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Topic: 1970's Music Man 115 R P |
Jay Fagerlie
From:
Lotus, California, USA
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Posted 2 Jan 2005 10:47 am |
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A friend just bought one of these off of eBay. The ad (and the amp) say 100 watts. I was looking at a picture of it and noticed it had only two output tubes. They are either 6L6 or EL34 (6CA7)....So....how does MM get 100 watts out of two tubes?
Any help would be appreciated.
Thanks
Jay |
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Jerry Erickson
From:
Atlanta,IL 61723
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Posted 2 Jan 2005 9:44 pm
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| There's either 2 tubes missing or it's not a 100 watt amp. Look at the picture and see if there are 2 more tube sockets on the amp. If not then it's a MM65. |
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Stephen Gambrell
From:
Over there
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Posted 3 Jan 2005 5:41 am
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I've been waiting for an answer to this one. I've got one of these amps. The nameplate says "115RP", then
underneath, "one hundred," and the back plate is stamped "output 100 WRMS!" It seems like I read on a tube chart a long time ago a way to get about 40-something watts out of a 6L6, but I can't find that chart on the 'Net. But my amp has 2 6L6's, no empty tube sockets, and is LOUD! Not sure if it's as loud as a Twin a friend and I put together, but it'll get the job done! |
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Jay Fagerlie
From:
Lotus, California, USA
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Posted 3 Jan 2005 5:46 am
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Hey Jerry, thanks for posting.
Beyond that already....
Two output tubes. MM claims it is a 100 watt amp, even on schematics....If anybody wants to see what I mean, look at this: http://www.scaryoak.com/jay/schematic/GP3A.gif
Check out R64/R65, right after the line out jack, that's the only difference I see between a 65 watt and 100 watt model.
It has me scratching my head....
Jay[This message was edited by Jay Fagerlie on 03 January 2005 at 05:47 AM.] |
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Jay Fagerlie
From:
Lotus, California, USA
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Posted 3 Jan 2005 5:49 am
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Stephen,
My friend bought it 'cause he likes lots of clean headroom, ala Chet.
Do you think he'll be happy with it?
Is it clean loud?
He has a few 50 watt amps that just don't have the clean headroom he needs....
Thanks
Jay
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Jody Carver
From:
KNIGHT OF FENDER TWEED
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Posted 3 Jan 2005 5:56 am
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There were 2 models of the RP and RD MM amps.
One was 100 RMS and the other was a 65 RMS.
I'm puzzled as well. I'll look up at my info when I return home in a day or so.
RP "Reverb Phasor" "RD Reverb Distortion".
I have all the technical informatiom and will check it in a day or so. I repped those amps and I should know,but my memory fails me. |
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Jay Fagerlie
From:
Lotus, California, USA
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Posted 3 Jan 2005 6:19 am
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Hey Jody, glad to see you back on the forum.
I'd appreciate anything you could find.
BTW< your Hot Club CD has become one of my all time favorites....thanks for making it available again. Did you ever post your tunings and/or tabs for that session? Talk about the ultimate lesson in the art of steel guitar! There's a ton of killer stuff on that disc!
Jay |
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Ken Fox
From:
Nashville GA USA
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Posted 3 Jan 2005 6:38 am
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Tube specs:
6L6-GC Ratings
PaMax 30 watts (Plate Max wattage dissipation)
EL34 Ratings
PaMax 25 watts
Ah the spec game! If you rate an amp at a higher distortion level you can claim more output power! I have only gotten 100watts max out of a 135watt Twin, and believe me I have tested quite a few!
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David Doggett
From:
Bawl'mer, MD (formerly of MS, Nawluns, Gnashville, Knocksville, Lost Angeles, Bahsten. and Philly)
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Posted 3 Jan 2005 6:38 am
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| I just picked up a Music Man RD112, and it also is 100 watts with only two power tubes. These were made by people who had been building late model silver face Fenders with the ultralinear transformer. Those Fenders were getting 135 watts from the same four tubes that black face Fenders got about 80 watts from. So they knew how to get the maximum amplification from those tubes. In addition, the MM amps have a solid-state preamp. This may boost the input to the power stage more than previous tube preamps. That's just a guess, but somehow they got those MM amps to really scream, with lots of bottom end and clean headroom. And they are very small and light. The tone is somewhere between solid-state and all tube. It makes a killer practice amp for pedal steel. |
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David Doggett
From:
Bawl'mer, MD (formerly of MS, Nawluns, Gnashville, Knocksville, Lost Angeles, Bahsten. and Philly)
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Posted 3 Jan 2005 6:43 am
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| Ken's post came in whili I was writing mine. There are a number of discussions about this in the past on the Forum. One thing I remember that seems true is that the rating on the back of Fender amps is not the output, but the speaker recommendation. It makes sense that they would recommend a speaker with a little more power handling than the amp's maximum output. I don't know if this was also the policy at Music Man, but since former Fender people made MM amps, it may well have been the same policy. |
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Jay Fagerlie
From:
Lotus, California, USA
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Posted 3 Jan 2005 6:51 am
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One thing I did notice is that the plates are at 700 V through the Xformer and the grids are at 350 V...a bit different than normal tube amps.
I'm wondering if the tubes are actually only part of the total output power, being "up the rail" as opposed to supplying the total swing of output (AB, of course) and that the SS driver section is actually the other "half" of the output section....
Ken?
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Jay Ganz
From:
Out Behind The Barn
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Posted 3 Jan 2005 7:08 am
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It's also a question of whether they're
figuring RMS (continuous) wattage or peak
(instantaneous)wattage output. |
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Stephen Gambrell
From:
Over there
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Posted 3 Jan 2005 7:48 am
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| Jody, I was hoping you'd get in here. Jay, my amp has a Black Widow speaker, but it's clean, an loud, and I use it for a steel amp a lot! I don't know how they sound with the original speaker, probably pretty doggone good, but mine's gonna stay here---at least till I get that Christmas Tree!! |
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Pete Burak
From:
Portland, OR USA
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Posted 3 Jan 2005 8:38 am
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Peak to Peak RMS, anybody? 
I had the 112RD (also had 2 EL's) and it was a loud amp that worked well for Steel (in 65W applications) and was really loud with a 6 string electric. The one I had had a JBL in it. A nice compact and capable amp, but in the end, it went the way of the buy/sell/trade jones. |
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John Daugherty
From:
Rolla, Missouri, USA
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Posted 3 Jan 2005 9:48 am
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| When you read the tube specs in a tube manual, the specs are for a given operating condition (class). Somebody correct me if I am wrong because it has been a while since I looked at Fender schematic...... As I remember, the Fender power transformer had a tap to furnish about (-)70v for the control grids on the output tubes. This allowed the tubes to be driven harder to get more output without distortion. Just my thoughts from the past...........JD |
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Andy Zynda
From:
Wisconsin
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Posted 3 Jan 2005 9:49 am
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If you look at the schematic, you'll see that the cathodes of the 6L6's are tied to transistors Q1 and Q2. There appear to be configured as drive transistors, pushing the 6L6's up, and extending the total dissapation for the output section.
Looks like a that's where the 15-20 Watts RMS per side is coming from.
Just a guess, but I'll bet that those two transistors are the large T0-3, heat sinked, output types.
-andy-
[This message was edited by Andy Zynda on 03 January 2005 at 03:34 PM.] |
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Jay Fagerlie
From:
Lotus, California, USA
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Posted 3 Jan 2005 9:57 am
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My thoughts exactly Andy, thanks.
Jay |
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Ken Fox
From:
Nashville GA USA
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Posted 3 Jan 2005 1:43 pm
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Well, I never fot mopre than 100 watts RMS out of a 135 watt Twin (Ultralinear transformer). 30 Watts is typical per tube is the max rating fot class AB2, which Fender used. Far less rating at class A. The Ultralinear transformer was an idea Leo borrowed from the hi-fi world. It created far less distorion, a more perfect sine wave could be reproduced. Borrowed from another site:
"It's a transformer with a tap at about halfway between the B+ connection and the plate connection to which you can attach the output tube's screen grid. This connection provides some feedback to the screen grid as well as a bias voltage and has been found to act like a connection halfway between pure pentode modes and pure triode mode, with lower distortion than either. It's almost a requirement for tube hifi ampliers. Bass amplifiers use it to get large amounts of clean power. It usually sounds too "sterile" or clean for guitar players' tastes. "
Another page I located states 27.5 watts for Class AB2. It states 55 watts at class AB1.
http://tdsl.duncanamps.com/show.php?des=6L6GC
[This message was edited by Ken Fox on 03 January 2005 at 01:47 PM.] |
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Jay Fagerlie
From:
Lotus, California, USA
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Posted 3 Jan 2005 2:02 pm
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Take a look at the schematic.
The plates are connected to B+ thru the xformer at 700 volts!
Last I looked, 6L6's (5881's) are rated at 400 volts MAX.
They must be biased way up the voltage rail with the SS parts, as Andy stated.
I think the trannies are T092 type.
I would sure like to get the real teck-poop on these circuits...they were supposedly designed by Tom Walker, anybody know of him?
Jody?
Jay |
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Ken Fox
From:
Nashville GA USA
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Posted 3 Jan 2005 3:10 pm
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| A word to the wise, few tubes built today can handle the plate voltages of a Fender Ultra-linear amp (over 500VDC on the plates) or the Musicman amps. The one I use is a Telsa 6L6GC, it will do the trick! |
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Andy Zynda
From:
Wisconsin
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Posted 3 Jan 2005 3:45 pm
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I dont think that Leo had a hand in the UL amp's designs. Those amps didn't exist till several years after Leo sold the boat.
The UL stuff might have been Rivera ideas?
Jody would know better than anyone.
-andy-
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Ken Fox
From:
Nashville GA USA
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Posted 3 Jan 2005 7:24 pm
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| Yes you are right Andy! Not sure, but is was the CBS era for sure. |
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Jody Carver
From:
KNIGHT OF FENDER TWEED
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