Help with Ugly sound

[GearNut]

Hope someone has a few ideas here as this has been driving me nuts for a few days.
I have an RM20 head that I bought new in Dec. but do to too many other projects in the studio I've only managed to put a couple of hours on this thing in the past couple of weeks.

I've done all testing as far as different guitars, cabinets, cables, outlets you name it and have ruled all of that out.

This thing sounds like you are playing through a 5 inch blown speaker that is laying on the floor somwhere without a cabinet. Sometimes it's worse than others, today it is horrible.
It does it with 4 modules that I have Blackface, Top Boost and KH1 and 2 even at low volumes but the higher the gain the worse it gets.
In one part of my troubleshooting I decided to immediately play without warming it up and it sounded great for a few minutes but on subsequent tries that didn't matter whether it was warmed up or not.

When I first got a chance to fire up the amp it had this sound but only very slightly but now after trying it the past few days the sound has gotten considerably worse.
I'm hoping it's maybe only a tube problem but since I just can't go out and buy them ( it's a pain living in so called paradise) I was hoping someone had some other ideas.
Also, even though biasing the tubes show that they are matched to within 0.01 of each other, I can only get them to bias within a point and a half of each other. eg. one tube reads 18 the other will be 19.3 or further away no matter were I choose to set them. Any ideas?

I also noticed that when I took the back rail off of the amp to check to see if the tubes were seated properly that there is a big dent in the windings of the tranny but since this sound has gotten worse in just a few hours playing time I don't think that would be it?

Any help would be appreciated as I need this amp next week as I have a couple of great guitarists coming in and I have been touting the virtues of this amp to them.

Sorry for the long post.

Thanks, Rick

 

[Julia]

You did buy it new, right? Call customer support on the Randall home page. With a dent in the transformer, I don't know but something may have happened to the amp. It should get checked out.

You did register the product and still have or can get a copy of the sales receipt, right? I typically staple them inside the manuals.

 

[GearNut]

Thanks Julia

Ya I bought it new and have all the receipts and everything.
It's more than a little frustrating because for the first time in awhile I have a chance to catch up on my own projects and now I'm playing with a piece of junk. Not to mention that I NEED it for other projects.
The worst is that because of my location (a long way from nowhere) it's hard to get anything done.
The transformer had to have been put in like that because it is right behind the bar across the back so it makes me wonder about Randall letting something like that go in the first place.

Edit: Sorry about the rant but this Randall thing has been a bit of a fiasco since the day I ordered it on Nov. 17th. Long story.

 

[Julia]

Was it shipped direct from Randall?

Well I can't speak for Randall, but I can speak for UPS.... The exterior box of my Lynch Box arrived at a local store with a portion of it missing, dented and looking like it got worked over by this guy:

http://www.youtube.com/watch?v=B2ZeIoLz8FE

Fortunately it still worked fine.

I had a Fender amp once that also arrived in horrid condition. I saw the UPS guy grab it out of the truck, drop it on the street, close the door on the back of the truck, and then pick it up and drop it on my front porch. It said "FRAGILE: Electronic Equipment" all over what was left of the box.

The A/C unit I got from Costco met with the same fate from UPS.

Windings? or the heat sink on the transformer? Still, your step is to call Randall. Explain that it's been this way since day one, and let them figure out what to do with it.

If you have to ship it, have UPS pack it for you. They seem to take better care of stuff if THEY pack it because they can't come back and blame the shipper that way.

 

[GearNut]

Thanks again Julia

LOL that video says it all about most of the shippers I've dealt with.
I once met the courier truck to pick up some gear and just as the guy opened the back door a whole stack of boxes fell over and the guy didn't even flinch. The whole back of the truck looked like a tornado had gone through it. Luckily my box was on the floor with other stuff on top so I knew it didn't fall too far.
I actually bought the amp at the only dealer in the area (about a 2 hour drive) but he hasn't been very good right from the start about wait times and many other things so I have a feeling this is going to be fun.
I've also been told by two other dealers that they no longer sell Randall stuff because of the headaches they had. They didn't elaborate but maybe I should have asked before I bought.

I will be taking it back to the dealer but my problem is the down time without it. I sold 2 amps and have another lent out to my son in law who is on the road with it right now so this leaves me ampless with some important writing and recording sessions coming up with some very good people.

I'm still hoping that someone else has had a similar problem and may be able to chime in and say "oh ya just change out this transistor or check this loose solder joint" or something and I'll be back in business.

It's the windings on the tranformer that are dented but I don't think that should be the problem as the amp did seem to work for a bit.

I've actually found 2 new problems with 2 modules as well that makes me wonder about the quality control of this company.

One way or another I plan on having this sorted out, without having the downtime that I cannot afford to have at this point in time.

Thanks again for your concern.

 

[maximus1]

put different tubes in it, your 1 ma bias window isn't a problem, change the pre amp tubes as well, it can't be too costly to retube an rm20 right?

 

[GearNut]

That will have to be my next step at troubleshooting I suppose.

The amp is the same regardless of what module is in it so I'll give the EL84s a try.

Edit
I think it might be bigger than that though because just now as I was doing some other troubleshooting at a very quiet volume the speaker went. It sounds like the voice coil just fried and the amp was turned up to about 1/4 volume.
Is there a safe way to check to see if maybe the amp is putting out some DC voltage or something out through the speaker jack without putting undue load in an improper place?

 

[Julia]

I had a horrid problem with a Marshall JVM410H, which is how I ended up in Randall country. As tempted as I was after getting this amp, the 410 taught me never to be without a backup because it was broke more than it worked, and that was when i got my 5150 II -- it's a workhorse. Sometimes you get a lemon. On the 410H I got a lemon. There are many many people who own those amps and have had zero problems.

But the bottom line sound like you're going to have to send it in for service.

From what you wrote it sounds like you're using it for recording in the studio and for reamping stuff. In that case it might be good to pick up a POD XT Live or X3 Live or one of the PRO versions. Or just something you can get some live sound out of and use a package like Peavey's Revalver or Digidesign's Eleven for applying amp and cab models to tracks until the unit gets back. Save the original clean track though in case you want to re-amp with a tube circuit when you get your RM20 back in working condition.

 

[kc2eeb]

If you have a dent in the laminations of the transformer, I'm assuming the
output tranny, the amp will sound horrible. All those laminations are insulated from each other by a thin coat of enamel or lacquer and if they are dented they are shorting to each other and distorting the magnetic field. Also, if it got hit hard enough to do that damage, the internals have to be checked too.

 

[Sven S.-M.]

Gearnut.
You're not alone with this issue. Yesterday my RM50 started going bananas with the same symptoms as your RM20, except fo the speaker thing.
I tried swapping the power tubes, but that didn't help. So now I am considering taking it to a tech. Some friends gave me the advice to try replacing preamp tubes and phase inverter tube, - I don't have clue about where that is located. Someone might have a scheme over those cirquits, but I can't find them online anywhere. Could be educating to see what's in it.

Hoping for somebody to shed some light on this.

/Sven

 

[JKD]

There are three preamp tubes in an RM50 chassis located under metal covers. The covers come of with a little pressure and a twist until they pop off - there's a small notch on either side.

The first preamp tube is at the front of the chassis near the guitar jack input. This is the 'input' tube ie 'v1' this can be the source of many problems being the first amplification stage the signal from your guitar sees.

The phase inverter 'v5' in the Randall isclosest to the power tube. This is the last preamp tube before hitting power tubes.

The other preamp tube 'v4' is a buffer/line driver for the effects loop.

Preamp tube replacement is easy - they should come out with a gentle pull/wiggle but they are glass so be careful and give your amp a little time to cool down...

Replacement is made simple ad the tubes are 'keyed' via a missing single pin and corresponding blank on the socket. Tube type is 12ax7/ECC83/7025 which are equivalent.

v is traditional nomenclature for 'valve.'

v2 and v3 are in the modules of course, hope that helps.

 

[Sven S.-M.]

Yes tremendously. Thanks alot JKD.
Don't know if this will fix the culprit, but it sure helps me nailing down the cause of the issues and this I can manage.
I'll replace the tubes v1, v4 and v5 some time during the next couple of days and post here if that helps or not. But I'm optimistic and I believe this will fix the problem. Thanks again.

/Sven

 

[JKD]

Yes tremendously. Thanks alot JKD.
Don't know if this will fix the culprit, but it sure helps me nailing down the cause of the issues and this I can manage.
I'll replace the tubes v1, v4 and v5 some time during the next couple of days and post here if that helps or not. But I'm optimistic and I believe this will fix the problem. Thanks again.

/Sven

My advice...do it one at a time..makes it easier to track down the problem.

 

[bruce egnater]

Is the HT fuse on the rear panel blown? If so, that would indicate a bad power tube.

 

[Sven S.-M.]

Is the HT fuse on the rear panel blown? If so, that would indicate a bad power tube.

Bruce.
Kind of you to chime in. Fuse is okay. It seems it was v1, as JKD suggested. I just swapped it 30 mins ago with a cheap (Yugoslavian :shock: - didn't know of any Yugo-tubes) 12 AX7 I found in a drawer, and so far it acts normal.
I do need to get me a good clean highgrade 12AX7 (probably a TAD 7025/E83CC Highgrade) because this one really sounds like crap :lol: but it's ok for now.

/Sven