Hi,
If I have a shematic with a certain AC voltage PT & a tube rectifier,
Do I have to make any changes to the schematic to use silicons?? If yes, what are the changes? How (& on what basis) are the new values figured out?
Someone told me that the silicon rectified DC voltage will be higher than that with tubes. He also told me that adding resistors to decrease the voltage will affect regulation.
I got a 400-0-400 PT out of an HH Scott & I want to use it in a project with the same voltage but using a 5V4G rectifier. I want to substitute the tube with silicons & I want to know how to do this substitution myself for future projects, so please help.
Thanx
If I have a shematic with a certain AC voltage PT & a tube rectifier,
Do I have to make any changes to the schematic to use silicons?? If yes, what are the changes? How (& on what basis) are the new values figured out?
Someone told me that the silicon rectified DC voltage will be higher than that with tubes. He also told me that adding resistors to decrease the voltage will affect regulation.
I got a 400-0-400 PT out of an HH Scott & I want to use it in a project with the same voltage but using a 5V4G rectifier. I want to substitute the tube with silicons & I want to know how to do this substitution myself for future projects, so please help.
Thanx
the forward voltage drop for a silicon diode is approximately 0.7V but varies with current.
A rectifier bridge has two diodes operating in series and drops +1.4V.
Compared to estimates of 15V to 25V volts drop for a tube (valve) diode, the silicon drop is insignificant.
A FET controlled slow switch on using a circuit like a capacitor multiplier will achieve a delay that you can pre-set to your requirements.
Finally, a relay to short out the FET and send full voltage to your circuit, or keep the multiplier in circuit if you require the lower voltage. The output voltage tracks the mains voltage, but you can preset the volts drop across the multiplier. Use your highest quality caps after the multiplier.
Sorry, I meant to say earlier that the voltage drop figure I've seen for 5V4G was 25v at 175mA. A half-way point between a normal tube rectifier and SS is to use TV damper diodes. They drop only about 8-10v.
BTW, if you intend using a regulator for B+ then it's very easy to build in a delayed ramp-up of the regulated voltage.
BTW, if you intend using a regulator for B+ then it's very easy to build in a delayed ramp-up of the regulated voltage.
Will these work well to delay B+? .. I see them pop up on ebay all the time
http://cgi.ebay.com/Power-Supply-De...ryZ39783QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
http://cgi.ebay.com/Power-Supply-De...ryZ39783QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
Hi Shoog,
I have read this before.
If this is a problem, can the slow build up of the capacitance multiplier be used to protect the down stream valves (tubes) and then use the timed relay to short out the FET dropper to feed the downstream circuit directly from SS B+. Will this bring back the sound quality?
I have read this before.
If this is a problem, can the slow build up of the capacitance multiplier be used to protect the down stream valves (tubes) and then use the timed relay to short out the FET dropper to feed the downstream circuit directly from SS B+. Will this bring back the sound quality?
I wonder if and how much this affects sound quality when implementing a multiplier?
This should produce a very good compomise I would think.
My take on the sonic impact of the cap multiplier is that the chosen transistor has a frequency response which is superimposed onto the whole of your circuit (rather like the HT transformer does). I suppose that if you chose a very linear transistor this would be reduced, but then finding such a beast at the voltages you will be dealing with might be difficult and expensive.
Shoog
Hi,
I think it is more to do with source impedance of the supply being presented to the amplifier.
I also think that a stack of parallel motor run capacitors as the output decoupling will convert the supply into an acceptable source for most valve amps. It just the cost and bulk that remains the problem.
I think it is more to do with source impedance of the supply being presented to the amplifier.
I also think that a stack of parallel motor run capacitors as the output decoupling will convert the supply into an acceptable source for most valve amps. It just the cost and bulk that remains the problem.
Tweeker said:
Really? I thought this was a potential issue because most tube guitar amps seem to have an AC switch and a B+ switch, meant to be turned on after the AC's been on for a minute so the heaters had a chance to warm the cathodes.
Even if stripping isn't a huge issue, with 6550s/KT88s running at 500 to 600 volts and $40 each, a two buck switch isn't a big deal if it helps the tubes live a bit longer.
Considering that I do not really consider cathode stripping to be an issue, I still generally use a time delay on the +B coming on line. This is a very simple single transistor relay setup which helps me sleep a tiny bit easier in my bed. I also mainly use it to eliminate nasty warm up noises.
Shoog
Shoog
The heaters are hot in a matter of seconds, not minutes. Even the slowest of heaters intended for direct mains use in series strings are up in <~15 seconds. This and the relatively low voltages involved are why I think a thermistor might be adequate. You might want more delay if theres a soft start on the heaters though. Soft starting the heaters is likely to be a greater contributer to long life, its definitely a large factor in direct heated tubes.
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