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Thread: Valves for Croft Micro 25/Series 7

  1. #1
    Join Date: Sep 2010

    Location: High Peak, Derbyshire

    Posts: 2,247
    I'm Keith.

    Default Valves for Croft Micro 25/Series 7

    I recently picked up a second-hand Croft Micro 25 Pre and a Series 7 power amp on another forum. The units are both in mint condition, but I don't know how many hours the valves have on them. As I'm hoping to do lots of listening over the Christmas break, it occurs to me that it may be prudent for me to obtain some spare valves now 'just in case'.

    As these amps are my first foray into valve gear, I know little about valves and am looking for some advice as to which ECC83 valves to buy and where to buy from. Obviously, time is getting a bit tight as I want these here before the Christmas break, so I need a recommendation for a reliable supplier who can post them to me first class within the next couple of days.

    As for which brands to buy, I'm not really interested in tube rolling for now and am just looking to have a spare set of 'cooking quality' values that are at least as good as the stock ones currently fitted.

    Also, the pre-amp gain is very high and I'm currently using a pair of Rothwell attenuators (-10dB) on the power amp input. The gain is still somewhat high even now. Can anyone confirm that replacing just the single line-stage ECC83 with a 5751 instead will result in 30dB less gain on all inputs and if so which 5751 tube I should buy?

    Cheers,
    Keith
    Keith
    Analogue: Lenco L75 with 'PTP5' top plate in heavy birch ply plinth/re-wired Rega RB300/SAE 1000e HOMC Cartridge/Trans-Fi Reso-Mat/Moth RCM
    Files: Voyage MPD/Custom PC/Supra USB/Beresford ASYNCH-1/Beresford TOSlink cable
    CDP: Inca Katana SE
    DAC: Beresford Caiman MkII (LiPo Battery powered)
    Pre-Amp: Croft Micro 25 Power-Amp: Croft Series 7
    Speakers: DIY Frugel-Horn Mk3 ('FH3') + REL Strata subwoofer
    Headphones: Beyer Dynamics DT990 Pro (250 ohm)/Schiit Asgard Headphone Amp
    Cables - Interconnects: Mark Grant G1000HD Speaker Cables: Van Damme Blue
    Mains: Belkin PF30/Mark Grant DSP2.5 & DSP1.0 Rack: Target

    Office System: HP Win8 Laptop/JRiver/MF V-Link2/Beresford Bushmaster MkII/Topping TP20 Mk2/Mission 771e
    Bedroom System: Raspberry Pi/Raspbrian + MPD/HiFiBerry DAC/Topping TP20 Mk2/Mission 760i or DIY Hybrid Valve-MOSFET Headphone amp + Sennheiser HD595


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  2. #2
    Join Date: May 2012

    Location: London

    Posts: 409
    I'm Spartacus.

    Default

    Quote Originally Posted by keiths View Post
    Also, the pre-amp gain is very high and I'm currently using a pair of Rothwell attenuators (-10dB) on the power amp input. The gain is still somewhat high even now. Can anyone confirm that replacing just the single line-stage ECC83 with a 5751 instead will result in 30dB less gain on all inputs and if so which 5751 tube I should buy?
    I would not use any attenuators as these roll off the highs and kill the sound. You can try an ECC82 in the line stage which will reduce the gain. If the amps sound fine I wouldn't worry too much about replacing valves at this stage. There's little that can go wrong with the 25 and the S7 only uses one valve in the input stage. Welcome to Croft and enjoy!
    Cheers, Jeff

  3. #3
    Join Date: Sep 2010

    Location: High Peak, Derbyshire

    Posts: 2,247
    I'm Keith.

    Default

    Quote Originally Posted by rubber duck View Post
    I would not use any attenuators as these roll off the highs and kill the sound.
    Thanks Jeff - I'm only using the attenuators as a stop-gap. Without them, I can only use about 10-degrees of the volume control range, which makes matching the channels nigh-on impossible.

    Quote Originally Posted by rubber duck View Post
    You can try an ECC82 in the line stage which will reduce the gain.
    I wasn't aware I could swap-in an ECC82. Does that give less gain than using an 5751 in that position?


    Quote Originally Posted by rubber duck View Post
    If the amps sound fine I wouldn't worry too much about replacing valves at this stage. There's little that can go wrong with the 25 and the S7 only uses one valve in the input stage. Welcome to Croft and enjoy!
    Cheers - the amps sound great and I am not trying to 'improve' them by tube-rolling at this stage. I just want to have some spare valves sitting in a draw just in case one blows over the Christmas period and leaves me without any music.
    Keith
    Analogue: Lenco L75 with 'PTP5' top plate in heavy birch ply plinth/re-wired Rega RB300/SAE 1000e HOMC Cartridge/Trans-Fi Reso-Mat/Moth RCM
    Files: Voyage MPD/Custom PC/Supra USB/Beresford ASYNCH-1/Beresford TOSlink cable
    CDP: Inca Katana SE
    DAC: Beresford Caiman MkII (LiPo Battery powered)
    Pre-Amp: Croft Micro 25 Power-Amp: Croft Series 7
    Speakers: DIY Frugel-Horn Mk3 ('FH3') + REL Strata subwoofer
    Headphones: Beyer Dynamics DT990 Pro (250 ohm)/Schiit Asgard Headphone Amp
    Cables - Interconnects: Mark Grant G1000HD Speaker Cables: Van Damme Blue
    Mains: Belkin PF30/Mark Grant DSP2.5 & DSP1.0 Rack: Target

    Office System: HP Win8 Laptop/JRiver/MF V-Link2/Beresford Bushmaster MkII/Topping TP20 Mk2/Mission 771e
    Bedroom System: Raspberry Pi/Raspbrian + MPD/HiFiBerry DAC/Topping TP20 Mk2/Mission 760i or DIY Hybrid Valve-MOSFET Headphone amp + Sennheiser HD595


    Gallery

  4. #4
    Join Date: May 2012

    Location: London

    Posts: 409
    I'm Spartacus.

    Default

    Hi Keith, I think the 5751 is the equivalent of the ECC83. Glenn recommended me the ECC82 as a lower gain alternative. I do think you're being a little too concerned about tube failure, especially as there are no output tubes involved. But for peace of mind try the JJ-Teslas from Watford Valves.
    Cheers, Jeff

  5. #5
    Join Date: Aug 2009

    Location: West Yorkshire

    Posts: 1,430
    I'm Stephen.

    Default

    Hi Keith
    I have a Croft 25R (and Series 4s) and have spent many hours tube rolling. There is no such thing as a "perfect" tube as they really do alter the sound but for me the "best" tubes in the preamp are GE 5-star triple mica 5751's (slightly lower gain than standard 12ax7/ECC83). "Runner up" are Mazda silver ecc83 and Siemens Halske 12ax7 but others will give you other suggestions.
    In my preamp I use the GE's in the phono stage, a Amperex 12BH7 in the line stage and 2 Siemens Halske 12ax7 in the power stage. After multi- swaps this gives me the sound I like.
    In the S4S I use the Mazda ecc83's (plus all the other tubes).

    If you get any of the above they will be very good and "better" than the stock new issue Sovteks or JJ's but whether you like what they do is another matter.
    For new issue tubes I use watford Valves - not the cheapest but reliable and good quality control.

    Steve
    Always a little further

  6. #6
    Join Date: Sep 2009

    Location: Essex, UK

    Posts: 3,469
    I'm Andy.

    Default

    Hi Keith, why not try to get used the sond of the amps as you have just picked them up?



    Disregard the above statement if you are already used to the sound of the stocktubes.
    System; Michell Gyrodec SE/ Orbe Clamp/ Gert Pedersen armboard mod/ HR PSU/ SME V / J7 Tonearm cable/Ortofon Cadenza Black// Jez Arkless Turbo nutter B------ /Trichord Dino+

    Amplification and loudspeaker set up is at the moment being split into two groups, comprising the following;


    1. Same sources as above; SONY TAF-770ES/SONY CDP761E/Cable Talk 3.1 loudspeakercable/ Harbeth Compact7ES2/ Stands

    2. Virtue Audio Sensation M451battery PSU, ClarityCaps upgrade/ Sensation M901/Russian PIO caps with Teflon bypass caps upgrade/ JT Dynamic PSU with various tweaks/ Connex Audio 5N Litz loudspeaker cable, Impulse H6 Loudspeakers.




















    Me so horny- Impulse H6 Horny

  7. #7
    Join Date: Sep 2010

    Location: High Peak, Derbyshire

    Posts: 2,247
    I'm Keith.

    Default

    Quote Originally Posted by rubber duck View Post
    Hi Keith, I think the 5751 is the equivalent of the ECC83. Glenn recommended me the ECC82 as a lower gain alternative. I do think you're being a little too concerned about tube failure, especially as there are no output tubes involved. But for peace of mind try the JJ-Teslas from Watford Valves.
    Thanks again Jeff. I'm sure you're right about me being unnecessarily worried about valve failure, but I'd still rather have a couple of inexpensive replacements on hand 'just-in-case'. Looking at the specs, the ECC83 has an amplification factor of 100, whilst the 5751 would appear to have a factor of 70.

    I've ordered two JJ Tesla ECC83s to keep as emergency spares and a GE 5751 to try from Watford Valves. Thanks for your help.

    Another quick question - how do I identify the line stage valve in the pre?

    Cheers,
    Keith
    Keith
    Analogue: Lenco L75 with 'PTP5' top plate in heavy birch ply plinth/re-wired Rega RB300/SAE 1000e HOMC Cartridge/Trans-Fi Reso-Mat/Moth RCM
    Files: Voyage MPD/Custom PC/Supra USB/Beresford ASYNCH-1/Beresford TOSlink cable
    CDP: Inca Katana SE
    DAC: Beresford Caiman MkII (LiPo Battery powered)
    Pre-Amp: Croft Micro 25 Power-Amp: Croft Series 7
    Speakers: DIY Frugel-Horn Mk3 ('FH3') + REL Strata subwoofer
    Headphones: Beyer Dynamics DT990 Pro (250 ohm)/Schiit Asgard Headphone Amp
    Cables - Interconnects: Mark Grant G1000HD Speaker Cables: Van Damme Blue
    Mains: Belkin PF30/Mark Grant DSP2.5 & DSP1.0 Rack: Target

    Office System: HP Win8 Laptop/JRiver/MF V-Link2/Beresford Bushmaster MkII/Topping TP20 Mk2/Mission 771e
    Bedroom System: Raspberry Pi/Raspbrian + MPD/HiFiBerry DAC/Topping TP20 Mk2/Mission 760i or DIY Hybrid Valve-MOSFET Headphone amp + Sennheiser HD595


    Gallery

  8. #8
    Join Date: Sep 2010

    Location: High Peak, Derbyshire

    Posts: 2,247
    I'm Keith.

    Default

    Quote Originally Posted by worrasf View Post
    ...If you get any of the above they will be very good and "better" than the stock new issue Sovteks or JJ's but whether you like what they do is another matter.
    For new issue tubes I use watford Valves - not the cheapest but reliable and good quality control.

    Steve
    Many thanks Steve - I'll bear all this in mind when I try tube rolling.
    Keith
    Analogue: Lenco L75 with 'PTP5' top plate in heavy birch ply plinth/re-wired Rega RB300/SAE 1000e HOMC Cartridge/Trans-Fi Reso-Mat/Moth RCM
    Files: Voyage MPD/Custom PC/Supra USB/Beresford ASYNCH-1/Beresford TOSlink cable
    CDP: Inca Katana SE
    DAC: Beresford Caiman MkII (LiPo Battery powered)
    Pre-Amp: Croft Micro 25 Power-Amp: Croft Series 7
    Speakers: DIY Frugel-Horn Mk3 ('FH3') + REL Strata subwoofer
    Headphones: Beyer Dynamics DT990 Pro (250 ohm)/Schiit Asgard Headphone Amp
    Cables - Interconnects: Mark Grant G1000HD Speaker Cables: Van Damme Blue
    Mains: Belkin PF30/Mark Grant DSP2.5 & DSP1.0 Rack: Target

    Office System: HP Win8 Laptop/JRiver/MF V-Link2/Beresford Bushmaster MkII/Topping TP20 Mk2/Mission 771e
    Bedroom System: Raspberry Pi/Raspbrian + MPD/HiFiBerry DAC/Topping TP20 Mk2/Mission 760i or DIY Hybrid Valve-MOSFET Headphone amp + Sennheiser HD595


    Gallery

  9. #9
    Join Date: Sep 2010

    Location: High Peak, Derbyshire

    Posts: 2,247
    I'm Keith.

    Default

    Quote Originally Posted by Tarzan View Post
    Hi Keith, why not try to get used the sond of the amps as you have just picked them up?



    Disregard the above statement if you are already used to the sound of the stocktubes.
    Hi Andy - yes, I don't want to change the sound of the amps - I'm certainly not ready to start tube rolling yet. It's just a case of me wanting to lower the pre-amp's gain so I can ditch the Rothwell attenuators and use more of the volume control's range and also to have a set of valves 'in stock' in case one goes 'pop' especially over the Christmas period when I intend to do little other than chill out and listen to my system for an extended time and wouldn't want that ruined by a valve failure.
    Keith
    Analogue: Lenco L75 with 'PTP5' top plate in heavy birch ply plinth/re-wired Rega RB300/SAE 1000e HOMC Cartridge/Trans-Fi Reso-Mat/Moth RCM
    Files: Voyage MPD/Custom PC/Supra USB/Beresford ASYNCH-1/Beresford TOSlink cable
    CDP: Inca Katana SE
    DAC: Beresford Caiman MkII (LiPo Battery powered)
    Pre-Amp: Croft Micro 25 Power-Amp: Croft Series 7
    Speakers: DIY Frugel-Horn Mk3 ('FH3') + REL Strata subwoofer
    Headphones: Beyer Dynamics DT990 Pro (250 ohm)/Schiit Asgard Headphone Amp
    Cables - Interconnects: Mark Grant G1000HD Speaker Cables: Van Damme Blue
    Mains: Belkin PF30/Mark Grant DSP2.5 & DSP1.0 Rack: Target

    Office System: HP Win8 Laptop/JRiver/MF V-Link2/Beresford Bushmaster MkII/Topping TP20 Mk2/Mission 771e
    Bedroom System: Raspberry Pi/Raspbrian + MPD/HiFiBerry DAC/Topping TP20 Mk2/Mission 760i or DIY Hybrid Valve-MOSFET Headphone amp + Sennheiser HD595


    Gallery

  10. #10
    Join Date: May 2012

    Location: London

    Posts: 409
    I'm Spartacus.

    Default

    Quote Originally Posted by keiths View Post
    Another quick question - how do I identify the line stage valve in the pre?
    It's the valve on the right.
    Cheers, Jeff

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