vacuum tube power amplifier 2 x 50 W

[968driver]

The module with the seven adjustments pots is ready.
Most passive components of the amp are also mounted on this board.
I used the Tektronix ceramic mounting strips.
This module will be fitted under the main chassis.
More to follow later.

Best regards, 968driver.

 

[audiowize]

Giving Schaeffer-AG some of those hard earned Euros?

 

[nigelwright7557]

I would be inclined to add grid stopper and 100pf to grid of first valve.

I just finished a valve/TDA7294 hybrid amp and it oscillated on the output.
The valve was picking up noise and a 47k resistor and 100pf on first grid sorted it out.

 

[968driver]

I would be inclined to add grid stopper and 100pf to grid of first valve.

I just finished a valve/TDA7294 hybrid amp and it oscillated on the output.
The valve was picking up noise and a 47k resistor and 100pf on first grid sorted it out.

In a couple of months, I will try (and implement if needed) your suggestion.
I am not in this construction fase yet.
Thanks anyway!

Best regards, 968driver.

 

[968driver]

Giving Schaeffer-AG some of those hard earned Euros?

Hi,

I really see no other way to get a decent looking finish.
I think Schaeffer is a great and valuable firm for one-off projects.
I want my finished project to look 100% like I have it in mind.

Best regards, 968driver.

 

[968driver]

The project is advancing slowly...

 

[pelayostyle]

Damn 968driver, that looks amazing.

 

[stocktrader200]

what is the advantage of cascoding tubes?
in SS, it improves switching speed and VAS voltage capability.
Tubes appear to be free of these problems and have very low miller capacitances

 

[TonyTecson]

i have yet to try cascoding, with tubes, cascoding is used to get pentode gains
without the partition noise of a true pentode....
for rf, this is done, for audio, there are not many amps that used this,
i saw one, the Gromes 360 if i am not mistaken...

 

[TonyTecson]

hey 968driver , take your time and have fun doing it....
i frown on anything done in a hurry....

i have done a 6550 power amp, with mosfet regulated G2 supply,
sound was very good....

 

[TonyTecson]

Of course, my Pyramid!

planning to make one in 2018, can you tell me what irons you used in this amp? thanks..

 

[audiowize]

Boy, cutting it close on spacing between the OT's and rectifier tubes.

 

[968driver]

Boy, cutting it close on spacing between the OT's and rectifier tubes.

I agree with this remark, but I think it will not be a problem.
We will know within a couple of months...

 

[968driver]

It's aliiiiiiive !!!!!!!!!!!

I just finished the amplifier and burned it in all day today.
I had to reverse the primary wires of the output transformer of one channel to stop a heavy oscillation.
Also I added a 100µF/100V electrolytic capacitor parallel with R41, to minimize any possible hum.
I made no other modifications to the original RCA schematic.
After many hours of playing, the amp does not get hot, it just gets lukewarm.
That' nice!
Sound is very good and powerfull.
With my ears close to the speaker, NO hum and NO noise.
Next to do is to make a nice wooden plinth and a bottom panel.
I will post pictures later.

Best regards, Frans.

 

[jazbo8]

Nice work! Congrats!

 

[kodabmx]

Nicely done. What/how did you use for the lettering?

 

[nigelwright7557]

Nice work! Congrats!

Excellent.

 

[968driver]

Nicely done. What/how did you use for the lettering?

Lettering is engraved and coloured by Schaeffer, Germany, who made thé alu chassis panel.

 

[MEPER]

Do you use a drill for making the hard twisted wires?

 

[968driver]

Do you use a drill for making the hard twisted wires?

Yes, electric hand drill and vise.