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Thread: Valves for Croft Micro 25/Series 7

  1. #11
    Join Date: Dec 2011

    Location: Far Away

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    Quote Originally Posted by rubber duck View Post
    I would not use any attenuators as these roll off the highs and kill the sound
    A properly designed attenuator at line level just reduces gain it does not alter frequency response. The Rothwell ones work really well in this respect, so Keith don't worry about using them if they work for your system.

    The circuit you have is optimised for ECC83s so stick to them. I would not give JJs house room and Sovtek are the least I would use personally. FWIW the best new ECC83s I have heard lately are the Harma Retro ones from Watford Valves, I recently compared them to the original Mullard ones they are based on and they sound spot on to me and they are only 16 each. I now have all 5 ECC83s in my system running these.

    Welcome to the wonderful world of thermionics.

    Paul S

  2. #12
    Join Date: Sep 2010

    Location: High Peak, Derbyshire

    Posts: 2,247
    I'm Keith.

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    Quote Originally Posted by PaulStewart View Post
    A properly designed attenuator at line level just reduces gain it does not alter frequency response. The Rothwell ones work really well in this respect, so Keith don't worry about using them if they work for your system.
    Thanks for the reassurance Paul.

    Quote Originally Posted by PaulStewart View Post
    The circuit you have is optimised for ECC83s so stick to them. I would not give JJs house room and Sovtek are the least I would use personally. FWIW the best new ECC83s I have heard lately are the Harma Retro ones from Watford Valves, I recently compared them to the original Mullard ones they are based on and they sound spot on to me and they are only 16 each. I now have all 5 ECC83s in my system running these.

    Welcome to the wonderful world of thermionics.

    Paul S
    Thanks for the recommendation. I did see the Harma Retro ECC83s on Watford Valve's site. I'll certainly consider those at some future point.
    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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  3. #13
    Join Date: Sep 2010

    Location: High Peak, Derbyshire

    Posts: 2,247
    I'm Keith.

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    Quote Originally Posted by rubber duck View Post
    It's the valve on the right.
    Thanks Jeff - you mean the one I've circled here?:

    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. #14
    Join Date: Mar 2012

    Location: Gloucestershire

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    I'm Paul.

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    Hi Keith

    I've had several sets of the Croft amps now and I'd stcik with the standard 83's as that is what they were deisgned for. The gain is altered (and set) by Glenn using feedback resistors. You can lower the gain by changing the value of the feedback resistors. Standard is 470K, intermediate gain is 220K and low gain is 100K.

    picture from Glenn explaining this below:



    Glenn uses JJs and the new issue 803s is a cracking valve and a very reliable valve. I would recommend a set of the JJ803s gold pins if you can get them. There appears to be a snobbery thing against these valves but they sound great in Croft gear and are ultra reliable. JJ have been going an awful long time and know how to produce decent valves.

    The amp didn't seem to sound vastly different rolling different valve brands but the 803s sounded the best of the bunch that I tested with the Micro 25 Pre and series 7R power (that included Mullards, Brimars, crappy EH 12ax7s and Tung Sols (same as EHs...in fact they are from the same factory))

  5. #15
    Join Date: May 2012

    Location: London

    Posts: 409
    I'm Spartacus.

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    Quote Originally Posted by keiths View Post
    Thanks Jeff - you mean the one I've circled here?:
    Yes.
    Cheers, Jeff

  6. #16
    Join Date: May 2012

    Location: London

    Posts: 409
    I'm Spartacus.

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    Quote Originally Posted by PaulStewart View Post
    The circuit you have is optimised for ECC83s so stick to them.
    Quote Originally Posted by Reffc View Post
    I've had several sets of the Croft amps now and I'd stcik with the standard 83's as that is what they were deisgned for.
    I don't disagree with this. But gain and hiss can be a problem, in which case substituting valves can be a solution. If in doubt you could always contact Glenn.
    Cheers, Jeff

  7. #17
    Join Date: Sep 2010

    Location: High Peak, Derbyshire

    Posts: 2,247
    I'm Keith.

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    Quote Originally Posted by Reffc View Post
    Hi Keith

    I've had several sets of the Croft amps now and I'd stcik with the standard 83's as that is what they were deisgned for. The gain is altered (and set) by Glenn using feedback resistors. You can lower the gain by changing the value of the feedback resistors. Standard is 470K, intermediate gain is 220K and low gain is 100K.

    picture from Glenn explaining this below:

    Thanks Paul - unfortunately the image isn't working for me.

    Quote Originally Posted by Reffc View Post
    Glenn uses JJs and the new issue 803s is a cracking valve and a very reliable valve. I would recommend a set of the JJ803s gold pins if you can get them. There appears to be a snobbery thing against these valves but they sound great in Croft gear and are ultra reliable. JJ have been going an awful long time and know how to produce decent valves.

    The amp didn't seem to sound vastly different rolling different valve brands but the 803s sounded the best of the bunch that I tested with the Micro 25 Pre and series 7R power (that included Mullards, Brimars, crappy EH 12ax7s and Tung Sols (same as EHs...in fact they are from the same factory))
    Oh well. I've just changed my order at Watford Valves from gold pin Teslas to the Harma Retros. Never mind - as long as I've got a few spare valves 'just in case', I'll be happy.
    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. #18
    Join Date: Sep 2009

    Location: Essex, UK

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    I'm Andy.

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    Quote Originally Posted by keiths View Post
    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.

    Sensible Keith.
    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

  9. #19
    Join Date: Jan 2013

    Location: Birmingham

    Posts: 3,932
    I'm James.

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    Ok I know this is quite an old thread but still very current for us Croft owners.

    Any thoughts on the Series 7 input valve ECC83. Anyone tried different valves in this position with better results rather than the standard JJ's?

    For what its worth I run a GE JAN 5751 in this position which works well and reduces gain a little although I would like to try a NOS GE 5 star 5751 1960's tube if I can get hold of one. The JAN GE is a bit lean and etched.

    Got a really nice NOS Tesla ECC83 Gold Pin 32 coming to try in the Series 7 this week so will report back once I have tried it.
    VPI Scout 1.1 - Ortofon 2M Black - Croft 25R+ - Croft Series 7 - Spendor SP2

  10. #20
    Join Date: May 2010

    Location: Brisbane

    Posts: 1,589
    I'm Bernie.

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    I've just ordered a couple of NOS Tungsram ECC83s to be used in the line stage of my 25R and series 7. I'm currently using Harma retros, which can be a bit bright but seem to have a nice, wide soundstage. Before I use them I want to go back to the JJs for a comparison since using the Harmas for the last few months.

    I'm always up for other's experiences tube rolling with the Crofts.
    Bernie.

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