a very easy way to tame the drive of an amp to give a smoother sound.

As for the reverb, have you tried switching it with and without the footpedal plugged in?

Turns out the amp has an extra 12AX7 and 12AT7 in the power amp... this is what happens when you have a proper look at both the amp itself and the specs rather than rushing it!

Just had a quick look at the amps specs, just a guess as I haven't seen a schematic, but the two different preamp tubes COULD be used for the 'punch' function (reads as adding more distorsion to the 'classic tube sound')

I think you might be right... can't double check the manual right now though, but I do remember it mentioning that the other valves are for.

Out of interest if I were to simply pull out all the valves and replace them with new ones what would be recommended?

Unless you are used to the effect that changing a valve can have, it is always best to stick with the same valve you remove, for makes, there are only a handful of factories left worldwide that still produce them, for instance Mesa Boogie and Fender (GT TUBES) do not make their own!!
They are made in a eastern block factories in Russia, Slovakia, Poland etc!!!!


The tubes I swear by and have never had any problems (microphonic feedback, short life span etc) are JJ Tesla tubes, i use www.voc-rock-guitars.com for tubes, very reasonably priced and fast shipping.


Just looked at the tube layout for your amp,
Pre Amp: 3x 12AX7's used for the preamp and reverb return loop and 1x 12AT7 for the reverb drive.

Power Amp: 6x 6L6GC for the power tubes and 12AT7 Drive and a 12AX7 for predrive.

This thing has an overly complicated preamp system,
From having a quick read of some blurb on the 1st page of the owners manual, the amp has an 'american drive' sound and a 'english rock sound.

Personally because of the complicated arrangment of the preamp due to the 'punch' system I would leave the valves as they are and replace with new (not gonna be cheap!)

The preamp valves (12AT7's and 12AX7's) you can buy individually but the power tubes (6L6GC) you would need to get as a matched set.

These tubes usually need biasing, but I cannot see a bias adjusting pot on the schematic

http://www.peavey.com/media/pdf/manuals/roadmaster.pdf

Hope that helps!?!