thyratron switching

[astouffer]

Ok here is a question that nobody seems to have asked before. If a thyratron were used to switch the b+ supply on and off, would it create a loud pop on the output?

 

[kevinkr]

Ok here is a question that nobody seems to have asked before. If a thyratron were used to switch the b+ supply on and off, would it create a loud pop on the output?

Like an SCR once conducting you can't switch it off easily. This is not a problem with AC however because once triggered it conducts until the 0 crossing at the beginning of the next half cycle.

You could use a pair of them in a classic center tap full wave rectifier circuit and remove the trigger voltages from their grids to shut them off. In addition you can do some very interesting things with voltage regulation by controlling their firing angle. (This would probably work best with choke input and I don't know what the noise implications might be.)

 

[astouffer]

Like an SCR once conducting you can't switch it off easily. This is not a problem with AC however because once triggered it conducts until the 0 crossing at the beginning of the next half cycle.

The reason for switching the b+ is for a warm up delay. It only has to trigger once when power is first applied. Mechanical switches are guaranteed to produce a "pop" after the tubes are warmed up. Nobody has ever really said if a solid state device causes any audible noise.

My original idea with the PIC chip sequencing mute and b+ relays works fine but now looking at the chassis the board simply takes up too much room. I'll save it for another project.

 

[Eli Duttman]

The reason for switching the b+ is for a warm up delay.

IMO, you should take the EASY path. Use damper diodes to rectify the B+. The rail rise time is in the vicinity of 45 seconds. Also, the forward drop in damper diodes is quite small.

If B+ draw requirements are not overly large, the 6BY5 dual damper gets the job done from a single Octal socket.

 

[SpreadSpectrum]

would it create a loud pop on the output?

I would think that this would be highly circuit dependent. In an SE amp I would think that it would, since the thyratron isn't going to hold back once it is triggered and anode voltages will rise quickly and be coupled to the speakers.

However on my push-pull amp, I turn on filaments, then all of the voltage amplification stages, then the power stage (with mechanical switches on the primaries of separate power transformers). I hear a small sound, but not much.

What is your amplifier's topology?

 

[astouffer]

What is your amplifier's topology?

It uses 429A pentodes in push pull, with a 407A gain stage and cathodyne phase splitter. The power supply is UF4007 diodes with a choke input filter for about 250vdc. Someone mentioned that the 429A has a longer than normal warm up time and being Western Electric I want to baby these tubes as much as possible.

 

[SpreadSpectrum]

Well, one way to really baby them would be to power up the voltage amplifiers/phase splitter first, then power up the power stage B+. The concern is that as the anodes of the stage previous to the power tubes suddenly come up in voltage, this will couple to the power stage and cause a current surge in the power tubes since they are already warmed up.

For this reason, some would argue that standby switches are harder on the power tubes than applying the B+ to cold tubes. I actually read a paper somewhere on this subject, but can't remember who wrote it or where I got it.

This is really kind of complex, though. Just a thought.