The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Dynaco VTA tube amp kits, all Tubes4hifi.com products and all Dynakitparts.com products


    5AR4 Orange lightening bolt

    Share
    avatar
    CletusB

    Posts : 191
    Join date : 2018-02-11
    Age : 63
    Location : Trinidad & Tobago

    5AR4 Orange lightening bolt

    Post by CletusB on Mon Sep 24, 2018 1:14 pm

    Just noticed an orange "lightening Bolt" run down the inside of the 5AR4 envelope when the relay energized. Don't recall noticing that before. But the amp works just fine. Your thoughts on this please (I do have the "yellow sheet diode mod" installed).
    avatar
    peterh

    Posts : 1041
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: 5AR4 Orange lightening bolt

    Post by peterh on Mon Sep 24, 2018 1:23 pm

    CletusB wrote:Just noticed an orange "lightening Bolt" run down the inside of the 5AR4 envelope when the relay energized. Don't recall noticing that before. But the amp works just fine. Your thoughts on this please (I do have the "yellow sheet diode mod" installed).
    This is not what the tube wants, it's slow or fast destroying it. The cause is that
    a relay closes and the rectifier tube takes a surge to charge large caps.

    Sudden application of large currents is the cause.
    See http://www.tronola.com/html/maximize_tube_life.html for a discussion.
    avatar
    CletusB

    Posts : 191
    Join date : 2018-02-11
    Age : 63
    Location : Trinidad & Tobago

    Re: 5AR4 Orange lightening bolt

    Post by CletusB on Mon Sep 24, 2018 2:11 pm

    Here it is in real-time followed by two attempts at slow motion.
    avatar
    CletusB

    Posts : 191
    Join date : 2018-02-11
    Age : 63
    Location : Trinidad & Tobago

    Re: 5AR4 Orange lightening bolt

    Post by CletusB on Mon Sep 24, 2018 2:13 pm

    I guess I'll just order a couple Chinese 5AR4 tubes. I do have a Weber WZ68 that I've never used.
    avatar
    PeterCapo

    Posts : 543
    Join date : 2008-12-05

    Re: 5AR4 Orange lightening bolt

    Post by PeterCapo on Mon Sep 24, 2018 5:25 pm

    Two things:

    1) What are the values of the capacitors along your B+ nodes?  The original had 30µF immediately after the 5AR4, then 20/20/20 downstream.  I had a Chinese 5AR4 arc with just that much.  What value capacitors do you have?

    2) consider trying one of the newer Tung Sol or Gold Lion 5AR4/GZ34 tubes.
    avatar
    CletusB

    Posts : 191
    Join date : 2018-02-11
    Age : 63
    Location : Trinidad & Tobago

    Re: 5AR4 Orange lightening bolt

    Post by CletusB on Wed Sep 26, 2018 8:35 am

    Ok, a Gold Lion GZ34 is on order from uncle Jim McShane.  In the meantime, I've retired the 5AR4 and stuck the Weber WZ68 in there (that sucker runs as hot as a tube) and re-biased the rig.  These old ears cannot detect a sonic difference at this time, will audition it more acutely tonight. bounce

    Dale Stevens

    Posts : 92
    Join date : 2014-07-06
    Age : 69
    Location : Loris, SC

    Re: 5AR4 Orange lightening bolt

    Post by Dale Stevens on Wed Sep 26, 2018 3:26 pm

    C, FMI ; why a delay relay when you are running a TUBE rect? Thanks, Dale
    avatar
    Peter W.

    Posts : 933
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: 5AR4 Orange lightening bolt

    Post by Peter W. on Wed Sep 26, 2018 3:37 pm

    Dale Stevens wrote:C, FMI ;  why a delay relay when you are running a TUBE rect?  Thanks,  Dale

    It will delay B+ until the output tubes are fully warmed up. The 5AR4 is a slow-onset rectifier tube - or so it was back in the day. I am not so sure it remains as slow an onset tube as it was, today. What with all the burn-outs and failures reported here after only a relatively few hours, I have to question their quality in general. The Dynaco-marked tube in my very vintage 70 has many thousands of hours on it as to my Siemens 6CA7s and RCA 7199s.
    avatar
    CletusB

    Posts : 191
    Join date : 2018-02-11
    Age : 63
    Location : Trinidad & Tobago

    Re: 5AR4 Orange lightening bolt

    Post by CletusB on Wed Sep 26, 2018 3:40 pm

    To keep the B+ off the outputs till they have arrived at operating temperature, but if using a tube rectifier or the Weber WZ68 , you don't really need it. But more importantly, insurance that power can't be cycled between off and on states without a 17-sec delay, as when a brief power outage occurs, which is VERY common in my area.
    avatar
    CletusB

    Posts : 191
    Join date : 2018-02-11
    Age : 63
    Location : Trinidad & Tobago

    Re: 5AR4 Orange lightening bolt

    Post by CletusB on Wed Oct 03, 2018 3:43 pm

    Gold Lion GZ34 from Jim McShane came in today. Got it plugged-in and re-biased the KT-88s. Bass response sounds a tad more pronounced, but have not really listened enough, so that can't really be confirmed at this point.
    avatar
    cci1492

    Posts : 198
    Join date : 2016-05-09
    Age : 57
    Location : Bergen County NJ

    Re: 5AR4 Orange lightening bolt

    Post by cci1492 on Wed Oct 03, 2018 9:44 pm

    The Gold Lions work nicely on the M125s as well.
    avatar
    CletusB

    Posts : 191
    Join date : 2018-02-11
    Age : 63
    Location : Trinidad & Tobago

    Re: 5AR4 Orange lightening bolt

    Post by CletusB on Wed Oct 03, 2018 10:04 pm

    I think I am starting to dislike the relay board. I do also have a GFCI "latch-out" on the mains should there be a power failure.
    Maybe, Bob or Jim can correct me if I had too many beers here (LOL). 
    Even with this new rectifier, I see an ever so  tiny arc at the base when the relay kicks-in (really disturbing). I think the relay kicks in and the rectifier sees a sudden "dead-Short" instantaneously as the depleted caps receive B+
    Will study the diagrams tomorrow again, maybe I'll flip the amp over and bypass the B+ carrying contacts allowing the voltage to rise slowly, as the suite of tubes, especially the rectifier, come up to temperature.
    Nonetheless, still the sweetest amp I've ever had! bounce
    avatar
    tubes4hifi
    Admin

    Posts : 1478
    Join date : 2008-11-30

    Re: 5AR4 Orange lightening bolt

    Post by tubes4hifi on Fri Oct 05, 2018 2:32 pm

    you only need a TDR if you are not using a rectifier tube.
    Also, check to see what the timing of the relay is.
    Standard is about 17 seconds. The longer the time, the greater the current surge when it does kick in.
    avatar
    CletusB

    Posts : 191
    Join date : 2018-02-11
    Age : 63
    Location : Trinidad & Tobago

    Re: 5AR4 Orange lightening bolt

    Post by CletusB on Sat Oct 06, 2018 10:26 am

    Yup, I think I'll shunt those two relay switch-points with the unused mono/stereo switch. That way I can have no TDR when using the tube and TDR active when using solid-state rectification.
    Just hate the idea of chopping into my perfectly running amp.

    UPDATE:
    Easier way to defeat the TDR:  Switching-in a 1K resistor across R3 would energize the relay almost instantaneously on power-on, T = 1.1 * R3 * C3 (0.036 secs)    ....think I'll go this route
    avatar
    CletusB

    Posts : 191
    Join date : 2018-02-11
    Age : 63
    Location : Trinidad & Tobago

    Re: 5AR4 Orange lightening bolt

    Post by CletusB on Sun Oct 07, 2018 8:43 am

    Ok, just implemented the latter TDR bypass method and it works a peach!
    I can now use the otherwise useless stereo/mono sw to go between "instantaneous" or 17-sec delay, depending on weather I'm using a GZ34 or some solid-state tube look-alike (the WR68 does have a short delay built-in).
    No more tube arcing! bounce
    avatar
    ggnarley

    Posts : 12
    Join date : 2018-05-11
    Location : Columbus, Ohio

    Had same thing happen to me

    Post by ggnarley on Sun Oct 07, 2018 8:48 pm

    I also just bypassed my TDR relay.  After swapping the SS for a tube rectifier (didn't like the SS sound) I watched it faintly flash white when starting up once.

    Sponsored content

    Re: 5AR4 Orange lightening bolt

    Post by Sponsored content


      Current date/time is Thu Oct 18, 2018 5:28 pm