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Old 4th July 2009, 01:41 PM   #21
kegger is offline kegger  United States
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Join Date: May 2004
Location: michigan
The main issue I personally would have with your suggestion an giving the amp back to
the customer is the removing of the 10ohm cathode resistor and biasing the amp with a
scope, at that point the customer has no clue how to check his amp, replace tubes, ect.

Cathode bias and triode are things known and understood, even for the guy just listening.

(I do appreciate the suggestions though, thanks)

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Old 22nd April 2015, 10:50 AM   #22
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Join Date: Nov 2002
Anyone have a schematic of the ST-85 power amplifier that they would share?
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Old 22nd April 2015, 07:37 PM   #23
ColinF is offline ColinF  New Zealand
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Join Date: Jul 2009
This link isn't of the st-85 but the st-75 would be very similar, but it uses kt90s instead of el34s.
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Old 22nd April 2015, 07:57 PM   #24
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Join Date: Jul 2003
Location: Ann Arbor, MI
That is lunacy; 550V on U-L rigged audio tubes? I have no issue doing this( actually 600V ) to 813 and 4E27, but they are not in the same class as these KT90...LOL
the Tnuctipun will return
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Old 18th May 2015, 06:46 PM   #25
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Join Date: Feb 2013
I had my 1998 st-85 rebuilt new caps the board and beefed up bias circuts and ceramic
tube sockets cardas binding posts and rca jacks with Mullard reissue kt88's
worth every damn cent. Don't tall Bea at VTL thay will say i'm wrong.
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Old 19th May 2015, 07:53 AM   #26
multi is offline multi  Australia
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Join Date: Jan 2011
I repaired a VTL amp using Triode connected 807's running at 600 volts. When I received the amp some one had set the Bias to 70Ma and the 807"s where bright red. Found out from VTL that it should be set to 26Ma. Later I built a Triode 807 amp Fixed bias and ran it at 560 volts for many years. No problems. The data recommends no more than 400 volts, cathode bias.
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Old 22nd May 2015, 01:06 AM   #27
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That was the reason for the tube switch from el34's to kt88's, the amp was eating tubes every 300 hours or so.
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Old 16th August 2015, 07:37 PM   #28
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Join Date: Aug 2015
Location: berlin
Default circuit diagram vtl st-85

because I did not find a diagram, I have drawn one. Sorry I am not an artist. Power supply was left out. Please send me PM for request. Donīt know how to insert a .jpg file here.
best regards, frank
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Old 18th August 2015, 07:25 AM   #29
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Location: berlin
hope this link for ST-85 diagram works https://www.dropbox.com/sh/dwx3uhblb...St-85.jpg?dl=0
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