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The "$250" Amp? - 6LU8 Compactron SE, UL

Go ahead and post here that is fine, It's just I've posted a lot with my stuff and don't
want to be the originator an show to many different things to confuse anyone.

I don't have a lot of experience with LED's or know where mine came from, I got them
somewhere along the way, and it is not so much the voltage and current as it is that
the plate load resistor is at least 47k, I did testing with different loads and found the
best at that time was at least 47k.
 
As long as there built with a little headroom so as they can run at or near there ratings
that tranny should be fine, my "guess" would be they have the headroom as all of there
other offerings are underated to a degree, with that tranny you can just get away with
an EZ81 rectifier as well if you went tube rectified, soild state rectified you have plenty
of extra available with that tranny.
 
Ikoflexer tranny model ?

A shout out to Ikoflexer, I grabbed your LTspice model for the 6LU8 from your earlier post and am going to "sneaker net" it upstairs tommorrow for a try out (hoping that it is close enough to 6LR8) but I was wondering what you did to model the OPT. I will be using the Edcor 5K open frame.

mike
 
I tried out the models. The triode worked right out of the box. The pentode didn't work with the standard LTspice pentode symbol apparently because it was passing 5 (pentode) parameters and the model only wanted four.

I changed the parameter order in the model to correspond to the symbol and got it to work. Using the official schematic values I got very close to the voltages and currents shown on the schematic. Not knowing how to model an UL tranny I ran it in triode mode. The only thing that looked a little odd is that LTspice claimed no node current at the screen. That can't be right so there is a limitation there.

I modeled the OPT using the K directive and an inductance ratio equal to the impedance ratio. Since Edcor apparently doesn't know the primary inductance I made a total guess of 20H.

mike
 
mashaffer said:
I tried out the models. The triode worked right out of the box. The pentode didn't work with the standard LTspice pentode symbol apparently because it was passing 5 (pentode) parameters and the model only wanted four.

I changed the parameter order in the model to correspond to the symbol and got it to work. Using the official schematic values I got very close to the voltages and currents shown on the schematic. Not knowing how to model an UL tranny I ran it in triode mode. The only thing that looked a little odd is that LTspice claimed no node current at the screen. That can't be right so there is a limitation there.

I modeled the OPT using the K directive and an inductance ratio equal to the impedance ratio. Since Edcor apparently doesn't know the primary inductance I made a total guess of 20H.

mike
Click to expand...

Sorry, I've been busy with a phono stage in a different part of the internet world and didn't visit here in a while. Yes, that's what I did too for the OT, nothing special, just so I get some sanity values from the simulation. I'm still listening to this amp on headphones and it sounds GREAT! It's my reference amp now. Headphones because I didn't have the right OT for 8ohm output, so I used some inverted power trafos that I had idle here, and the impedance matches nicely my headphones. I'm a bit busy right now, but I'll be back with more comments about the triode/pentode models.
Cheers
 
Is there a BOM yet?

Hello, this is my first post on the AK forum.

I have been following this discussion for a while and haven't seen much activity lately. Has there been a BOM published yet?

John
 
Welcome.

The parts have been orded by Squidward from all the suppliers for the BOM.

But until after AKFEST.
http://www.akfest.com/

The BOM build is on hold till after that, sometime shortly after I do believe..:)
 
There may be a kit, but Squid wanted to order all the parts in the BOM to make sure
everything worked out all right before "sealing the deal", hopefully were covered.. :)
 
I have a couple of 220uf/300V 'lytics that I was planning to use as the cathode bypass caps on the pentode section but am concerned that such a high voltage cap might have some negative sonic characteristics. Would you think that these would be OK if bypassed with an orange drop or polyester cap?

Has anyone tried it with unbypassed cathode resistor? I guess we would lose about 3dB of gain and some voltage swing but I wonder how it would sound.

mike
 
Thanks

Thanks for the update on the BOM. I have a small stash of the 6LU8 tubes. This looks like it would be a nice project. Will the "kit" be in various levels of completeness or will there be one basic one?

AKFest looks like fun. I used to live in Tecumseh, which is near Livonia. My family moved away in '59. Fifty years ago!, does that ever make me feel old....

John
 
Ok I couldn't wait two weeks to keep planning this...

So this is a continuation of the thread I started about tube heaters. I am hoping to build this compactron amp this summer and learn alot in the process.

Here is what I am thinking:

I'm going to start with the basic compactron amp, then add a preamp for the phono input, tone controls, and panel output monitors. I drew up plans for the design (aesthetic not electrical) which I attached.

Am I biting off more than I can chew? I feel like this will be a pretty involved project.

-Nate
 

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I've used 220v lytics with no issues so I'd say your fine.

As to bypass or not, I tried not doing the bypass on my paralell version, (by mistake)
and I can tell you it did NOT sound good, quite nasty actually, I had forget to do them
but everything else was done so I wanted to fire it up, everything checked out fine, put
it in my system and said "what the heck kinda piece of crap is this I built" I wasn't really
thinking the bypass caps would fix what I was hearing but boy did they.

I'd be curious if you tried it and see what your results are...:D

mashaffer said:
I have a couple of 220uf/300V 'lytics that I was planning to use as the cathode bypass caps on the pentode section but am concerned that such a high voltage cap might have some negative sonic characteristics. Would you think that these would be OK if bypassed with an orange drop or polyester cap?

Has anyone tried it with unbypassed cathode resistor? I guess we would lose about 3dB of gain and some voltage swing but I wonder how it would sound.

mike
Click to expand...
 
If I were you I'd build the standard amp first an make it work correctly,
if you want to add later that would be fine just build it on a BIG chassis. :thmbsp:

NateP said:
So this is a continuation of the thread I started about tube heaters. I am hoping to build this compactron amp this summer and learn alot in the process.

Here is what I am thinking:

I'm going to start with the basic compactron amp, then add a preamp for the phono input, tone controls, and panel output monitors. I drew up plans for the design (aesthetic not electrical) which I attached.

Am I biting off more than I can chew? I feel like this will be a pretty involved project.

-Nate
Click to expand...
 
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