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Re: [TenTec] Centaur Tubes odd ones in parallel

To: "'Discussion of Ten-Tec Equipment'" <tentec@contesting.com>
Subject: Re: [TenTec] Centaur Tubes odd ones in parallel
From: "Rick - DJ0IP / NJ0IP" <Rick@DJ0IP.de>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Thu, 2 Apr 2015 08:52:20 +0200
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
YEP!  This sounds like it will do the trick.  Thanks Mike.

I actually read that long ago but wasn't interested at the time, and simply 
forgot about it.
I suppose you could adjust the value of each grid resistor to adjust the idle 
current of each tube.  

It is currently a none issue for me since both of my 'big' amps have only a 
single tube.
However I will try this out on my HA-14 - if I ever find time to build a power 
supply for it.

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


-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Mike Schatzberg
Sent: Thursday, April 02, 2015 8:25 AM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] Centaur Tubes odd ones in parallel

Here you go, read the last sentence Mr. Measures writes here:

ANODE AND GRID GLITCH PROTECTION
A glass-coated resistor can serve as a peak current limiter between the HV 
supply and the anode circuit. A $2 resistor can save an approx. $150 3-500Z or 
an approx. $650 8877. If a glitch such as a parasitic oscillation occurs, the 
fuse-resistor absorbs most of the stored energy from the filter capacitors. If 
low VHF-Q parasitic-suppressors have been installed in a HF amplifier, this is 
less likely to happen, but it's best to be on the safe side. Even though Eimac® 
recommends it, the TL-922 and the SB-220 have no glitch resistor protection 
between the amplifier-tubes and the HV filter-capacitor bank. The glitch 
resistor is an ordinary 10 Ohm, 10W glass-coated wirewound unit. It has enough 
inductance to replace the small VHF RF-choke, TL-922's L2 [12µH], which is 
inside the tube compartment.
The grid fuse-resistors [1 per tube] are 27 Ohm to 33 Ohm, 1/2W, carbon-film 
type.[6] They replace the two grid to ground, 470µH chokes, L7 and L8.
The grid fuse-resistors also provide about 3.5V of DC negative-feedback per 
grid under maximum signal condition. This helps to equalize the currents in two 
3-500Zs that are not a matched pair.

Nothing new really. 

73,

Mike
W2AJI 

Sent from my iPhone

> On Apr 1, 2015, at 11:59 PM, Rick - DJ0IP / NJ0IP <Rick@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@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@DJ0IP.de> wrote:
>> 
>> Mike, that's a good procedure.
> 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@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@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@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@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@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@twc.com>
>>>> To: tentec@contesting.com
>>>> Subject: [TenTec] Centaur Tubes odd ones in parallel
>>>> Message-ID: <20150331193940.EK621.275017.root@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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