2 wrote:
>
>
>>2 Wrote:
>>
>>>>
>>>>Paul and I favor the TL431-TIP147 bias circuit because we supply our
>>>>different control boards for a large range of tubes, so we need a 'one
>>>>circuit fits all' solution. Maybe that makes us biased?
>>>>
>>>I am biased toward simple, minimal-cost, glitch-resistant circuits that
>>>work. The [Figure 7] optoisolator/10A, Si-npn switch/3A diode-string
>>>will reliably handle a 3cx3000A7 and it switches in under 7uS.
>>>
>>>>However, if you're also going to use EBS, the TL431-TIP147 circuit has
>>>>everything you need - the power transistor and the switching facility
>>>>too. To bias off the tube, simply switch the control gate of the TL431
>>>>to its anode (collector of TIP147). Switching time is a few
>>>>microseconds.
>>
>>Both circuits can make equally valid claims of simplicity, low cost
>
>What is the cost in quid [£] of the TL431-TIP147 circuit ?
>
You can have it in green stamps: under $5.
For that, you get: adjustable voltage from 5V to 40V, all the current
capability you need, better regulation than you'd ever need, and EBS
capability. The same $5-worth can handle anything up to a YC156.
Compare with a 20W stud-mounted zener at $10 over here (and it ain't big
enough) or a 75W one for $25... for one fixed voltage.
I didn't include a heat sink in the calculations, but either solution
would require that.
For cheapness, neither the active regulator nor zeners can compete with
a string of diodes... but frankly that's a competition neither Paul nor
I would want to be involved in.
>>and glitch resistance.
>
>What is the I-peak withstanding ability of TL431-TIP147 circuit?
>
More than you need. With the grid directly grounded and the meters
protected by diodes (as recommended by Rich), none of the glitch current
actually goes through the cathode bias circuit anyhow.
But just to be sure, I routinely test my amplifiers by dropping a wrench
into the anode compartment. They shut down automatically with no drama
and no damage, not even a blown fuse... no fun at all, really.
--
73 from Ian G3SEK
www.ifwtech.co.uk/g3sek
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