CHAMP ELECTRONICS -" THE VALVE AMP HOSPITAL"

NOTTINGHAM, ENGLAND

 

MODIFICATIONS TO A c1963 BIRD GOLDEN EAGLE 15 Watt GUITAR AMPLIFIER

 

 

Hello all you Bird amp collectors/enthusiasts out there. This is certainly not the first of these Bird amplifiers across the bench and, almost certainly not the last. However, I felt that it was time to do a detailed write-up on one of these things.

Being originally manufactured by the Bird Company, Poole, Dorset, UK, the various models of Bird combo amps were all quite refreshing and colourful to see. Yes, we had Vox, Selmer, Wem and a few others but Bird certainly joined the line-up at some point in time, though never really reaching the heights of their competitors. Bird was really an organ company and Iím not sure if they actually designed their amps for guitar use or whether people just used them for guitar anyway, as they were all simply "comboís". The Bird Golden Eagle 15 (this example) seemed to be the most popular one from the small range of choices. It used a pair of EL84ís for the output and three Elac 6" x 10" speakers with specially wound 2.5 ohm voice coils, hence making them a little different to the other companies amps which were generally fitted with normal 8", 10" and 12" circular speakers. The coils of the three speakers in the Bird are so wound in order to achieve a total load of 7.5 ohms with the three speakers wired in series.

 

The Golden Eagle's internals as assembled by Bird.

Though I distinctly remember the Bird amps back from the sixties, it is only in recent years that a few of them have "crossed my path" on the workbench. I don't want to sound too hard on the Bird company or their designers, but........... I have to say that I think they are disgustingly horrible things. Sorry, but I think the circuit design, the choice of some of the valves, and the general layout of these amps has to be one of the worst ever done!! The only thing that the Golden Eagle has going for it is the fact that this was the first British amplifier to have an integral reverb unitÖ..bravo for that at least!

The reverb spring tank uses two, up-turned, old (well not then) record player Acos pick-up cartridges, with the main central spring laying in the "V section" where the needle would normally sit. An ingenious idea really but, as the Accutronics reverb unit used in all the Fender amps (originally designed for the Hammond organ) uses a coil winding at each end, (much more reliable than a crystal cartridge) I donít know why Bird didnít follow suit here. Who knows?

 

The original Bird Reverb Unit.

 

What follows here, I feel, is a very true statement.......and Iíd bet my reputation on it!!

When any company is going to design a valve (tube) amplifier, the first thing they must do after deciding on the output power and tube(s) to be used, is to refer to the tube manufacturerís details. In the case of Bird and this particular model, which uses a pair of EL84ís, this would almost certainly have been Mullardís data sheets. The Bird Golden Eagle 15 was marketed as having an output of 15 watts. Er, well, that is what it is supposed to be, but that aspiration is far from reality! I sincerely believe that some of these early sixties companyís used to design and build amplifiers expecting them to be "XXX" from the said data sheets but they then never seem to have really testing them for "true results". Please let me explain:-

It is common knowledge that a pair of EL84ís would, under the right conditions and voltages, give us about 15 watts (and likewise a quad will produce 30 watts, as-in the good old Vox AC30).  Yes, this they will do this, but on this Bird model there are several reasons why this cannot happen: 

Firstly there are two, 250 ohm wire-wound resistors in the AC supply to the EZ81 rectifier. Why?! This drops the main HT on load, and the amp simply struggles to achieve 10 watts, let alone the stated 15!

Next, the output stage of these is in ultra-linear mode. OK, ultra-linear was introduced many, many years ago and is particularly good for reducing distortion in second and third harmonics. However, in most cases, there is a noticeable drop in output power too! It became quite "trendy" to use ultra-linear in Hi-Fi amplifiers (and rightly so), but to use it in a guitar/organ amplifier is pointless! You would be very hard pressed to get 15 watts from a pair of EL84ís in cathode (self) bias, 43% ultra-linear, and especially with the "sagging HT line" (remember the two 250 ohm resistors mentioned earlier?) of a Bird Golden Eagle! In-fact, Mullardís original data sheets quote a maximum of 17 watts (or thereabouts) from just a pair, but... not in 43% ultra-linear mode!

Yet another bad design are the output tapings on the output transformer. Itís not that the manufacturer of the said transformers made any mistakes. In-fact the output transformers on these amps are well made and use the highest grade "78 type" laminations that were available way back then, butÖÖÖthere are simply two alternatives on the tapings. Two windings of 3.75 ohms which, if paralleled give simply 3.75 ohms. If put in series they give 15 ohms. (Trust me this is correct. Power factor is measured in square-root, as-in x 4). However, the three speakers at a total load of 7.5 ohms (discussed above) are simply wired to one of the 3.75 taps and the other is left un-used. They havenít even paralleled the two windings; this would allow for a little more currant at least! As the output transformer doesnít have a 7.5 ohm tap, this could never be matched correctly!!

 

Inside the Bird, showing the original layout and components - right hand side.

 

Next we must consider the circuit itself. Though all the components originally, when new, would almost certainly have been fine, the use of the Eire (metal capped ended) resistors is a bad idea as these change in value tremendously over time. They were cheap and rubbish! The same applies to the chosen "Hunts black capacitors". These too, over time, are renowned for "dying"!

Lastly I would like to point out that two EF86ís were used in the circuit. Uuuuurrrrrrr!! I hate those things. They started to appear, once again in Hi-Fi equipment/amplifiers, in the fifties and sixties and I suppose that they do have a place in there somewhere, but, they were always a noisy, troublesome bottle. To use them in a guitar/organ amplifier is once again absolutely pointless. I think I can prove my point quite easily here, by simply saying "find me a modern guitar amp of any kind that uses EF86ís in its circuit nowadays" Point made?

 

Inside the Bird, showing the original layout and components - left hand side.

 

Another couple of points that I forgot to mention above are the bass and treble controls. The treble isnít really a treble, but simply a "top-cut" (as in a Vox AC30). Turning it up doesnít boost the treble; it simply brings it from below to flat. As for the bass control, this is incorporated in the feedback circuit. What a stupid idea! These things hardly ever worked correctly or satisfactorily!!

I can remember a very close friend of mine, back in 1964, having a Bird 4/25 model and we used to play bass guitar through this. Why they called it a 4/25 I donít really know. Yes, it was about 25 watts from a pair of EL34ís but it had a single 15" Wharfedale speaker! I remember it sounded really good back then with this 15" driver and a bass guitar. Whether I would feel the same about it nowadays is another matter! I have spent much time on these Bird amps, putting them back to original, but even with todayís reliable, modern components, Iím sorry to say they still sound awful!! The best thing anyone can do with one of these "expensive doorstops" nowadays is to have it completely re-built with a different circuit, such as my own (not wishing to sound swell headed!). That is especially a good idea as in virtually every case, all the components need changing anyway! 

I think Iíll let my dear friend Steve (Russell) of the Vintage Hofner and Selmer websites tell you the rest of the story from hereÖÖ 

Cheers, John.

 


 

 

STEVE'S ANGLE ON THE GOLDEN EAGLE:

"My first guitar amplifier was a Bird Golden Eagle which I bought brand-new, following the advance of several years pocket money when I was age 15 in 1962. I bought this amp because it was the only one available with reverb at the time.......within the constraints of my budget! I used it for gigging with my first band for about six months, before it became only too apparent that it did not have sufficient volume, or tone, for my role as lead guitarist. I then traded it in for a second-hand Selmer Selectortone, and at last I could be heard over the drummer! 

During the time that I owned my first Golden Eagle, I discovered one or two peculiarities with it. Firstly, the reverb was very sensitive to mechanical shock. I always remember one gig on a very bouncy stage. When (at last) the audience got up to dance, the stage vibrated so much that the reverb springs in the amp started bouncing about. That resulted in loud thunder noises emanating from the amp, which brought the music to a halt, but seemed to amuse the audience more than our playing ever did. On later occasions, we used this "effect" to our advantage. At the start of a number called "Telstar" (The Tornados - remember?), I gave the amp a kick in order to simulate the opening special effects used by Joe Meek on the Tornados recording.

The other oddity of the amp was that it was designed to be mounted on legs. Special threaded plates were fitted by Bird to the underside of the amp in order to accommodate standard coffee-table legs, which were all the rage in those days. This gave the amp a very "1960's domestic" appearance. It also made the problems with the reverb mechanical spring noise much worse!

A couple of years ago, I noticed a Golden Eagle for sale on Ebay. Being nostalgic by nature, I thought that it would be a good idea to buy the amp......just for old time's sake! After a skilful game of bluff and counter-bluff in the auction, all opposition was left standing and I won the old amp with my bid of £130.

After a long drive down to Essex and back to pick up the amp, I finally plugged my guitar into it back home. That glorious nostalgia was rapidly overtaken by memories of just how bad these amps were! Low output with a total lack of "attack", no tone range, a heavy pulsing through the speakers when the tremolo was switched on, weak reverb signal, and.........that hum! However, I told myself that I hadn't bought this amp to gig with. It was purely for re-living the good old days of 1962! I therefore lived with it for a year or two, only plugging into it when I wanted to prove to myself myself how good my several vintage Selmer and Watkins amps really are.

In the meantime, I had got to know John Chambers through my website. John was providing me with in-valuable help with technical information, together with photographs of the "internals" of vintage amps that crossed his workbench. One day, John told me that he had just received a Bird Golden Eagle from another website contact to "do something with". After another day or two, I received the report that John didn't think much to the "internals" of the Bird and that he would have to do something drastic.......like re-build it! A further week or so past, and I received an email from the owner of the amp to say that he now had got it back and that he was amazed at the transformation. That did it..........I decided that my old bird (sorry Bird) must have the Champ treatment.

To cut a long story short, the day finally arrived when I went down to pick up my own Golden Eagle from John's workshop in Nottingham. John asked me to bring one of my guitars along so that I could make sure that I was happy with the amp before accepting it back. Happy ???............. I couldn't believe my ears! The whole character of the amp had changed. It was like dealing with a hot-rod! The old girl is loud, very loud for a 15watt rated amp. It has now found a sharpness that I have found to be present in only one or two other amps that I have encountered in the last 40 years or so........and certainly never before in a Bird! The tone range is also now outstanding.

I very rarely use the tremolo function on my old amps. Who does? However, the tremolo on the Bird now sounds so good, with a very wide range of control, that I have used it a lot since I got the amp back home. The old reverb has been changed for a modern unit, and this now sounds like any other quality reverb effect should sound -  i.e. it is now useable! Also the old hum has gone. This is now a very quiet amp....but only as far as background noise is concerned! 

What I really like though is that the sound that the amp makes is fully controllable and suitable for use in the home. As it only puts out 15 or 20 watts through the three quaint elliptical speakers, one doesn't need to be in a large concert hall to be able to turn the volume up to that stage where the amp really does begin to perform. I also have a Mesa Blue Angel amp which seems, in my opinion, to have a comparable quality of sound to the (modified) Bird, but it does have to turn out a lot more decibels in order to produce it! It also has considerably more background hum!

My advice to other Bird Golden Eagle owners out there. - Get your amp around to Champ Electronics for a re-build. It will not be cheap, but you will own a little monster of an amp when you pick it back up! And it will still work out at a fraction of the price of a hand-wired, custom built, "boutique" amp!

Many thanks, John! "

- Steve Russell

 

SOME PHOTOS TAKEN DURING THE RE-BUILD:

 

      

The main board stripped down.

    

The original printed circuit board.

 

The modified printed circuit board.

 

         

Before & After wiring of the control panel. 

 

 

Everything out!

 

Checking and cleaning of the three Elac elliptical speakers.

 

After re-building power and output stages, onto test before continuing. 

 

Right hand side chassis completed.

Left hand side chassis completed.

 

Chassis, speakers, and the new reverb tank installed.

 

The completed job!

 

Extra Sockets now installed.

 

 


 

Return to CHAMP ELECTRONICS AMPLIFIER MODIFICATIONS PAGE

Return to CHAMP ELECTRONICS - BIRD AMPLIFICATION WORK PAGE

Return to CHAMP ELECTRONICS MAIN PAGE