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Hallo ! Have this amp on the bench and it needs new powertubes . Original
are 6550´s but I´m thinking KT88 would be a bit more rugged ( perhaps last
more hours ? ) I have read some good about EH KT88 but the owner is more
interested in Tung Sol reissue 6550 . What powertube would You guys re-
commend for this 30 year old D70 at reasonable price ? Thanks for some
advice. Steven
Follow Ups:
Stewen,The Audio Research D70 and SP8 with Acoustat 2+2's was the system at a Los Angeles shop that inspired me into the world of tube gear- in 1985. I initially used the D70's cousin, a D115 MKII with an SP8, and later changed to the SP10, but kept the D115. and I also have the SP8 still with it's original tubes. In some ways, the D70 is a bit smoother and more delicate than the D115, and I though over the years of having one as at for a second system as they were not extremely expensive used. Instead, as this was my office system I chose ARC solid state- an LS3 and D130.
I've been lucky that the entire time, I've used GE 6550A's with a couple sets of Philips ECG thrown in- but neither of these are around in sufficient quantities anymore. Our friend Jim McShane was the last seller that had a lot of the GE. In a couple of years, I'll be in the same boat trying to work out the best modern tube for it, and the Tung Sol 6550's would be high on my list.
My memory though of the D115- and by family association the D70 is that ARC and the magic Leonard in service made loud noises about avoiding KT88's. I forget the reason, but I think they were supposed to be hard sounding and/or not very dynamic. They may have upset the power supply in some way- I don't remember the details if was aesthetic, technical or both. Sorry to be vague, but the KT88 was definitely strongly discouraged in any of the ARC 6550 designs.
As to the big blue electrolytic caps, they do like to eventual retire from capaciting and if they've never been changed, it's a good opportunity to do it. My memory is that the D70 and D115 used the same one- only a different number of them. They are extremely expensive from ARC, but the identical model Mallory was available from Mouser >
Electrolytic capacitors for D115 (5)- Mouser Pt/ CGS801T450V4
http://www.mouser.com/ProductDetail/Cornell-Dubilier/CGS801T450V4L/?qs=%2fha2pyFadui8mf0wOL%2foW35eR2P5ZZ6FrYxIS99c09pIjGbQxGUoig%3d%3d
If these are not the correct values, I suspect Mouser will have the right ones.
The painting is called "Theatre for the Death of a GE 6550A".
Cheers.
BambiBoom
Edits: 05/21/14 05/21/14
The sound the reissue TS 6550s are very good.The early ones had issues when run over 450v on the plate but I think that issue has been corrected.
Make sure you tend to the amp and check solder connections, bias voltage,and screen voltages because that's the biggest enemy of new tubes living a long life. I would check with Jim McSHane as he has all that info on that amp and which tubes to use.
Honest amplification is better than excessive 2nd order distortion anytime.
Thanks Michael ! The owner says this amp haven´t been used during the last
10 years ! I also have some problem to find new filtercaps ... to a reasonable price .... they are about 2"x5" and 800uF/450V . Today perhaps smaller in size . I have found chinese 1000uF/450V , about 1½"x2½" , marked
KMH ,105 oC , to only $6.99 each . Seems OK , made in large quantities ,
but I´m uncertain about the quality . The amp also have a single cap , 530uF/150V , seems also difficult to find . Any suggestion ? Stewen
The best palce to find the electrolytics you need is Mouser Electronics. I would stay away from Chines capacitors.
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