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hi i want improve my st-70
i have a triode kit (with solen and
another normals caps)

Can I improve the sound with any upgrade caps?
i can obtain here in my country mundorf

Someone has changed this caps with auricaps, mundorf or
another better caps ?

I've used Auricaps with very good results.

Also the Russian K40y paper in oil caps are very good, there are readily available on e-bey. These are very similar to the vintage US made Sprague "Vitamin Q" PIO caps (which have not been produced for a very long time).

HTH

/ed B

- Illinois Capacitor MPW's
- 715 or 716 series Orange drops

Both will handle the heat well too (Solen's don't like any heat... they were originally designed for X-over caps)

Cheers!

What is the minimum voltage needed for these capacitors? I might get some of those Russian PIO capacitors, but if I don't need 600V capacitors, I'll stick with something lower.

Kyle

No coupling cap in an ST-70 should be less than 600V.

Say your 6.3V dies or the tubes aren't warm with SS rectifier... Bias ~ -40V, unloaded rectifier voltage ~510V.... there's 550V across on the grid couplers alone.

Cheers!

I don't believe in solid state rectifiers...! :-) Does anyone add a standby switch for the B+ so you can give the 6.3V tubes time to warm up (with the SS rectifier)? Or, are there any ways to "smooth start" the B+ so that it creeps up over a few seconds?

Kyle

On ST-70's the 5AR4 lives a hard life. My fix is SS rectifiers and a TV damper tube inserted between the diodes and the first cap so you have a slow turn on.

Damper tubes are only a single rectifier but handle a LOT of current, plentiful and cheap for NOS.

Here's a pic of a '70 with this mod. Kevco now owns it. The tube is a 6DW4B.



If there were two rectifier sockets you could use two damper tubes as the rectifiers like in this amp.

Not only do I own that amp, but I've been running it daily for almost a year with that very same damper tube in place and not so much as a hickup. I bought a spare for $4 but it's gathering dust. That amp has taught me a lot about tube tech and electronics in general. A true war horse, thanks Terry!

Gorgeous build, Terry!

Cheers!

if i replace a 4 caps output coupling Solen
( 0.22uF 400V Output Coupling Capacitor)

with this:

http://www.madisound.com/catalog/product_info.php?manufacturers_id=170&products_id=8114

or this:

http://www.madisound.com/catalog/product_info.php?manufacturers_id=142&products_id=1433

this upgrade can be a good (choise) upgrade for improve my st70 ?
and... wh?t about capacitors board 390 and 270mf ?

the questions is: what changes are needed to improve the sound in st70?
.

Hi,

mati1979 wrote:...... wh?t about capacitors board 390 and 270mf ?

There is no 270pF cap... only 390pF @ 1000V and 82pF @ 500V in the stock ST-70.

Cheers!

Just realised my 390pF silver mica cap is rated 500V and not 1000V - should I change it ASAP?

- John

Dyna70 wrote:Just realised my 390pF silver mica cap is rated 500V and not 1000V - should I change it ASAP?

- John

That would be a good idea.

It's tied to the screen witch sees some good peak-to-peak swing PLUS the B+.

I have some in stock if you don't have any.

Cheers!

Many thanks for the kind offer but it's easier for me to source them (and quicker) here in the UK.

Best,

- John