Akai M-8 SEP amps (tracker-x mods)

BmWr75

AK Subscriber
Subscriber
Here are some pictures of my new to me Akai M-8 SEP amps. Bought these in a Akai "suitcase" RtR (see unmolested pics here) a few months ago. Read about AKer tracker-x's mods and the cabinets AKer Raul has AKer JohnW make for him.

A month or so later.....here are the results (see pics).

I only had one problem after completing the mods. One of the amps had a loud hum and I could only faintly hear the music playing. Ended up it was the amp that has the two piece slide-bar on top that must be pushed to the left to make these amps work as standalone amps. The short piece of the slide bar moves independently and I had not pushed it to the left. As soon as that was remedied, hum problem was solved.

I'd like to thank:

1. JohnW for making these white oak cabinets with the ammonia fume finish.

2. Raul for posting the pictures of his M-8 amps. http://www.audiokarma.org/forums/showthread.php?t=345501

3. Tracker-x for posting his M-8 amp mods. http://www.audiokarma.org/forums/showpost.php?p=1100906&postcount=9

An easier to read version of the tracker-x mods is posted here: http://www.audiokarma.org/forums/attachment.php?attachmentid=309141&stc=1&d=1320615983

I'm still running the stock NEC tubes in all positions and these amps sound sweet. :music:

Update 1: These amps should probably not be stacked as I've shown them in the pictures. They put out some heat.

Update 2: List of capacitors purchased for the refurbishment (I ordered a few extra of some of the less expensive.......just in case):
Tube Depot
Quantity 9 - Sprague Atom 25 uF 25V
5 - Sprague Atom 20 uF 500V
2 - multi-cap cans 20 uF x 20 uF 600V
6 - Orange Drop .022 uF 600V
8 - Orange Drop .010 uF 600V
2 - Orange Drop .0047 uF 600V

Digikey
2 - 3.3 uF 350V electrolytic radial
3 - 1 uF 350V electrolytic radial
2 - 360 pF 500V mica radial (kind of pea shaped actually)
2 - 15 pF 500V mica radial

There is a great possibility I already had some of the required caps lying around which are not reflected in the above orders. They would have been Orange Drops though, probably the .022 uF size.

Update 3: Added pictures of the bottom of the amps after all the umbilical cords have been stripped out. Pics show the locations of many of the caps there were replaced.
 
Last edited:
I believe it is the 770X (first pic). Thing with the 770 (second pic) is the face plate is one piece making it more difficult/involved to make two separates. Not sure if there was a comparable Akai version with an integrated face plate, any one know?

Cheers

Lar
 

Attachments

  • Roberts 770X.jpg
    Roberts 770X.jpg
    20.1 KB · Views: 192
  • Roberts 770 picture.jpg
    Roberts 770 picture.jpg
    23.3 KB · Views: 197
I believe it is the 770X (first pic). Thing with the 770 (second pic) is the face plate is one piece making it more difficult/involved to make two separates. Not sure if there was a comparable Akai version with an integrated face plate, any one know?

Cheers

All of you are inspiring me to buy my friend's M8.Based on The VU meters model,The Robert 770 almost has same appearance with my Akai M7 and 770 X like my friend's M8.
I will take M8 to accompany my existing AKAI RTR: AKAI 1710W+SW50 Speakers since 1967,NOS AKAI 1710W+NOS SW50, AKAI M7 + SS100 speakers.Thanks.Regards to your BMW R75 from my Haflinger Steyr Puch.
 
Last edited:
Good job! I like the cases. AK'er Sloober and I did these mods on an M-8 and and a Roberts at the same time, he kept the Roberts and I kept the M-8. I've got a hum in one of mine that I need to track down.
 
I came across a pair of the Roberts 770x amps about 15 months ago and did
the tracker-x mods exactly as described.
I was very impressed with the results of the mods, so yes the Roberts 770x
units will respond to the tracker-x Akai M-8 mods, I think the circuits are
the same or very close.
I also am using the stock NEC tubes and they sound good in these mono amps.
 
BmWr75-
you are welcome. Great work! Did JohnW made the cases for you or did you built them?
A question: how much gain/volume have your modded M-8 amps? Mine, with a standard CD player as input, have a rather low volume and I must turn up the knobs at maximum to have a rather good listening volume. I connected these to a pair of Dynaco A-25 that surely aren't the most sensitive speakers around, but I was able to drive them with other small EL84 SE amps, like the ones removed from Magnavox consoles.
 
Last edited:
BmWr75-
you are welcome. Great work! Did JohnW made the cases for you or did you built them?
A question: how much gain/volume have your modded M-8 amps? Mine, with a standard CD player as input, have a rather low volume and I must turn up the knobs at maximum to have a rather good listening volume. I connected these to a pair of Dynaco A-25 that surely aren't the most sensitive speakers around, but I was able to drive them with other small EL84 SE amps, like the ones removed from Magnavox consoles.

Try the Mic inputs, but turn the volume down first :yes:

Cheers

Lar
 
BmWr75-
you are welcome. Great work! Did JohnW made the cases for you or did you built them?
A question: how much gain/volume have your modded M-8 amps? Mine, with a standard CD player as input, have a rather low volume and I must turn up the knobs at maximum to have a rather good listening volume. I connected these to a pair of Dynaco A-25 that surely aren't the most sensitive speakers around, but I was able to drive them with other small EL84 SE amps, like the ones removed from Magnavox consoles.

Raul,

I've not tried them with speakers yet, just headphones and there is plenty of gain for headphones.

Yes, JohnW made the cabinets for me.

As the prior poster said, the MIC inputs are high gain. Plug your CD player into them and give it a try. Be sure and have the volume turned all the way down on the amps first though.

Scott
 
Some folks do away with that first tube (EF86), but heck, that's my favorite low noise pentode. Also be aware that there is no RIAA equalization on the phono input, so you need to run a phono pre of some sort if you want to play rekkids.
 
I've never seen a set of those made too look so great before! I absolutely love those cabinets!
 
The tube you can do away with is the 6AR5 isn't it? Sumpin to do with erase head oscillator?

+1 on the cabinets, lovely wood work there. I've been thinking that since my Roberts 770 has an integrated face plate that it would be interesting to fabricate a clear poly face plate for each individual amp. You'd be able to see the tubes then. :thmbsp:
 
Yes, the 6AR5 can be removed. I did. Everything is working as it should without it.

I left the phono tubes in the amps. Will try it with a TT eventually.

Note: I added the list of replacement caps to the OP.
 
Back
Top Bottom