Has anybody built the Matthew Reidsma Experimental 45?

[arnoldc]

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

has anybody heard one? i wonder why such a simple circuitry did not become popular?

 

[qwad]

😀 pretty obvious if you look at the o/p tube and it's availability / price and the o/p power that can be excpected from one which if my memory serves me right is miniscule even back in the days of sound practices they were a right rare tube to get even used the price was pretty substantial [ if you could find one!] cheers TC

 

[Positron]

interesting circuit

Since the voltage regulator isn't perfect, some positive feedback is applied.

 

[arnoldc]

guess i just have to make one

 

[Positron]

Be interesting.

Would be interesting to see how it sounds. Simple circuit and all.

 

[AudioGeek]

can this be scaled up?

what is the possibility of it being scaled up to say a 300B circuit using parallel VR tubes in the cathode?

any advantages to this versus say a choke or CCS?

Thanks!

 

[RS]

Re: can this be scaled up?

what is the possibility of it being scaled up to say a 300B circuit using parallel VR tubes in the cathode?

No go! You can use voltage regulators in series, but not in parallel.

Regards

Ralf

 

[qwad]

😀 well if you can find some used 45's at a reasonable price, it is a very simple circuit and using the hammond 125 e op xfrm it may be a nice and simple amp to build BUT I would use the hammond 125 se as being a better choice and by all accounts performs quite well in 2a3 se circuits. cheers TC

 

[ThorstenL]

Re: can this be scaled up?

Konnichiwa,

what is the possibility of it being scaled up to say a 300B circuit using parallel VR tubes in the cathode?

Not directly, but by combining a VR Valve AND something like a KT88 you can make a "power shunt regulator that keeps the voltage on the KT88 Anode quite constant. Then apply a choke with an apropriate series resistorto load the driver and bias the output valve, voila, done. But a resistor/capacitor parallel combo in the output cathode will do not really any worse, if the capcitor is high quality or perhaps WE/UP connection is employed.

Sayonara

 

[marz.tv]

I like the idea of using VR tubes in cathodes. Does anyone know any other circuits with this approach?
(I have only 2 45's. Ancient used ones. Wouldn't dare risking them in anything experimental ^^ )

 

[zobsky]

bump, ...

could i use 46 tubes in the same / similar circuit? fairly inexpensive.

is this design fraught with all the dangers typical of direct coupled amps? 🙂

thanks

 

[kmtang]

Surely it is a bit dangerous to run the 45 tube with this direct coupled configuration.

I would prefer running it with the RC coupled and it is almost fail safe.

I believe the VR might cause some more noise and distortion in comparison with cathode resistor with bypassed capacitor. Just a guess.


Johnny

 

[rdf]

Also, as drawn the VR tube is within 4 ma of its maximum current. Wouldn't the 0D3 would be operating well outside of spec at anything above very low output levels?

 

[zobsky]

Also, as drawn the VR tube is within 4 ma of its maximum current. Wouldn't the 0D3 would be operating well outside of spec at anything above very low output levels?

i thought i saw someone else raise the same concern on another forum.

thanks