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Author
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Topic: MusicMan 112 RD Fifty Hum
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Rainer Hackstaette
Member From: Bohmte, Germany
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posted 06 January 2003 09:45 AM
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Tube amp wizards, please help!  I`ve just acquired a MusicMan 112 RD Fifty through Ebay. The amp works fine, except for a loud hum that is independent of the channel (clean/limiter) and of the setting of the volume and tone controls. The 2 6L6 power tubes are Groovetubes of uncertain age and glow normally.
What is the cause of that loud hum? Should I replace the 6L6`s and the 12AX7 in the limiter preamp? Could it be the caps or a transistor? Or even (please not!!) the transformer?
The amp runs on 230 V at 50 Hz (Iīm in Germany)and the frequency of the hum is close to the A note of a guitar (55 Hz). Again: the amp works, but the hum is simply too loud. I would like to use the amp as a practise amp at low volumes for steel and as a guitar amp for my Strat on gigs. Any help is greatly appreciated!
Rainer ------------------
Remington D 10 8+7, Sierra Crown D 10 gearless 8+8, Sierra Session S 14 gearless 8+5, Peavey Session 400 LTD |
Ken Fox
Member From: Ray City, GA USA
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posted 06 January 2003 09:57 AM
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First and most likely culprit is the power supply filter caps. I have had a bad power tube hum somewhat too. Have you got some tubes you could substitiue temporarily? |
Rainer Hackstaette
Member From: Bohmte, Germany
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posted 06 January 2003 10:17 AM
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Ken,I received the amp just yesterday. I plan to change all three tubes eventually. I only want to make sure first that there is no other problem with the amp that would perhaps damage the new tubes. Matched pair GrooveTubes arenīt quite cheap. Would it be a good idea to exchange ALL caps in the amp? As far as I know the amp is from the early eighties and hasnīt had the caps renewed yet. Thanks for your help!
Rainer |
Ken Fox
Member From: Ray City, GA USA
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posted 06 January 2003 02:48 PM
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Not all the caps! Coupling caps are usually not a problem, Electrolytics used for filtering and cathode bypass might need replacing. If caps are causing the hum, it will not damage the new tubes. |
Manfred Schall
Member From: Langenfeld, Germany
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posted 06 January 2003 03:24 PM
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Hi Ken and Rainer out there.
It's cool to see you on one post.
A big cheers to you Ken. Thanks again for your support and hospitality during my last
years stay. Rainer is the nice guy who bought that S14 from me.
And to Rainer, Ken is really a great guy to get any advice - not only about amps - from.
Hope to see you within this year. 
Take care, have a good time and keep on steelin.
Manfred |
Rainer Hackstaette
Member From: Bohmte, Germany
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posted 06 January 2003 03:37 PM
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Ken,I just talked to a friend of mine on the phone (heīs a radio technician), and he - like you - thinks it is the power supply filter caps. He told me to bring the amp to him and heīll fix it.
Thank you very much for your help, I really appreciate it. Iīm a dunce when it comes to electricity, let alone electronics!!  Hi Manfred, long time no see! 
The S-14 is still going strong, infact, itīs getting better every day. Wish I could say the same about me ...
Drop me an email, if you find the time. Rainer |
Ken Fox
Member From: Ray City, GA USA
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posted 06 January 2003 04:36 PM
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Hi, Manfred Good to hear from you, too! Enjoyed your visit this year. Just saw Pete B. the other night, we went out to hear Harley James (steel player and superb vocalist) and the Buckles. Awesome Bakerfield sound! Larry Behm was there, too! We had a great time.
Rainer, hope that MusicMan amp gets working for you! It should be a nice sounding amp. It is good you have friend that a technician!!!
[This message was edited by Ken Fox on 06 January 2003 at 04:39 PM.] |
Ivan Posa
Member From: Hamilton, New Zealand
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posted 06 January 2003 06:39 PM
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Rainer, I have this same amp and it is the best sounding guitar amp, and I have tried just about every make and model over many years playing. I use a 77 Tele with Barden pups and sounds great, better than all the new and old Fender amps I have owned. I have JJ 6L6 output tubes and a Sovtek 5751 in the limiter pre-amp. The biggest improvement is to replace the standard speaker with a Celestion Vintage 30 which will really make it sing. A good Tech will fix the hum no problem, Mine puts out 75 Watts RMS and can get very loud when needed. Great amp, dont part with it....IP------------------
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Ken Fox
Member From: Ray City, GA USA
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posted 06 January 2003 06:55 PM
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I thought that model amp looked familiar! i worked on one for a friend a while back. Interseting circuit. Used a zener diode as a regulator for the bias voltage. Someone had ran the tubes so long in this one that it took out the zener! I had a chance to play it on a gig. It was a great sounding amp. I recall it had 2 each 6L6GC and a 12AX7 in a drive channel, I believe. It was one of the few Musicaman amps to have a preamp tube at all. It is a hybrid (transistor frontend) amp and the 12AX7 was compressor/limiter on the drive channel, I do think. Also a nice hand-wired amp, too.
Good amp, you should be really pleased with it. Here is a link to a great site on the old MusicMan amps:
http://pacair.com/mmamps/ [This message was edited by Ken Fox on 06 January 2003 at 06:57 PM.] |
Rainer Hackstaette
Member From: Bohmte, Germany
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posted 07 January 2003 02:11 PM
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Yep, right! Itīs a hybrid amp with one solid state preamp ("clean") and one 12AX7-driven overdrive channel ("limiter"). It puts out 50 watts RMS through 2 6L6GC tubes. Cranked up it can make your ears bleed!! For country-style lead guitar I havenīt heard a better amp.Mine has an electro-voice EV 12L speaker. I believe these amps came with celestions from the factory. The EV 12L makes the amp quite a bit heavier (about 25 kg or 50 lbs) than the stock model. I am really looking forward to using the amp on a gig. The lead guitar player in my band has the same amp and I canīt wait to cross swords with him! Thanks for all your help and nice comments! Rainer ------------------
Remington D 10 8+7, Sierra Crown D 10 gearless 8+8, Sierra Session S 14 gearless 8+5, Peavey Session 400 LTD |
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