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
>>>>
>>>> _______________________________________________
>>>> TenTec mailing list
>>>> TenTec@contesting.com
>>>> http://lists.contesting.com/mailman/listinfo/tentec
>>>>
>>>>
>>>> ------------------------------
>>>>
>>>> End of TenTec Digest, Vol 147, Issue 34
>>>> ***************************************
>>>>
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