[Amps] HIGH FILAMENT VOLTAGE

[w8hw at comcast.net]

Caution... Yes you can but... In the case of 3-500 tubes each diode would 
dissipate 8.5 watts (14 amp * .6v) so for Continues use, you would need 15 
watt or better yet 25 watt diodes and that would be chassis mount. They are 
not cheep. Less than that, they could short and you would never know it as 
the amp might still work, just the fill voltage issue not fixed. 
Additionally voltage spikes can happen causing the diodes to fail where 18 
ga wire survives.

73, Bruce, W8HW


-----Original Message----- 
From: Jim Hargrave
Sent: Saturday, December 10, 2016 23:38
To: 'amps'
Subject: Re: [Amps] HIGH FILAMENT VOLTAGE

You can reduce the voltage with parallel back to back diodes in series with 
each tube filament.
20 amp/40v diodes are cheap and do not present a mounting challenge.

73, Jim – w5ifp at gvtc.com

>> -----Original Message-----
>> From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of
>> w8hw at comcast.net
>> Sent: Saturday, December 10, 2016 6:41 PM
>> To: Mike Waters <mikewate at gmail.com>; amps at contesting.com
>> Subject: Re: [Amps] HIGH FILAMENT VOLTAGE
>>
>> Mike is correct. I have used 27 inch of #18 wire on 3-500 tubes many
>> times and got voltage down to 4.97 volts for each tube. The wire is
>> just one big resistor and gets warm, but works fine. The life of 3-500
>> drops real fast with high filament voltage.
>>
>> 73, Bruce, W8HW
>> ========================
>>
>> -----Original Message-----
>> From: Mike Waters
>> Sent: Saturday, December 10, 2016 19:15
>> To: amps at contesting.com
>> Subject: Re: [Amps] HIGH FILAMENT VOLTAGE
>>
>> No need to use #12. Smaller wire = more compact. A shorter piece
>> of #16 (or maybe even #18), would do fine.
>>
>> Depends on the current.
>>
>> 73, Mike
>> www.w0btu.com
>>
>> On Sat, Dec 10, 2016 at 5:58 PM, kenneth Johnson
>> <wa6rtp at hotmail.com> wrote:
>>
>> > I used # 12 wire …total of 24 inches long  wound in a two inch coil
>> > placed in each filament lead .
>> > this  droped  the voltage on my henry 2k-3  filaments into
>> specifation.
>> > your problem is finding enough room to get the coil in there.  at
>> any
>> > rate …a length of wire is the way to go.
>> >
>> >
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