[TenTec] Centaur Tubes odd ones in parallel

Rick - DJ0IP / NJ0IP Rick at DJ0IP.de
Thu Apr 2 04:07:00 EDT 2015 

Well done, Wade!
As Mike showed us, it indeed can be done that way.

73 - Rick, DJ0IP
(Nr. Frankfurt am Main)


-----Original Message-----
From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Wade Staggs
Sent: Thursday, April 02, 2015 9:26 AM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] Centaur Tubes odd ones in parallel

*Wouldn't using a Bypass Capacitor place the tube at RF Ground? Surely, the
Grid could be at RF Ground but, DC Biased. Am I missing something here?
Maybe, my theory of thermionic emission, needs a refresher course. With the
Grid at RF Ground, couldn't the gain be controlled with a Grid resistor? I
may be way out in Left Field here. Some of the Big Brains can answer this
one? *
*                                             73 to All from Wade*

On Thu, Apr 2, 2015 at 12:59 AM, Rick - DJ0IP / NJ0IP <Rick at dj0ip.de> wrote:

> Mike,
>
> Do you mean to unground the grounded grid and connect it through a 
> resistor to ground?
> Hmmm, not sure about that.  Might work.
> Normally the 3-500z has two pins connected with big straps to ground 
> (if I remember correctly).
> This gives it some really solid grounding.
> Raising with a small resistor would enable controlling the current, 
> but how good of quality of RF ground would it then be?
>
> I'll tell you what.  You try it with your amp and let us know!  (hi) 
> These tubes are now a couple hundred bucks a piece.
>
> 73 - Rick, DJ0IP
> (Nr. Frankfurt am Main)
>
> -----Original Message-----
> From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Mike 
> Schatzberg
> Sent: Wednesday, April 01, 2015 10:39 PM
> To: Discussion of Ten-Tec Equipment
> Subject: Re: [TenTec] Centaur Tubes odd ones in parallel
>
> Why not equalize the grid current for each tube. Small resister to 
> ground should do the trick. Some folks turn it into a grid fuse by 
> using a very small wattage resister. If the grid current goes too high,
they pop open.
>
> I've played with that concept, but I'm not a fan.
>
> 73,
>
> Mike
> W2AJI
>
> Sent from my iPhone
>
> > On Apr 1, 2015, at 2:06 PM, Rick - DJ0IP / NJ0IP <Rick at DJ0IP.de> wrote:
> >
> > Mike, that's a good procedure.
> > Unfortunately I haven't figured out a way to do that when you have 
> > multiple triodes.
> >
> > With Sweep Tube amps it was very simple.
> > We biased the grid directly and using diode strings, each tube got 
> > its own dedicated tap.
> >
> > But what can we do to match multiple triodes in grounded grid?
> >
> > 73 - Rick, DJ0IP
> > (Nr. Frankfurt am Main)
> >
> >
> > -----Original Message-----
> > From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of 
> > Mike Schatzberg
> > Sent: Wednesday, April 01, 2015 7:23 PM
> > To: Discussion of Ten-Tec Equipment
> > Subject: Re: [TenTec] Centaur Tubes odd ones in parallel
> >
> > You can check the match both statically and dynamically by 
> > installing one triode at a time, and double checking you don't short 
> > the unused
> plate
> cap.
> > Follow all safety precautions and all interlocks should be engaged.
> > Always allow time for the capacitor bank to bleed down and then 
> > short the HV to ground while the amp is open.
> >
> > Key the amp with no drive and observe the idle current for that triode.
> > Remove that tube and replace with the second triode.
> >
> > The results should be very close for well matched tubes.
> >
> > If you wish, you can plot input drive vs output power through the 
> > useful range of the limits of plate and grid current for each triode.
> > Again, the curves should be similar for a matched pair.
> >
> > A good quality dummy load should be employed.
> >
> > You will also observe the linearity of the amp and the saturation 
> > point when additional drive no longer produces a linear output.
> >
> > Obviously, good quality instruments should be used to produce the
curves.
> >
> > It takes only minutes to do the static test. Why guess if you will 
> > have an issue?
> >
> > This methods can help determine the needed bias voltage for best 
> > linearity also. I usually build a diode string and add or subtract 
> > diodes to get the desired idling current. The 3-500 is a zero bias 
> > tube and is pretty easy to deal with. The higher the idling current, 
> > the hotter the tube runs, and the easier it is to drive to full output.
> >
> > 73,
> >
> > Mike
> > W2AJI
> >
> > Sent from my iPhone
> >
> >> On Apr 1, 2015, at 9:30 AM, Rick - DJ0IP / NJ0IP <Rick at DJ0IP.de> wrote:
> >>
> >> Bob, you have been very lucky if you have never had any problems 
> >> with unmatched tubes.
> >> I certainly have.
> >>
> >> In fact I finally decided not to own any multi-tube amps anymore.
> >> That solved that problem. (almost)
> >>
> >> I now only have two amps, each with a single 3-500z, but...
> >> I also have an old Heathkit HA-14 mobile amp with a pair of 572B tubes.
> >> Can't seem to find a replacement for that one.  There are no tiny 
> >> amps with single tubes running that much power.
> >>
> >> I don't care much for most transistor amps.
> >> Their linearity is the pits!
> >> Though I wouldn't mind having the Elecraft 500w amp...
> >> Jim sure raves about his!
> >>
> >> 73 - Rick, DJ0IP
> >> (Nr. Frankfurt am Main)
> >>
> >>
> >> -----Original Message-----
> >> From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of 
> >> Katz Ajamas
> >> Sent: Wednesday, April 01, 2015 5:14 PM
> >> To: Discussion of Ten-Tec Equipment
> >> Subject: Re: [TenTec] Centaur Tubes odd ones in parallel
> >>
> >> Kris-
> >>
> >> Are these 811 or 572?  I've never owned a Centaur but have not had 
> >> any trouble with non-matched tubes in other amps, provided they 
> >> were from the same OEM.
> >>
> >> A single used 811 or 572 should be pretty cheap, so how about 
> >> hunting up one each of the missing?
> >>
> >> 73, Bob ah7i/w4
> >>
> >>
> >>
> >>
> >>
> >>
> >>> ------------------------------
> >>>
> >>> Message: 9
> >>> Date: Tue, 31 Mar 2015 15:39:40 -0400
> >>> From: <km2km at twc.com>
> >>> To: tentec at contesting.com
> >>> Subject: [TenTec] Centaur Tubes odd ones in parallel
> >>> Message-ID: <20150331193940.EK621.275017.root at dnvrco-web01>
> >>> Content-Type: text/plain; charset=utf-8
> >>>
> >>> Ok, guys, here is the scoop.
> >>>
> >>> My trusty Centaur seldom needs to be re-tubed, BUT now I have two 
> >>> pairs of tubes,  one pair Taylor, and the other pair Svetlana 
> >>> because over
> >> time one
> >>> tube left the troika for the electronic dump.   Yes, matched tubes are
> > the
> >>> ideal, but having a couple of pairs sitting around doing nothing 
> >>> for me and no foreseeable makes me wonder.  Just what would happen 
> >>> if they were a mixed troika.  That would leave one tube in the bin 
> >>> ready for
> >> another time.
> >>>
> >>> Any ideas on dire consequences?
> >>>
> >>> Many thanks,
> >>>
> >>> Kris KM2KM
> >>> MERSCHROD
> >>> 123 Warren Road
> >>> Ithaca, NY 14850
> >>>
> >>>
> >>> ------------------------------
> >>>
> >>> Subject: Digest Footer
> >>>
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> >>>
> >>>
> >>> ------------------------------
> >>>
> >>> End of TenTec Digest, Vol 147, Issue 34
> >>> ***************************************
> >>>
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