Conchord, info needed

Read more on the Linear Conchord in our home audio section

Bill Brewer2004-02-27 02:31

Do you have any info on an old Linear Conchord valve amp. It includes two EF86 and a GZ34, a huge ”De Luxe” mains transformer and has two 3 ohm and one 15 ohm output. It has a high and low gain inputs, two vol. controls and a base and treble. also has 6.3 volt output. There are two large unmarked valves or devices and an empty base for another small valve which I want to identify. Can\'t find much reference to Linear Conchord. There is a large brass post on the front with an 8mm hole. It isn\'t connected to anything except the casing so may be some kind of quick earthing point. I\'m a plumber really but this thing looks interesting. Many thanks.

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Steve Rowley2004-02-27 02:32

I was reading the October 1962 copy of Practical Wireless (as you do) and came across a Linear advert. Apparently the company, Linear Products Ltd., was at the Electron Works, Armley, Leeds. The ad makes mention of no less than seven amplifiers. These are:

Does anyone know any more about Linear? Any literature or circuit diagrams? Best regards, Steve Rowley

Steve Rowley2004-02-27 02:33

Hi, I too have a Linear Conchord. I would tend to agree with Greg Walsh, it is probably based on the Mullard 5-20 and 5-10 designs.

I\'ve just been tinkering with mine, which came complete but not working. The 470 Ohm resistors connecting the cathodes to ground are scorched for some reason - so much so that one has burnt through the tag strip, which will have to be replaced complete with its components. Surprisingly, it still works in a fashion! The knobs on mine are long tapered ones with a collet screw on the front of the knob. Unfortunately one is missing.

Has anyone managed to obtain a circuit diagram yet? I would greatly appreciate a copy. If anyone has any other info on Conchord amps, about the company, where they were made, the duration of the company, other models, etc etc, that would be great.

I\'m hoping when its restored to use it as a simple, minimalist guitar amp. Best regards, Steve Rowley

Chris Wright2004-02-27 02:33

I have a Linear Conchord 30w in poor repair; I bought it secondhand from a musical instrument shop in 1965 as a guitar amplifier, and used it for a few years as a lead guitar amplifier. I played through a cabinet with a Fane twin cone 12” 25 watt speaker and a Baker 12” 25 watt speaker in parallel from 15 ohm output. This gave a bit of distortion but was a bit louder.

The group I played in used a 50 watt Linear Conchord bought secondhand for PA, a 30 watt Linear Conchord bought new for bass guitar, and a 15 watt Linear Conchord (EL84 in push-pull) bought new for rhythm guitar. The Linear Conchord range was sold as a PA or Guitar amplifier in Practical Wireless magazine in the early to mid sixties. I too think it is based on the Mullard 20-watt twin EL34 design. I think the 50 watt had an extra ECC83 stage, and it definitely had much bigger mains and output transformers, making it very heavy to lug about.

My 30 watt was built in 1958 according to the original components in it. It was overhauled by a friend some 20 years ago after a electrolytic cap blew to pieces with a lot of impressive smoke, and then played well, but it badly needs some attention really. I now have three solid state amplifiers(30 watt, 40 watt and 150 watt) which are much louder, and much less trouble, but not really the same.

Mike Billing2004-02-27 02:33

Hi, I have just found a Linear Conchord amplifier at my local tip which seems to be complete. Although I have not tried it yet I can tell you the full valve line up of mine. The two large output valves are EL 34s and the small one your missing is a ECC 33. The output on the rear is for connecting a second power amp to make it stereo.

Ii hope this of some use to you and if you want to sell it please email me as I would love to make a pair. If not, good luck and I will do my best to answer questions if I can. Mike.

Andries Van Der Walt2004-02-27 02:34

Hi Bill, I am in possession of one of these amplifiers, it uses EL34 tubes in the output stage, the little tube in the middle (not screened) is an ECC83, the other two input tubes are EF86 tubes. I am in the process of refurbishing one, have already traced most of the circuit diagram, must clean up the drawing though.

I believe that the amplifier used to be built into electronic church organs, possibly the old German Ahlborn models. Apparently the amplifier was available in 30W or 50W configurations. Mine is 30W and came out of spare stock, the valves are still original Mullards!! The amplifier runs in ultra linear mode, with taps on the output transformer and with a feedback loop back to the pre-amp. As far as I can ascertain pretty much a standard EL34 design.

I am using the amp as a guitar amplifier, however the existing pre-amp is not really suited to that, difficult to overdrive, it will only start to clip once the volume is all the way open. I will eventually build a new preamp for it (possibly based on the design in the Dutch Elektuur book: Audio- en Gitaarschakelingen met Buizen). I will also take out the feedback circuitry and possibly build in a triode / pentode mode switch. I am going to bench test the amp soon and get proper measurements at all the right places. I have not established yet at what % the taps are on the output transformer, would guess at about 40%. Will keep you guys up to date as I progress.

I bought my amplifier second-hand in Cape Town. Where are you people based? Where is Bill Brewer based and where did he acquire his amp?. Cheers, Andries van der Walt

John Chambers2006-10-30 22:01

Hi Guys, I think you all might find this interesting on my site!? Cheers, John. http://www.chambonino.com/work/work1.html and http://www.chambonino.com/carlsbro/Concord%2030%20watt.pdf

Ron Owen2019-09-08 22:54

Hi, I also have inherited a Linear Conchord amp and am concerned that the circuit diagram, given as the one to use differs from the coloured wiring diagram; their seems to be a modified circuit somewhere. Where the PSU electrolytic has been up'd to 64 uF.


The wiring diagram has 47pF capacitor in the bass control circuit, whereas the circuit diagram shows it as 0.047 uF.

I see that the last subittance is 2006, so I might not get any response to this.

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