[Amps] Tube swap

[William Turner]

Please keep in mind two things:

1. The AADE meter measures inductance at a very low frequency. At VHF 
the inductance can be considerably different due to distributed 
capacitance between windings. The best tool is an impedance analyzer 
which applies the actual VHF frequency and costs about $10k. I don't 
have one either. It was that or a house.  :-)

2.  There is no such thing as "non-inductive". Even a short straight 
piece of wire has inductance. If someone tells you a resistor is 
non-inductive, they are prevaricating.

73, Bill W6WRT


------------ ORIGINAL MESSAGE ------------

On 1/29/2014 5:31 PM, Bryan Swadener wrote:
> I measured new Ohmite pn OY470KE (47ohm/2W) resistors at 1.6uH inductance.
> The instrument used was a new factory-assembled and calibrated
> "Almost All Digital Electronics" L-C Meter (http://www.aade.com/). According
> to the manufacturer, it compares closely to several high-end L/C/R
> instruments.  I verified mine, compared to a few other pieces of HP gear that
> I trust.
>   
> Before making any measurements, I first nulled the internal inductance
> with the terminals shorted, using a 1" length of 14ga wire (about 17nH).
> A NOS Allen-Bradley 47 ohm/2W carbon composition resistor then
> measured 20nH, and a 3-1/2 turn 14ga parasitic suppressor inductor
> (Heathkit SB-220) measured 80nH. The OY "resistor" measured 1.58uH.
>   
> The datasheet for the Ohmite OX/OY resistors
> (http://www.ohmite.com/cat/res_ox_oy.pdf) says only:
>
> "The OX/OY resistors can often replace carbon composition resistors
> which can be difficult to source."
>
> They make NO claim that they are without inductance.  In fact,
> nowhere in the datasheet is the word "inductance" or "reactance"
> used, or inferred.
>   
> eBay seller "bigsmythe74" always seems to have
> A-B Carbon Composition resistors available for reasonable prices.
> I have no connection with him other than as a customer.
>   
> vy 73,
> Bryan WA7PRC
> ----------------------------------------------------------------------
> Date: Tue, 28 Jan 2014
> From: Carl
> Subject: Re: [Amps] Tube swap
> For 4-1000's and 30-40 years ago I was using a 50 Ohm Globar when I could
> find one, or 3 150 Ohm 2W carbons in parallel.
> These days 3 of the Ohmite OY series work well or use a bulletproof 25-50W
> Carborundum type from fleabay. Value can be roughly 50 Ohms +/- 30% or so.
> If you are pushing the power over 1200-1500W then use strap or small tubing
> for the inductor.
> [snip]
> Carl
> KM1H
> ----- Original Message -----
> From: Bill WA4LAV
> Sent: Tuesday, January 28, 2014 2:48 PM
> Subject: Re: [Amps] Tube swap
>
>> Many years ago I got one of his kits for my single 4-1000A amp and the
>> suppressor went with a bang. I went to normal suppressor. The point is
>> to simply introduce loss, lower the Q, of VHF parasitic resonances that
>> can exist in the plate circuit of the amplifier.
>> 73
>> Bill WA4LAV
>>
>> ________________________________________
>> From: Karel VA3KO
>> Sent: Tuesday, January 28, 2014 2:36 PM
>> To: Don W4DNR
>> Subject: Re: [Amps] Tube swap
>>
>> Sorry, I met him over internet right after his write-up for AR Handbook
>> was
>> rejected and that was a long time ago. I brought up his name here once
>> before and got slapped for it, sorry, I should know by now. I owe cup of
>> coffee to all. Hopefully we will meet some day.
>>
>> I still have his suppressor package for two 4-1000A 's to be installed.
>> Without bringing his name out again, can someone warn me about using it?
>>
>> I installed his suppressor package on my friend's Henry 2K. It lasted few
>> years, but his plate transformer croaked recently, I wonder if the
>> suppressor had anything to do with that.
>>
>> Karel VA3KO
>>
>> ----- Original Message -----
>> From: Don W4DNR
>> Sent: Tuesday, January 28, 2014 10:56 AM
>> Subject: Re: [Amps] Tube swap
>>
>>
>>> Quoting Karel VA3KO:
>>>
>>>> Hardy,
>>>> yes I made myself a Hi-pot tester as well. I forgot the specs, but I
>>>> believe I can go up to 20 kV. (It may be one of Richard Measures
>>>> designs).
>>> Don W4DNR
> ------------------------------
> Date: Tue, 28 Jan 2014 20:44:20 -0800
> From: Bill W6WRT
> Subject: Re: [Amps] Tube swap
> What does thickness of the grid leads have to do with VHF parasitic
> frequency? It would seem that thin leads, having less capacitance to
> everything else, would tend to raise the frequency, if anything.
> 73, Bill W6WRT
> On 1/28/2014 6:14 PM, Carl wrote:
>> Old tubes will have their parasitic down at low VHF, often right
>> around 6M due to long thin grid leads.
> ------------------------------
> Date: Wed, 29 Jan 2014 02:03:14 -0500
> From: Roger K8RI
> Subject: Re: [Amps] Tube swap
> On 1/28/2014 6:11 PM, Carl wrote: The handbook has a good section on
> designing them, but after you get all the info, and calculations, you
> have to take into account stray inductance and capacitance.  IE, they
> give you a base design that likely will need to be modified to fit the
> layout of the amp and tube, or tube. So as Carl says, pick an amp with
> the same tube and similar layout and build a supressor like theirs and
> it'll likely work with little or no modification.
> 73
> Roger (K8RI)
>
>> Suppressors are usually tube and layout/construction dependent for the
>> inductor part.
>>
>> Look at commercial and good HB ham amps that have the tube you want to
>> use and go from there.
>>
>> Having a quality brand of GDO helps a lot as an economical tool..
>>
>> Carl
>> KM1H
>>
>>
>> ----- Original Message -----
>> From: Karel VA3KO
>> To: Carl; Don W4DNR
>> Sent: Tuesday, January 28, 2014 5:53 PM
>> Subject: Re: [Amps] Tube swap
>>
>>
>>> Thanks Carl,
>>> I just have to figure out what the factory design should be. I will
>>> definitely use ceramic resistor. Any suggested lead to better
>>> suppressor setup?
>>> Values, arrangement? Thanks,
>>> Karel, VA3KO
>>>
>>> ----- Original Message -----
>>> From: Carl
>>> To: Karel VA3KO; Don W4DNR
>>> Sent: Tuesday, January 28, 2014 4:26 PM
>>> Subject: Re: [Amps] Tube swap
>>>
>>>
>>>> Stick to factory designs, they work fine for decades without problems.
>>>> The Ohmite OY series of ceramic resistors do well in place of out of
>>>> tolerance carbon composition.
>>>>
>>>> Sell the voodoo crap on fleabay to a CBer
>>>>
>>>> Carl
>>>> KM1H
>>>>
>>>>
>>>> ----- Original Message ----- From: Karel VA3KO
>>>> To: Don W4DNR
>>>> Sent: Tuesday, January 28, 2014 2:36 PM
>>>> Subject: Re: [Amps] Tube swap
>>>>
>>>>
>>>>> Sorry, I met him over internet right after his write-up for AR
>>>>> Handbook was rejected and that was a long time ago. I brought up his
>>>>> name here once before and got slapped for it, sorry, I should know
>>>>> by now. I owe cup of coffee to all. Hopefully we will meet some day.
>>>>>
>>>>> I still have his suppressor package for two 4-1000A 's to be
>>>>> installed. Without bringing his name out again, can someone warn me
>>>>> about using it?
>>>>>
>>>>> I installed his suppressor package on my friend's Henry 2K. It
>>>>> lasted few years, but his plate transformer croaked recently, I
>>>>> wonder if the suppressor had anything to do with that.
>>>>>
>>>>> Karel VA3KO
>>>>>
>>>>> ----- Original Message -----
>>>>> From: Don W4DNR
>>>>> To: <amps at contesting.com>
>>>>> Sent: Tuesday, January 28, 2014 10:56 AM
>>>>> Subject: Re: [Amps] Tube swap
>>>>>
>>>>>
>>>>>> Quoting Karel VA3KO:
>>>>>>
>>>>>>> Hardy,
>>>>>>> yes I made myself a Hi-pot tester as well. I forgot the specs, but
>>>>>>> I believe I can go up to 20 kV. (It may be one of Richard Measures
>>>>>>> designs).
>>>>>> Don W4DNR