Vacuum Tube OTL power amp!!

[Alastair E]

The Capacitance of the G1 of 6SN7 is--7pf according to data sheet. The additional is a guess, but wouldnt be far out IMO...

--Close enough for 'Audio' work anyway!

[M Gregg]

Originally Posted by Alastair E

The Capacitance of the G1 of 6SN7 is--7pf according to data sheet. The additional is a guess, but wouldnt be far out IMO...

--Close enough for 'Audio' work anyway!

Can I get a data sheet for the lottery numbers? thats not far out...LOL


I'll go with 10K...and see what happens..


Regards
M. Gregg

[M Gregg]

Just for fun post..

Capacitive Reactance Theory

Regards
M. Gregg

[Mark Allen]

Thanks for the input Alastair! I totally see what you are doing and will continue to follow this thread. I am still going through with the Tim Mellow but what I will do is to make your input-driver stage interchangable with the Tim Mellow circuit... as an assembly. That would allow some easy comparisons.

Thanks,
Mark

[Dimitris AR]

Originally Posted by M Gregg

I will try using a direct connection...and see what happens.

I think you suggested 10K..I have seen some other schematics with a direct "no resistance connection"..what value do you use in your amps?

Regards
M. Gregg

I suggested 10K or lower , I usualy 1k - 2,2 K . By the way the data of 6SN7 gives 2,2 - 2,6 pF input capacitance . Here is my post number 442 - Well , I talk about input capacitance of the 6SN7 and not about input impedance , in this circuit the 470KΩ resistor with the input capacitance of the 6SN7 Cgk wich is 3pF plus the capacitance of the tube socket plus the capacitance of the circuitry , makes an RC filter wich its cutoff frequency is from 42,5Khz to 56Khz ( Fc = 1/ 2 * pi* R * C ), remember that the output impedance of the previous stage will added to this resistance and then the cutoff frequency will be smaller , so there is no need to lower the frequency of the amp ( in open loop ) that much .With a more powerfull tube , I didn't mean output power tube , maby the use of low output power tube , and I say it only to reduce more the upper output ( anode ) impedance ( with smaller Ra and Rk ) of the phase spliter to reduce the Miller effect of the output tubes , and have a better frequency response , and there is no need to drive the output tubes in classAB2 . Thanks Dim.

[M Gregg]

Just for interest,

Looking at this there should be an improvement with the change in input resistor.. Page 7 & 8 of this link ..put togeather..

http://www.kennethkuhn.com/students/...ve_testing.pdf

I have some components on order and will try it on the next strip..just for fun of course...

Run out of solder..LOL..solder sucker needs a new tip..

Regards
M. Gregg

[M Gregg]

Just a reflective thought,

I have used a full 100gm roll of Cardas in this amp...I wonder what 100gm of wonder solder would sound like..LMAO...

Regards
M. Gregg

[cnpope]

Originally Posted by M Gregg

Full 6c33c..

At 8/9/10/11/12V...I did manage 13V however the 1.6A T fuse blew..so no picks ...didn't want to try it again..drawing 1.7A
Again X10 probe so you have to multiply..


Regards
M. Gregg

Just want to check I'm reading this correctly. You are getting a maximum of about 12V peak-to-peak, into 7.9 ohms? That would be about 2.8W continuous power. That seems pretty low. Are you sure about the voltages? You mentioned blowing a 1.6A fuse at 13V peak-to-peak, but that would be only 4.6V rms, which doesn't seem like it should be enough to blow the fuse.

Could something be wrong with your voltages?

Chris

[cnpope]

Here are a couple of traces for the Tim Mellow OTL, with a 1KHz sinewave input, driving an 8 ohm resistive load. Scope is set on 10V per division. The first trace is just before clipping, and the second is when clipping is just beginning. A DVM across the load confirms about 14V rms (i.e. about 40V peak-to-peak) just before clipping. This implies about 25W continuous power just before clipping.

Chris

[M Gregg]

I agree something is not right,

Just looking at your wave on the scope..

I will have a look there is something strange...

If power is that low...it does not sound low...

Regards
M. Gregg