[Heathkit] sb200 R15 question

[Mark K3MSB]

On the last SB-200 I worked on,  one of those 33 ohm resistors was
around 33 ohms, the other was 161 ohms!!   Yanked that one out and
verified it on the VTVM and DVM;  161 ohms!!

Oh yeah, I did replace it....

Mark K3MSB

On Thu, Sep 25, 2008 at 8:18 PM, Carl <km1h at jeremy.mv.com> wrote:
> What you mentioned are the 33 Ohm 1W resistors at the grid socket of each
> tube. Their purpose is to act as a parasitic suppressor as well as offer
> some degree of forced tube matching.
>
> R-15 is the grid metering resistor located on a terminal strip in the lower
> region of the amp......it cant really be called a chassis.
>
> Carl
> KM1H
>
>
> ----- Original Message ----- From: <KHeck73 at aol.com>
> To: <w5rkl at yahoo.com>; <heathkit at mailman.qth.net>; <ka9cch at arrl.net>
> Sent: Thursday, September 25, 2008 6:46 PM
> Subject: Re: [Heathkit] sb200 R15 question
>
>
>> I'm sending this a second time as the first one wasn't plain  text...
>>
>> Many years ago (more than I care to think about), my high school station
>>  had
>> an HW-101 running into an SB-200. Once or twice a year somebody would try
>> loading up the amplifier full power with the bandswitch set in the wrong
>> position vs. the band set on the transceiver. This would blow one (or
>> two?)  'grid
>> bias' resistors. I don't have a schematic in front of me, but I recall
>> them
>> being 1/2 watt carbon. This situation happened more than once. It didn't
>>  seem
>> to hurt the amp, and probably prevented further damage elsewhere inside.
>>  So,
>> if it was R15 that I remember, I'd consider the 1/2 watt rating a safety
>> feature not to be changed It inexpensively tells you if something is set
>> wrong
>> (with a pop and then the smell, because I did it once  ;).
>>
>> -Karl.
>>
>> In a message dated 9/25/2008 10:48:40 A.M.  Eastern Daylight Time,
>> _w5rkl at yahoo.com_ (mailto:w5rkl at yahoo.com)   writes:
>> R15 along with R16 and the bias supply through the relay is part of the
>> standby cut off bias as well as the normal transmit -2VDC operating bias.
>> Changing the values of one or both resistors can and will affect the cut
>> off and
>> operating bias voltage to the grids of the tubes.
>>
>> I would not  substitute the original 1.5 ohm 1/2 watt resistor with a 2
>> ohm
>> resistor. A 2 ohm  resistor is an increase in resistance of "40%" (1.5 +
>> 40% =
>> 2.1ohms) of the  original value. I would order a new resistor from Mouser
>> or
>> your favorite parts  outlet instead of using a 2 ohm resistor.
>>
>> Why did R15 burn open? A  shorted tube could cause R15 to burn  open..
>>
>> 73
>> Mike
>> W5RKL
>>
>>
>>
>> --- On Wed, 9/24/08, labernathy <_ka9cch at arrl.net_
>> (mailto:ka9cch at arrl.net) >
>> wrote:
>>
>> From: labernathy <_ka9cch at arrl.net_ (mailto:ka9cch at arrl.net) >
>> Subject: [Heathkit]  sb200 R15 question
>> To: _heathkit at mailman.qth.net_ (mailto:heathkit at mailman.qth.net)
>> Date:  Wednesday, September 24, 2008, 8:35 PM
>>
>> I'm working on an old SB200. In the process of changing out the bias
>> cap  (C3) and C19, I found that r15 (1.5 ohm 1/2 watt) was in two pieces.
>>
>> I have some questions:
>> 1. Any ideas as to what would cause this resistor  to overheat and break?
>>
>> 2. How critical is the resistance, will 2 ohms work just as well?
>>
>> 3. Is this resistor expected to open as a "safety device"? I know
>> that  in some Kenwood xcvrs, a resistor doubles as a fuse and changing
>> to a higher  wattage unit can shift the failure to an expensive part.
>>
>>
>>
>>
>>
>>
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>
>