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Amp Craftsman 86
Amp Craftsman 86's picture

Speaker Jacks in SERIES?

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....

mm210
mm210's picture

I don't remember ANY 130

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?

mgriffin155

Some are and some aren't

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_2275-130... 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

Amp Craftsman 86
Amp Craftsman 86's picture

The Amp in Question

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 !

Amp Craftsman 86
Amp Craftsman 86's picture

Backplate Photos

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

Images: 
Tom Lance

speaker jacks on back panel....

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.

Amp Craftsman 86
Amp Craftsman 86's picture

Backplate Photo 2

... 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)

Images: 
mgriffin155

Series or Parallel

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

Amp Craftsman 86
Amp Craftsman 86's picture

Awesome...

Will do, and thanks!...

Fronek

External 8ohm+Internal 8ohm conjunction

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

mm210
mm210's picture

OK-I know there is a language

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

mgriffin155

I think he meant

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

Fronek

MM 112RD Fifty speakers impedance

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

mgriffin155

The switch is in the jack

The external speaker jack is wired in such a way so that when used, it will switch to 4 ohm output impedance on the output transformer. See this schematic for how it is wired. http://pacair.com/mmamps3/sites/default/files/docs/1650-rd.pdf -mgriffin

Fronek

The switch is in jack

Hi,
thank you very much yours sincerely MF

Tonedog

Speaker jack impedance on a 210-65

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.

mm210
mm210's picture

No, you SHOULD normally have

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.

chromatic1
chromatic1's picture

210-65 speaker out question

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 !!

lmv

Yes it will

Hello chromatic1

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

Cheers
Lars Verholt

chromatic1
chromatic1's picture

Thanks !

Thanks Lars !!

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