stereo SE kt88 build ... abdellah diyaudioprojects design

[seel34]

hi davide
wich schematic do you use? i see you use 2 driver tubes
kind regards ko

[Nikon1975]

The schematic is exactly the same that is in the first post. There are changes in the power supply, as I could not get a 375 V transformer (I have 360 and 400, but open circuit I have 389 and 420)

I am not using both the triode in the driver, just one, and I use only one triode. I posted this question some time ago, and it looks like other people did like this. The first triode is just unconnected.

Thanks,

Davide

[scitizen17]

Hi,

I'm trying my best to join the SE triode party, however I ordered my OPTs from Hong Kong on Nov. 3rd, still waiting. I think they must have fallen off a conveyor belt somewhere and have been swept into oblivion. I've gone about as far as I can with my build. I can't mount the PT & choke because I think it would be too difficult to manipulate the chassis for the OPT cutouts. I have attached a couple of photos of my progress.

Scott

[rotaspec]

Originally Posted by scitizen17

Hi,

I'm trying my best to join the SE triode party, however I ordered my OPTs from Hong Kong on Nov. 3rd, still waiting. I think they must have fallen off a conveyor belt somewhere and have been swept into oblivion. I've gone about as far as I can with my build. I can't mount the PT & choke because I think it would be too difficult to manipulate the chassis for the OPT cutouts. I have attached a couple of photos of my progress.

Scott

Looks nice Scott.
One thing I would suggest is to anchor the PCB style electros on your tagstrips together just for a bit of mechanical resistance. If you put a blob of silicone sealant between each large electro and its small neighbour, they will share their weight on two sets of leads. I've seen these electros fail due to "wiggling" on their leads.
I would have gone for axial-leaded capacitors, but it comes down to what you have on hand.

I have a question too: What's with all the holes around the tube sockets (or did I miss something in the forum discussion)?

Gary

[seel34]

Originally Posted by scitizen17

Hi,

I'm trying my best to join the SE triode party, however I ordered my OPTs from Hong Kong on Nov. 3rd, still waiting. I think they must have fallen off a conveyor belt somewhere and have been swept into oblivion. I've gone about as far as I can with my build. I can't mount the PT & choke because I think it would be too difficult to manipulate the chassis for the OPT cutouts. I have attached a couple of photos of my progress.

Scott

looks nice , there is some problems with honkong post the last months ,i had to wait 5 weeks for my rotary switch wich normally takes 7 days ,i heared the same story from other people at this moment ,so there is a good change they will arrive soon
grtz ko

[scitizen17]

I like the idea for the silicone sealant, I'll do that. The caps are Elna Silmic II, only available in radial lead. I wanted to use them as I had read good reviews about these caps.

Theoretically the holes allow for a chimney-effect for cooling when there is a corresponding vent area on the bottom plate. I have seen others do this, and I personally like the way it looks. The overall effect is probably 30% function, 70% aesthetics. One of the members here, jmillerdoc, had posted a parts site that sells plates for this purpose.

seel34, I guess it's not really good news that the HK post is having problems, but it is good to hear that I still might get those OPTs after all. Thanks.

Audio Catalog

Originally Posted by rotaspec

I would have gone for axial-leaded capacitors, but it comes down to what you have on hand.

I have a question too: What's with all the holes around the tube sockets (or did I miss something in the forum discussion)?

Gary

[Nikon1975]

Please give me some hint on how to troubleshoot my amplifier. I am in the dark.
As I said in my previous mail, the amplifier is exactly how is proposed on the first post. The power supply is slightly different, as I had a different power transformer. I put a 39nF/1000V capacitance at the input of the rectifier, then I have a C-LC-RC filter with the following value 4.7uF-10H(81ohm)+100uF-150ohm+100uF. The 100uF are electrolitic, maybe not the best choice, but I don't think this is the problem now. I have 2V p-p ripple on the HT at 100 Hz.

The voltage I get as B+ is too high (460 V) the current drain from the power supply is too low 49mA, and the cathode voltage of the KT88 is too low.
On the output I get 140mV of hum.

At this stage what worries me is not the hum, but the current drained and the cathode voltage.

If there is some test I can do or measurement, let me know.


Thanks,

Davide

[scitizen17]

Hi,

I checked your schematic against the "control copy" and I don't see any errors. I would check and double-check ALL connection points for a possible cold solder joint or faulty ground. I don't think you should have that much ripple on your power supply.

Originally Posted by Nikon1975

Please give me some hint on how to troubleshoot my amplifier. I am in the dark.

[Nikon1975]

I forgot to tell about the ground: I connected for each ground a wire with a connector. The idea was to have the possibility to play around with the star in the tuning phase. At the moment ALL the connector are tied together with a screw, including the earth of the transformer and from the power plug. The ground is NOT connected to the metal plate.

Thenks, for the advice.

best regards,

Davide

[seel34]

hi davide
p=u X I so if your voltage[ u] is higher your[ i ]is ampere will be lower
to get the same p [ watt ] out of your tube ,i don,t see the use of a condensator before the rectifier if i understood you right
for me it would be transformer , rectifier , small elco [10uf] choke
bigger elco , b+ to trafo decoupling, ,then with a resistor to 6n1p, check if this tubes works
in the right way , if these don,t work your b+ on the kt88 also might difference
[sorry engles is not my native langues ]i am trying to translate from dutch
i hope the above ,brings you on a idea that brings you solutions
what the hum concers if you use a ac 6,3v filiament for the tubes look if there is a zero in the middel of the 6,3v output on the trafo,conect this to ground
grtz ko