KT88

sweet & juicy SE amp for 1626 Darlings and the 6L6 family

KT88

Postby lakerat » Sun Aug 19, 2012 11:49 am

I did a search for this first, but need clarity.
Can i roll kt88's into my chub clem without tying pins 1-8 together?
They are reproduction gold lions new manufactured.
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Postby Shannon Parks » Sun Aug 19, 2012 11:59 am

You are fine. G3 (the suppressor) is internally tied to the cathode at pin 8 already.

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Postby lakerat » Sun Aug 19, 2012 8:25 pm

Thanks for the quick reply Shannon. It sounds terrific with 6l6's but thought i would try the 88's. Your board made it a piece O cake to build quiet and sweet sounding!
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Power transformer for clementine

Postby gtasound » Sat Oct 06, 2012 9:31 pm

Could a 600VCT power transformer be used instead of 660VCT
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Re: Power transformer for clementine

Postby Shannon Parks » Sun Oct 07, 2012 6:17 am

gtasound wrote:Could a 600VCT power transformer be used instead of 660VCT
'

Sure! You might decide to re-bias the output tubes (i.e. change the cathode resistors), but it will work fine.

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Postby gtasound » Sun Oct 07, 2012 6:26 pm

Shannon, thanks for your reply, a friend of mine is building the clementine for me, with me providing the chassis layout and other pertinent info to be able to finish the amp the way we like, could you please tell me using your standard setup for a KT88 output which I will be using, what the bias current on the Kt88 would be.
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Postby gtasound » Wed Oct 17, 2012 3:59 pm

Not having gotten an answer to my previous question re bias current on the Kt88 and being a complete novice in this I had a look at the schematic which showed the plate voltage and the two parallel cathode power resistors assuming this would give about 50 to 55ma current and about 20 watt dissipation, would this be about right?.
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Re: KT88

Postby gtasound » Fri Jan 11, 2013 8:07 pm

DSC04419_A2.JPG
DSC04419_A2.JPG (188.75 KiB) Viewed 6057 times

This is my new Clementine with KT88 in triode mode sounding excellent.

Question? I would like to use a 350-0-350 power transformer to run KT120 & KT88 only, changing the cathode resistors R17,R19,R18,R20
to 800 ohms each giving 400 ohms per cathode at 32 watt dissipation, would the 6sl7 still be alright to drive the KT120 & KT88??.
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Re: KT88

Postby Shannon Parks » Sat Jan 12, 2013 7:21 am

Looks great! (y)

gtasound wrote:Question? I would like to use a 350-0-350 power transformer to run KT120 & KT88 only, changing the cathode resistors R17,R19,R18,R20
to 800 ohms each giving 400 ohms per cathode at 32 watt dissipation, would the 6sl7 still be alright to drive the KT120 & KT88??.


The 6SL7 won't have a problem driving them. The main thing to be careful about with the 700VCT power transformer is the high B+ at power up (with no current draw) and steady state B+. You definitely will need the CL90 and probably a 500V rated cap at the input.

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Re: KT88

Postby jukingeo » Sun Jan 13, 2013 11:35 am

I was just following this thread and I was curious as to what a KT-88 Clementine would put out power wise?

Seeing this I am also curious if the Clementine board could be used to create a sort of 'universal' amplifier such as the JE Labs EL34?

Thank You,

Geo
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Re: KT88

Postby gtasound » Sun Jan 13, 2013 3:40 pm

Shannon, thanks for you reply.

I did not think about the in rush of the higher B+, would it be ok to use a 15uF 600V ASC film cap instead of
the Electro as the first cap I feel more comfortable using the higher voltage cap , have modeled this in PSUDII
and it seems to be ok, also would like to use 1K cathode resistors instead of 800 ohms to bring the dissipation
down for the KT88's.

Your input is very much appreciated.

Thanks
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Re: KT88

Postby Shannon Parks » Mon Jan 14, 2013 6:21 am

jukingeo wrote:I was just following this thread and I was curious as to what a KT-88 Clementine would put out power wise?


Just looked at my records, and a stock circuit put out 4.2W at 5%THD and 4.7W at beginning of grid current (i.e. max driver swing). 700mV and 800mV input respectively with 18dB gain.

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Re: KT88

Postby Shannon Parks » Mon Jan 14, 2013 6:27 am

gtasound wrote: would it be ok to use a 15uF 600V ASC film cap instead of
the Electro as the first cap I feel more comfortable using the higher voltage cap , have modeled this in PSUDII
and it seems to be ok, also would like to use 1K cathode resistors instead of 800 ohms to bring the dissipation
down for the KT88's.


Just keep an eye on your ripple at C3 on PSUDII (Diff between Min and Max). Make sure it stays close to value with the regular input cap. That might mean more capacitance at C2 or C3 or a bigger choke, or two 1H chokes (maybe easiest solution).

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Re: KT88

Postby Shannon Parks » Mon Jan 14, 2013 6:27 am

gtasound wrote: would it be ok to use a 15uF 600V ASC film cap instead of
the Electro as the first cap I feel more comfortable using the higher voltage cap , have modeled this in PSUDII
and it seems to be ok, also would like to use 1K cathode resistors instead of 800 ohms to bring the dissipation
down for the KT88's.


Just keep an eye on your ripple at C3 on PSUDII (Diff between Min and Max). Make sure it stays close to value with the regular input cap. That might mean more capacitance at C2 or C3 or a bigger choke, or two 1H chokes (maybe easiest solution).

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Re: KT88

Postby gtasound » Mon Jan 14, 2013 1:37 pm

KT120_power_supply.jpg
KT120_power_supply.jpg (136.86 KiB) Viewed 5966 times

This is PSUDII simulation using 30uf ASC Film cap as the first cap.

Thanks for your response and your thought on this please.

Hope you can zoom the simulation to read the numbers.'
Dieter
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