Vacuum Tube OTL power amp!!

[Alastair E]

I have about 120V on the anode, and a little less on the grid of the phase-splitter...

Sounds like you're nearly there!

 

[M Gregg]

Thank's,

I still have to complete the 6c33c wiring...

Also mount the FETS. A bit busy at work at the moment.
Its getting there.LOL

Regards
M. Gregg

 

[M Gregg]

Just more progress,

Driver/ pre board completed.




Regards
M. Gregg

 

[M Gregg]

Post 162#

Error - S's & N's....late night...lol

Should say DC heaters for the 6SL7's and AC for the 6SN7.

Markings are wrong on pic 2 should have 2x 6SL7 and 1X 6SN7.
Now corrected

Wiring is correct to schematic. <<< accepting numbers for pin out should be 6SL series tube.

Back on track I guess...

Regards
M. Gregg

 

[M Gregg]

Just to show correctly.

Regards
M. Gregg

 

[M Gregg]

Just some more progress

Regards
M. Gregg

 

[flatheadmurre]

Very inspiring thread.

Getting the itch, must not start another build

A nice toroid for the input tubes HT and heater perhaps ?

Then it´s all toroid powered.

The amp is looking good !!

 

[Alastair E]

Looking very nice....

My only concern, is the gate-stoppers for the mosfets....

They look to be mounted some distance from the fet itself, so could cause an issue.
--Bit difficult to see, as there's sleeving by the fet terms.

Personally, I mounted the zener diode and the G.S. actually on the fet itself....

But, Looking a very nice bit of construction, puts mine to shame! I'm getting quite excited for you now its nearing completion, Hoping it runs as good as it looks!

 

[PiCBuRn3r]

Hi, this amplifier is a AB class one ?

 

[Alastair E]

Yes, it would be AB1 as we are not driving the grids positive...

 

[flatheadmurre]

Inspired by M Greggs nice build i searched the storage and found the tubes needed.

So the itch won again.

Why doesn´t mine look as good

Must have read the schematic upside down.

 

[M Gregg]

Looking very nice....

My only concern, is the gate-stoppers for the mosfets....

They look to be mounted some distance from the fet itself, so could cause an issue.
--Bit difficult to see, as there's sleeving by the fet terms.

Personally, I mounted the zener diode and the G.S. actually on the fet itself....

But, Looking a very nice bit of construction, puts mine to shame! I'm getting quite excited for you now its nearing completion, Hoping it runs as good as it looks!

Alastair,

I thought the Gate stoppers may be an issue when I mounted them. I will move them onto the FET gate. May save some issues later.

Thank's
M. Gregg

 

[M Gregg]

Nice to see another build..how is it that you already have the tubes and chassis? An amp from a past life?

Regards
M. Gregg

 

[flatheadmurre]

Chassi is a recycled Oltronix PSU.

Top fabricated last night.

Signal tubes is RCA 5692 and 6j5.

Bought the russians at some hamfest never tried OTL building so this is going to be fun.

Found a 2x117 toroid in the drawers.

A nice toroid for small signal HT is on the wishlist.

Any suggestions on a good brand ?

Did you go ahead and use electronic chokes in PSU ?

 

[Alastair E]

I havent done the electronic chokes/ripple-filters yet, on the 'to-do' list though, Not shure about M.Gregg though, I think he's done something with them...

Flatheadmurre--

If your 6C33 are brand-new, dont forget to burn them in heaters only for a good few hours first, (A day or so is best) then an hour or three with +B supplied and no signal before you attach your speakers, Use a dummy-load across the speaker-terms--Just in case....

Its the brand-new, unused tubes that seem to give the biggest trouble with arcing/flash-over....

 

[atmasphere]

If your 6C33 are brand-new, dont forget to burn them in heaters only for a good few hours first, (A day or so is best) then an hour or three with +B supplied and no signal before you attach your speakers, Use a dummy-load across the speaker-terms--Just in case....

Its the brand-new, unused tubes that seem to give the biggest trouble with arcing/flash-over....

A week in standby is better....

 

[flatheadmurre]

Thanks for the advice, a week for burn in is longer than i thought.

Still looking for a nice small signal HT toroid no luck this far.

 

[flatheadmurre]

Sockets installed.

Just had to stuff them.

Hope the chimney effect will help cooling the 6c33c.

Amplimo got a chunk of my money and in a week they promised i have some toroids.

So it´s gonna be an all toroid PSU.

 

[Alastair E]

A week's burn-in heaters only is possably a bit overkill....

48 hours is the longest Ive burned heaters-only as I recall, then with +B supplied for a couple of hours seems to sort 'em...

I think the shortest time I burned heaters only was about 8 hours...
Didnt have any issues with any of those tubes. Only ever had issues with the ones I didnt burn in at all--They arced in the space of an hour, Lesson learned!....

 

[atmasphere]

Alastair, that is good news. Most people I know usually do it longer; but if you get good results with that little time that is awesome. Certainly if you don't precondition this tube you are asking for trouble!