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-   -   Help power up akai M8 amps (http://www.diyaudio.com/forums/tubes-valves/210867-help-power-up-akai-m8-amps.html)

Eric123 16th April 2012 11:08 AM

Help power up akai M8 amps
 
I need help in powering up the tube amps off a Akai M8 reel-to-reel.

Each of the tube amps has its own transformer, but what consfused me was the voltage selector transformer which sets the appropriate voltage for particular country. Being an Australian we use 240 volts and I don’t have this selector and transformer. And I’m not sure if this transformer is a step up or down one either?

Can I connect 240v power to the amps main transformer? On one side I assume is the primary, there are 2 groups of 3 terminals – 250v, CT, 250v @ 60mA D.C. and 117v, 100v, 0v. The other side of the transformer has 2 terminals for each – 5.7v(0.3A), 6.3v(0.6A) and 6.3v(1.8A).

I was planning to use it as a hifi amp, guitar amp and other things. They both have all the connection sockets for various things on the front, its just a matter of powering them up.

Anyway, does anyone know?

thanks

Eric123 16th April 2012 01:36 PM

Just to add a little more, I’ve got a fully working Akia M8 reel-to-reel to compare, as well as the service manual. It’s a little hard to trace things because the wiring is spaghetti and clamped too well. The mono blocks look identical and complete in comparison to the reel-to-reel, except for the power selector transformer which sit’s up higher next to the motor.
Anyway I’m fairly new to tubes compared to transistors, but this is what I got so far;


This link suggest if my power is 120 volt then I could wire it up as 117volt tap, neutral to 0 tap and ground to chassis?
http://messageboard.tapeop.com/viewt...=asc&&start=15

and,

http://beyondsanityproductions.com/i...ask=view&id=13


But I’m using 240 volts power, in this link he is asking whether it’s safe to have both 117v in series.
http://www.groupdiy.com/index.php?topic=40846.0

Maybe all I need is simply a commercial step-down transformer that both amps could plug into?


thanks

DF96 16th April 2012 05:57 PM

117V, 100V, 0V is a tapped primary for for incoming mains in the region 90-125V. You will need a step-down transformer to convert 240V to 120V.

250-0-250 is the HT secondary.

Eric123 17th April 2012 09:24 AM

Quote:

Originally Posted by DF96 (Post 2987749)
117V, 100V, 0V is a tapped primary for for incoming mains in the region 90-125V. You will need a step-down transformer to convert 240V to 120V.

250-0-250 is the HT secondary.

I think I might be able pick a up a commercial step-down unit that I can just plug into like any other american appliance.

I think that would be a more practical excersize if I want work on the amps.

thanks

Eric123 17th April 2012 09:54 AM

What about these step-down units?

50VA 240VAC to 115VAC Stepdown Transformer - Jaycar Electronics

and


120W 240 - 115V Isolated Stepdown Transformer - Jaycar Electronics

HollowState 17th April 2012 03:38 PM

I hope you're using the amplifiers for some other purpose besides using it with the M8 transport. That machine has nice electronics, but has a horrible problem of developing flutter due to cogging in the supply turntable.

Eric123 18th April 2012 11:29 AM

Quote:

Originally Posted by HollowState (Post 2989057)
I hope you're using the amplifiers for some other purpose besides using it with the M8 transport. That machine has nice electronics, but has a horrible problem of developing flutter due to cogging in the supply turntable.

Yes I am. The amps are for variouse uses beside hifi like guitar and synthesizer.

Since Im in Australia and I need a step down transformer I possible might be better off whith a 240v to 100v converter since the 117volt tap is free and the wires go to 100v and 0 taps.

I might as well include a general description of soughts.

It’s a bit of a brain tease for me this voltage selector combination. The power plug active goes straight to the selector and its transformer has 6 taps. 2 of those taps, bottom(ground) and top and power plug neutral go to a plug socket. On the amp transformer the 250v section looks like it goes to a tube and there are a few wires connected to the 100v tap and 0 tap. The tubes the amps take are EF83 *2, 12AX7 *2, 6BQ5 *2, 6X4*2, 6ARS *1. That last tube is only on one amp(the top one I think). There are 2 additional smaller transformers in each amp, lots of capacitors and resistors. They are 6 watt/8ohm amps.

Far as controls and sockets in the amps, there is your volume knob, one tone knob with a bias knob in the centre of that. It sounds best on the highest bias setting. Each one has its own VU meter which reads the speaker outs I think. Far as sockets are concerned, there is a line-in socket and microphone socket. There is also a turntable-in preamp socket and preamp-out(line-out) socket. Each have their own speaker-out socket. Each has a power switch. Finally, the top amp has the record light and “push to motor” push-button switch, and the bottom amp has “push to sound on sound” push-button and headphone socket.


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