Croft tubes

dari

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How often would I need to change tubes in Croft 7 power amp and Croft 25 preamp, providing they would be in use at least few hours every day?
 

dari

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I haven't got these yet, trying to get some info before buying.
 
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rabski

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Glen runs valves properly and nothing is pushed beyond its normal sweet spot from what I've seen. Despite the quoted figures, there is no valve 'lifetime' apart from some military spec stuff. It's possible for valves to fail at any time, though much less likely for small signal uses. It will also depend on the make of vale, as most new production is bettered by older stuff, though the provenance is more certain.

For the sort of valves used in the Croft, and the way they're used, you should be looking at probably around 5000 hours before anything starts to decrease in efficiency, though less or more is perfectly possible. Some small signal valves can still be good for a lot longer than that.
 

dari

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Thank you.
Do you know what tubes are originally fitted into the Croft 7 power amp and 25 linestage?
Also, what tubes should I look for/buy once the original ones need to be replaced?
 

rabski

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Thank you.
Do you know what tubes are originally fitted into the Croft 7 power amp and 25 linestage?
Also, what tubes should I look for/buy once the original ones need to be replaced?
I don't have the schematic for either, but most I have seen (and the schemas I do have) use assorted 12AX7, 12AU7 and 6922. The voltage regulated ones I think all use a CV449 and an ECL85 in the power supply.

Once you've determined the actual valves in it/them, I'd put a post up here to see what other people are using. I have my own favourites, but they're all NOS and getting excessively pricey these days. Also, I don't really use 9-pin stuff for anything other than power supplies so doubtless someone will come up with some 'latest discovery'. IME, for 12AU7 it's very hard to better the Mullard CV4003 KQDDK ones, though the RCA clear-tops are nice. For 12AX7, any (real) Telefunken or Siemens will be up there with the best. For either, the new production JJ Gold Pin ones are way better than they have any right to be at the prices. Every other new production 9-pin I've tried has been OK but a bit average compared with NOS stuff.

Bear in mind that with very few exceptions, valve rolling is a thankless task as you'll spend a fortune in cash and then spend a fortune in time trying to persuade yourself that the differences are immense. They aren't. The differences are small and subtle, unless something is broken.
 

Jazid

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You could send Glenn an email, he's pretty responsive when the cricket isn't on. He might have something tucked away. I've never seen a duff valve from Glenn, although he uses new production now (as far as I know).
 
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The Bish

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Dari, the standard valve in the non regulated Croft 7 is an ECC83, and in the 25 phono also has 3 ECC83s, all of them are JJ edicron types.
 
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dari

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You could send Glenn an email, he's pretty responsive when the cricket isn't on. He might have something tucked away. I've never seen a duff valve from Glenn, although he uses new production now (as far as I know).
I have emailed him yesterday.
 

dari

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Dari, the standard valve in the non regulated Croft 7 is an ECC83, and in the 25 phono also has 3 ECC83s, all of them are JJ edicron types.
Thank you for that. To replace them wouldnt be very expensive then.
 

Ian

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I have a mix of Jan GE 5751, a Mullard and Genelex Gold Lion ECC83 in my 25R. These were bought quite some time ago when prices weren't what they are now. I'll be completely honest and say my motivation was more to have 'good stuff' in there as it felt nice and I could afford it at the time.

I really couldn't put my hand on my heart and say the difference was the cliched 'night and day'. These are wonderful amps with the stock JJs in them.
 
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