Home » Audio » Thermionic Emissions » New Production Tung Sol 6550, Penta KT88s (Concerning Audio Quality)
Re: Demagnetizing Tung Sol 6550, Penta KT88s [message #97818 is a reply to message #97810] Tue, 02 July 2024 00:14 Go to previous messageGo to previous message
positron is currently offline  positron
Messages: 113
Registered: May 2020
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gofar99 wrote on Fri, 28 June 2024 20:46
Hi, I get asked all the time on the Oddblock amps as to how often the tubes should be replaced. I used the original tubes (blue glass JJ KT88s) for 12 years in class A U/L at 36 watts dissipation (A+S) and they still were sounding fine and tested good. My estimate was nearly 8000 hours. Well beyond the 2K or so they spec for. Since I switched to the KT120s in the amps I figure they will last to the next century at about 25 watts dissipation. That BTW is a sweet spot in the sound, not done to be be frugal. The preamp and drivers either NOS Phillips JAN 5751 or NOS JAN Sylvania 12SL7s will likely never need replacing. In the past 15 years I have had one fail due to an internal short but none ever tested or sounded bad. BTW I suspect the Blue JJs were probably not no lead but I could be wrong. Sometimes the socket is the issue and not the tube. I normally use Belton ones. They can be testy as they grab the tube really hard though and can make it difficult to get out. I now always use SMPS for heater power that are well filtered, isolated and closely regulated.
Hi Go,

I thought the russians were having trouble with the KT120/150s? But then
at 25 watt plate dissipation, that is quite easy operation.

Personally, due to rising NOS prices decades ago, I set out to design
the perfect preamplifier and amplifier using new tubes. (Proper ics
are extremely important along with proper component jacks, part of
the accuracy equation.)

I used the JJs E88CCs due to the extremely low distortion, and
very wide frequency response without global feedback. The JJ KT88s
are not known for low distortion, about twice that of the russian
tubes. Chinese tubes are also known for high distortion, although
I have not measured all the output tubes available.

The ultra, ultra low distortion of the JJ E88CCs basically eliminates
the higher orders created by combining the driver and output tube
harmonics.

Another reason I designed around new tubes because I saw that the
prices were rising and limited quantity. Although not as long lasting,
the JJs do allow me to produce a perfectly accurate preamplifier and
near perfect amplifier. This after sophisticated listening testing.

I have heard good things concerning the Beltons.

I have to be really really careful as a near all poly cap
power supply audio system is extremely, extremely sensitive.
For instance, it is extremely important to have the speaker
wires connected wrench tight at the amplifier's jacks for
consistent bass tightness. Finger tight is insufficient.

Next few months, will keep track of the filament hours and
oxide quality of the E88CCs. Thanks for the tip on the KT88s.
I am running approximately 6.0 volts on the filaments.

cheers

pos
 
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