Carl,
I located the 4 bypass caps and the VHF choke you mentioned, I will replace
these items as you suggest.
The bypass caps as you know are two .002 disc ceramics in parallel, I think I
will use .004 doorknob caps to replace
the .002 ceramic disc pairs. And also install the wirewound resistor to
replace the VHF choke.
Checked my bandswitch over and I don't see any evidence of arcing yet, I will
dope them as you describe with Q Dope.
Where are the steel tube clips you are referring to ? I will check them also.
Thanks for the tips Carl, much appreciated !
Bob
K6UJ
On Mar 13, 2011, at 12:33 PM, Carl wrote:
> The 4 bypass caps down by the plate choke have been known to go and I always
> replace that little "VHF" choke with a 10-15 Ohm 20W real wirewound.
>
> Another common failure point is the bandswitch at the wafers to support screw
> on the right hand side. On 160 it will arc from the solder terminal, thru the
> nylon washer to the support screw. If they look OK I give that area on both
> wafers a good coat of Q Dope (liquid polystyrene). Never tried Corona Dope,
> dont know its RF ratings.
>
> Another nasty spot is the cheap steel tube clips, they rust bad on the inside.
>
> Alpha wants $300 per wafer but it is only $250 or so for a complete switch
> thru Mouser. I just got thru with a 76PA complete switch meltdown 2 weeks ago
> for a customer. A 76PA is also my 2nd station amp which I obtained as a
> meltdown in more than just the switch.
>
> Carl
> KM1H
>
>
> ----- Original Message ----- From: "Robert Harmon" <k6uj@pacbell.net>
> To: "Carl" <km1h@jeremy.mv.com>
> Cc: <amps@contesting.com>
> Sent: Sunday, March 13, 2011 3:00 PM
> Subject: Re: [Amps] doorknob cap suppliers ?
>
>
> Carl,
> Yes that is what is in there, two 2000pf 6kv discs in parallel.
> I'm going through and upgrading caps in the amp, already replaced the
> electrolytic filter caps in the power supply,
> thought I might upgrade these two disc ceramics while I was at it.
> It makes sense to replace old electrolytics but these two disc ceramics look
> just fine, maybe I should just leave them alone.
> (They just don't look beefy enough with their little twisted together wire
> leads, hi,hi)
>
> Bob
> K6UJ
>
>
>
> On Mar 13, 2011, at 10:22 AM, Carl wrote:
>
>> The 76 family uses two 2000pf 6KV discs in parallel. If they look like the
>> wax has boiled out I replace with 3 1000pf 6KV discs but Ive never found one
>> yet that shows leakage at even 3000V.
>>
>> Carl
>> KM1H
>>
>>
>> ----- Original Message ----- From: "Robert Harmon" <k6uj@pacbell.net>
>> To: <amps@contesting.com>
>> Sent: Sunday, March 13, 2011 10:20 AM
>> Subject: [Amps] doorknob cap suppliers ?
>>
>>
>>> I am upgrading my Alpha 76CA plate capacitors and I'm looking for two
>>> 2000pf doorknob caps
>>> to replace the two pig tail caps. Found used ones at RF parts. MGS doesn't
>>> show any of this value on their site,
>>> Found exactly what I want on the HEC home page for new ones but can't find
>>> a supplier.
>>> Any recommendations on suppliers ?
>>>
>>> thanks,
>>> Bob
>>> K6UJ
>>> _______________________________________________
>>> Amps mailing list
>>> Amps@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>
>
>
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