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    Tube Newbie

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    sKiZo

    Posts : 1286
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Tube Newbie

    Post by sKiZo on Mon Sep 19, 2016 10:37 pm

    LeGrace wrote:I can do a diode mod, except I wonder if its so great why has it not been incorporated into the standard design already? What's the catch? Or the thermistor mod? Even if I knew what this was the watch out for the HOT comment is alarming!?

    Keep in mind, there's a diode mod, and there's a diode mod. The "yellow sheet" mod doesn't replace the tube rectifier - it simply adds a couple diodes in line with the transformer leads to prevent reverse flow that can kill a tube.

    Arrrr!!  affraid

    I can buy GZ37 or GZ33 tubes, the only examples of which I can find are NOS GZ37's at a cost of ~$150 USD each! By the time I get them into Canada with duty etc close to $500 for the pair. Sadly I cant afford this after what I've already invested. Was a stretch to start with.

    I'd be hard pressed to afford them at that price as well. Lucky me, I got a couple nice old Canadian military surplus Mullards (circa mid '70's) for $80 each a couple years back. NOS! Arrrr !!! Probably the last two available at those prices. Timing can be everything.

    Arrrr ...  Sad



    The Webers are working fine. Except for how long, plus the amps seem to have lost some of their mojo vs the tube rectifiers.

    Can't say as I cared for the tone of the WZ68 here, but it's good for a spare. Some problems apparently with longevity, but I'm thinking a lot of that may be due to the high VAC coming out of the average wall nowadays. I used mine driving a quad of KT120's kickin' it hard with prog rock at ridiculous volumes with nary a problem.

    Arrrr !!!   pirat

    corndog71

    Posts : 444
    Join date : 2013-03-19
    Location : It can get windy here

    Re: Tube Newbie

    Post by corndog71 on Tue Sep 20, 2016 12:43 am

    LeGrace wrote:Hilarious pic Skizo, except for the reality it reflects. Here is my take so far from the feedback:

    1) I can do a diode mod, except I wonder if its so great why has it not been incorporated into the standard design already? What's the catch? Or the thermistor mod? Even if I knew what this was the watch out for the HOT comment is alarming!?

    2) I can buy GZ37 or GZ33 tubes, the only examples of which I can find are NOS GZ37's at a cost of ~$150 USD each! By the time I get them into Canada with duty etc close to $500 for the pair. Sadly I cant afford this after what I've already invested. Was a stretch to start with.

    3) The Webers are working fine. Except for how long, plus the amps seem to have lost some of their mojo vs the tube rectifiers.

    Arghh!!!

    The answer to your first question is pretty simple. This is primarily a forum for lovers of Dynaco designs and back then they used tube rectifiers. Bob sells essentially replicas with better circuitry for better sound quality. The main reason you don't see diodes is they drift away from those classic designs. Plus it's an extra glowing tube which we all love!

    Well, after rebuilding an ST70 and building a pair of MKIVs I went through many tube rectifiers. (Some back to back Evil or Very Mad JJ). Next I studied the ST35 which uses diode rectification. ...like a lot of "modern" tube amps. So when I decided to tackle a modified version of the VTA120 losing the rectifier tube was an easy move and one I don't regret. I do power it at 117vac through a variac to keep internal voltages in their proper place.






    deepee99

    Posts : 1260
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Re: Tube Newbie

    Post by deepee99 on Tue Sep 20, 2016 11:28 am

    I do like the "purity" of tube rectification but if you're going that route, expect to pay for it. I've tried JJs and Sovteks and had as much the same experience as Corndog71. They last anywhere from initial start-up to a couple of weeks if you're lucky. A decent British Mullard is pretty spendy, yes. The Webers are a decent compromise and you should get a couple of years out of them for 1/8th the price of NOS Mullards. But they don't glow in the dark, although they get just as hot.

    LeGrace

    Posts : 49
    Join date : 2016-08-07

    Re: Tube Newbie

    Post by LeGrace on Tue Sep 20, 2016 12:55 pm

    Ok thanks for all the replies. Maybe its all in my head but it just seems the amps don't have quite the same slam as before. I contacted Jim McShane regarding possibly recommending a more reliable tube. His advice, if its a M125, do the diode mod. Since I'm not likely to score old Mullards at anything reasonable like "lucky dog" Skizo guess I need to round up some diodes. And order yet more tubes. Rolling Eyes

    deepee99

    Posts : 1260
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Re: Tube Newbie

    Post by deepee99 on Tue Sep 20, 2016 1:04 pm

    A guy can't ever have enough power tools, or tubes.
    Just find a rectifier system that works for you, then focus on the driver and pre-amp tubes. They're really where the sound flavour comes from.

    Peter W.

    Posts : 84
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: Tube Newbie

    Post by Peter W. on Tue Sep 20, 2016 5:13 pm

    Now, after all this, I would like to see a cogent reason to use a tube rectifier. Yes, a 5AR4 is a slow-start device, allowing the rest of the tubes to heat up before being slammed by full B+. A relay can also accomplish this.  Yes, a tube rectifier will help drop B+ somewhat in these troubled times of high line voltage. But is it enough to make a difference?

    On the support side of SS rectification, the much loved ST35 uses SS as a point of departure.
    SS rectification allows a faster recovery if there is heavy draw on the rectifier, or even no sag at all if the other components are rugged enough. And, last I looked, DC is DC is DC.

    Thoughts?


    Last edited by Peter W. on Wed Sep 21, 2016 7:58 am; edited 1 time in total

    corndog71

    Posts : 444
    Join date : 2013-03-19
    Location : It can get windy here

    Re: Tube Newbie

    Post by corndog71 on Tue Sep 20, 2016 5:32 pm

    Peter W. wrote:Now, after all this, I would like to see a cogent reason to use a tube rectifier. Yes, a 5AR4 is a slow-start device, allowing the rest of the tubes to heat up before being slammed by full B+. A relay can also accomplish this.  Yes, a tube relay will help drop B+ somewhat in these troubled times of high line voltage. But is it enough to make a difference?

    On the support side of SS rectification, the much loved ST35 uses SS as a point of departure.
    SS rectification allows a faster recovery if there is heavy draw on the rectifier, or even no sag at all if the other components are rugged enough. And, last I looked, DC is DC is DC.

    Thoughts?

    Oh yeah, I forgot to mention I use the Time Delay Relay as well.

    deepee99

    Posts : 1260
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Re: Tube Newbie

    Post by deepee99 on Tue Sep 20, 2016 5:49 pm

    Well, the rectifier isn't in the audio signal path. So it's really more a matter of aesthetics. I've used Webers (s/s/) without a TDR and never blew an output tube.I just like the look of the GZ-33s and -37s. But let me get on my high horse again: Get a manual-reset ground-fault interrupter and stick in the wall plug! That will do you more good than any gizmo you can add to your amps. Amazon <$30 or so.





    Peter W.

    Posts : 84
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: Tube Newbie

    Post by Peter W. on Wed Sep 21, 2016 8:01 am

    Agreed on the aesthetics. But in this household, what with cats, dogs and grandkids running about in various quantities, cages and/or remote/high locations for hot tubes is the rule. So the visual impact greatly reduced.

    LeGrace

    Posts : 49
    Join date : 2016-08-07

    Re: Tube Newbie

    Post by LeGrace on Wed Sep 21, 2016 10:07 am

    Dug a bit more into the subject, came across this interesting post, particularly as it relates to amp power. My apologies if this is old news:

    Tube or Solid State Rectification

    This makes me very nervous about using any 5AR4 tube in my M125's, irrespective of the diode mod. As well as vindicating Bob's recommendation around the copper tops. A few hours in with them and things are starting to sound much better now. I keep neglecting needing to allow for sufficient break in time with this stuff! Embarassed

    sKiZo

    Posts : 1286
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Tube Newbie

    Post by sKiZo on Thu Sep 22, 2016 2:45 pm

    deepee99 wrote:Well, the rectifier isn't in the audio signal path. So it's really more a matter of aesthetics.

    Yahbutt ...

    It does affect the overall slew and response time of the amp ... and that ain't what you'd call inconsequential in the great scheme of things. Sorta like how components in the power supply will affect the clarity and accuracy of the end result.

    oooooOOOOOoooooohhhhmmmmm ...

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