[R-390] RT301 current regulator tube

[Jim Whartenby]

Hydrogen appears to be the genie who refuses to stay in the bottle!HNY,Jim

Too much agreement kills a chat.  E. Cleaver

-----Original Message-----
From: Jordan Arndt <Outposter30 at shaw.ca>
To: Jacques Fortin <jacques.f at videotron.ca>; 'Jim Whartenby' <old_radio at aol.com>
Cc: 'R390A' <r-390 at mailman.qth.net>
Sent: Fri, Dec 31, 2021 10:01 am
Subject: Re: [R-390] RT301 current regulator tube

I use a 12BH7A tube with jumpers soldered to the pins to replace the 
3TF7...The 3TF7 doesn't drop enough voltage and the BFO and PTO tubes get ~7 
volts each...

73...Jordan VE6ZT

----- Original Message ----- 
From: "Jacques Fortin" <jacques.f at videotron.ca>
To: "'Jim Whartenby'" <old_radio at aol.com>
Cc: "'R390A'" <r-390 at mailman.qth.net>
Sent: Thursday, December 30, 2021 9:15 PM
Subject: Re: [R-390] RT301 current regulator tube


> Hi Jim,
>
> You are right.
> Only a small diode bridge, a LM317 and a resistor are needed.
> And no need to use a GND connection...
> However, the resultant current waveform into the filaments will be a kind 
> of trapezoidal shape.
> The exact value of the LM317 current-setting resistor have to be found by 
> measuring the current value with a true rms meter.
>
> But, I still prefer the 12BY7 / 12BH7 solution, partly because the 
> non-availability of a 12BY6 tube (it doesn't exist, in fact).
> I use a 6BY6 in the BFO circuit to replace the 6BA6 / 5749 and use it as a 
> product demodulator as it provides more output than a 6BE6.
> The circuit is based on the W3JHR / W7DI ideas.
>
> 73, Jacques, VE2JFE in Montreal
>
> No need to rectify and filter.  If you want to go the LM317 rout, all you 
> will need is to add a bridge rectifier to the current regulator circuit. 
> The AC leads go to the appropriate pins of the RT-301 socket and the +/- 
> leads go to the LM317 appropriate connections.  No matter what part of the 
> AC cycle, the LM317 will always see the correct polarity and limit the 
> current to the set value.  I just checked the circuit at 
> https://www.bristolwatch.com/ccs/LM317.htm   and see no need for a ground 
> connection, but since I haven't tried that particular circuit, a ground 
> connection for the bypass cap might be prudent for stability.
> But if you go from a 6 volt heater to 12 volt heater oscillator tubes, you 
> can save a few watts of actual heat in either flavor of R-390 by 
> eliminating the current regulator all together.
>
> HNY,Jim
>
>
> Hello Tisha,
> When you mention using a LM317, is it used in Voltage regulator, or in 
> Current regulator configuration ?
> In both cases, you will need to rectify and filter the 25.2 Volts AC 
> supply, then use the LM317 thereafter to supply constant 12.6V DC to the 
> filaments or 300mA DC, whatever.
> And full-wave rectification cannot be used there, unless you modify the 
> BFO
> + PTO filament wiring...
> As the maximum voltage across the filtering capacitor will reach about 
> 35V, it also means that a quite substantial heatsink for the LM317 will be 
> needed.
> Worst case, 6.72W have to be dissipated from it (in either configuration).
>
> I prefer to use the 12BY7/12BH7 trick...
>
> 73, Jacques, VE2JFE in Montreal
>
> ______________________________________________________________
> R-390 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/r-390
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:R-390 at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html