Help sorting out 5e3 voltages

Discussion in 'Amp Tech Center' started by AJBaker, Jun 1, 2019.

  1. AJBaker

    AJBaker Friend of Leo's

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    So I did some measuring inside my tweed deluxe clone today, and I'm wondering if I should be concerned about anything.

    It has a Hammond 290bex transformer with a 240V primary. Wall voltage here is actually 230V, so the heater voltages are a bit low: 4.5V (instead of 5V) on the 5y3, and 5.8 (instead of 6.2V) on the others.
    Is this an issue?

    Next, I checked the bias: plate current is about 37.7mA per tube (calculated by deviding bias resistor R by voltage drop across the resistor, then deviding that by 2).
    Multiply this by the 351V plate voltage and I get an average plate dissipation of 13.2W per tube.


    Looking at the specs of my Tung Sol tubes, it would seem they're over biased. (http://www.tungsol.com/specs/6v6gt-tung-sol.pdf)

    The specs call for max 12W dissipation, max 35mA, and max 315V plate voltage.

    Am I still in the green, or should I change something?

    Thanks!
     
  2. peteb

    peteb Friend of Leo's

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    Nothing looks unusual



    Yes.



    The tubes are normally considered 14W, cathode bias can go as high as 100%, and 6V6s regularly see 400+ volts.


    The tube only sees the plate minus the cathode voltage, so yours is closer to 315 than 400. It’s good.
     
  3. AJBaker

    AJBaker Friend of Leo's

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    Thanks, that's reassuring!
     
  4. Silverface

    Silverface Poster Extraordinaire Ad Free Member

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    Also - do you have NOS Tung Sols, old "pulls" - or brand new ones?

    Those specs ONLY apply to the new tubes - The specs for NOS tubes are different. The are "Tung Sol" 6V6's only in name.

    The reissues are not the same tube as the originals. They are Russian tubes with somewhat similar performance that New Sensor slapped a Tung Sol screen print on and stuck in a pretty new box. They bought the rights to the name but the tubes are all different - some for the preamp tubes, and the new "Mullard" line.
     
  5. AJBaker

    AJBaker Friend of Leo's

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    I've got new ones made in Russia.
     
  6. flyswatter

    flyswatter Friend of Leo's

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    14W plate dissipation is not uncommon in a 5E3. I've build several and serviced two originals from the 1950s, and they all had about 13-14 W dissipation and 340 - 350 VDC on the plates. The RCA Receiving Manual lists 14W as the max diss. for 6V6s -- which of course applies to vintage stock. However, I've had a pair of Tung-sols in one of my 5E3s for the past few months. 14W dissipation. That amp is currently on a major tour with a customer, running daily for the last month on a 2 hour show, and has been performing without a hitch.
     
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