I would always use isolated wires for mains use and the bias shouldn't drift much but who knows with the age of the unit/capacitors/tubes. 

22 minutes ago, spritzer said:

I would always use isolated wires for mains use and the bias shouldn't drift much but who knows with the age of the unit/capacitors/tubes. 

Got it! Thanks!

Can I ask for one final confirmation before I proceed with plugging the 007tA in and switching it on?

Here are some photos after the modification:

Should I do any sort of voltage or impedance measurements, so I can check in advance if everything was done correctly? If yes, what and how exactly to measure?

Also, do I have to change the fuse (which in my case is 1,6A)? Haven't touched the bias or anything else.

Thanks a lot!

Looks good to me and not sure about the fuse as that is some silly audio grade fuse... 

3 hours ago, spritzer said:

Looks good to me and not sure about the fuse as that is some silly audio grade fuse... 

About the fuse, I meant if it being 1.6A can cause any electrical issues after the voltage change (think someone mentioned 1A fuse on his).

And about the measurements - although I doubt that soldering was done incorrectly, but still, are there any precautionary measurements that I can make in order to be 100% sure that all's fine prior plugging it in?

Spitzer, thanks a lot for helping out, really appreciate it!

1.6A should be fine and you can always measure the resistance of the windings.  There should be a resistance reading when measuring from one end of the windings to the other when they are set to 240V. 

Mission accomplished. All seems to be working fine after the modification. Just to confirm - there should be 3 red leds ON when the device is in working state (couple of D3s and a D4), correct?

And again, is it advisable to go through readjusting the bias after the 100V-240V conversion? Unit is ~ 6 years old, tubes are RCA cleartops with a run time of ~ 150h, capacitors - I have no idea.

Just check the offset and balance, if they are within spec (+/-20VDC) then it should be fine. 

Here to bump the thread up.

Does anybody knows the spec of SRM-007T transformer?

I am currently working on a SRM-007T repair and the transformer showing signs of leakage on one secondary HV rail. Measured about 160VAC w/o load and showing some magic smokes... also DCR on corrupted rail is lower than normal ones (79ohms vs 50ohms).so I feel theres some insulation breakdown in the sec side.

 

I ask some workshop to see if they can rewind the transformer.they ask me detail about specs of all the rails.

from schematics KG kindly provided me.I am sure HV should be two 270VAC ,filament is 12.6V CT (6.3-0-6.3).but I still need:

AC Voltage on LV side (I assumed  30VAC CT)

current rating on all secondary side rails

thanks!

Edited September 27, 20232 yr by ang728