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

Hey Kegger or Squidward , will either of you be at Dennis' house for the June SMAC meet ? If so , is there a working version of this still around someone could bring . I cant remember if djnagle built one yet . I would like to see one if it's possible . :smoke:
 
I talked to Squid and he is bringing the origanal prototype to drive my big ass Heils in my big system.
 
Well, my output iron came in Friday and I'm just waiting on the power transformer. I was going to wait until I can test it myself but I figured I might ask anyway:

In the power supply schematic, the output voltage of the AnTek tranny is shown as 289V instead of 275V. Is this because it outputs at higher than rated or because of higher wall supply voltage than 115V?

I've run 275V through the Duncan Amps power supply software and I couldn't get to 300V B+ without going with a much larger first cap than 7 uF. After trying several rectifiers in the power supply sim, about the only way to get there starting with 275V was to use damper diodes.

And what size fuse should be used?
 
The unloaded voltage of the power tranny is 289v (that is what you use in PSUDII)
(Use a 7uf input cap and parallel more onto it if your voltage is not high enough)
(also the 5V4G in PSUDII will sub for the 6BY5)

The 8uf cap in the datasheet is a "design center value" so is quite often spec'd low.
(in other words ignore it here and I'd consider at least 25uf to be safe) :)

For a fuse 1-1.5A should be fine. (tube rectified 1.5A fuse)
 
Questions about using non-UL transformers

I have a stash of the nice Tamura/TamRadio 5K transformers that were used in some Sony Tape Decks that ran 6AQ5 tubes. They do not have ultralinear taps. I would like to use them with this project.

If I understand it correctly, I have two choices. The first is to run in pentode mode and the other is to strap the tube as a triode. For pentode would I connect the lead from R12 now going to the #3 tap of the OT go to the #5 tap instead? For triode would that same lead from R12 go to the #4 pin (plate) of the 6LU8 instead? Would the value of the R12 resistor change?

Or am I booger eating moron?

Any chance of a rough draft of the BOM?

John
 
I've ran them in both pentode and triode, pentode was not the sound I wanted.

Triode they sound just fine, they'll produce less output but sound very good here.
And yes take R12 and attach it to pin 4, and you'll have the tube triode strapped.

If going triode I still say leave R12 the same value, these tv tubes usually need a
decent sized grid stopper like the one in the schem, cathode resistor is the same.

Nope no boogers, triode is fine..:) (And I'M STILL WAITING ON ED FOR THE BOM!!!)
 
Well, if No One else wants to do this, I will...Just disregard the Fuses & Rectifier..They were for other Projects...This is just a start...You will also need Compactron Sockets, & 6LU8's and a Rectifier Tube...I used a 5V4G....And Of Course a Power Tranny..I used a $50 Hammond 270FX..275V/150ma....Good Luck...
 

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...And after 6 months of Running it with 290V from the Hammond, with 325V B+...The 6LU8s Hardly Glow...I'm Rolling them now, and have a Set of No Names that Sound Better then the RCAs..Go Figure...But you Can't tell what these Are just by looking at them....Like a 12AX7...
 
Volume control

How are users of this amp controlling the volume? Are you using a separate preamp with gain or using some sort of Alps pot/stepped attenuator for volume control?

John
 
sled108 said:
...And after 6 months of Running it with 290V from the Hammond, with 325V B+...The 6LU8s Hardly Glow...I'm Rolling them now, and have a Set of No Names that Sound Better then the RCAs..Go Figure...But you Can't tell what these Are just by looking at them....Like a 12AX7...
Click to expand...

Post a pic of your no-name tube. There seems to be quite a bit of variation with these tubes, I have GE, Sylvania, Philco, and Magnavox. They all have different internal construction.

An old TV tech here told me to stay away from RCA's, he said they were prone to failure.

Jeff
 
electrovice said:
How are users of this amp controlling the volume? Are you using a separate preamp with gain or using some sort of Alps pot/stepped attenuator for volume control?

John
Click to expand...


I use 1 of several preamps around here myself, but say using a 100k pot could be added to the amps input quite easily..
 
I am right in the middle of building a power strip, and I have most of the parts for a PP 807 amp.....but.....the rest of the parts will cost me about three times as much as the cost of building this amp.....so, I am thinking about building this amp first as money is fairly tight around here these days. So is the Edcor and Antek still the trannies of choice???
 
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