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Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com

Opinions on plate voltage and plate current on vintage 6V6GT tubes

Discussion in 'Glowing Bottle Tube Amp Forum' started by theprofessor, May 26, 2017.

  1. Commodore 64

    Commodore 64 Friend of Leo's Ad Free Member

    Age:
    41
    Mar 1, 2010
    Kent, OH
    I, for one, am an observer who appreciates that the 'side bar' is front and center. ;) Good readin', thanks.
     

  2. Bendyha

    Bendyha Tele-Afflicted Ad Free Member

    Mar 26, 2014
    Northern Germany
    Here is a copy of the the RMA (JEDEC aas it was by then) #201D (tentative) and the follow rejection to the change of tranfer function.
    upload_2017-8-17_19-42-55.jpeg
    upload_2017-8-17_19-44-36.jpeg
     

  3. Old Tele man

    Old Tele man Tele-Afflicted

    May 10, 2017
    Tucson, AZ
    FWIW - those "higher" gm values for 6V6GT are a better 'match' for the numbers you get when backsolving for gm from the Class-A and PP Class-AB1 circuit examples in the data books. It also "hints" as to why such a w-i-d-e array of gm values can be found in different manufacturers data books.

    RCA could make it's 6V6's meet those values, whereas most of the other companies didn't want to change (read: improve) their production methods AND fight a "my tube is better than his tube" marketing battle, hence the push-back (Raytheon was one who didn't agree with RCA).
     
    Last edited: Aug 17, 2017

  4. ocduff

    ocduff TDPRI Member

    65
    Nov 17, 2003
    USA
    Love all this reading Old Tele Man - the 1960 GE data sheet lists the 6L6GB as a 24 watt tube. I have a 1956 NY made pair of these but run them as 19 watt tubes. Thoughts?

    And rectifiers drop voltage but also change the feel and break up characteristics of the amp - and even at that different brands (while usually consistent in voltages they provide) can sound different.

    I too like the punchliness of the GZ34 in a DR. Tighter bottom and more headroom. Later models did come with a 5U4 though.

    I have considered this question myself and too have found Gerald Weber's opinions to be misleading (this guy gets raked over the coals a lot - I think his books were ahead of their time and still useful as a resource especially for handy layouts and schematics). When he said Western Electric designed the 5F6 circuit you have to start taking what is said with a grain of salt. Also his "mods" to amps assume we all want more gain and overdrive. Not helpful to us clean guys.

    But I've redplated tubes a long time but have found that high current is more detrimental and can cause sudden tube failure than the former.

    I ask myself these questions - what's worse, running 6L6GB (rated for 360 volts) at 400 volts and 70% dissipation or 435 volts and 50% dissipation.

    My feeling is I will be less apt to sudden shorts with higher dissipation and lower plate voltage. Bonus is the amp they are in (5E8-A) sounds way better at 70% and also it's voltages are thus correct to schematic - which I think helps curtail a lot of the cathodyne phase inverter distortion I've been fighting in that amp.

    As for me DR - I preferr a cooler Bias. Mine runs 430v and 18ma with a pair of 1958 GE 6V6GT. I might run the bias a little hotter but much hotter than that and you lose some cleans.

    All that said - none of us have empirical data on the OP's question and really until then we don't have an answer to this question.
     

  5. ocduff

    ocduff TDPRI Member

    65
    Nov 17, 2003
    USA
    Also - zener diodes get mentioned a lot but it's a major project and gets a bit confusing.

    Have you all ever wired a 20 watt ceramic Resistor of about 68 ohms from rectifier to standby switch?

    This will lop about 6-10 volts off. It can induce a bit of sag but it's quick and easy way of getting things down a few Volts and the changes don't sag as much as a switch from GZ34 to 5u4.
     

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