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PostPosted: Fri Feb 26, 2016 8:52 pm 
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I decided to try the KT88 tubes in the Trip Top to get a bit of extra volume. I haven't had a chance to really run them in yet but the volume boost seems promising so far. The sound also seems to be in the same ballpark which is great.

A couple of things people should probably be aware of is that if you use a standard 52mm KT88 they will be touching each other. I used Electro-Harmonix KT88EH tubes and put a very thin high-heat rubber washer between the tubes to keep them from rubbing together.

The other thing is that if you use tubes which connect pin 1 to the metal base (like the KT88EH) you will have your bias voltage on the external base of the tube. If you use metal base tubes it probably makes sense to buy the powder-coated cage. I think I will move the tie point away from pin 1 as you never know if the next person will know there is voltage there, in my case about 50+ volts DC.

When the KT88s go I will replace them with plastic base 6550s.

Anyone else running the KT88s?


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PostPosted: Thu Mar 03, 2016 10:13 am 
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Holy Ghost
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Joined: Sun Mar 13, 2005 4:10 pm
Posts: 7181
Location: Brighton, Canada
Yes, they are tight but I think OK. We used 6550 in our test but it can handle KT88. You can bias them high and get more power out of them.
Next round of chassis manufacturing, we plan to open the separation between the power tubes a bit.

Typically, we have used 6L6 in all demos and loaners since that's the standard. It doesn't seem to be lacking though!

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Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps


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PostPosted: Tue Mar 06, 2018 11:26 pm 
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Long term update:

I can not recommend this amp highly enough. You guys hit this one out of the park!

After almost 3 years and hundreds of hours of playtime, there has been zero problems with my Triptop. The only issue is that the KT88s are too close together and it sounds like Trinity has addressed this point with wider spacing between tubes on the chassis. On the original chassis, I have the tubes separated using the red gasket rings but so much heat is generated that they have melted. The tubes have not exhibited any problems though.

I ran 6L6GCs in it for the first year. It has been run for the last 2 years on KT88s. Even with the KT88s, the power transformer is barely warming.

In case anyone is interested, I took some bench measurements on it tonight.

    All measurements were taken using the normal channel.
    Fixed bias was used, cathode bias resulted in lower values.
    Bias on each set of tubes was set to 70% dissipation.
    Voltage output did not vary much when frequency was varied but both tubes lost a bit of output as frequency dropped below 500Hz. In both cases it was less than a volt down to 50Hz.
    A 4 ohm resistor was used as the output load.
    Measurements were taken using an oscilloscope at the point of visible distortion in the waveform.
    Higher power is possible with distorted waveforms.

I used the following formula to calculate power out: (Vp-p/2 * 0.707)^2 / 4 ohms

To summarize my results:

KT88
Diode Rectification
Plate Voltage = 490 Vp-p
Bias Current = 50 mA
Peak voltage = 46.0 Vp-p at 1KHz
Output Power = 66.1 Watts

6L6GC
GZ34 Rectifier
Plate Voltage = 473 Vp-p
Bias Current = 43 mA
Peak voltage = 40.4 Vp-p at 500Hz
Output Power = 51 Watts

tldr: Great amp. Great Sound. Buy one.


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PostPosted: Wed Mar 07, 2018 1:31 pm 
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Holy Ghost
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Location: Brighton, Canada
Thanks for the long - term update It's great to see this sort of feedback. Love the detailed calculation of the power output.
So glad to hear that it has been so good to you!!

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Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps


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