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In Reply to: RE: I use the VTA low gain board in an ST-70, so there is no difference......... posted by Michael Norona on March 17, 2012 at 10:18:12
I have been fighting off a respiratory infection so I haven't posted much here but I can tell you that you want to use a box of caps on that board..I would use either k40s for the ones from driver to output and use the panasonics for the .1s or even russian silver mica caps...You really need paper in oil caps on the VTA boards or they will be too analytical and dry sounding.Vird is correct in that the .1s make a huge difference. The panasonics are one of my favorites of the film caps at a reasonable price.Bob Latino sells the k40s as an upgrade kit on his amps that use the VTA board.
Also,remove 47uf bypass cap on the cathode of the first stage..It is the R9 resistor and the cap is c9.
When problems become increasingly difficult,we can always rely on our collective knowledge and seek relief.
Follow Ups:
Michael,
Am aware of three types {Panasonic} one polyester, one metallized poly,
and one is black of unknown composition.
Which one are you referring to?
The Mind has No Firewall~ U.S. Army War College.
..for the .1s I like Auricaps, and they are not too spendy in these values. You can't use oilers for the .1s as you don't have the real estate available.
GE is a nice, inexpensive 12BH7. What you might like is an RCA clear top for the input/phase splitter and GE 12BH7s for the drivers. Alternately, an RCA clear top for the input/phase splitter and some more RCA 12AU7s for the drivers. Pretty cost effective.
For output tubes I have tried lots and, if you have the money, I think that the Tesla E34L with black base beat most of the vintage tubes that I own in this amp, Mullard XF2, Amperex brown base, GE 6L6 and 6CA7, etc.
Of the currently available output tubes, I know that Mike likes the 6P3S-E and I have a set in there right now, juiced up to 42ma. For currently available tubes my favorite is the JJ E34L blue glass, but there are reported reliability problems. I like them so much that I really don't care. A distant second would be the 6P3S-e, followed by the older, big body Sovtek EL34 of the 1970s, followed by the much-maligned Sovtek EL34G then the Electo Harmonix 6CA7. But these are completely matters of taste and each of us will have our own favorites.
You can use the .1@400v k40s just fine.On the vta 70 board you just hang them all underneath.I have used all k40s and it worked great..You can also put some on top and some below.This particular st70 has 6 k40s and 2 silver micas.The Silver Micas are tan ones mounted on each side of the chassis..You can see tho there was plenty of room for 2 more k40s.This amp is fantastic as it has a mostly all film cap power supply.
When problems become increasingly difficult,we can always rely on our collective knowledge and seek relief.
Edits: 03/18/12
nt
Thanks
When problems become increasingly difficult,we can always rely on our collective knowledge and seek relief.
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