Another Burns of London, Amplifier on my bench for repair ...

[Jon Snell]

I wonder what it is ...

Fully transistorised, (very modern) germanium transistors throughout ...

More to follow.

[mhuss]

I like the "Orbital" speakers (and the dangling geraniums!)

[Helmholtz]

Control panel on the rear, very odd.

[Jon Snell]

The stated fault is poor sound and crackling selector switch.
First inspection shows aged electrolytics , mainly 100u 10volt and 470u 25volt with a couple of 5u 10v and a 1u 5volt.
All three large capacitors measure perfectly fine with no sign of any issues, no measurable leak and all three have an ESR reading of less than 1 Ohm.
Fresh capacitors fitted;
The few old types that are still in circuit decouple the emiters of the pre amp germaniums and are in good condition.

More to follow ...

[The Dude]

Side Note: That mains voltage selector switch looks to be a simple easily accessible toggle switch. WAAAY too easy to switch by accident, IMO.

[The Dude]

I like the "Orbital" speakers (and the dangling geraniums!)

Yes, that's quite the transistor mounting system isn't it (rubber grommets)?

[Helmholtz]

As the early Ge transistors could be damaged by heat during soldering, they came with long leads and not shortening them was a precaution.Transistors were expensive then.

[Jon Snell]

As the early Ge transistors could be damaged by heat during soldering, they came with long leads and not shorting them was a precaution.Transistors were expensive then.

Indeed, a heat sink is required when changing/soldering Ge transistors.
I use a pair of flat bladed pliers and a hot soldering iron for speed.

[mozz]

Indeed, a heat sink is required when changing/soldering Ge transistors.
I use a pair of flat bladed pliers and a hot soldering iron for speed.

I have thousands and build pedals all the time, never damaged one from soldering. I was military certified soldering in 1980 so i may have learned a little about get in get out.

[Stratfordade]

As the early Ge transistors could be damaged by heat during soldering, they came with long leads and not shortening them was a precaution.Transistors were expensive then.

you’ve reminded me of the ubiquitous OC71s and AC127/128 pairs of my youth!

[Jon Snell]

This amplifier employs NKT403 output transistors, transformer couple to an NKT404 running from a stabilised 32volt DC supply. NKT = Newmarket Semiconductors.

The pre driver is an NKT213 and another NKT213 with an OC702 pre amp.
Surprisingly quiet, noise wise and the replaced leaking capacitors, have stopped the nasty crackling noises from the selector switch.

Some snippets of how they put it all together and what the various parts do.


Sounds exactly as I remember these with the Elac loudspeakers. One of the plastic magnet covers was loose and I had to glue it back on, taking a photo of the makers name first.


Another great piece of history up and running again in our local recording studio.
Thank you for looking.

[mozz]

I've seen the name elac miracord on turntables here in the US.

[The Dude]

Nice work, Jon!

[Jon Snell]

Nice work, Jon!

Thank you.

[J M Fahey]

Control panel on the rear, very odd.

Tell that to Fender Champ, Bassman, VOX AC30 , Sessionette , and thousand others