[Hammarlund] HQ-129x recap

[Carl]

----- Original Message ----- 
From: "Richard Knoppow" <1oldlens1 at ix.netcom.com>
To: <kgordon2006 at frontier.com>; "William A Kulze" <wak9 at cornell.edu>; 
<hammarlund at mailman.qth.net>
Sent: Thursday, August 11, 2011 3:09 PM
Subject: Re: [Hammarlund] HQ-129x recap


>
> ----- Original Message ----- 
> From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
> To: "William A Kulze" <wak9 at cornell.edu>;
> <hammarlund at mailman.qth.net>
> Sent: Monday, August 08, 2011 10:11 AM
> Subject: Re: [Hammarlund] HQ-129x recap
>
>
>> On 8 Aug 2011 at 13:03, William A Kulze wrote:
>>
>>> Back in Jan I picked up an early model(red letter) 129x
>>> and have begun
>>> a recap. Someone previously had done a partial job of it.
>>> The can
>>> electrolytic was 3 sections of 20mf, 2 at 250V and one at
>>> 25V, with a
>>> separate 8mf/250V cap for one of the 10mf sections. My
>>> question is, is
>>> having 20mf of filtering ok on this instead of the 10mf?
>>> I've heard
>>> some things of over filtering and that some issues can
>>> arise
>>> concerning charge/discharge times and in-rush current at
>>> power up. I
>>> can get the 10mf caps if I need to, but I'd like to know
>>> what problems
>>> can come up with 20mf instead.
>>
>> I think if you examine the original electrolytic caps
>> carefully, you
>> will find that their specs are something like "10 mfd
>> +100/-80
>> percent", or something very similar.
>>
>> Therefore, using a 20 MFD cap in place of a 10 MFD cap
>> could still be
>> within spec.
>>
>> I wouldn't worry about it.
>>
>> What you are referring to is that higher capacitance in a
>> capacitor-
>> input filter can raise the peak current both at the
>> rectifier and the
>> power transformer to unacceptable levels. However, the
>> increase in
>> capacitance must be VERY substantial in order for this to
>> adversely
>> effect the power transformer or rectifier tube.
>>
>> In your case, as I said, I wouldn't worry about it.
>>
>> Ken W7EKB
>
>     Something else; since the rectifier is a vacuum tube
> the slowly heating filament will limit the turn-on current.
> The original values for the filter caps were probably chosen
> on the basis of cost and physical cost. As pointed out above
> the original tolerance of the caps was really a minimum
> value with the maximum up to double the case value. I rather
> think that going considerably higher would not hurt
> anything. The second cap follows the filter choke which will
> limit inrush current all by itself. Actually, I think you
> will get better filtering with no drawbacks by using larger
> caps.
>     Note that modern electrolytics have much closer
> tolerance than the old ones.
>
>
> --
> Richard Knoppow
> Los Angeles
> WB6KBL
> dickburk at ix.netcom.com


Since when is a 5U4 slow warming?

Carl
KM1H