Speaker Jacks in SERIES?

Amp Craftsman 86

I own 3 HD130 reverb heads- two are restored and used by my son. As I was looking at the third to consider some repairs and building a new rig around it, I see the back plate specifies "Speaker Jacks Wired in Series". This surprised me, because the other two heads say "Speaker Jacks Wired in Parallel"... And I presumed all MM heads were in parallel configuration. Can someone enlighten me as to why MM would have done this? It's going to make my planned use of two 8 ohm cabinets not viable....

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MM 2-10-65

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mm210 Wed, 04/19/2017 - 08:32

I don't remember ANY 130 heads being IN parallel. Everything I had seen was in series. You say they are all 130's? Are they all tube drivers or the other two SS driver? That IS confusing. I remember some of the other MM's were in parallel but never saw a 130 in parallel. Are they all US models? No x's here are they? Anybody else?

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Mike Griffin
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MM 112-RD-65

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10 years 9 months

mgriffin155 Wed, 04/19/2017 - 16:24

Hi Mike, The all tube output in the 2nd schematic has parallel speaker jack wiring. http://pacair.com/mmamps3/sites/default/files/docs/2475-130_and_2275-13… Just sayin', but I don't know what the vintage is? All of the other "130" schematics show series wired speaker jacks. The 21XRH OEM speaker cabs are 4 ohms which is why they proly went to series wired jacks on hi power amps. Maybe that's how Johnny Winter caught his amp on fire. mgriffin

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Steve Nordstrom
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I collect and restore amps and speaker cabinets- particularly Music Man...
212-65 Combo
HD 130 Reverb Head x 3
115 Reflex Horn Cab
212 Reflex Horn Cab

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Amp Craftsman 86 Thu, 04/20/2017 - 15:06

Yup, this one is a tube preamp, early HD130r. The other two are also 130r 's with tube drivers. Now, you have me stumped on whether they are US models- I didn't think a 130 was ever built outside the USA - only some of the 80s models. These are all three 74-77...
I'm going to see him play tonight and I'll double check the back plates... I'll report back after further research !

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Steve Nordstrom
Music Man Equipment
I collect and restore amps and speaker cabinets- particularly Music Man...
212-65 Combo
HD 130 Reverb Head x 3
115 Reflex Horn Cab
212 Reflex Horn Cab

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9 years 3 months
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Amp Craftsman 86 Sat, 04/22/2017 - 14:20

Okay, so here's a photo of the backplate of the 130 im working on....

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Tom Lance

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Tom Lance Mon, 08/06/2018 - 13:11

I know it states that they are wired in series, BUT if you pull the chassis/amp out and look you will see that they are indeed wired in parallel. ALL of the rear panel speaker jacks are in parallel. I would know I was the production dept. from '79 to '83 and hung every chassis in every amp during that time and as part of MY quality inspection I looked to see IF everything was soldered.

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Steve Nordstrom
Music Man Equipment
I collect and restore amps and speaker cabinets- particularly Music Man...
212-65 Combo
HD 130 Reverb Head x 3
115 Reflex Horn Cab
212 Reflex Horn Cab

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9 years 3 months
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Amp Craftsman 86 Sat, 04/22/2017 - 14:25

... And the backplate of the 130 my son gigs with... His amp doesn't specify whether the jack are wired in series or parallel- so is there a method for me to find out through testing without removing the chassis? (Sorry these photos are sideways)

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Mike Griffin
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MM 112-RD-65

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10 years 9 months

mgriffin155 Sun, 04/23/2017 - 14:46

Hi Steve, Here's a simple test that should work. If the jacks are wired in parallel, the main speaker jack must be used before the extension jack can be used. Conversely, if the jacks are wired in series, the extension jack can be used with nothing plugged into the main jack. Try this with a guitar plugged in and the volume controls set low. -mgriffin

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Steve Nordstrom
Music Man Equipment
I collect and restore amps and speaker cabinets- particularly Music Man...
212-65 Combo
HD 130 Reverb Head x 3
115 Reflex Horn Cab
212 Reflex Horn Cab

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9 years 3 months
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Amp Craftsman 86 Tue, 04/25/2017 - 15:00

Will do, and thanks!...

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Fronek Miloslav
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Music Man RD112 Fifty Oxford speaker

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7 years 4 months

Fronek Mon, 08/21/2017 - 08:20

It's possible in my MM RD112 Fifty amps internal 8ohms speaker with external 8ohms speaker conjunction/together?
Thank you.Mila

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MM 2-10-65

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10 years 9 months
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mm210 Mon, 08/21/2017 - 14:34

OK-I know there is a language barrier but this doesn't make any sense to ME. Please try to clarify. Mike.

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Mike Griffin
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MM 112-RD-65

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mgriffin155 Mon, 08/21/2017 - 18:00

I think he meant "Is it possible to connect an external 8 ohm speaker?" The short answer is yes. BTW:That is some clever wiring on the external jack. -mgriffin

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Peter Sunesson
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Music Man 112RP Sixty-Five
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Boondocks Sun, 01/20/2019 - 11:16

I moved my post.

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Fronek Miloslav
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Fronek Tue, 08/22/2017 - 01:44

Hi,
excuse my english isn't good.Amp from the 82s=rear panel=without speaker impedance switch!when i use extension speaker+
internal speaker/together=series impedance R1+R2=8ohm+8ohm=finally 4ohm.
Mila

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Brad Hollis
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MM 210-65 Hybrid Combo

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7 years

Tonedog Sun, 12/31/2017 - 18:13

All very good questions and responses, but I'm not clear if I need to switch from 8 Ohms to 4 Ohms if I connect an external cabinet that has one 8 Ohm speaker to the second speaker jack (connected in series with the 1st jack) and run it simultaneously with the two onboard speakers.

Thanks much.

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mm210 Mon, 01/01/2018 - 10:47

No, you SHOULD normally have it on 4 ohms if using only the internal speakers and switch to 8 if using an outside cab. You're actually going to have 12 ohms and the amp will take a 100 percent mismatch or more so 8 is what you use. Mike.

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John Rocklin
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210 65

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chromatic1 Mon, 10/08/2018 - 07:02

I would like to use a 210 extension cabinet to effectively make my 210-65 a 4 x 10. The extension speaker cabinet is marked 4ohms at input. I assume this means it has 2 8ohm speakers. If I run this cabinet from speaker out is that correct and safe ? will it run all 4 speakers ? Thanks in advance for any help !!

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Lars Verholt
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lmv Mon, 10/08/2018 - 19:35

Hello chromatic1

Set the impedance switch to 8 ohms and you are in business.

Cheers
Lars Verholt

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John Rocklin
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chromatic1 Tue, 10/09/2018 - 04:06

Thanks Lars !!

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Bill Kasper
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czech-one-2 Thu, 04/23/2020 - 07:05

Ok, I have an RD-50 mini head on the way [not here yet]
Anyway, it has two speaker jacks, both labeled 8ohm.
I'd like to connect just ONE jack to a 4ohm cabinet and leave the other jack unused. Is it ok or do I need an 8ohm cabinet?
I guess what I'm asking is, when both speaker jacks are hooked up to an 8ohm load does the amp see a 4ohm load?

Thanks in advance, 1st post here! (surely more will follow! ;-)

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Bill Kasper
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czech-one-2 Fri, 04/24/2020 - 13:18

Found the answer as the amp came with the original manual. You can run a single 4ohm output if you plug a dummy jack into the extension speaker out jack, Cool!

However I'm gonna have to start a thread on this amp as the mods done to it are worthless. The effects loop is pure feedback and I want to remove the front panel cut and brilliance mod and put a treble and bass pots back in, but I would need some assistance returning this thing to stock. All the electrolytics are original and probably need changing and the reverb has a loud hum. Not real happy about my new amp day.... :-(

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Lars Verholt
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lmv Fri, 04/24/2020 - 15:28

The unconnected plug is not shorted, it's open.

Cheers,
Lars Verholt

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Bill Kasper
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RD-50 HEAD

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czech-one-2 Fri, 04/24/2020 - 15:30

Right, fixed that.
Thanks Lars!

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John J Martinez
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JohnJMartinez Thu, 12/10/2020 - 11:13

What's the process for a non-gear head to test is speakers are blown, or if it's other components?
Last played in 2015, sound went out during bar jam while volumes set at 10. I did not know how to set the amp for distortion and volume. Now using this site to get amp back into biz. Myself as well.

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