In article , says...

I think any plastic film cap that has a suitable capacitance and meets or
exceeds the original's voltage rating would be fine. I have some old
paper caps but I'll never use them. Maybe I'll give them to some guitar
amp guy.



You may want to list the old ones on ebay. Those audio people often pay
big bucks for some of the older types such as those black ones with the
stripes. Think they call them bumble bee caps.

On Mon, 22 Oct 2018 10:37:14 -0400, Ralph Mowery wrote:

In article , says...

I think any plastic film cap that has a suitable capacitance and meets
or exceeds the original's voltage rating would be fine. I have some
old paper caps but I'll never use them. Maybe I'll give them to some
guitar amp guy.



You may want to list the old ones on ebay. Those audio people often pay
big bucks for some of the older types such as those black ones with the
stripes. Think they call them bumble bee caps.

I've saved a few over the years but I've been reluctant to sell my
useless junk on ebay. I mean, it's fine if some eccentric wants to spend
a ridiculous amount of money on junk but I'd rather not deal with some
K00K who feels ripped off and screams to ebay "YOUR JUNK IS GARBAGE!! I'M
FILING A COMPLAINT!!!!!!!!!!!"

I recently bought a couple of Nationals, a NC-60 and a NC-109 from a
guitar amp guy who didn't have the time or inclination to fix them up.
Maybe he will be interested in some sort of exchange of useless junk.

I have the NC-60 open right now and, for what it's worth, National used a
paper cap to couple the 1st audio amp to the power amp. They used a disk
ceramic from the wiper of the volume control to the 1st audio.

In article , Frank wrote:

I have the NC-60 open right now and, for what it's worth, National used a
paper cap to couple the 1st audio amp to the power amp. They used a disk
ceramic from the wiper of the volume control to the 1st audio.

The power amp stage has considerable grid capacitance, so the input impedance
is fairly high, and so a larger value cap is needed. The first audio stage
doesn't have so much capacitance, so you can get away with a smaller valued
cap. And the name of the game is to keep costs down.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

On Wed, 24 Oct 2018 08:59:28 -0400, Scott Dorsey wrote:

In article , Frank
wrote:

I have the NC-60 open right now and, for what it's worth, National used
a paper cap to couple the 1st audio amp to the power amp. They used a
disk ceramic from the wiper of the volume control to the 1st audio.

The power amp stage has considerable grid capacitance, so the input
impedance is fairly high, and so a larger value cap is needed. The
first audio stage doesn't have so much capacitance, so you can get away
with a smaller valued cap. And the name of the game is to keep costs
down.
--scott

Both caps are .01 ufd. Maybe they were thinking that the larger voltage
deviation after the first audio stage would make a difference.

On Wed, 10 Oct 2018 15:02:53 -0400, Ralph Mowery wrote:

When restoring the old tube equipment (tube receivers ) does it make any
difference if the old paper capacitors are replaced with the ceramic
disk or should another type be used ?

I know for RF one needs to use capacitors that are rated for rf but in
the audio stages does it really matter what kind of capacitor is used as
long as it is the correct value ?


Reason for asking is that I bought an old receiver that someone has
replaced many of the capacitors. The book says pape capacitors for some
but they have been replaced by the ceramic disk type.

So, I dug out my old Hallicrafters S-38 and did a side by side comparison with the National NC-60. The S-38 has only film caps in the audio path and does sound better than the NC-60.

I'm done with working on the NC-60. It's working pretty well and I'm not going to take the time to chase down nit-picky problems like that. So, I don't really know what's causing the audio imperfections. Could be the caps, could be a dozen other things.

This might be informative but I know it's certainly not conclusive.