Very simple SE Triode Help

[ambience exists]

Can anyone help me?

I am looking to build a very low powered SET amp for use with high efficiency speakers. I have seen an interesting KT88 SE amp with a 6N1P driver. Is there a way to build this without a driver stage, as just a power amp? Am I being stupid? I want no caps in the signal path if possible, and would like to use easy to find transformers AND keep the cost down.

Has anyone built anything like this?

Some schematics would be useful.

[AKlein]

Ambience,

I'm currently in the final stages of mikael's KT88se, i'm sure before too long Alex will post a reply soon. He's a very helpful, friendly chap that will give you a more considered response.

I've configured mine as a power amp, which is simply done by removing the pot and placing a 100k resistor across the input.

You will need the driver stage, including the coupling cap between the driver valve and the KT88. I dont think you have any options on this (Anybody?). Is it the 6n1p you have issues with? You can re-do the circuit to accomodate another driver valve, but you will need one either way.

Cheap transformers in the US can be obtained from Hammond or even cheaper Edcor, have a look at the following which tests them on a SE amp:-

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

Output trannies are key to the amps performance. I had bespoke mains TX, OPT's and Chokes custom made by Sowter UK for £700 Sterling () Also there are only a few components so get the best you can. Mine's my pride and joy so i'm pulling out all the stops and i'll post pictures soon (She's a beaut! ).

Maybe the SimpleSE would be prefereable? ready made PCB.

[alexg]

Originally posted by ambience exists
Can anyone help me?

I am looking to build a very low powered SET amp for use with high efficiency speakers. I have seen an interesting KT88 SE amp with a 6N1P driver. Is there a way to build this without a driver stage, as just a power amp? Am I being stupid? I want no caps in the signal path if possible, and would like to use easy to find transformers AND keep the cost down.

Has anyone built anything like this?

Some schematics would be useful.

What do you mean without the driver stage? Do you mean without the 6n1p driver? I don't think it would work without a driver stage, not unless your preamp can drive the KT88 directly.

I have built Mikael's 6n1p driven KT88 SE amp and it sounds excellent.

If you don't want caps on the signal path, then you can DC couple the 6n1p to the KT88, but you would need higher B+, I would estimate around 600+VDC. Or you can use an interstage between the 6n1p and the KT88, a Lundahl 1660S configured as SE to SE would work (I have tried it and it sounded great).

A great output transformer will be the James 5K OPT, I think it is the 6123, though a suitable Hammond or Edcor would also sound nice.

HTH.

[porkchop61]

I'll be the third to recommend Mikael's KT88se amp. Very nice sounding, and extremely easy to build with such a small component count.
Just pay attention to the power supply (well filtered), and as AKlein said, good output transformers are worth the investment.
It's a very good starting point for some tweaking later on.
Good luck.
Glenn

[ambience exists]

would it sound good as a triode?

I have decided I have no problem with the driver tube!

I was just curious.

Is there a way to modify the circuit to use EL34's?

[DougL]

Search for Spud amps.

That's what a 1 tube low power tube amp is called.
There should be several designs floating around.

Doug

[ambience exists]

Thanks, maybe I'll just build both...

Can you do a spud amp with a EL34?

[mashaffer]

KT88... very low power???

[alexg]

Originally posted by ambience exists
would it sound good as a triode?

I have decided I have no problem with the driver tube!

I was just curious.

Is there a way to modify the circuit to use EL34's?

I wired a switch on mine so I can listen in triode or ultralinear mode, but most of the time, I listen to triode mode. You get slightly higher power on ultralinear, but I personally like the triode sound better.

With Mikael Abdellah's circuit, these power tubes will work in lieu of the KT88: 6550, EL34, and 6L6.

I like the Siemens EL34 on this circuit for vocals though the JJ EL34 does not sound very bad either, Svet 6550 and Tungsol 6550 reissue will give you great bass, and JJ KT88 will also give you great bass as well as very clear highs. This amp gives you a lot of choices for power tubes. If you can get the original GEC KT88, it sounds superb on this amp.

When I did my first iteration of this amp, I used motor run capacitors on the power supply. The second one I built, I used electrolytic capacitors on the PSU. If I have to redo the second built, I will use motor run capacitors, they sound much better.

As suggested, use a well filtered PSU. I would highly recommend the use of a 5 to 10H choke on the PSU.

HTH.

[porkchop61]

As Alexg said, you can run quite a few tubes in this amp, of course the bias will not be optimum for each tube. I also have the "mode" switch that Alexg has to select between UL, Triode, and Pentode. You will need to tie pins #1 & 8 together for using EL34's.

I'm actually in the process of adding a switch for selecting different bias resistors for each type of tube.

Lately I've been running Shuguang KT66's in mine. Nice sounding tubes for the money, and they look cool

Here's mine running EL34's:
Mikael's SE KT88 running with EL34's