KT88 amp schematic/parts list

[kgrant67]

kt-88 amp schematic/parts list

I am new to this whole DIY thing. I have been doing some reading online and I think I want to make a stereo amp using kt-88 tubs and hammond 1650N output and 274 power transformers. Can someone recommend where to find schematics and parts list?

 

[arnoldc]

If you search the forum you will see Mikael Abdellah's SE KT-88 which some have built. There's a thread about that.

 

[ray_moth]

Bonavolta has some SE and PP KT88 amp schematics.

 

[Sherman]

Re: kt-88 amp schematic/parts list

... a stereo amp using kt-88 tubs and hammond 1650N output and 274 power transformers. Can someone recommend where to find schematics and parts list?

Based on the output transformers it appears you want to make a push-pull amp. There are tons of schematics online for that and some partial kits to help you on your way.

One idea might be to build clones of Dynaco's MK III amp. You can go to TubeZone.Net and check out the driver board kits. You would need a chassis, sockets for the KT88s plus your transformers and whatever connectors you decide on.

Mikael's KT88 amp that Arnold mentioned (and that I have built and use every day) is a single-ended amp. If single-ended is OK for your needs then I can highly recommend that schematic. Very good sound with the right transformers and quite easy to build.

 

[castlesteve]

Kt88 amp.

I can second the Se amp that Sherman mentioned. Mine is used daily and sounds really nice. If your going Push Pull then you might try Diytube for their Eiclones which are PP kt88 monos.
Steve.

http://www.diytube.com/phpBB2/index.php

 

[tinitus]

You say you totally new in DIY, and want to build a tubeamp

Well, you might be able to build this one, its SE with KT88, and there is a lot of reading there too

But at least you should train your soldering skills first

http://www.tubelab.com/SimpleSE.htm

 

[kgrant67]

Thanks guys. Let me ask this. I haven't heard any of these amps. The push/pulls are at higher wattage but I hear rave reviews of the se amps. Are the SE amps more efficient? Meaning, when one of those is listed at 8 watts, is it deceptive to compare that to a 25w or 50w rating of a push/pull as to volume, fullness of sound, etc.? I do like volume. And I would like them to run them through a pair of mirage frx7s (rated 25w to 100w, I believe) that I have until I get into the diy speaker thing too!!

 

[Sherman]

One thing that those coming to tubes from solid state seem hung up on is power output. It is much less important than most people think.

Consider this- a 3dB increase in volume is noticeable as being "a little louder". That 3dB increase requires double the power. In the end the difference between a 50W amp and a 100W amp is 3dB or "a little louder". If your speakers have an efficiency of 89dB/1W/1M and you change to 92dB speakers you have effectively doubled the power of your amp.

Here are some numbers-

Mikael's KT88 single-ended design should make 7 or 8 watts per channel (mine come in at almost 8).

Push pull KT88s in triode mode can make anywhere from 15 to 30 watts per channel in most schematics I've seen.

Push pull KT88s in ultralinear mode will probably give you 40 to 50 watts.

Push pull KT88s in "pentode" mode (they are actually beam tetrodes but the way they are connected is the same) will make 60 to 70 watts. Some designs can go higher.

In the end it comes down to-
* how efficient are your speakers
* what size is your listening room
* what type of music do you listen to
* how loud do you listen

I find that my KT88 SE amps play as loud as I want 99% of the time when paired with either Dynaco A25 or Advent/1 speakers (neither is particularly efficient). I listen to everything from rock to jazz to classical.

 

[maynardg]

I build this schematic, using old Eico HF20 output transformers.

http://www.arrakis.es/~igapop/iga6550.htm

A very nice amp - top notch actually. Not quite as sweet as my KT88 single ended in the mids - but much more authoritative in the bass.

A lot depends on your speakers and how loud you like to listen. The SE is normally enough, but to rock out, you will appreciate the power of the push-pull.

 

[pchw]

I build this schematic, using old Eico HF20 output transformers.

http://www.arrakis.es/~igapop/iga6550.htm

A very nice amp - top notch actually. Not quite as sweet as my KT88 single ended in the mids - but much more authoritative in the bass.

A lot depends on your speakers and how loud you like to listen. The SE is normally enough, but to rock out, you will appreciate the power of the push-pull.

Very interesting, I also have 2 Eico HF-20's sitting in the corner doing nothing, and I don't know know what to do with them ....... Sorry for the threadjack.

 

[maynardg]

I actually built this schematic on the HF20 chassis. Power transformer runs a bit hot, but has not failed. Using KT90's.

 

[pchw]

Hi MG,

Did you use the original Eico PT's? If so, did you use separate heater trafo? I was told that they were not even good for EL34 when I planned to build an Eico HF-35 out of them.

 

[maynardg]

I used all the original iron, without an additional heater supply. Everything is new but the iron, including a Hammond 159P choke in the PS. PT runs quite hot to the touch. I'm probably pushing it, but it has held together. With a GZ34, the B+ runsa bout 4230V.