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KT120 on Copland CTA-405 integrated amp

Hi everyone,

Looking for some guidance... I hope you can help!!
I own a Copland CTA-405 integrated amplifier (great gear btw). Runs as a standard with 4 x KT88 delivering 50 wpc.

I am considering replacing my set of KT88 with a KT120 quad.

Being aware of the precautions to be taken (it is generally advised to check with the manufacturer, due to potential impact on power/output transformers, considering the KT120 characteristica) and since it's not possible to contact Copland directly, I asked 3 different official Copland dealers in 3 different countries, which gave me the following feedback:

- dealer #1 & #2: checked with Copland and no problem as long as bias is set at the same level as for KT88 (0,45V). From what they explained, it's something they verified with the manufacturer, who gave "green light" and recommended same bias setting.

- dealer #3: stated that "main transformer will over run if KT120 are used and could create a mechanical noises. We do not recommend to use KT120 on this unit". Not sure if this comes from the manufacturer or if it's the dealer's own advice. Not sure neither if they reached such conclusion thinking on the typical / optimum bias setting for a KT120 or considering that they would be biased below optimum spec at the same level as KT88.

From Copland's product brochure:

"The current capacity of the CTA405 power supply and output transformers is fully sufficient for a 100 Watts output power. However, with operation conditions set for minimum variation of plate and screen current in the output stage, excellent performance is obtained with very low feedback at 2x 50 Watts per channel."

I am only aware of 2 people having changed to KT120 with this same amplifier: one good friend of mine (he biased at KT88 level) and he's having no problem at all so far since about 3 months, and another person I read about in another audio forum, for whom the swap seems to be working fine as well but no way of verifying... :-)

Anyone here tried this with this amp already, or can provide some guidance/advice? I would really appreciate... since I got some contradictory feedbacks from dealers and I would prefer to play it safe...

Thanks !!!

BTW I have no clue about the plate current, etc of the amp (not mentioned in the manual)
yater
yater OP
20 posts
 
Hi again,

Just wanted to share with you that after 3 weeks now with the KT120 in my Copland I can only say 2 things:

- great sound, bigger, more refined and extended, more weight in the lower frequencies and no harahness in the treble. Better in my opinion than the KT88 and 6550 that I tried from EH, Tung-Sol, Gold Lion and Svetlana SED-C.

- no issues at all. Actually my perception is that the amplifier runs cooler. No hum at all.

Thanks everyone for your contributions.
wolf_garcia
6,695 posts
 
I was going to order some GL KT88s for my Jolida and decided "meh"...the KT120s are doing such a great job I'm leaving them in there for now (note: Yhey hold their bias settings amazingly...I don't need to check that really but I do anyway out of curiosity and to justify having a meter) besides, do I really need 4 sets of output tubes for that amp? (rhetorical question...please do not respond)...
energyguy999
1 posts
 
Hi Yater,

I just bought a used 405 and would like to try KT120's...

Copland does have an upgrade kit but seems very expensive for what it is...my question to you is did you BIAS at 45mv or something different? Also, did you do any other kind of modification?

Thanks kindly,
EG
smokeyjansz
1 posts
 
I am Looking to MODIFY My Amp Which has * X EL34 to Take *x KT88 On its OUTPUT Stage and Modify My Input Stage which has Got 5X 6NI Input Tubes to Take ECC85 TUBEs to Improve The Sound Quality, I an after 2 X Main Transformers @ 2X Power Output Transformers WHO Makes Them or Where can I get Them to SUIT My MUSIC ANGEL XDSE AMP Made in CHINA. Please Help me out. I need The Output Transformers at around 560 Volts to Operate The KT88 , and Capable of Giving me around 90 to 100 Watts Per Channel in LINEA Mode and around 45 to 60 Watts Per Channel in Triode MODE., Your Help will be Gratefully Appreciated.
KInd Regards
Francis Jansz
Post removed 
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