Valve replacement in a Croft Micro 25

[camtwister]

If I were to replace the line input ECC83 on my Croft Micro 25, do I need to make any adjustments other than simply replacing one valve with another?
Thanks folks.

[DSJR]

NO is the simple answer.. Glenn's designs don't stand or fall on one make or another of valve used, they just tilt gently this way and that on a pretty neutral starting block :)

PLEASE correct me if I'm wrong, but if you have an ECC83, then isn't there a lower gain mil-spec one you could use instead (5751 or somesuch)? This would mean the volume controls aren't quite so cramped at the lower end of their range.

Glenn is easy to talk to by email and has NEVER been condescending or pompous in his responses. One of the reasons why I and others love his gear so much. Ask him and see what he says. He used to like original Mullards I remember.

[Marco]

Hi Johnny,


NO is the simple answer.. Glenn's designs don't stand or fall on one make or another of valve used, they just tilt gently this way and that on a pretty neutral starting block.


Dave's right.

However, having carried out some extensive tube-rolling recently with my Croft preamp, there are some considerable gains to be had from improving on what's fitted as stock (Glenn simply uses good quality current production tubes these days, which although decent, can be bettered - everything is built to a price, after all), and 'tuning' the sonic and musical signature of the amp to better optimise that of your system, and also what your ears may prefer.

As Dave says, Glenn had a preference for vintage Mullards, and I can say that those work very well indeed, having recently fitted a NOS Mullard CV4004, which is the 'military spec' equivalent of the M8137/ECC83 'common valve'. This is a superb sounding tube, and also guaranteed to last for over 10,000 hours.

I bought two, and if you're interested, I'd be willing to let the other one go, as after a recent buying spree for my tube-rolling sesh, I've got more ECC83-type tubes now than I know what to do with! :eyebrows:

Anyway, PM me if you're interested and we can come to a deal :)

Marco.

[camtwister]

Hello Dave,

I understand the point that you're making. I was just concerned about whether I need to make any technical adjustments. Sonic issues aside, will the amp readily accept a new valve of the same type, if not the same manufacturer. For example, if the existing one is damaged.

But since you raised the topic...I know Marco has experimented at length with tube rolling in his Croft. Has anyone tried it in a Micro 25?

Cheers,
John.

Posted before I saw Marco's response above!!

[Marco]

Hi John,

Nope, you're safe as houses experimenting with valves of the same type in any of the Croft designs. No other adjustments would be necessary afterwards. And The Micro 25 is no exception :)

Marco.

[DSJR]

Langrex had some supposed CV4004's for sale, which were claimed to sound good. I bought a quad of these for the phono stage of my preamp (the line stage uses 82's/Cv4003's/JAN5841A?) and they're fine indeed, if modern far eastern I suspect. Low hum and noise (with the Decca) and no distortion or softness and with a great "open" quality to them.

[Marco]

Hi Dave,

CVC (Chelmer) are the best chaps for genuine NOS CV4004s, which come in their original military boxes. That's where I got mine from :)

I've got a spare that has only been used for testing, which I'd let John (or anyone else) have at a reduced price. Chelmer sell them new for £60 + VAT.

Marco.

[DSJR]

That's why I couldn't go for them - £60 + VAT each? I'd keep a spare at that price :)

[Marco]

Well, you know I like to spread and share da love... :grouphug:

Marco.

[DSJR]

:king:

[kininigin]

PLEASE correct me if I'm wrong, but if you have an ECC83, then isn't there a lower gain mil-spec one you could use instead (5751 or somesuch)? This would mean the volume controls aren't quite so cramped at the lower end of their range.


This is exactly what i have just done after buying some JAN GE 5751's from steve (worrasf) and yes they allow greater control of volume.

No adjustments needed,just a straight swap with very pleasing results.

[DSJR]

By the way, Watford Valves Cryo-Treat theirs -

I seem to remember that early Decca London's were cryo-treated too. A long time ago and fuzzy memories, but I'm sure the magnets or coils were thus treated :confused: I hope HiFi Dave has the particular HiFi Sound mag this was in :)