• 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
#401
hello jeff
thanks for the advice ,yess i did build the amp as on original schematics only using el34 instead of kt88 , i am a litlle low on b+ , but will fit a new power transformer wich arrived yesterday today🙂 my local tube suplier was out of eh kt88 ,so i was looking the web for some other good brands ,and in the test
i found the talks about gu50 wich is very easy to get and very cheap,i know a ebay tube dealer in the ukraine who delivers in 5 till 7 days to the netherlands
so that made me think of using them ,maybey i should be patience and wait for a new bats of kt88 to arrive with the local tube dealer [about 1 month]
greetings from a snowy and cold amsterdam
ko 🙂
 
#402
jmillerdoc said:
Well, I have described it in detail a couple of times on this thread a few pages back so I won't repeat everything here. I run the bias with the 560R setting. My coupling caps are Russian PIO K40 type, all of my resistors are PRP and most wiring is silver in the circuit path. BG bypass caps and ASC and Solen filter caps. All Edcor Iron too.

I am using NOS RCA, circa 1960's which might have alot to do with it as well. There still is plenty of power too with the 6L6 but not as much as the KT88 of course. Each build is going to have it's own sonic fingerprint so it is likely that the 6L6 may never sound the way you like on you particular build.

I have also used some EL34 with good results......just about every tube I have tried sounds really great really.

Jeff
Click to expand...

Hi Jeff,
Thanks for your information.
It seems that we getting different results on the 6L6 even though we used the same schematics. Your selection of components used differ a lot from mine.

So far i like the EL34 in triode mode and KT77 in UL mode sounds great to me 🙂
 
#403
seel34 said:
hello jeff
thanks for the advice ,yess i did build the amp as on original schematics only using el34 instead of kt88 , i am a litlle low on b+ , but will fit a new power transformer wich arrived yesterday today🙂 my local tube suplier was out of eh kt88 ,so i was looking the web for some other good brands ,and in the test
i found the talks about gu50 wich is very easy to get and very cheap,i know a ebay tube dealer in the ukraine who delivers in 5 till 7 days to the netherlands
so that made me think of using them ,maybey i should be patience and wait for a new bats of kt88 to arrive with the local tube dealer [about 1 month]
greetings from a snowy and cold amsterdam
ko 🙂
Click to expand...

Hi,
Seems like the GU50 is an interesting tube. Maybe I will try it after I completed my "round" of tubes that is used the same socket before trying out the GU50. My next trial will be 6550 follow by KT88
 
#404
seel34 said:
hello jeff
thanks for the advice ,yess i did build the amp as on original schematics only using el34 instead of kt88 , i am a litlle low on b+ , but will fit a new power transformer wich arrived yesterday today🙂 my local tube suplier was out of eh kt88 ,so i was looking the web for some other good brands ,and in the test
i found the talks about gu50 wich is very easy to get and very cheap,i know a ebay tube dealer in the ukraine who delivers in 5 till 7 days to the netherlands
so that made me think of using them ,maybey i should be patience and wait for a new bats of kt88 to arrive with the local tube dealer [about 1 month]
greetings from a snowy and cold amsterdam
ko 🙂
Click to expand...
I don't know if you follow the weather news in USA but we just had one of the most severe ice storms on record and where I live is right in the center of the worst hit area. We got about 4-5cm of ice on everything and it has essentially been declared a disaster zone......so I wish I were in Amsterdam (and not just b/c of the weather)!

As far as the GU50. I have done a little more reading on it and it appears to be an interesting tube. It obviously is not a drop in replacement for any of the KT line of tubes but with a little modification I think it could be done. It's bias point is different altogether so a few things will need to be changed.....b/c of the weather I haven't had too much access to the computer (only at work) and my Tube Cad program is on my home computer without power. It is too crazy at work right now for me to put much time into anything DIY (I work at the only hospital open for 50 mile radius, the other ones are in-accessable to public so you could imagine what my work load is like). But when I get a chance I would like to play around with some load lines myself and see how this tube might be able to be used in this circuit too. I am reading it is the "crown jewel" of these power pentodes according to some on the web. And it is cheap too!


It would be fun to use this tube in a PP circuit, it looks like it can really put out some serious power. I was thinking of trying to adapt it to my Oddblock KT88 monoblocks which use a CCS in a SIPP configuration, might be as easy as rearranging the pinout and using a different set resistor to change the current through the CSS. When I get a chance in a few days I will do a little more studying on this tube to see what I can come up with.

Thanks,
Jeff
 
#406
hi jeff
happy that you do some research on it, i am not so good in this computer simulation programs for tubes etc etc , the tube sockets are easy to get ,i found 4 sellers on ebay
and even my local electronica surplus shop had the on the self
for e2,50 a piece
Buisvoet voor GU50, LS50 - Buisvoeten - Radiobuizen & Buisvoeten
tubes are so much on ebay from about 2 euro,s a piece when i buy 8 pieces
even cheaper when you buy more
and the 12volt filiament is easy to get from a small switching power suplly,
or for testing purposes a old computer power suplly
grtz ko
 
#409
Ccs

As I have a kind of modular amp with this configuration, I started playing with CCS. I have built the most fancy one according to AudioXpress, with a IXYS10M45 followed by an LM317T. This should be a perfect load for the driver up to 200 kHz

I can regulate the current and I tried to play both changing the current and the cathode resistor. I also tried leds.

I have the right channel with standard configuration 47k at the anode and 1k at the cathode. From what I measured the driver drains around 4mA. I have 205 V on the plate.

The left channel has the CCS configured for 6mA and the LEDs at the cathode with a total drop of 3.5 V. 195 V on the plate.

I could not make any listening, as here in night now and people sleep, but from the scope I observed the following:

1) The gain increase with the CCS. (This was expected)

2) Observing the square wave, the channel with the CCS I think that shows less distortion, as there I have a visible overshoot in the channel without CCS, that is absent with the CCS.

3) increasing the current the gain increase, but over 12mA nothing comes out any more. Probably the B+ goes too low. I should decrease the resistor before the CCS, that now is 10K ohm.

I hope I will have more time tomorrow to post some more detailed results.

Now the question is: how to choose a working point ?

BR,

Davide
 
#410
Ccs

Nikon,
I am most interested in your results. Although I am not using the fancy Audioexpress CCS I did pick up several of the budget K&K Audio CCS units and have aspirations to eventually use them on my KT88SE. I have 2 of them wired up as plate loads on the driver (5687) on the 2A3 Clarion I am still in the process of building. Haven't gotten very far lately with the ice storm we just suffered, gotta have electricity at home to solder (at least I do).

I am interested to hear what you find as the optimal current for the driver.

The budget K&K Audio CCS uses a single Supertex DN2540N5 and I am hoping it will give me some increased performance. It was cheap, $8 for the kit and, it only takes about 5 minutes to wire together.

So please, when everybody is awake let us know.....
Jeff
 
#413
tim614 said:
Hi guys!
I've been keeping up with this thread and im also in the process of my own SE KT88 but i have one quick question about the choke, i have 20H@100ma and my concern is the current rating. Is it too low?
Click to expand...
Tim,
It is too low and really overkill as far as henries. There are several low cost alternatives out there, I picked up a vintage Westinghouse 10H 250mA on eBay for $25, works like a dream. The best prices for Hammond chokes I have seen are at Angela Electronics, check their website out.

Also, for the best bargains on oil filled motor run caps check this place out: https://www.surpluscenter.com/sort....rd=EMRC&catname=electric&UID=2228011921541531

370VAC should be more than enough for DC filtering in this circuit.
Jeff
 
#415
jmillerdoc said:
Tim,
It is too low and really overkill as far as henries. There are several low cost alternatives out there, I picked up a vintage Westinghouse 10H 250mA on eBay for $25, works like a dream. The best prices for Hammond chokes I have seen are at Angela Electronics, check their website out.

Also, for the best bargains on oil filled motor run caps check this place out: https://www.surpluscenter.com/sort....rd=EMRC&catname=electric&UID=2228011921541531

370VAC should be more than enough for DC filtering in this circuit.
Jeff
Click to expand...

thanks Jmillerdoc!
i also bought some asc from allied these should be good right?
40uf@440vac and two 50uf@440vac
 
#416
tim614 said:
thanks Jmillerdoc!
i also bought some asc from allied these should be good right?
40uf@440vac and two 50uf@440vac
Click to expand...

The ASC should work great on this amp. I even tried ASC's on my cathode bypass for the KT88 and they sounded better, unfortunately I don't have space left on my chassis for them. Next iteration, there will be no electrolytic cap on the amp.
 
#419
Status
Not open for further replies.
Top Bottom