Help, I need your advice - What Next?

[chrish]

G'Day Rob,

Sorry I cannot answer your question directly about the tube glow of 300b valves, as I don't have any

I do have a couple of directly heated rectifier valves like this http://cgi.ebay.com/5C3S-5U4G-5U3C-...ryZ58174QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
The filament construction looks similar to directly heated triodes. I think that as the heater is the cathode, rather than the cathode being a coated metal tube around the heater, it does not have to get as hot to emit electrons. My 5U3C rectifiers do not have that same bright orange glow that the other indirectly heated valves have. It is a very subtle, almost unnoticeable glow in daylight, and only a soft glow in lower light. From memory, this looked about the same glow that I have seen in a 2A3, another direct heated triode.

BTW, moving to "Glamarama" in August, so would love to check out your work when you are finished!

Also, if you are wanting to have a little taste of how SE sound can be different to PP before committing to spending the money, happy to let you borrow my SimpleSE for an audition. I do realise it is more at the "budget" end of the spectrum, but of the four amps I have built now, it is the one I have in my main system! Oh, and it does have one of the 5U3C rectifiers...

Cheers,

Chris

 

[Sheldon]

I have not seen the gas rectifier tubes but I will look into them. I will have to think about how to work them into this particular circuit, a task which may seem simple and intuitive to some but one that poses challenges for me as I am more of a 'recipe' builder at this stage.

Rob

In that schematic, you would leave out the final cap in the bias supply and substitute the regulator tube. You would need to adjust the series resistor in the supply to keep the current through the tube within its ratings. The only problem you have, is that now bias is regulated and the output is not. If you are in an area where line voltage could spike up for significant periods, you have less safety margin than with an unregulated bias supply. With an unregulated supply, the bias will track with the line (and hence B+), providing some compensation.

Sheldon

 

[Rob11966]

Thanks Sheldon, great advice.

Hi Chris, "Glamorama" is certainly that - a great place to live and a convenient taxi trip to the airport for you. When you set up, I would love to hear your amp in it's native environment.

I am not sure that my amp will be finished by August, for various reasons, I will not be able to begin to build until just after July but this will give me plenty of time to work out exactly what I am going to make.

Look forward to catching up and checking out your latest creations.

Cheers,

Rob

 

[Sheldon]

In that schematic, you would leave out the final cap in the bias supply and substitute the regulator tube. You would need to adjust the series resistor in the supply to keep the current through the tube within its ratings. The only problem you have, is that now bias is regulated and the output is not. If you are in an area where line voltage could spike up for significant periods, you have less safety margin than with an unregulated bias supply. With an unregulated supply, the bias will track with the line (and hence B+), providing some compensation.

To finish the thought; With that bias supply, you would have about 150V before the series resistor. Let's say you use an OB2 (7 pin tube, neon orange glow, 105V). You'd want to have the current through the tube set to about 20mA. That means you have to drop about 45V or so across the resistor. So instead of 5.6k, you'd use about 2.2k. Or, even better, you could use a 10M45 current regulator, set to about 20mA. Then finish it off with about a 0.01uf cap across the reg tube.

Now, if you want to kick up the glamour factor, use one of the octal varieties: http://www.mif.pg.gda.pl/homepages/frank/sheets/141/g/GL874.pdf

The different tubes light up with different colors. Ask around for the most dramatic.

Sheldon