stax t8000 clone (well sorta)

[joehpj]

3 hours ago, JoaMat said:

I can’t hear any noise - same as lsk389 input. Be aware my ears are old and I also suffer from some light tinnitus.

Seems you have 500 ohms at current sink input stage while 300 at other of your amplifiers. Any particular reason?

Did you use regulated supply for front end tube heater?

[JoaMat]

No, 6.3 VAC.

Just changed input tube on the last built board and powered on - no blow up but funny smell. Have to send it for repair. But I had an working stereo amp for a few hours and it did sound promising.

[joehpj]

sounded promising is tempting! detail please.

[JoaMat]

OK, back on track. One burned resistor replaced. I guess the malfunction was due to the input tube, but I actually don't know for sure. So I took a new tube and the balance servo wasn't able balance it out. Tried two more still not able to get balance but eventually I found a tube that worked. I should have made room for a balance trimmer and jumper for the servo on the board.

For the sound. I'm not very good at describing how something sounds, so you won't get any details from me, sorry. How does it compare to the T2? I'll pass on that one as well but I think Kevin somehow is hunting the T2….. We should let the blood hounds (Kerry, Birgir, et al.) join him.

Edited June 22, 2017 by JoaMat

[MattN]

I've built the Carbon-Triode with the new servo using Kevin's boards. The board works, as does the servo, but it sometimes latches to B+ at startup. Is there an obvious cause of that I should check for? It doesn't happen when the servos are disconnected, and one channel seems more susceptible than the other. I had to change the tail resistor to 200R to get the offset to zero.

 

[JoaMat]

Interesting.  The tail resistor, is that 120R on the silk screen?

[MattN]

Yes. The one connected to the trimmer. 

 

[JoaMat]

Since you are one of the first builder if not the first builder of Carbon-Triode I guess we have to ask you about this new amplifier.

Is the tube preheated when high voltage is switched on? For how long time does it latches to B+? Both + and - outputs are at B+?

Pictures are always appreciated.

[kevin gilmore]

the resistor marked open, put 100k there and see if it makes any difference.

but with all tube amps, you really need a delay on the high voltage, most of the current high voltage boards have a switch, but you need a delay board to drive them.

[chinsettawong]

Hi Kevin,

How do you connect a delay board to drive the high voltage switch in the current high voltage boards?

Edited June 27, 2017 by chinsettawong

[kevin gilmore]

5V thru a resistor or 12V driving the cpc1117N opto coupler

so after 30 seconds you apply a voltage, delay timer 555 or similar, same as T2

 

[congo5]

46 minutes ago, chinsettawong said:

How do you connect a delay board to drive the high voltage switch in the current high voltage boards?

the GRHV "sw" boards are the original size with the optocoupler switch (CPC1117)

and the sws boards which are the shrunk size with the optocoupler switch.

the opto will both turn on soft, and turn off soft. the opto is normally on, which keeps the

power supply off, applying 5 volts thru a 10k resistor turns the opto off which allows the power supply to start

So power your choice of  timer board and send output to the switch with a resistor to limit current through the opto

check data sheet, think its 3-5ma

[JoaMat]

Look! Top plate, 1.6 mm copper clad single sided. I do think we have copper polish somewhere in the house…

[MattN]

Adding a 100k resistor worked. The problem seemed to be only with one channel but caused the effect in both when they were connected to the same power supply (!?).

Latching was to B+ on both outputs, permanently, immediately after the high voltage was applied. I use a cpc1117N as a delay retrofitted to the GRHV boards that didn't have it built in, so the tubes are pre-heated. I've attached a picture below. I'll test more thoroughly but probably not till the end of the week.

Happy to *try* to answer any questions: though I've built quite a few different KG amps and can follow instructions, I wouldn't say that I *understand* anything.

[nopants]

Look! Top plate, 1.6 mm copper clad single sided. I do think we have copper polish somewhere in the house…

i like it a lot, reminds me of the audio note stuff, wanted to do something similar for the t2

maybe i'll try it out for the t8000 tube ccs version

[steefdebruijn]

5 hours ago, congo5 said:

the GRHV "sw" boards are the original size with the optocoupler switch (CPC1117)

the opto will both turn on soft, and turn off soft. the opto is normally on, which keeps the power supply off, applying 5 volts thru a 10k resistor turns the opto off which allows the power supply to start

So power your choice of  timer board and send output to the switch with a resistor to limit current through the opto

check data sheet, think its 3-5ma

Hi how did you come to these values? As far as I understand the data sheet says typical 1.2Vf at 5mAf. With a 12V power supply (which I have on a megatron) running this through an online led resistance calculator gives a resistance of 2.2k

can you enlighten me?

tia

steef

[Whitigir]

3 hours ago, JoaMat said:

Look! Top plate, 1.6 mm copper clad single sided. I do think we have copper polish somewhere in the house…

Am I seeing Mullard steel base 4x ? Holy cow!

[Pars]

2 hours ago, MattN said:

Adding a 100k resistor worked. The problem seemed to be only with one channel but caused the effect in both when they were connected to the same power supply (!?).

Latching was to B+ on both outputs, permanently, immediately after the high voltage was applied. I use a cpc1117N as a delay retrofitted to the GRHV boards that didn't have it built in, so the tubes are pre-heated. I've attached a picture below. I'll test more thoroughly but probably not till the end of the week.

Happy to *try* to answer any questions: though I've built quite a few different KG amps and can follow instructions, I wouldn't say that I *understand* anything.

 

I've seen that occur (not on this amp) when oscillation is present. Oscillation goes thru the common PSU to the other board, at least that is my theory.

Do you have a scope? Maybe check the boards with the previous resistor and see if you can detect any oscillation.

[congo5]

1 hour ago, steefdebruijn said:

can you enlighten me?

not really

when I played with it the values needed did not line up with a Led online calculator

or what I expected, So not a normal Led?

The point is to check it and adjust if needed

don't remember what I used.

Yes think it was much lower resistance.

 

 

[kevin gilmore]

in other news I have a tracking number now, so the t8000 is on its way

 

[fat joey]

15 hours ago, kevin gilmore said:

in other news I have a tracking number now, so the t8000 is on its way

 

 

 

is the t8000 the most advaned (i mean the architecture) ESD amp now? although it's not as powerful as us diy projects.

 

[JoaMat]

Still another rainy day.

Here with DHT. Shortest distance between tubes is 0.3 inch. This built was not intended for the huge triodes…

...but it is a good sounding thing.

 

Edited June 29, 2017 by JoaMat

[Whitigir]

Wow....I would love those tubes...expensive things

[kevin gilmore]

8 hours ago, fat joey said:

 

is the t8000 the most advaned (i mean the architecture) ESD amp now? although it's not as powerful as us diy projects.

 

definitely not.  srm727 output stage running at 5 to 6 ma, and tube front end.  but we will have schematics soon.

[spritzer]

Yeah, it is very run of the mill and reception is "mixed" to say the least.  The guy I bought this one off, sold it after only two hours.  Simply didn't like it and kept his other Stax amps.