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She died in a flash of light. And now trying to revive my ARC D90
She died in a flash of light. And now trying to revive my ARC D90
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Old 14th March 2018, 01:05 AM   #11
Refugee1 is offline Refugee1  United Kingdom
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Check the grid voltages with the output tubes removed.
If the voltage is above 0V change the grid capacitors.
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Old 14th March 2018, 08:22 PM   #12
6A3sUMMER is offline 6A3sUMMER  United States
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Careful when operating the amp without output tubes.
The B+ Voltage may rise above the ratings of the power supply capacitors, and B+ bypass caps.
And the other tube circuits will also have higher voltages too.
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Old 15th March 2018, 08:35 AM   #13
JacquesPlafond is offline JacquesPlafond  Netherlands
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Thanks for the tips :-) @Refugee1: I did so and the grid is nicely around 0V. No issues here. @6A3sUMMER: I always check this at the very moment I turn an amp on without output tubes installed.
I am now awaiting the replacement tube to arrive, and then I expect all to be fine. I hope to enjoy the D90 for another few years. (As it really mates well with my Infinity IRS Gamma loudspeakers.)
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Old 22nd April 2018, 05:37 PM   #14
JacquesPlafond is offline JacquesPlafond  Netherlands
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And a final update on this one:
I didn't manage to get it right with the Chinese tubes. Those tubes were fine, but the D90 just doesn't take them. So I ended up inserting TAD 6L6WGC's instead.
The amp makes wonderful music, but in the meantime I have aquired an ARC D79C. That's another story. ;-)
Thank you all once more for your very kind help with this one!
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Old 22nd April 2018, 06:20 PM   #15
kevinkr is offline kevinkr  United States
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She died in a flash of light. And now trying to revive my ARC D90
The D90 was designed at a time when new American production of 6550 were still available from both GE (MPD) and Sylvania, these tubes were selected for a specific range of transconductance at a given plate voltage. Later designs have somewhat more adjustment range to accommodate the changing tube situation.

The original zeners were probably selected for forward voltage at a given current so replacing those probably slightly raised the available voltage due to zener tolerances.

Back in the late 1990s in my power crazed phase I designed a 120W per channel power amp running 4 x 6550 at 550V and about 50mA each. Those amps are still running 20 years later, and come in periodically for service. I replaced all of the output tubes with Russian made Genalex Gold Lion KT88, which apparently are New Sensor's best KT88 - at least I can report they have been reliable over the past 4 years. (The last generation of Svetlana SV6550C lasted 15 years in those amps which is a testament to their final quality)

I know you are overseas but one potential source is here: www.thetubestore.com - Genalex - Gold Lion KT88 Audio Tubes not a bad idea to tell them what you will use them in.

Strangely I found that Chinese made beam tubes and pentodes generally sounded very good right up until they blew up which happened with great regularity. I have avoided them ever since. Their quality is improving, but having been badly burned in the past I still avoid them.
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Old 22nd April 2018, 07:45 PM   #16
JacquesPlafond is offline JacquesPlafond  Netherlands
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I love your comments, Kevin. And I do agree with all you say. Especially the part about the reliability of Chinese tubes. Although it has to be said: The 6L6's I'm using are sourced from China (and selected in Germany) but they seem to be very reliable. (According to some folks who abuse them in guitar amps.)
Cheers,
J.
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Old 22nd April 2018, 08:12 PM   #17
kodabmx is offline kodabmx  Canada
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Welcome to TubeDepot.com! is good, too. Also better prices.


I have Chinese KT88 running 550V B+, 90ma, triode strapped for ~30W and they've been fine for a year now.
I've also had good results with KT120, and since the Pd is 60W, they should last a very long time when used in a KT88 amp without changes to the operating point.
On the other hand I've had 2 Chinese 6550 tubes fail due to a failed screen grid, They also arced over.

Electro Harmonix are apparently made in the Reflektor plant, and I've had great results with anything that came from there.



Cheers.
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Old 22nd April 2018, 09:34 PM   #18
kevinkr is offline kevinkr  United States
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She died in a flash of light. And now trying to revive my ARC D90
Almost all of the New Sensor products (EH, Sovtek, Tungsol, Mullard and Genalex) are made in the old Reflektor plant as they now own it. (The plant is currently known as Expo Pul.)
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Old 22nd April 2018, 10:27 PM   #19
stokessd is offline stokessd  United States
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I had a similar experience as Kevinkr. I have a friend with a Citation II who was using Chinese KT88's in his amp (in the mid 90's), and fire shot out of it one evening as an output failed. He switched to KT90s. I'd like to think that the chinese power tubes have improved in the last 20 years, but I'm still not using them in my gear.
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