Vacuum Tube OTL power amp!!

[flatheadmurre]

I´m back to katodbias but with a mosfet assisted zener for the moment.

Gives me ~10w no adjusting needed.

Amp was giving best THD at 45w disipation but now i´m down to 30w not wanting to make bigger hole in the ozonlayer .

 

[Dimitris AR]

Nice , 10 watts is quite good , you are runing the 6C33c in the half of its maximum power , something similar with me, I am runing the PL36 at 5.5 W ( each one ) when max power dissip. is 13W . I suggest to use the 6SN7 as PI / driver and parallel the two sections , this will give you a good driver for your amp .

 

[flatheadmurre]

I agree on the 6sn7 for PI it´s on the to do list.

I modified my PSU added a couple of small chokes and some more C.

I Have 7 huge 6800uF RIFA Elyts i want to use but they just don´t fit the chassi.

I think it´s time to assemble and enjoy.

And start planning for the next one

 

[Dimitris AR]

How much capacitance for each rail now ? . And what is the next plan ?

 

[flatheadmurre]

7x680uF+680 between + and -

I have a box of E130L another of PL36 and a 9pin surprice.

 

[Dimitris AR]

E130L I think its similar to EL136 , it would be so nice in an new OTL amp !! .

 

[Dimitris AR]

E130L I think its similar to EL136 , it would be so nice in an new OTL amp !! .

 

[flatheadmurre]

The 9 pin has 10w disipation and is made for telephonerepeaters driving long copper cables.

Have a box to fry so must be tested.

 

[Dimitris AR]

I guess you are talking about the 6C19P or another one similar .

 

[flatheadmurre]

Something LM Ericsson made for swedish telecom company.

 

[Dimitris AR]

So , you will keep it as a secret ?

 

[flatheadmurre]

Not a secret just has a number from telecom company no regular tube number and some data from the equipment used in.

Some low Ra variation of Ericssons 6761 perhaps.

Inner structure a bit bigger then a 6BQ5.

Gold pins indicate longlife.

 

[Dimitris AR]

Can you post a picture of it ?

 

[flatheadmurre]

I´ll give it a try later when when the new years party gets out of my system.

Wishing you all a happy new Year.

 

[M Gregg]

Happy New year...

Lets hope it brings good things

Best wishes
M. Gregg

 

[M Gregg]

Just for fun.

Just trying the HV Mosfet...20A device...


Regards
M. Gregg

 

[flatheadmurre]

Looking good !

I switched to a TO-3p to just for comparsion of heat transfer.

TO-3/TO-220 didn´t do much difference when topplate heats up the device drifts a bit.

 

[M Gregg]

I have an idea,

I intend to leave the top plate alone,
I have a dividing plate that the tube bases are mounted on, (I'm going to leave this alone as well) and mount another false plate under the dividing plate. This I intend to use as the heat sink for the Mozener. The dividing plate has large holes for air flow so the hope is the air will travel across the new plate and through the holes...

Regards
M. Gregg

 

[flatheadmurre]

Your layout is probably better than mine with several heat barriers.

I thought of putting the Moz on the side of the case.

 

[M Gregg]

Your layout is probably better than mine with several heat barriers.

I thought of putting the Moz on the side of the case.

I find that a double skin works well even with just a 3-5mm between as long as there is air flow across / between the surfaces.

I also found that there is little point in trying to cool an area of metal sometimes its better to isolate it from the chassis and let it do its thing..The reason is anything attached to it to try to cool it will just come up to the same temp...and cause even more problems.. The wooden sides prevent heat transfer between levels..also stops ringing..as long as the heat is managable on each plate..
another thing that works ok is to put a row of holes between two areas of the metal the heat transfer is slower and a heat reduction can be had across each side of the holes...down side is loss of strength caused by the holes..

Regards
M. Gregg