stereo SE kt88 build ... abdellah diyaudioprojects design

[ppchiu]

I have a couple spare parts at home. can they be used for this amp? 5v4g, 3.5k opt trans?

[seel34]

thanks everybody for all the answers and good advice
made some changes yesterday
replaced the el34,s with sovtek kt88
i like the sound ,it handels my speakers with more ease
replaced the 5u4gb with a sovtek 5ar4
the b + went up with 43 volts to 415
the whole amp seems to be more powerfull ,better bass response
i think i leave it a few weeks like this ,to simply enjoy the music
instead of lissening for a better bass or crispyer high etc etc
i am queit satifyed with the sound at the moment
and the weather is getting better, so my old vintage vw baywindow bus [1976] is asking for maintaince [a lot of it]
greetings from a sunny amsterdam
ko

[scitizen17]

Originally Posted by seel34

thanks everybody for all the answers and good advice
made some changes yesterday
replaced the el34,s with sovtek kt88
i like the sound ,it handels my speakers with more ease
replaced the 5u4gb with a sovtek 5ar4
the b + went up with 43 volts to 415
the whole amp seems to be more powerfull ,better bass response
i think i leave it a few weeks like this ,to simply enjoy the music
instead of lissening for a better bass or crispyer high etc etc
i am queit satifyed with the sound at the moment
and the weather is getting better, so my old vintage vw baywindow bus [1976] is asking for maintaince [a lot of it]
greetings from a sunny amsterdam
ko

Yeah, getting that B+ up a little above 400V makes a big difference doesn't it? I too really like the KT88 tubes. Glad it's sounding great for you.

[Nikon1975]

I have done some more experiments using CCS. The conclusion is that the original design is very optimized.

With a CCS and led I can bring the distortion of the driver from 1.3 % to 3 % at 10V swing, but the overall distortion of the amp increases slightly, compared to 47K resistor. Probably there is the distortion cancellation effect between the first and second stage that plays a role, as someone adviced.

To reduce overall distortion the only way I found is to decrease the cathode resistor of the KT88. From my calculations you can go down to 330-350 ohm and still be on the safe side. like this you will drain around 90 mA and still be inside the max plate dissipation.

I have to do some listening, tired of 1 KHz tone :-)

Any comment ?

Davide

[Nikon1975]

Sorry, read " bring the distortion of the driver from 1.3 % to 0.3 % at 10V swing"

D.

[alecu7]

Hi all,

I am in process of building this amp but I got stuck in OPT.
Would it be sufficient to use GXPP15-8-5K from Edcor, considering it's a 15w transformer or I must go with CXSE25-8-5K ?

Thanks,
alex

[tim614]

i built mine with the CXSE25-8-5k, i have use the gxp15 and theyre good for the price but for this built "KT88" i i prefered the bigger iron looks better too.

[alecu7]

Thanks Tim.

Awesome amplifier you built here.
Just waiting for an answer, I browse 5u4-gb datasheet. What they say here is that you MUST NOT connect the tube directly to the transformer but to use a resistor so that the transformer resistive value +the additional resistor should be in the range of 170Ohms. I didn't buy the transformer yet as I was looking at Edcor XPWR033 or XPWR002 , tube 5u4-GB 33uF - 10H (Hammond 193J) 220uF. Could you please share your working schematic?

Thanks,
alex

[AmadeusMozart]

Originally Posted by Nikon1975

I have done some more experiments using CCS. The conclusion is that the original design is very optimized.

With a CCS and led I can bring the distortion of the driver from 1.3 % to 3 % at 10V swing, but the overall distortion of the amp increases slightly, compared to 47K resistor. Probably there is the distortion cancellation effect between the first and second stage that plays a role, as someone adviced.

To reduce overall distortion the only way I found is to decrease the cathode resistor of the KT88. From my calculations you can go down to 330-350 ohm and still be on the safe side. like this you will drain around 90 mA and still be inside the max plate dissipation.

I have to do some listening, tired of 1 KHz tone :-)

Any comment ?

Davide

Davide

I am building a SE with 6L6GC-STR in the finals (RH807 / Kegger used as base). What I am doing is putting a variable resistor in the cathodes of the output tubes. There are some very nice and small 12.5 Watt, 500 Ohm rheostat from Ohmite on eBay at this moment at a very reasonable price. After I got the first pair in I ordered this week a second pair just to have them for some future project.

At this moment there are over 10 available and shipping to New Zealand is USD 6.00.
( OHMITE 500 OHM 12.5 WATT RHEOSTAT - eBay (item 400092245495 end time May-15-10 18:07:40 PDT) )

This allows me to easily adjust the anode current for the "sweet spot".

AM

[AmadeusMozart]

Originally Posted by alecu7

Thanks Tim.

Awesome amplifier you built here.
Just waiting for an answer, I browse 5u4-gb datasheet. What they say here is that you MUST NOT connect the tube directly to the transformer but to use a resistor so that the transformer resistive value +the additional resistor should be in the range of 170Ohms. I didn't buy the transformer yet as I was looking at Edcor XPWR033 or XPWR002 , tube 5u4-GB 33uF - 10H (Hammond 193J) 220uF. Could you please share your working schematic?

Thanks,
alex

Alex

depending on voltage different transformer resistance values are required but also be carefull of not using a capacitor larger than specified. These values are required to prevent too large peak currents through the recitifier tube. Model the PSU in PSUD II (duncanamps.com), it takes only a short time to get familiar with the software and prevents a lot of troubles later on.

AM