My layout for the stereo KT88 SET
Ok, can some of you "experts" please take a look at my component layout and see if this looks to be a good arrangement?
Thanks everyone.
Glenn
KT88 Stereo layout
Ok, can some of you "experts" please take a look at my component layout and see if this looks to be a good arrangement?
Thanks everyone.
Glenn
KT88 Stereo layout
Thanks for that info.
I've only built guitar tube amps before (mono), so I wasn't sure about the orientation of the 2 OT's. I knew about the PT and OT laminations being 90 degrees apart, but I didn't know about the OT's, thanks!
I also didn't look carefully at the pinouts of all the tubes yet.
I also like using turret boards for ease of modifications (if needed).
I did have a question about SE amps in general. I've heard that this design tends to distort a sine wave type signal on one side, is this true? I believe transmitters use this type of design, but they use some complex RC filter network to fix this issue. Any info on this?
Thanks again.
I'll post progress pix as I go along.
If anyone would like dimensioned chassis drawings, I can also post those.
Glenn
I've only built guitar tube amps before (mono), so I wasn't sure about the orientation of the 2 OT's. I knew about the PT and OT laminations being 90 degrees apart, but I didn't know about the OT's, thanks!
I also didn't look carefully at the pinouts of all the tubes yet.
I also like using turret boards for ease of modifications (if needed).
I did have a question about SE amps in general. I've heard that this design tends to distort a sine wave type signal on one side, is this true? I believe transmitters use this type of design, but they use some complex RC filter network to fix this issue. Any info on this?
Thanks again.
I'll post progress pix as I go along.
If anyone would like dimensioned chassis drawings, I can also post those.
Glenn
As only one tube is amplifying the whole wave (positive and negative parts), there is no distortion besides the one induced by the amplifying element (make that tube or transistor).
What could make that to a perfect sine wave would be a push-pull topology, where one tube takes care of each part of the wave, though most would be an "out of phase" between both cycles, on poor designs..
Bu even so, what could induce that type of distortion you mention would be the amp clipping.
I'm sure other members can explain this better, and more correctly
Cheers!
What could make that to a perfect sine wave would be a push-pull topology, where one tube takes care of each part of the wave, though most would be an "out of phase" between both cycles, on poor designs..
Bu even so, what could induce that type of distortion you mention would be the amp clipping.
I'm sure other members can explain this better, and more correctly
Cheers!
Hmmmm, looks like other amp designers have their output transformers with the laminations parallel to each other:
SET design
Maybe its just as I thought, only the PT and the OT have to have their laminations 90 degrees apart?
Glenn
SET design
Maybe its just as I thought, only the PT and the OT have to have their laminations 90 degrees apart?
Glenn
porkchop61 said:
Glenn,
As Simpleton said, most builders orient the OPTs 180 degrees from each other and 90 degrees from the PTX. Some OPTs can't be easily oriented that way (vertical mount types, such as the James) but if they can I think it would be good to do it.
I really like your layout, it keeps the dirty side away from the clean side really well. I'm assuming you will run the heater wires along the front of the chassis and then run one down the middle to the right KT88, branch off to the 6N1P and then continue to the left edge of the chassis and then down to the other KT88. That keeps things separated about as well as you can.
I think the space between the volume pots and the heater wires is sufficient but I'm far from an expert in these matters.
Thanks Sherman.
Yes, I'm going to do exactly as you said with the wiring.
Do other people use DC for running heaters? It would eliminate any noise problems, and the routing of the wiring would not be as fussy.
I was actually considering laying-out this chassis with the power supply down the middle in the arrangement as it looks now, but having the preamp tube in the center, and the KT88's & OT's on each side.
Looks good to be symmetrical, but probably not for noise.
I was also going to give those oil filled motor run capacitors a try for this build.
I assume that polarity doesn't matter for those types of caps?
Thanks to everyone for the tips.
Glenn
Yes, I'm going to do exactly as you said with the wiring.
Do other people use DC for running heaters? It would eliminate any noise problems, and the routing of the wiring would not be as fussy.
I was actually considering laying-out this chassis with the power supply down the middle in the arrangement as it looks now, but having the preamp tube in the center, and the KT88's & OT's on each side.
Looks good to be symmetrical, but probably not for noise.
I was also going to give those oil filled motor run capacitors a try for this build.
I assume that polarity doesn't matter for those types of caps?
Thanks to everyone for the tips.
Glenn
porkchop61 said:
Glenn,
I used AC heaters with no problems. Just keep the heater wires tucked up into the top corners of the chassis as they run around and it should be fine.
You can of course use DC if you want but then you'll have to add something like a CRC filter to that as well. Plus rectifying the 6.3V tap on the PTX will give you more than 6.3VDC so you'll need to choose the resistor value in the filter carefully to get things back to 6.3V with the heater load. I wouldn't bother.
I also used motor run caps for both my SE KT88s and the SE EL84 I just "finished" today. They do the job! They are non-polar so you can hook 'em up however works out for you. I used quick-disconnects to connect all my wires to them, HT, HT center tap, B+ to 6N1P and B+ to OPT. It makes it very easy to unplug sections for testing or to "break into" a circuit to measure current.
Sherman said:
Not that I'm an expert (just ask around), but would it be worth applying regulated DC to the heaters instead? I'm a stupid schmuck and I was able to implement this in Thorsten's phono pre without any trouble.
I'm probably off base on this one, but I thought I'd try to contribute to a productive discourse for once.
Kofi
Kofi Annan said:
On a phono pre I imagine the difference between AC and regulated DC on the heaters would be huge. I used DC heaters (though not regulated) on a preamp I built from a kit and the difference from the stock AC setup was also huge.
Whether it would be worth it for this project, I don't know. It might be interesting to try though and as Glenn said it would pretty much eliminate worries about heater induced hum and could simplify wire routing.
Re: Possible to put a Pentode switch on this design?
Here is a link to some curves for the KT88 in triode, ultralinear and pentode.
http://www.mclink.it/com/audiomatica/tubes/kt88.htm
As designed Mikael's schematic is ultralinear. I've been thinking of putting in a switch for triode/pentode for the SE EL84 amp I just built. It appears to be pretty trivial. I don't think Mikael's design would be any harder. A two pole, 3 position rotary switch would allow switching between ultralinear, triode and pentode modes.
porkchop61 said:
Here is a link to some curves for the KT88 in triode, ultralinear and pentode.
http://www.mclink.it/com/audiomatica/tubes/kt88.htm
As designed Mikael's schematic is ultralinear. I've been thinking of putting in a switch for triode/pentode for the SE EL84 amp I just built. It appears to be pretty trivial. I don't think Mikael's design would be any harder. A two pole, 3 position rotary switch would allow switching between ultralinear, triode and pentode modes.
hello, i have been following this thread with a lot of interest and am keen on building the amp as a stereo version. whilst i have built kit el 34 amp, a morgan jones headphone amp and am currently building an enhanced version of the mj am [the bcj headphone amp], my knowledge of electronics is superficial. give me a schematic and tell me to solder A to B and i can pull it off
so here goes my question, bearing this in mind - if i were to get a trafo winder to wind a ptx and output trafo for me, what specs should i be giving him?
any help gratefully appreciated
cheers
so here goes my question, bearing this in mind - if i were to get a trafo winder to wind a ptx and output trafo for me, what specs should i be giving him?
any help gratefully appreciated
cheers
mikey115 said:
The specs for the PTX would vary depending upon how you plan to do the rectification. In the end the schematic calls for a B+ of 400V. Using tube rectification you might need 350-0-350 (that's what I went with) and with sand rectification you could do with less.
Also you need enough current from the PTX to handle two KT88s and a 6N1P. In my amps the KT88s draw 82mA and the 6N1Ps draw about 5. I'm only using 1/2 the 6N1P so figure 10mA if you use both sides. That means 172mA is required from the PTX and I would give it a bit of a margin.
If you are planning to use SS rectification then you only need 6.3V for the heaters for both the 6N1P and the KT88s. I think the KT88 heaters draw 1.6A each and the 6N1P draws about an amp but you should double check that.
With tube rectification you would need the above 6.3V plus whatever the tube diode requires, the 5U4-Gs I used need 5V @ 3A.
The OPT called for in the schematic has a primary Z of 5K with outputs to whatever impedance speakers you will use. The Hammond 1628SE has the right specs as does the James 6123HS (which sadly isn't listed on the Euphonia site any more).
Make sure your OPT can handle the current of the output stage (82mA in my case). Since this is a single ended design bandwidth of the OPT is improved when it isn't carrying close to the max current so an OPT capable of 100mA to 150mA should be good.
HTH,
Re: Voltage ratings for oil caps? (motor run)
To be safe I'd use 1.4 x the AC rating. I've been told that one can safely double the AC voltage rating but I don't know for sure.
In my amps I also used 370VAC run caps. With a B+ that ended up at 425V that is well within the 1.4 x AC rating.
porkchop61 said:
To be safe I'd use 1.4 x the AC rating. I've been told that one can safely double the AC voltage rating but I don't know for sure.
In my amps I also used 370VAC run caps. With a B+ that ended up at 425V that is well within the 1.4 x AC rating.
Resistor ratings on this design?
Can anyone tell me if 1/2 watt resistors are acceptable
for the 1k cathode resistor on the 6N1P,
and the 470k on the grid (g) of the KT88?
Im not sure how much current is running through these 2 resistors.
Also, do people prefer to use carbon or metal film resistors
with these types of amps? This is my first hi-fi amp,
I usually use carbon for my guitar amps.
Are metal film quieter?
Thank you.
Glenn
Can anyone tell me if 1/2 watt resistors are acceptable
for the 1k cathode resistor on the 6N1P,
and the 470k on the grid (g) of the KT88?
Im not sure how much current is running through these 2 resistors.
Also, do people prefer to use carbon or metal film resistors
with these types of amps? This is my first hi-fi amp,
I usually use carbon for my guitar amps.
Are metal film quieter?
Thank you.
Glenn
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