Conflicting Tube Info!!!

I'm trying to get some spare tubes for my 112 RD 100,(this is all the info I've got on the amp without removing screws)
Ch No 2100-RD,
ID2100,
Serial No 08949DP,
weight 27k
Black background logo
Year ? '83
and I'm getting conflicting information.This guy Derek from Watford Tubes is telling me that The Sylvania 6L6 tubes that are in it are the wrong ones and they should be 6ca7's and that MM amps do not have a plate voltage of 700.In an email that I recently sent to you Steve you said it did have 700pv,now I tend to believe you cuz you da man and you know what you're talkin about and, you don't want to sell me anything.I've been screwin' around for the last month trying to get specific information from here there and everywhere and am getting nowhere fast.All I want is a set of spare tubes in case one blows cuz they've been in there so long I think they're the originals!Your advice would be appreciated as well as any info as to build year ,it's got a white sticker on the back of the chassis with
83-1 on it Could it mean 1983.Thank fuck for this site.

You need to look inside your amp and see if it has GD2,GD2A, or GD1 written in it anywhere. THe GD2 amps used 6ca7's, the GD1 amps used 6ca7's, the GD2A amps used 6L6's. Confusing, huh! No matter what, those amps DO have 700v or so on the plates. Tell that guy to look at the freking schematic before he shoots his mouth off. That's a good way to blow things up. I don't know for sure which amp you have but 6L6's were used in somne of those amps. You'll have to open it up and look for any other numbers but I would guss that the 6L6's would be right for that last series of amps and 83 was near the end. Mike.

Hi Mike,
Jaysus! I'll have to get the screwdriver out, last time I did this it was a real pain in the ass gettin those bitchin' screws that hold the chassis, back in,Ha! Ha! Ok ! But it's gotta be done.BTW if you look at the top of my posting you'll see it's an RD112 100w and very nice too,best Amp I've ever owned.I think I'll be in touch!
Thanks Man

Ill say 6L6.... too new for the older 6au7 tubes...

6ca7....sorry

Hey Michael
O.K.....I slipped out the Chassis and went lookin for the clues but didnt'find any Gd's anywhere but I got the transformer Numbers the big Mofo on the left
200-130 250 EIA 606 - 103....,other side
4-130 EIA 606 - 121...The only other writing was on a strip of paper near the fuses reads.....
1 200 200 8A
AT MAT MAT 50v ....thats it no more writing anywhere..So is this gonna help that is the question? Thanks
Hey Mr Anonymouse,that you Derek Rocco???

Oh!... BTW the Tube chart says 6L6's....So there shouldnt be any question...Right!!

Nope

OK, call me what you want, but my head is spinning from too much information. I have tried surfing the site heavily so as to not ask stupid questions. No luck. Per this thread, I also have a 112 RD 100. I do not know what year it is. I also took everything apart and could not find the "gd" marks as mentioned. When I bought it (late 80's) it had 6Ca7's and I had an extra pair of GE 6Ca7's that I don't even remember where I they came from. I recently (before I found this site) replaced them with Groove Tube EL34's, because I thought they were equivalent. The 34's work. The amp sounds good. Could it sound better ? At this point I don't know. A little feedback please. The end of this thread seems to suggest that, if it's a 112 RD 100, you should be using 6L6's. Please bring this down to the small brained folk like myself. If it's supposed to be using 6L6's, should the amp even function with EL34s ? If it is supposed to have 6Ca7's, what are the real world implications of replacing them with EL34's. Is the amp being harmed ? Is the tube life less, but the amp is fine ? Is there a sound quality issue ? Should I have it re-biased (whatever that means) ? Thanks for putting up with a amp rookie. These amps rule, I have been gigging with this thing since '86. Great site.

The short version: The earliest RD65 and 100 amps were probably shipped with EL34s or perhaps the very earliest with 6CA7s. The U.S. made 6CA7 is a mechanically stronger tube and better suited to the MM amps than the EL34 mainly because of the larger physical spacing between the tube elements in the 6CA7 (which is more compatible with the high plate-voltage found in the MM amps). The 6CA7 was the tube these amps were originally designed for.
The 6CA7 was an American-made tube that was a really strong and reliable unit in guitar amps. Unfortunately, by the late '70s they were going out of production so Music Man substituted the European EL34 tubes. They are not the same tube but equivalent enough to work as long as the amp is biased for them. They do not stand up to as much physical abuse so it is safer to run the amp on low power unless you need high power.
Biasing is like setting the idle on your car... it is a fairly simple adjustment for an amp tech to make and it is best to have it done each time a new set of output tubes is installed. This can be somewhat avoided by buying graded and matched tubes (like Groove Tubes) and always get the exact same grade so that a good bias adjustment on the first set will probably be close enough on succeeding sets of the same grade.
After about 1980, all Music Man amplifier models were redesigned to be optimized for 6L6 style output tubes because they were still available. The main differences between the newer and older model tubes are the heater current and the biasing. The circuits really didn't change all that much.
I would continue to use what you have been successfully using and not worry about it too much. If your amp hasn't had a cap job in the last 10-15 years, I would have that done along with fresh quality tubes and biasing and you'd probably be ready for the next 20 years!
Steve