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Akai/Roberts tube preamp mods
Old 26th July 2012
  #1
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3 Reviews written
🎧 5 years
Akai/Roberts tube preamp mods

Hi
I am trying to convert a pair of Roberts 997 reel to reel preamps into Rod C's "Boris" mod. .. I wish he were right outside my door right now!

I have two questions : are the ak networks the red square pieces marked "lover Japan" on the 997?
Are the values on this schematic correct or look correct from a quick glance? The values and part numbers do not match for my model of Roberts r2r :p

Much thanks

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Attached Thumbnails
Akai/Roberts tube preamp mods-uploadfromtaptalk1343332336646.jpg  
Old 27th July 2012
  #2
Here for the gear
 
🎧 10 years
The schemo looks pretty much like the 700 series I'm familiar with, minus the input xformers. Never seen those. Is this schematic for the 'boris' or is the what you have stock? Getting everything sorted out from the record/play mode differences is a pain. "AK" network? "Japan lover?" I'm no help there.
Old 27th July 2012
  #3
Lives for gear
 
3 Reviews written
🎧 5 years
Hey!
Yeah this is the schematic for the Boris. I am curious about the values of the componentw I'm the top left side, to make sure that they look relatively "correct" to someone with experience and not switched around. Specifically the 250k, 1 meg, and 2 k resistors around the ef-86 stage.

The Japan lover parts and ak networks are something I got from the beyond sanity website where rod c posted instructions on how to do these mods on akai m7/8s and the 700 series Roberts.

I'll take some pictures and save a couple thousand words!

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Old 28th July 2012 | Show parent
  #4
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12ax7's Avatar
 
🎧 10 years
Quote:
Originally Posted by enginefire ➑️

I'll take some pictures and save a couple thousand words!
I would certainly appreciate it.

(And yes, algebraically speaking, a word IS worth 1/1000th of a picture.)
...I'm kind of interested in this because I think I know where one of these old beasts might be sitting about collecting dust, and I think I could get my grubby mitts on it for free.
.
Old 28th July 2012
  #5
Here for the gear
 
🎧 10 years
yeah... Not much in the way of 'mods' here. These seem to be bone-stock values, minus the extraneous, and some jacks added in spots where the rec/play switch would have broken the circuit anyway. A 'tidied up' circuit.
Just what I would have done some time ago if....
Old 28th July 2012
  #6
Lives for gear
 
3 Reviews written
🎧 5 years
These are not the mods you are looking for!
Akai/Roberts tube preamp mods-uploadfromtaptalk1343491525758.jpg

I see what you mean about the removal if the play record switches and jack replacements.

Also after closer inspection I think that the Japan lover parts are mica capacitors, and that the "ak" networks are mot used in this model, rather it is using individual caps and resistors.
Akai/Roberts tube preamp mods-uploadfromtaptalk1343491563112.jpg
Akai/Roberts tube preamp mods-uploadfromtaptalk1343491586001.jpg

As long as the schematic looks good I am going to proceed and turns these in to some nice Mic pres!


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Old 28th July 2012
  #7
Here for the gear
 
🎧 10 years
That's prolly spostuh be 'clover.' Pictures are nice, eh? There will be a lot of stuff to come out. Especially on the erase channel, the one with the 5AR4. No wait; 6AR5. Prolly a oscillator coil or two. Do you hve the complete schematics?
Old 28th July 2012
  #8
Here for the gear
 
🎧 10 years
does seem a shame to not use the 5w+ output capability of these
Old 28th July 2012
  #9
Lives for gear
 
3 Reviews written
🎧 5 years
Ah clover that makes a lot more sense, lover seemed like a strange brand name.

The 5w output should be maintained in the final version, the output transformer and output jack are still there. There are other mods that remove the power tube but the Boris keeps it and let you use each pre amp tube as an independent preamp. 4 preamps for each reel to reel!

I have a schematic and pictorial for an akai m7 which I have been told is identical. I am not so sure if it is tho, there are some discrepancies in part numbers and values between the akai list and rod C's schemagic.

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Old 4th August 2012
  #10
Gear Maniac
 
🎧 10 years
Quote:
I have two questions : are the ak networks the red square pieces marked "lover Japan" on the 997?
The AK networks are small and square and encased in a covering that looks very similar to a ceramic disk cap. It should have "AK" in big black letters clearly marked on the side. Never seen the lover Japan on any.
Old 22nd September 2012
  #11
Gear Nut
 
🎧 10 years
997

How's this going? I'd be interested to know if the 997 ends up working. I maintain a page (which may or may not be useful to you) at Roberts/Akai Preamp Mod that details a 720A conversion, and i'm just finishing an M7 conversion. I'll add the 997 to the "it works" list if you get yours going.

Thanks,
-c
Old 23rd September 2012
  #12
Lives for gear
 
3 Reviews written
🎧 5 years
Hey thanks! That is a great site you made. I will keep you up to date when I finish these, I got really side tracked with some health issues so I haven't given it any effort in a while. Hopefully soon I will get back to it... I really want 4 new pres!

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Old 23rd September 2012
  #13
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AndyFromDenver's Avatar
 
1 Review written
🎧 10 years
Doing a pair with my friend now.
As lassoharp said the ak is a little cap resistor package, and may be individual parts or the ak package depending on your model and year.
The Japan lover looks like a domino cap, I don't recall seeing one on mine.
Just have to really carefully follow the schematic and instructions. It's a tangled mess in there!! It's been nice doing this with a friend for checks and balances, we're done except being cheapskates on spending on inpt transformers....
Anyone have a lead on a cheap substitute?
(ps if this is an old thread I've been lured into, sorry...)
Old 23rd September 2012
  #14
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AndyFromDenver's Avatar
 
1 Review written
🎧 10 years
Quote:
Originally Posted by chconnor ➑️
How's this going? I'd be interested to know if the 997 ends up working. I maintain a page (which may or may not be useful to you) at Roberts/Akai Preamp Mod that details a 720A conversion, and i'm just finishing an M7 conversion. I'll add the 997 to the "it works" list if you get yours going.

Thanks,
-c
Oh cool!!! Didn't see your site. Will be reading. Thanks for sharing your builds
Old 24th September 2012
  #15
Lives for gear
 
3 Reviews written
🎧 5 years
A link for the visually inclined... Not me! Just something I found
http://m.youtube.com/watch?feature=r...&v=pU3qIR_H3hI

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Old 7th October 2012
  #16
Gear Nut
 
🎧 10 years
Just finished my M7. (pics in the slideshow)

Man, it's like having a kid... you forget how much work they are! How's progress? Stick with it, there is light at the end. :-)

-c
Old 16th March 2014
  #17
Here for the gear
 
Leraven's Avatar
 
🎧 5 years
I've got an Akai M-7 in great shape that I need to get rid of. Both channels work great. I don't have the time/money to convert, so anybody that is interested PM me! I'm in the DFW area.
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