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View Full Version : Do you know this valve pre?


nat8808
24-05-2011, 23:26
I bought this late last year but only just turned it on... an Ebay risk purchase, untested and £65.

Sounds great! Transparent, open and got that valve X factor - a bit like listening to vinyl after a boring CD player.

Got a bit of hum and one valve appears to glow more than the others so probably needs some adjustment.

But does anyone know what it is? Is it home-made or a kit or cottage industry product?

http://img651.imageshack.us/img651/6103/sg100660.jpg

http://img822.imageshack.us/img822/913/sg100658.jpg

http://img713.imageshack.us/img713/6307/sg100659.jpg

http://img809.imageshack.us/img809/5408/sg100661.jpg

Not actually dual volume control - one is volume and the other balance - and you may notice that the red and black on the sockets are opposite to usual.

I've not tried the phono stage yet..
zanash
25-05-2011, 07:51
its design style and layout of the pcb looks a bit like my beard valve pre ..so could be a bill beard design ?
Barry
25-05-2011, 08:01
It also uses the, now, outlawed Bulgin 3-pin mains connector; suggesting it is quite old despite appearances.

What is the valve line up and what make are the valves? Also are the capacitors of British manufacture?

Despite the description 'Made in England', the fact that the intended dual gain controls are now a single volume control and a balance control, makes me wonder if the circuit has been modified or is even a different design fitted into an older case and using the existing power supply.
anthonyTD
25-05-2011, 08:32
hi all,
looks a lot of preamp for £65-00 the case alone would cost more!
i would say it has good potential in the right hands, well done on your purchase, bargain!:)
typical 70's i'd say judging by the caps and mains connector.
Anthony,TD...
nat8808
25-05-2011, 08:58
Caps are all ITT (so quite industrial). Mullard valves (but can't remember what they are - probably ecc83s plus two others - I'll check when I get home).

Nice Black Beauty Alps pots too - I would have thought it was originally dual mono with two of those.

Couple of ICs in there too - would these be for auto bias, or for power supply regulation?

Also, most CD output is far too high a level for it and you can get it into valve distortion after about 10 on the dial - potentially purposeful if it was home-made and for use in a studio, but I doubt it. So I would say built before the advent of CD.

Also says 'KH9' on the front..

All the tracks on the PCB are quite obviously hand drawn too.

The seller was clearing out their deceased uncle or father's gear and I gathered he was a tinkerer from the other sales..
Macca
25-05-2011, 12:07
Could be me going mad but I am positive this is not the first time one of these amps has come up on AOS. Doesn't anyone else recall?
nat8808
25-05-2011, 12:35
Probably me previously with a thread asking the very same question - photos didn't load and I only got one response.. http://theartofsound.net/forum/showthread.php?t=8347


Thought I'd try again. Plus I've tried it out now and it sounds great so have renewed enthusiasm.
Macca
25-05-2011, 12:37
Probably me previously with a thread asking the very same question - photos didn't load and I only got one response.. http://theartofsound.net/forum/showthread.php?t=8347


Thought I'd try again. Plus I've tried it out now and it sounds great so have renewed enthusiasm.

Ah! thanks for that - good to know I am not trapped in some sort of temporal loop:)
nat8808
25-05-2011, 12:41
If I'd bothered reading my own previous thread, I could have told you the valve details!

They are:

4 x Mullard CV4004s and 2 x name-rubbed-off 12BH7As in the main section and

2 x Mullard CV4004s and 1x Mullard E88CC in the phono/RIAA stage (I'm guessing they are in the phono stage due to their location).
nat8808
25-05-2011, 13:23
Ah! thanks for that - good to know I am not trapped in some sort of temporal loop:)

It is always good to have that confirmed.. Although perhaps the loop is just longer than you first thought.
nat8808
29-05-2011, 21:46
If I'd bothered reading my own previous thread, I could have told you the valve details!

They are:

4 x Mullard CV4004s and 2 x name-rubbed-off 12BH7As in the main section and

2 x Mullard CV4004s and 1x Mullard E88CC in the phono/RIAA stage (I'm guessing they are in the phono stage due to their location).

Any more thoughts on the origin of this pre-amp?

I really don't know much about valve gear as whatever the kit is, it's often a case of fit and forget.. Are the valves good in themselves or is it worth trying some others (and how do I know which others to try or how many to swap out?)?
Rare Bird
29-05-2011, 21:51
Never seen that pre before, i can see that it's made over here but it looks so American..Looking at the ITT caps it could be 1970's.The TT Ground post is the same as on many of my 70's amps.
nat8808
31-05-2011, 08:54
Certainly not made for CD as it doesn't like a high input as it distorts (might actually use that as a good effect for making music).

Sounds really good though which is the main point (although does put out some mains hum on one channel - going to take it to a valve expert I know).

Compared to my XTC pre (which I think has been modified) it does something great - can't really put it in words, but can kind of see a visual description..

Imagine a very in-focus, fine but silky soft smoke (not all smoke is the same..) rising up in some fairly still air.

Is that what all valves do? Can solid state pre-amps do that too?