7868 tube for Sherwood 5000 II amp

HB27
HB27 Posts: 1,518
edited May 2009 in Wanted (WTB) Classifieds
I am in need of one 7868 tube for my Sherwood amp. I don't know of any interchangeable tube.
I broke one and just need one.
Harry
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  • Systems
    Systems Posts: 14,873
    edited May 2009
    http://thetubestore.com/7868types.html
    Testing
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  • HB27
    HB27 Posts: 1,518
    edited May 2009
    Thank you. I know they're available but would much rather deal with CP members. "Keepin' in the family" thing.
    Harry
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  • mhardy6647
    mhardy6647 Posts: 33,808
    edited May 2009
    Depending on the bias scheme in a S-5000II, you may need to replace a pair or all 4 of those or risk red-plating or even worse forms of amplifier immolation -- or find a replacement that matches the aged tubes in there already (not something easy to do).

    I have an S-5500II downstairs (7591 outputs) but I am not sure how these amps are biased (I am guessing cathode bias, but it is just a guess).
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  • HB27
    HB27 Posts: 1,518
    edited May 2009
    mhardy6647 wrote: »
    Depending on the bias scheme in a S-5000II, you may need to replace a pair or all 4 of those or risk red-plating or even worse forms of amplifier immolation -- or find a replacement that matches the aged tubes in there already (not something easy to do).

    I have an S-5500II downstairs (7591 outputs) but I am not sure how these amps are biased (I am guessing cathode bias, but it is just a guess).
    It's not as critical as you think. Tubes don't always age evenly even in quads and a good used tube "close enough" will do just fine.
    Thank you for the info. Still looking for a decent tube.
    Harry
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  • Systems
    Systems Posts: 14,873
    edited May 2009
    Cathode bias & I was refering to buying a quad of tubes. Best to do this and keep safe and sound better.
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  • mhardy6647
    mhardy6647 Posts: 33,808
    edited May 2009
    Yeah but if it's cathode bias and all four tubes are tied to one cathode resistor/bypass cap... if there's one that draws more current than the other three... it may not be pretty.

    Don't say we didn't warn ye.

    I'd recommend buying a quad of EH 7868s matched by a reputable dealer.

    I will check downstairs and see if I have a loose one floating about.
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  • HB27
    HB27 Posts: 1,518
    edited May 2009
    Thanks all. Got one used and amp is sounding and working A-1. I appreciate all concerns and thanks for help and suggestions.
    Harry
    (btw, I'm an electronics tech (have been since '67) so all is well in electrocution land)
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