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Old 3rd January 2013, 05:31 PM   #51
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Quote:
Originally Posted by Gotez View Post
Siliconray,

First of al a happy new year!

I've been enjoying my amp for almost a year now. Only recently one channel has started to fade. It is significatly quieter than the other channel. Switching pre-tube or end-tubes does not change anything. What could be the problem? Do you have any idea's what to look for?

Thank you
Get an ALPS volume pot or even better get rid of the volume pot all together and replace with a resistor.

You have a DMM - measure your voltages on the driver (6N1) pin 1 & 3 and pin 6 & 8, on your 6L6/6P3 measure pins 3, 4 & 8 both tubes... careful high voltages apply, dont NOT short to a heater pin with a DMM probe.

Cheers,
Bob
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Old 3rd January 2013, 09:30 PM   #52
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Thanks siliconray.
Is the second time I write a post, is the second time you ignore me.
My OPT still runs at 70 celsius degrees.

Thank you again
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Old 4th January 2013, 08:23 AM   #53
Gotez is offline Gotez  Netherlands
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Quote:
Originally Posted by bobrown14 View Post
Get an ALPS volume pot or even better get rid of the volume pot all together and replace with a resistor.

You have a DMM - measure your voltages on the driver (6N1) pin 1 & 3 and pin 6 & 8, on your 6L6/6P3 measure pins 3, 4 & 8 both tubes... careful high voltages apply, dont NOT short to a heater pin with a DMM probe.

Cheers,
Bob
Hi Bob,

Thanks for the tip. I'll change the pot and do the measurements
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Old 6th January 2013, 12:22 AM   #54
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Haven't seen your last post, sorry for that. Did you measure the temperature? If it's 70 celsius degree that's not too hot for a power transformer in tube amp. The transformer has no over budget power for it's application. You can also adjustment the bias current of the 6P3P to a lower value. The output power will be smaller but the transformer will keep cool.

Quote:
Originally Posted by ttroglodita View Post
Thanks siliconray.
Is the second time I write a post, is the second time you ignore me.
My OPT still runs at 70 celsius degrees.

Thank you again
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Old 6th January 2013, 12:23 AM   #55
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Yes the pot is also a source of problem. Check it first before checking the capacitors.
Quote:
Originally Posted by bobrown14 View Post
Get an ALPS volume pot or even better get rid of the volume pot all together and replace with a resistor.

You have a DMM - measure your voltages on the driver (6N1) pin 1 & 3 and pin 6 & 8, on your 6L6/6P3 measure pins 3, 4 & 8 both tubes... careful high voltages apply, dont NOT short to a heater pin with a DMM probe.

Cheers,
Bob
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Old 16th January 2013, 07:05 AM   #56
jounito is offline jounito  Finland
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Default 6p3p tube amplifier kit mod to KT88

Hello,

Is it possible to modify this amp kit to KT88 tubes?

BR, Jouni
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Old 16th January 2013, 12:32 PM   #57
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Originally Posted by jounito View Post
Hello,

Is it possible to modify this amp kit to KT88 tubes?

BR, Jouni
Only 300Vdc power tranny so probably not. For SE KT88 you need +400V or at least close to it. You can sub in 5881/6L6 tubes tho and will sound almost as good.

Cheers,
Bob
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Old 18th January 2013, 08:12 AM   #58
jounito is offline jounito  Finland
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Hei,

Thanks. PS is not a problem, I have Hammond 373BX ready for this.

How about output transformers, KT88 suggests 5k, this kit has 3.5k.

-jouni-
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Old 19th January 2013, 12:37 PM   #59
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Originally Posted by jounito View Post
Hei,

Thanks. PS is not a problem, I have Hammond 373BX ready for this.

How about output transformers, KT88 suggests 5k, this kit has 3.5k.

-jouni-
Are you going to keep the power supply as designed ? With a few changes to the schematic you could build a nice KT88 SE amp there but you really would benefit from ~400Vdc. Be sure all your caps and the choke/transformers can handle the extra voltage/current. 450v caps are ok, check the spec on the choke. 3.5K OPT will work with the kt88 but the current will be more depending on your bias, which I would expect you will be changing ... and you'll probably need larger cathode resistors, both in voltage and resistance 500ohm 10w is what I would use, those are 3x the size of the supplied resistors. Also I'd change the first cap to a poly cap like a Solen 10uF 650V one, 2nd and 3rd cap will be ok but I'd test the uF on the 2nd cap or just buy a new better one 220-330uF 450V.

Cheers,
Bob
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Old 19th January 2013, 07:22 PM   #60
DucTom is offline DucTom  Austria
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I think it will Not work behause of the Double heating current of KT88.
KT88 2A
6L6GC 0,8A

DucTom
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