AKAI M8 recapping

[Analogue man]

In the photograph of the missing valve, I notice that the spring return on the record switch on this channel looks a bit weak, either replace it or retention it as this is the spring which returns switch to play from record.

[RoyceVM]

Originally Posted by Analogue man

In the photograph of the missing valve, I notice that the spring return on the record switch on this channel looks a bit weak, either replace it or retention it as this is the spring which returns switch to play from record.

Hi Graham,

Thanks! I will check it and replace as needed.

Royce

[RoyceVM]

I am following the original list of Capacitors in the brochure and replacing it.

[Station X]

Don't replace any Mica capacitors, they're generally very reliable.

[RoyceVM]

Originally Posted by Station X

Don't replace any Mica capacitors, they're generally very reliable.

Hi Graham,

Thanks!

[RoyceVM]

Big disappointment!

The 6X4 replacement tube came today and I replaced the broken one, to my great surprise there was no audio now.
No sound at all from both channels.

Everything was working well until I accidentally broke the 6X4 on the right channel.
When I was waiting for the tube to come, I pulled all the tubes and cleaned the leads and holder and carefully put them back one by one.
So, every tube is in the correct holder.

All the electrolytic caps will come this week. I feel guilty and was greedy to make it all perfect with caps replacement.

There was a cracking sound after say 5 min running, and it went away, and that is why I wanted to replace all the electrolytic caps.

I don't know what I will do now.

[RoyceVM]

If the tube 6X4 is defective for some reason, will the audio completely cut off?
I hear nothing from the speakers.
It was sounding so nice before I tried to clean the tube pins and broke the 6X4 on the right channel.

[Analogue man]

If the replacement 6X4 is faulty and it sounds very likely that it is then the audio side will not work at all as this tube is the one that rectifies the AC to DC. Is the new tube lighting up? If not then definitely faulty.

[RoyceVM]

Hi Graham,

Thanks so much for your reply! Yes, the new tube is lighting a little more brighter than the other 6X4 on left channel.

For a quick check can I put the 6X4 from the left side and check for audio and power up?
One channel might not work right?

Please advise.

Thanks
Royce

[RoyceVM]

I will wait and order a 6X4 tube.

[Simon Gittins]

The strange thing is that you now have no sound at all from both channels.
Using information from this page:
https://museumofmagneticsoundrecordi...ersAkaiM8.html
Both amplifiers each have a 6X4 rectifier valve (tube) so a missing rectifier in the right side should leave the left side still working. I would suggest starting by seeing why the left side is silent, perhaps you have disturbed something. Some logical checks will be needed, you have already confirmed the valves are lit so that is a good start. Is there a normal level of hum and hiss from the left side or slight noise when the volume control is moved? If not, some voltage checks will need to be the next step.

[Station X]

Originally Posted by Simon Gittins

If not, some voltage checks will need to be the next step.

Hear Hear! I'd start by checking that HT (B+) is present on both channels.

[Analogue man]

Just a thought, have you accidentally left one of the multi pin plugs unplugged when you last was inside the machine?

[Welsh Anorak]

Agreed - if both channels are off (these use two self-contained amplifiers) then you need to look for a common connection between them..

[RoyceVM]

Originally Posted by Simon Gittins

The strange thing is that you now have no sound at all from both channels.
Using information from this page:
https://museumofmagneticsoundrecordi...ersAkaiM8.html
Both amplifiers each have a 6X4 rectifier valve (tube) so a missing rectifier in the right side should leave the left side still working. I would suggest starting by seeing why the left side is silent, perhaps you have disturbed something. Some logical checks will be needed, you have already confirmed the valves are lit so that is a good start. Is there a normal level of hum and hiss from the left side or slight noise when the volume control is moved? If not, some voltage checks will need to be the next step.

The left channel is silent. No noise when the VC is moved.

[RoyceVM]

Originally Posted by Analogue man

Just a thought, have you accidentally left one of the multi pin plugs unplugged when you last was inside the machine?

Thanks. I moved the two amp sections partially out to remove the tubes and clean the pins. I didn't unplug any multi pin plugs. I don't know if I let them loose while moving the amp sections out. I will check that soon. Thanks.

[RoyceVM]

Originally Posted by Simon Gittins

The strange thing is that you now have no sound at all from both channels.
Using information from this page:
https://museumofmagneticsoundrecordi...ersAkaiM8.html
Both amplifiers each have a 6X4 rectifier valve (tube) so a missing rectifier in the right side should leave the left side still working. I would suggest starting by seeing why the left side is silent, perhaps you have disturbed something. Some logical checks will be needed, you have already confirmed the valves are lit so that is a good start. Is there a normal level of hum and hiss from the left side or slight noise when the volume control is moved? If not, some voltage checks will need to be the next step.

Thanks! No normal level of hum when the VC is moved. It's all quiet now with the motor running and play mode also functioning well with no audio.

[Station X]

Here's the circuit.

Have you got 260VDC across both C25's?

[RoyceVM]

UPDATE

Those two white push buttons on both channels were in fully recessed position. I pushed them all the way in on both right and left and now I get the hum responding with the VC. Unfortunately, there is audio only on the right channel.
No music from the left channel.

[RoyceVM]

There is only very faint audio from the left channel.
I heard cracking a bit again when I started it but don't know if it ever came from the left and faded away. Cleaned the head again to make sure it is not from a dirty head.