Found this website might help a little.. only ever went to Rumbold once a long time ago
http://www.ozvalveamps.org/valvetechs.htm - assuming more guitar and bass amps
I would recommend Carlton Audio Visual for hi fi amps repair.. I'd ask at Music Swop Shop in Carlton for a guitar amp/speaker repair/recone guy/place if Ian Rumbold isn't doing work anymore.
Turntable services I've been having lots of issues personally.. was going to go to authorised Technics/panasonic repair a decade ago - JAV.. but took a TV in and took 4 months and died from same problem a few months after getting back. Took to 'Samurai AV' in Coburg, the main guy handed it to his underling who is now the only guy there doing repairs. He did an ok job but didn't calibrate the pitch properly or mention that I needed a new slider, even after taking it back a second time to get the unattended issues sorted. Thornbury Records a year ago advised they would be willing to undertake a mod job I want on my Tech 1200 that is simple but others were not prepared to do, but now say they are too busy to undertake repairs at all.
I saw 'Bounce Audio' a year ago before ending up going to Samurai AV, Bounce is in Cato street Prahran, near where DMC used to be. They are reasonable prices when I checked and apparently it was the guy from Koolism that was doing their repairs/services. Danielsan I think he went by. I emailed them a month ago while they were away from Christmas, but they have been back 2 weeks now and still no reply, so I might try calling them soon.
Carlton Audio Visual might be a place I end up going for repairs/servicing in the end, as they are the nicest guys and super transparent and knowledgeable. But they probably won't do mods.
Logitronics have been recommended to me but when I contacted them a year ago (and from online reviews read) they seem to be always super busy. They actually emailed saying they literally couldn't help me, as had a 4 month backlog. Not sure what they are like now, you might get lucky and find them at a quiet time, but it seems they just get more and more recommendations each year.
I know you didn't mention guitars at all, but if you ever need or know someone with a guitar service/repair/modification to be done.. I HUGELY recommend 'Freddy Frettin'. He is the ABSOLUTE MAN. He totally knows his stuff and completely transparent. The prices are fair for the work, you can find cheaper people around but I won't trust my gear with anyone else since finding him. No one else seems to have his extensive knowledge of rarer stuff to work on and extended range/odd tuned/7-8+ stringed guitars too. After going to the Music Swop Shop, my old regular place to get Dalby to install some Bare Knuckle Pickups, he didn't go online and check the wiring and tried 3 or 4 different brands of wiring techniques to my pups. Was super upset he could have wrecked them. Also the time before that I went in, I took my Fernandes Sustainer guitar to get the Sustainer electronics fixed up a little. Took the job on, set up the guitar and gave it back charging me for the setup and explaining he couldn't do the soldering. Freddy can do Fernandes installs no problems btw
http://www.frettinfreddy.com/
Lastly another option for turntable and other audio equipment repair I found recently.. Goldmine in Nicholson St Fitzroy Nth is now doing repairs and servicing, since changing from a CD to vinyl store.
http://www.goldminerecords.com.au/ Always loved shopping and browsing in there two decades ago so am keen to head in and check out what they can do to help me repair some of my gear.
There are other options out there for specific things too, like I found a place in the suburbs recently that say they can do my 8 track player and cassette deck. Anyway hope this helped, I'm always on the hunt too so if anyone knows people please post them
DMC is closed now too btw
So yeah my quest for someone to replace an on/off knob, pitch slider and quartz lock platter pressure mods continue.
Not sure why but since getting my turntable from Billy after two times, the pitch (if pushed quickly from -3% to +6%) can oscillate up and down.. sounds terrible, it gets stuck warbling up and down in pitch until you move the slider. Also the %3 and 6% aren't close to where they should be at all, you can see from the dots quite easily. MAYBE my pitch slider needed replacing, or the PCB etc, but he didn't mention that at all. So after a month and two looks at it, it really upset me that Billy (at that stage apprentice still at Samurai AV) couldn't at least tell me that it was fucked and needed replacing (would have got him some more $ to fix it).. or be honest and say it can't get any better without a replacement. Also, since I was getting a detent click removal it ended up being a waste of money, getting a new slider anyway. I got a M3D slider to avoid having to remove the detent click AGAIN. The best repair guys will admit their mistakes, or hold your hand when you are a noob to some gear.