ampless ac15 2x10 impedance

RnFR · Post by **RnFR** » 29 Apr 2010, 08:24

i picked up an ac15 2x10 missing the amplifier, and now i want to make something of the blues loaded in this nice sounding little cab. anyone have any idea what the impedance rating would be for 2 of these 10" celestions blues?
the celestion site only has info for 12"ers. thanks!

lolbou · Post by **lolbou** » 29 Apr 2010, 12:08

AC15s are 15 ohms... Are these unwired so that you can't figure out if these were in series or parallel?

Two 8 ohms in series could make it then... In another thread here, someone told me that the DC resistance of the coil would be a little below the actual impedance : did you check it?

BTW I remember that the impedance of the GT-75 I had in my old Valvestate was stamped with ink on the speaker frame.

RnFR · Post by **RnFR** » 30 Apr 2010, 03:18

they are wired in series. so 15 ohms? the amp i'm using is a bogen chb50, and it has adjustable taps for the output impedance. i believe one of which is set for a 16 ohm load. i'll give that a shot then.

thanks for the help, lolbou. i really need to study up on the whole subject of amplifier output sections. i still feel a bit vague im some areas.

JiM · Post by **JiM** » 30 Apr 2010, 20:32

About everything Celestion, do not hesitate to ask them directly :
http://professional.celestion.com/guita ... /index.asp

I had some kind and helpful answers from Dr Decibel about those in my old Valvestate (Lolbou : it's a 8240, do we have the same amp ?).

lolbou · Post by **lolbou** » 30 Apr 2010, 20:46

RnFR wrote:now i want to make something of the blues loaded in this nice sounding little cab.

What about finding an AC15 chassis and make yourself one? Would you like the sound of this amplifier for your own taste?

JiM wrote:Lolbou : it's a 8240, do we have the same amp ?).

Nope, I had two 8080 mk1. I really liked these -easy maintenance/mods when needed- but sold them both for a Hot Rod. I do miss the overdrive channel sometimes though...

JiM · Post by **JiM** » 02 May 2010, 12:57

lolbou wrote:
JiM wrote:Lolbou : it's a 8240, do we have the same amp ?).
Nope, I had two 8080 mk1. I really liked these -easy maintenance/mods when needed- but sold them both for a Hot Rod. I do miss the overdrive channel sometimes though...

And i was proud of my stereo setup ...

There were no built-in chorus in yours, though.

Just the overdrive channel is not very complex : http://www.drtube.com/schematics/marshall/pc0689.pdf
There's five opamps, but also a high-voltage 12AX7. You can do it without the need for the MS2015 switching opamp, which may be hard to find. You may try and replace the tube with JFETs à la Runoffgroove, and make it into a stompbox. I just don't know if a cathode follower transformed into a source follower still behaves the same (especially the grid-current thing).

Back on topic :
I seems that the speakers were series connected, at least in the '90s reissue : http://www.voxshowroom.com/uk/amp/ac15tbxrear.html
The various versions of AC15 amps all seem to have 8 Ohm and 16 Ohm taps on the OT. http://www.voxamps.com/support/circuits/
But i did not find precise info about a dual 10" blue version ...
Do you have pictures ? It might be a really rare and valuable item.

dread pierat · Post by **dread pierat** » 04 May 2010, 09:12

What happens if you measure the resistance over each speaker and multiply this value by 1.3?

Aharon · Post by **Aharon** » 04 May 2010, 12:17

WELL................if you have a meter measure the impedance.You don't have to multiply ,the reading will be more or less 7 Ohms for an 8 Ohm speaker and 15 for a 16 ....more or less.
Aharon