• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

stereo SE kt88 build ... abdellah diyaudioprojects design

Status
Not open for further replies.
Jump to Latest
#341
AmadeusMozart said:
Use two 5 position switches for each channel: switch 1 has five 100 Ohm resistors and switch two has five 20 ohm resistors. This gives 0 - 600 Ohm in 20 Ohm steps. Or use a variant starting halfway, endless possibilities. I am using cheap guitar switches on oBoy from HK (hongkongsuperseller) which are ceramic and can handle high voltage. (Recently bought 10 of him.)

I have an 100 mA meter in each anode lead and use the resistors to set the current.

AM
Click to expand...

I am not sure I understand how you use these 2 switches to get the R from 0 to 600 by 20R steps, can you draw it out or explain it a little further?
Thanks,
Jeff
 
#342
Jj kt77

Got some spare time last evening and visit the local hifi shop to get a pair of EH 6CA7 or EH KT88, however both are sold out and the next shipment will be a month later. I was recommended to get a pair of JJ KT77 which the shop owner claims to be better sounding than the EH 6CA7.

I was excited on hear these tubes but was shocked when my 5A fuse (for the 6.3V winding) blown upon power up. I got no problem with my Mullard EL34 and Tung sol 6L6GC-STR.

My 6.3V winding is rated 5A and is it too low for the JJ KT77 or other 6550 or KT88?
 
#344
cjctan said:
Got some spare time last evening and visit the local hifi shop to get a pair of EH 6CA7 or EH KT88, however both are sold out and the next shipment will be a month later. I was recommended to get a pair of JJ KT77 which the shop owner claims to be better sounding than the EH 6CA7.

I was excited on hear these tubes but was shocked when my 5A fuse (for the 6.3V winding) blown upon power up. I got no problem with my Mullard EL34 and Tung sol 6L6GC-STR.

My 6.3V winding is rated 5A and is it too low for the JJ KT77 or other 6550 or KT88?
Click to expand...

KT77 will draw 1.5A at 6.3V each tube for heater, so you will have a total draw of 3.6A for the 6n1p and two KT77. Your 5A fuse should not blow. The KT77 that you got might be defective.
 
Last edited:
#345
alexg said:
KT77 will draw 1.5A at 6.3V each tube for heater, so you will have a total draw of 3.6A for the 6n1p and two KT77. Your 5A fuse should not blow. The KT77 that you got might be defective.
Click to expand...

Hi Alex,
Thanks for your reply.
I also thought the tubes might be defective and went back to the shop the very next day. The tubes were tested ok. It seems that the initial current surge upon power up for these tubes are pretty high.
 
#346
jmillerdoc said:
This circuit has enough gain to be run without any preamp at all. I don't see why you couldn't hook your Akido right up to it.
Jeff
Click to expand...

For my case, I need to turn the volume knob around 12 to 1 "o'clock" for my normal listening level when I listen to my CDP. When I switch to my phono amp, I need to turn up the volume even higher to obtain the same level.

Is this due to the biasing of the 6N1P? I am using 2 ~1.5x red LEDs per channel on the cathode.
 
#347
cjctan said:
For my case, I need to turn the volume knob around 12 to 1 "o'clock" for my normal listening level when I listen to my CDP. When I switch to my phono amp, I need to turn up the volume even higher to obtain the same level.

Is this due to the biasing of the 6N1P? I am using 2 ~1.5x red LEDs per channel on the cathode.
Click to expand...

What speakers are you driving with this amp?

It might be that the speakers you are driving is too hard of a load for the amp.

Singapore is an audio diy paradise!!! Almost all parts are locally available!
 
#348
alexg said:
What speakers are you driving with this amp?

It might be that the speakers you are driving is too hard of a load for the amp.

Singapore is an audio diy paradise!!! Almost all parts are locally available!
Click to expand...


Hi Alex,
I am pairing this amp with my DIY FR using Hemp Acoustic FR8C drivers...

Singapore is just a small country and the retail shops for electronic components are located close together and makes it a bit convenient to source them for our DIY projects. However, still bought quite a number of component used in this amp overseas. 😀
 
#349
Base on KT88 has a wobbles - Useable or junk?

Darn! I heard the new Gold Lion KT88 crackle when I tried to grab the base and bottle at same time when removing it from the socket. It looks like the glue came undone. It's never been dropped.

Question: When the base wobbles, does it affect the performance of the KT88? Is the tube junk or is it perfectly usable?
 
Last edited:
#350
Hi 88man, re: Loose KT88 base.
It's junk! I'll take it off your hands. Send it to me ASAP!
Seriously google: "how to fix loose tube base"
There is a link to fixes from this site at the end of last year. The first link is to jacmusic with a caution about superglue or other methods causing the glass to crack. (Expansion when tube heats up.) I was going to try the clear nail polish until I read that as I have a few old tubes with loose bases. (Try to only pull a tube by the base)They are selling a glue for old tubes. Your new tube may use a different glue. Maybe the distributor/seller knows? You could probably contact Jim McShane as he sells them with a great reputation. His web site has his email address. Just google Jim McShane Tubes.

Also if its not too loose you may just leave it alone, as long as you don't twist it. My slightly loose tubes are in old radios and don't seem to hurt. Just have to remember to always grasp by the base!

Let us know what works!

Cheers,

Randy
 
Last edited:
#352
porkchop61 said:
Probably something like this:
An externally hosted image should be here but it was not working when we last tested it.
Click to expand...

Apologies for the late reply - was away. Thanks for drawing it up, it is almost correct except for the fixed resistor between the two switches which makes that the minimum value that will be happening (since it cannot be switched out of the circuit).

AM
 
#354
AmadeusMozart said:
Apologies for the late reply - was away. Thanks for drawing it up, it is almost correct except for the fixed resistor between the two switches which makes that the minimum value that will be happening (since it cannot be switched out of the circuit).

AM
Click to expand...

Yeah, I originally didn't have that in the circuit, but I didn't like the idea of having the possibility of no resistor in the bias 😀
 
#357
seel34 said:
you can try to put a slow 5 a fuse in it
grtz ko
Click to expand...

Thanks for your input!
I bought some slow blow fuses from 5A to 8A and my first attempt was a 5A SB fuse and the JJ KT77 and 6N1P can fired up nicely. 😛
The JJ KT77 indeed have much higher current surge than the Mullard EL34 and TS 6L6.

Only got a bit of time to listen to Susan Boyle CD and Radiohead Creep EP (Vinyl). Initial listening experience is indeed very nice compared to my Mullard EL-34. The lows and high are an edge better than the EL-34 and maybe better over time. I am glad I bought the last pair of the JJ KT77 in the store or maybe in my country. Seems like stocks of new tubes of various brands aren't replenished frequently here. 🙁
 
#359
seel34 said:
hello . i find the kt77 a very intresting tube , i looked at the specs
http://www.mif.pg.gda.pl/homepages/frank/sheets/086/k/KT77.pdf
i think i will try a couple my self , they are easy to get on ebay and a very reasanoble prices ,wich kathode resistor do you use ?
grtz ko 🙂
Click to expand...

Hi,
I am using 540ohms at the cathode as the JJ KT77 is rated at 25W
http://www.jj-electronic.sk/pdf/KT77.pdf

If u like listening to vocals then u might find this tube very nice which I am currently enjoying. 🙂

I read abt the various "issues" for JJ tubes in the past and that is why I prefer to buy from reputable tube seller. Be careful when u by them
 
Status
Not open for further replies.
Top Bottom