[Amps] Plate Voltage Not Stable

[Roger (K8RI)]

On 2/15/2014 6:40 PM, Carl wrote:
> I might add that Dentrons are notorious for bad caps blowing
> transformers. Part of it is due to using only a 500pf plate choke bypass
> and operating a lot on 80/160. Electrolytics do not like RF.

I had one of the low voltage caps in an almost new DTR2000 blow the can 
right off the cap.  It hit the top of the cabinet so hard, it looked 
like a 38 wad cutter that had hit something hard and it was LOUD!

73

Roger (K8RI)

>
> That meter indication is a classic for both diodes starting to break
> down and caps ready to short.
> Be very quick with the retest.
>
> The comment about meter multiplier resistors are valid BUT in that amp
> they used 1% precision HV resistors. OTOH the equalizing caps across
> each cap are garden variety carbon composition and one breaking down or
> way high in value could hasten a cap failure.
> Removing the lead from the HV board to plate choke will eliminate that
> path.
>
> Carl
> KM1H
>
>
> ----- Original Message ----- From: "Carl" <km1h at jeremy.mv.com>
> To: "Ken Durand" <N4zed at comcast.net>; <amps at contesting.com>
> Sent: Saturday, February 15, 2014 6:19 PM
> Subject: Re: [Amps] Plate Voltage Not Stable
>
>
>> If they are the originals they are long overdue. Pull the tubes first
>> and retest BUT still replace the caps in any case.
>>
>> I believe FAR Circuits has a new PC board that is for the modern
>> Snap-In caps.
>>
>> Carl
>> KM1H
>>
>>
>> ----- Original Message ----- From: "Ken Durand" <N4zed at comcast.net>
>> To: <amps at contesting.com>
>> Sent: Saturday, February 15, 2014 5:45 PM
>> Subject: [Amps] Plate Voltage Not Stable
>>
>>
>>> The plate voltage on my MLA-2500 amp has always been rock steady. It
>>> has a
>>> dedicated 220v line ran to it. The plate voltage has always been
>>> 2400v as
>>> read on the panel meter....
>>> After powering on the amp the other day this is what I get...Time to
>>> replace
>>> the caps and rectifier diodes? They are original.
>>>
>>> https://www.dropbox.com/sc/uvd3jcwbrk86226/lDmNszwxYP
>>>
>>> Ken
>>> N4zed
>>>
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>>
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>
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