6146B?

[artosalo]

I agree with the above.
A combination of local- and global negative feedback is recommended.
I maybe would use a long tail pair-type phase inverter and a Schade-type local feedback with limited amount of global NFB.

 

[Zero Cool]

In 1969 Ampeg used these for the first SVT Bass amps! this was the first really high powered bass amp and the stones used them on their US tour. there is an awesome history here: Ampeg : History

I had a 1970 Ampeg SVT and it sounded amazing! one of those amps that sounded so good you didn't want to stop playing! I have had many other models of later 6550 versions and none ever sounded as good...

But this is a Bass guitar amp and not a High fidelity home amp.

 

[artosalo]

I simulated a bit with 6146. The circuit is not a full power version, but a circuit with average supply voltage. The schematic diagram is below:

An externally hosted image should be here but it was not working when we last tested it.

The results seem very good. The circuit with 6146 is very linear. The THD-reading is achieved with no NFB at all.

Main features are added to the schematic, but I can make the summary:

Supply voltage..........450 V
Screen voltage..........200 V
Grid 1 voltage (bias)...-41 V
Quiescent current...... 40 mA (Ia + Ig2)
Pout........................ 65 W
THD......................... 0.92 % ( very low)
Ra-a........................ 4k3
Drive voltage............. 27 Vrms

 

[deicide67]

That's very promising. I suppose it couldn't hurt to build it with 6146 tubes.

My output iron is 5K, and rated at 100W. I'd be happy with 80W per pair.

If I don't like it, at least they use octal sockets. I can swap it out for 6550 or KT88s.

 

[artosalo]

Here is one possible circuit for complete 6146 PP amp.
The simulated performance at the schematic.
Linearity seems very good with low GNFB.

An externally hosted image should be here but it was not working when we last tested it.

 

[deicide67]

Thank you! That looks nice!

How hard is it to swapp out the primary impedance of the output transformer to 5K and raise the B+ to around 650V?

I wonder if the amp will have higher distortion with the components I have.

Blair

 

[artosalo]

I quickly simulated the output stage only with the values you wanted.
Pout = 97 W and THD = 0,96 % (without GNFB)

So it is obvious that the actual 6146 amplifier with 5k output transformer and 650 V supply voltage will give more than 80 W which I understood was your target.
And less than 0,5 % THD.

 

[deicide67]

Thank you!

I'll start resourcing and gathering parts for this since the chassis is already cut. What program is that if you do not mind me asking?

Blair

 

[artosalo]

I use LT Spice for simulations. It is free. Many diyers here use it.

Remember that the schematic I created is a result from simulation and it likely requires
some modifications.

 

[deicide67]

Of course! Thanks!