Bird Golden Eagle 2/15
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This page was last modified on Sunday, February 05, 2012 00:23
1) History
I remember using one of these when I was a spotty teenager. We used to hire one (new shop stock) from the local music/radio/television shop for 10 shillings (50p) a night and then plug everything in sight into it. Whoever eventually bought it got the equivalent of an ex company Cortina.
This one came from ebay and arrived complete with screw in legs (30 shillings extra) still screwed in and sticking out of the parcel. I wish I could remember who the carriers were because I'd use them again any day. What's left of the serial number reads F19984.
Instrument amplifiers were just a small part of Bird's activities and they don't seem to have kept up with the specialist manufacturers. What they did produce isn't particularly relevant today, but there aren't that many good examples around and I was quite pleased to find this one (until I tried it). Nostalgia rules!
For an interesting run down of Bird and it's products visit Steve Russell and Tim Fletcher's site
http://www.vintagehofner.co.uk/britamps/bird.html
Among other things you'll find a link to John Beer's visit to the Bird Organ Works in Poole back in the 60s.
To put prices into perspective, ten shillings then would be over £10 now and forty one guineas is getting on for £900 (depending on who's figures you believe).
My apologies if I've used someone's scan of the catalogue, but I can't remember where it came from.
For a complete history of the Sydney S Bird Company go to http://www.gracesguide.co.uk/wiki/Sydney_S._Bird_and_Sons
2) Overall condition is very good and it almost works. There are three main problems.
First is the level of hum and noise. Everyone I've spoken to says that this is normal and down to bad layout.
Second problem is the fragile speakers. Although they're all fine at the moment, they're difficult to find ellipticals by Elac series wired to give eight ohms.
The third thing that definitely needs looking at is the power switch. The original push button contacts have burnt out (see picture below) and there's a replacement toggle switch hanging on the back panel.
3) General views.
4) Below is the remains of the on/off switch. The right hand wiper arm has completely disappeared in a big bang.
I had another lucky find on ebay and came up with an almost identical replacement. It's an old Radiospares "Maka" Switch part which has the same moulding on a different mounting plate. The plate comes off and the moulding fits perfectly onto the Bird mechanism.
This picture shows The Radiospares mounting plate (left), the Radiospares switch mounted on the Bird plate (centre) and the old switch.
There's a small alloy casting which needs to be pressed onto the switch actuator. It's held on by spring action of the actuator and is a ****** to fit (but easy to drop).
Below is the new switch fitted into the front panel frame.
Spoke too soon! The new switch works back to front, i.e. it's off when pushed down and on when up. I took it apart again and it's the same switch with a slightly different configuration.
The paxolin contact carrier in the new switch (on the right) is upside down compared to the old one and it's not possible to reverse it without dismantling the switch.
I'm not suggesting that anyone else actually tries this but somebody's got to, so here we go.
Take out the spring and W plate. The wire holding it in will probably break but it can be replaced with part of a paper clip. Drill out one of the rivets from the back with a 2mm drill bit. Parts will fly everywhere so it's best done on a spread-out cloth. Now remove the paxolin and turn it over. The two mushroom-shaped contacts are loose and need to be removed and repositioned with the larger part underneath. Keep as much of the grease as possible.
Reassemble the switch and replace the drilled out rivet with an M2 screw (cut to length) and a nut. When it's tight, secure it with a small amount of solder around the nut. Job done.
5) Schematic.
Notice that there's no 110volt mains option. The mains wiring on this example had been modified but I think the fusing and voltage selection in the neutral line instead of live is probably correct. The external fuse and the voltage selector panel would be an accident waiting to happen if they were live.
23rd September 2011. Thanks to Stefan Wickenden for checking out his two amps. The selector and fuse are definitely in the neutral leg.
Stefan has a complete Golden Eagle for sale as well as lots of parts from another one. He's open to offers at electrocutester@gmail.com
This amp has a few differences to the circuit diagram I found on the internet, particularly around the bass control and the tremolo oscillator. R11, the odd combination of resistors in the oscillator feedback circuit, may have been selected during test but I'm really not sure. Anybody know?
6) The Reverb Unit.
The receive unit has a pair of unequal length, sympathetic springs which are anchored to the tray at one end.
The underside is heavily damped with thick fibre wadding.
The two foam pads (right hand photograph above) form the tray suspension system and are glued to steel plates with captive nuts.
The whole assembly is secured by two bolts through the bottom of the case.
The bolts on this one were seized solid and the foam had to be detached to get access to the nuts.
Send and receive transducers are Acos GP 71, stereo, crystal cartridges. These were also used by JMI in their early spring reverbs and turn up in several Vox amplifiers.
The closest information I've found is for the Acos GP 71-5. This output level sounds a bit on the low side so it may not be the same thing.
Output 200mV at 1.5cm/sec into 1M.
Frequency response 40 to 12000 Hz.
Stylus pressure 3 to 4 grams.
In any case, crystal cartridges of this age are unlikely to give anything like they're original performance.
The receive unit on the left has the stylus saddle pushed right up against the case, so it probably wasn't doing much (compare the send unit on the right).
Unlike old Sonotones, the spring mounting wires aren't soldered to the cartridge. To remove them, simply push the springs towards the output terminals and lift them up.
This is the original stylus.
Checking the outputs on a scope shows that they're both dead. Surprise surprise.
7) Switch On
Just did a quick bench test of the power amp section. After replacing a faulty EZ81, got a massive nine watts rms output. Can things get any better? Hopefully.
More soon.