Re: 475 questions


Eric
 

Bruce,

There are 2 fundamental differences that need to be taken in to account when replacing “vintage” caps. And I use the term vintage loosely. One is tolerance. In the worst case I can remember a capacitors value was +150% -%100 tolerance. The means that for a 1 uF the measured value of anything between 2.5 uF to .1 uF would be considered “in spec” old radios still amaze me they ever worked. Now a days +-20% is the normal. The service manual will tell you the tolerance of the filters. From memory I am guessing it is going to be +100% to -20 % so pretty wide design tolerance on the filters.

The other important spec is the voltage rating of the cap. And here vintage caps and modern caps differ greatly. Vintage caps were very tolerant of over voltage especially given how tube gear warms up before the tube’s comes in to operation the B+ will spike some times as high as 200 to 250 volts higher then when the device is operating and can hang there for about 15-30 seconds. This is not an issue in your 475 as it is solid state. However modern caps are completely intolerant of over voltage so if you have the physical space it is always good to bump up the voltage rating of the cap it wont effect anything to replace a 63V cap with a 400V cap excepta little cost in $ maybe one or 2 and physical space it will be slightly bigger then it’s modern lower voltage counterpart. However both are usually smaller then their vintage counter part even doubling the voltage the modern can will be smaller physically.

Eric

On 5/29/2020 12:50 AM, ciclista41 via groups.io wrote:
It might help if I posted the values of the capacitors that were originally in the scope. I'll do this below in the quoted text.

I have used Kemet in projects but mainly their surface mount stuff

I tend to lean to

Nichicon

Rubycon - Actual  (frequently found counter fit parts)

Veshay

and Illinois Capasitor


On Thu, May 28, 2020 at 05:59 PM, <ciclista41@yahoo.com> wrote:

‎Hi folks,

Here's my proposed parts order on Digi-Key, except that I haven't decided
between the first or second set of tantalums. The caps below those are to
replace the large C1412, 14, 42, 52, 62, and 72 capacitors. I tried to go up
a bit on the rating of both the capacitance and the voltage, but was hampered
somewhat by a lack of choice when only purchasing one or two of each. I'd had
Nichicon recommended to me, so I stuck with them where I could. Apparently,
Nichicon sold their tantalum capacitor manufacturing to AVX. I don't know
about Kemet, but couldn't find Nichicon near those specs. Also, I haven't yet
received the circular PCB's, so I assumed from the photos of them that they
can accommodate a range of lead spacings. Just thought I'd run it by you all
before I place the order in case I'd be advised to change anything.
To replace the tantalum I broke (C1091), and the other one I removed (C1093). Originals were 2.2μF 20V.
478-1870-ND‎
‎TAP225K025SCS‎
AVX Corporation
CAP TANT 2.2UF 10% 25V RADIAL
Immediate
0.46400
$9.28

or

478-8972-1-ND‎
‎TAP225M035SRW‎
AVX Corporation
CAP TANT 2.2UF 20% 35V RADIAL
Immediate
0.63500
$12.70
To replace C1414 1000μF 75VDC
‎493-17708-ND‎
‎UBY1K102MHL‎
Nichicon
CAP ALUM 1000UF 20% 80V T/H
Immediate
3.34000
$3.34
To replace C1412 350μF 75VDC
‎493-17783-1-ND‎
‎UBY2A361MHL6TN‎
Nichicon
CAP ALUM 360UF 20% 100V T/H
Immediate
3.18000
$3.18
To replace C1442 and C1462 5500μF 30VDC
‎399-19618-ND‎
‎ALC70A562BB040‎
KEMET
SNAP-IN HIGH CV 85C 5600UF 40V
Immediate
5.10000
$10.20
To replace C1452 5000μF 25VDC
‎493-14637-ND‎
‎UBY1V512MHL‎
Nichicon
CAP ALUM 5100UF 20% 35V RADIAL
Immediate
5.44000
$5.44
To replace C1472 3000μF 35VDC
‎493-14660-1-ND‎
‎UBY1V302MHL1TN‎
Nichicon
CAP ALUM 3000UF 20% 35V RADIAL
Immediate
3.02000
$3.02

Thanks for your input!

Bruce

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