ST-70 Coupling Caps questions for newbie

[syncro]

I have a stock-board ST-70 that I have re-built with new PRP resistors and capacitors - except for the coupling capacitors which are metal encased 0.10 uF as original specs call for.  Each one has the markings as follows:
M39022/01.
1487
8013 B
JAN 56289
.10uF 10%  600V

Can anyone tell me brand/type etc. about these?  For example, how they might compare to the 0.22 uF russian PIO caps recommended by Bob L on the Dynacotubaudio board.  The gentleman who sold me the amp said they were oil-filled and audiophile quality.  I do not have experience rolling caps, except as described below, and would appreciate advice regarding my particular caps, or more general guidance.

For kicks I have substituted some Mundorf F MKP M-caps of 1.0 uF value 400v.  I have not given them more than 15 hours, and as of yet they seem to lack the bass volume and power of the originals.  The treble is more clear and possibly extended however.

I  see that Bob L recommends 600V or higher, so maybe I should abandon this experiment with these inexpensive Mundorfs.

Are two of the four on the audio path, and the other two are not?  Which ones are "pairs"?  Any point in trying both in parallel?  Where would I find out more about all this?

Thanks in advance!  Cross-posted this on dynacotubeaudio forum.

[Paul Joppa]

It's a push-pull amp, so there's a pair for each side. Like the Bottlehead amps, they couple the driver to the output tube grid.

The Dynaco can climb to over 500 volts on startup, so I'd opt for 600v ratings.

Since this is an amp with plenty of feedback, I would not stray from the design capacitance by more than 20%. Feedback loop stability relies on careful management of the time constants.

In my experience, most caps take at least 50 hours to sound "right" - a few take much longer. I find they often sound worse at 10-20 hours than they did at first, then they slowly and steadily get better. So don't despair at 15 hours!

[Grainger49]

David,

Answering two of your posts in one morning.  I am a big fan of the KK Teflon caps.  These are large, no LARGE!  However they are cheap and exceptional sounding for the price. 

They do have 600V 0.1uF available if you look.  I just did a search and these are very low priced:

http://cgi.ebay.com/Russian-Teflon-Capacitors-FT-3-0-1uF-600V-1pc-more-/380234349360?pt=Vintage_Electronics_R2&hash=item5887bbbb30

Here is the rub.  Any Teflon cap takes some break in.  That is what PJ means by "a few take much longer."  Look here for a way to do it without wasting your tubes:

http://www.bottlehead.com/smf/index.php/topic,80.msg286.html#msg286

After 6 years of playing with the KK Teflons I have gone to a 300 hour break in for them.  But they are exceptional and dirt cheap.

[Paully]

I have Obligatto in mine.  Have also have Auricap.  Mundorf is a good name but Auricap is alway a great, great way to go and I like the Obligatto enough that I haven't felt the need to keep on rolling.  Russina Teflons and Grainger says are cheap and wonderful!  Per Paul's post maybe I shouldn't have done it but I increased my .1 to 1.0uf as well.  Also, I am not in front on my amp but aren't there some that are .01 because I remember increasing those to .1uf.  Seems like there was something about keeping those two in sync.

And for whatever reason my caps in that position in the Dynaco took several hundred hours to break in to my satisfaction.

[syncro]

Thanks for all the great information to help me along my low-slope learning curve.  Sure like the mood of this forum.

.... maybe I shouldn't have done it but I increased my .1 to 1.0uf as well.  Also, I am not in front on my amp but aren't there some that are .01 because I remember increasing those to .1uf.  Seems like there was something about keeping those two in sync.

And for whatever reason my caps in that position in the Dynaco took several hundred hours to break in to my satisfaction.

Okay, I tracked down the source of why I bought my "1.0 uF 400v" coupling caps for the ST-70 - the V*n Alst*ne recommendations.   Maybe you were taking advice from his article also?  There are .05 uF  also in the original boards, as well as 390 pF and 82 pF. 

I think I am going to leave well-enough alone on the ST-70.  I mean the coupling caps that came with it sound so good compared to these M-caps.  Maybe I'll put them on a burn-in circuit and try listening again someday.  I'm more interested now in upgrading the coupling capacitors on my Foreplay III.  In fact, I could use two of these 1 uF 400 v M-caps in that to try out something new.

[Paully]

"Okay, I tracked down the source of why I bought my "1.0 uF 400v" coupling caps for the ST-70 - the V*n Alst*ne recommendations.   Maybe you were taking advice from his article also?  There are .05 uF  also in the original boards, as well as 390 pF and 82 pF. "

No, probably would have been someone on the Dynaco asylum.  Can't track down the post and can't remember the reasoning anymore.  Sorry!