Mullard 2 valve preamp details

[sparkymike]

I have a reprint of the Mullard Tube circuits book and am a bit mystified by the layout of the two tag boards. (page 74) The lower drawing shows 10 post boards but upper drawing only shows 9.
Am I missing something here ,or is that a misprint ?
One other point, where in the UK can I buy the components for above amp without having to buy multiple items on ebay and just get one or two orders ?
I am also after suitable vintage looking components, not the caps or resistors that you almost need a magnifying glass to see !!
Mike.

[Valvepower]

Hello,

Well, it so happens I have an original very dog eared 1963 reprint of the Mullard Circuits for Audio Amplifier book on the bench doing some investigations and work on the 5-10 amplifier.

I had a look at the two-valve amplifier layout and yes, the top drawing of the tag panel layout has two 9-way tag panels (total 18 tags), and the bottom layout shows two 10-way tag panels (total 20 tags).

Without spending time matching the circuit to the layouts I’d go by the bottom tag layout as it could be something as simple as the top layout was from an earlier layout where parallel parts like the bypass capacitors (C6-R16 and C10-R22) were soldered directly across the resistor and on the bottom, which was a later layout, the bypass capacitor(s) had their own tags – I maybe wrong, but this is sort of thing that jumps to mind.

Are you making a mono or stereo version?

Terry

[Sideband]

I built the stereo version about 50 years ago and don't remember having problems with the tagboard layout....As far as I remember, the stereo version is basically two, two valve preamps knitted together. Perhaps look at the layout for that one.

[Valvepower]

Hello,

A good while ago I found a Mullard two valve preamplifier at a BVWS swapmeet.

Looking at the parts it looks to be an abandoned project dating back to the 1960s. The plan was to build the single EF86 preamplifier for the 5-10 amplifier from the first High Quality Sound Reproduction book and the Oct 1955 Technical communications, but it’s still on the round-tuit pile!

Pics attached.

Terry

[barrymagrec]

I have the Mullard 2 valve preamp my Dad Built when he was working at Mullard Mitcham in 1960 - it did sterling service for some years but has not been used since around 1982.

[sparkymike]

Yes I am constructing one of those preamps.
I have no idea where I could find one of the 6 position double banked switch, but looking at the drawing, it looks like two identical switches in parallel. However the wafer drawings in the Mullard book make it look more complicated.
If anyone has a part finished one of these amps would be glad to take it on board.
Mike.

[barrymagrec]

The wafer drawings are complicated because the switch is arranged to short out unselected inputs to cut down crosstalk.

In these modern days of possibly DC coupled solid state sources this is not terribly desirable which simplifies the switch.

[sparkymike]

I will only be using a tuner and possibly a record player so that should simplify things.
Mike.

[Sergeauckland]

Originally Posted by Sideband

I built the stereo version about 50 years ago and don't remember having problems with the tagboard layout....As far as I remember, the stereo version is basically two, two valve preamps knitted together. Perhaps look at the layout for that one.

I too built the stereo version in 1967/8 and used it throughout my University days. However, the phono stage was particularly noisy so soon replaced it with a much quieter SS pre-amp (PE Gemini!). I particularly liked all the switching for stereo, stereo reverse and mono. In those days, Makaswitch were easily available to make the required wafer switches with the grounding for unwanted inputs.

I've just finished the conversion of a Leak Point One mono preamp, also with two EF86s, to modern SS and stereo using 5532 ics. Complements my two GEC912+ visually.

S.

[barrymagrec]

Indeed, the EF86 is one of my less favourite valves, when Leevers Rich replaced them in the early sixties with an ECC83 design the replay noise figure improved by about 4dB.

[Valvepower]

Mike,

I’ve been thinking after you said… If anyone has a part finished amp I would be glad to take it on board’… Well, this preamplifier has been sitting on the round-tuit pile for far too long, and seeing you’re looking for parts to make the two-valve preamplifier you can have this one to get you started.

It owes me nothing, so It’s FOC and all I ask is a small donation to charity

Regards
Terry

[sparkymike]

Hi terry will PM you, thanks.
Mike.