Croft preamp puzzle...

[Haselsh1]

Before Christmas 2009 I bought a Croft Micro 25 Basic preamp from HiFiDave and have been using it for listening ever since. After Christmas I bought a matching power amp and was completely gobsmacked by the sound. I am now in the process of looking into changing the valves held therein and this has lead to a little confusion.
I was under the impression that the Micro 25 Basic had two ECC83 valves and one 5965...? How come then that mine uses three ECC83's...? When I change my valves do I ignore the supposed 5965 and just play with ECC83's...? I do understand that two of the valves are for the phono input with one being for the line inputs. I also understand that the power amp uses an ECC83. This I will not be changing for the time being. I wish to concentrate on the preamp.

[Themis]

Probably Glenn put a ECC83S instead of the 5965... Which means you have a special model ? :scratch:

Shaun, I guess the best move is first to ask Glenn of what to do and which valve to change.

If your preamp has a ECC83S, I already know Glenn's view on it : "If I was you I would stick with the Teslas"... :o

[Haselsh1]

The two phono stage valves are indeed JJ's but the line stage valve is an Edicron. I guess there is an issue with noise floor on some of these valves and the JJ's have a lower noise floor. Maybe I should just leave the bugger alone, it works fine.

I do intend soon to send the preamp back to Glenn to get the gain resistor changed on each channel so that I can use the thing properly.

[Themis]

Ask him whether you can put a JJ ECC83S (which equips the "normal" 25 Micro) instead of the Edicron. It's a fine tube with little or no microphonics and very extended highs. ;)

[DSJR]

I thought Glenn used edicrons throughout but his site pics show Electro harmonix valves being used. It probably depends what he can get hold of. A quick email to him will sort this out I guarantee. is the ECC83S a higher gain valve than the 5965?

[Haselsh1]

I've contacted Glenn about this minor issue and he has informed me that my preamp uses three ECC83's so that he can run down his stocks of old NOS valves. Nothing more, nothing less. He told me that any pin compatible valve will do.

[DSJR]

So that probably means that this model is pretty valve-rolling resistant :)

I don't know the specs, but a lower gain valve in the line stage should be an easy fix for the gain issue...

[Haselsh1]

So that probably means that this model is pretty valve-rolling resistant :)

I don't know the specs, but a lower gain valve in the line stage should be an easy fix for the gain issue...

Good thinking. I'll investigate immediately but I think it may be that a preamp trip back to Glenn is needed.