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12AU7 needs about 150mA filament current at 12.6V and 300mA at 6.3V..
Building your own stompbox / Re: Med-high voltage Valvecaster/Tube preamp project
« Last post by momo on Yesterday at 10:35:45 AM »
Update, major runaway current issue...

I re-did my breadboard wiring, everything seems legit.
Here are the mods I put up on circuit, the problem is that I get current going way higher than 150ma as I jack up the voltage gradually.
For now, there is no DC regulator circuit, just direct from variable DC source.

I'm going for a cleaner VC :  R2: 100k
                                          R3: 47K
                                          C3: non electro wima cap 0.1uf
                                          No tone circuit.

What can be causing this "semi-short" ?
A lady is either pregnant or not, so I'm not sure I'm semi-shorting....hehe
 Thank-you so much for all of the replies.  As always I learn something from the experts when I post a question here.  Hoping I can reciprocate somehow eventually but I am still a humble neophyte at the DIY pedals ... but I became addicted as something to do during covid ...
Thanks for the schematic too !  I had found some tagboard/vero board layouts but none were exact looking at the real thing ... this will save me a bunch of time ...
Thanks again guys !!
Building your own stompbox / Re: Biasing RDV Tonebender.
« Last post by antonis on Yesterday at 10:20:37 AM »
ΟΚ..Let's make things more simple.. :icon_wink:

You want Q2 Collector (with its Emitter grounded hence its Base at about 600mV), to sit at 0.4V to 0.8V (lets make it 0.6V for simplicity)..
Q2 Collector at 600mV means Q3 Emitter at 0V..!!
(no current through Q3 Emitter 220R + 1k trimpot hence no Q2 Base bias - very unhappy BJT.. :icon_cry:)

To distract Q2 from its misery, we will need about 600mV at its Base PLUS additional 600mV at Q3 Base (we DO want both BJTs happy, don't we..??) PLUS some mV drop across 100k feedback resistor.. :icon_wink:

If you like to calculate those "some" mV across 100k resistor, you can easily do it as follows:
For Q2 Collector at 1.3V, Collector current should be about 160μA (ignoring Q3 Base current for simplicity)..
For hFE = 78, Q2 needs a Base current of 2μA..
2μA across 100k result into 200mV drop..

What is the summation of 600mV + 600mV + 200mV..?? :icon_biggrin:

exersise: If we replace "600mV" (Si BJT VBE) with "300mV" (Ge BJT VBE) how much lower Q2 could be biased..??

Building your own stompbox / Re: Old telephone ringer stompbox
« Last post by duck_arse on Yesterday at 10:20:36 AM »
rocking armature, is that the right thing? I have an idea these run on DC, and when the coil energises one way [when the connections are in the right place] it breaks the connection to that end of the coil, and makes the connection to the other end. this throws the dinger, breaks the connection, makes the connection, etc. also large sparks.

so yes, probably connect to the moving plate part, but you really want PRR or maybe Ron to give you the good oil. there should be somewhere in your telephones collection one with a printed circuit diagram included. I think they were mandatory in phone equip here.
Building your own stompbox / Re: Old telephone ringer stompbox
« Last post by SeneX225 on Yesterday at 10:13:53 AM »
While searching on how to make a 555 oscillator, I found this at the same local radioshack:

It's some Arduino module and has DC 5-15V with 1Hz-200kHz frequency. Will it suffice for this particular project?
Building your own stompbox / Re: Tuning the Dandy Horse
« Last post by eh la bas ma on Yesterday at 09:53:05 AM »
I managed to calibrate it without oscilloscope, but I spent some time on it and tried new settings several times.

You can get different possibilities according to the trimmers settings. A modulation effect more or less prominent, with various textures.

Even with an oscillo, I am not sure I would be entirely sastisfied with the calibration. Shaping the modulation slowly, untill you really like it, is probably at least just as good, and maybe even better. It requires more time working on the build, but it's supposed to be fun.

I would recommend an oscilloscope if you'd want to build a lot of them fast and all at once.

I remember last time I tried, I noticed the modulation was more discrete, "musical", and less background noises, if I didn't set the volume difference too high with the Gain 1 trimmer. *Almost* the same level i'd say...

"Adjust the Gain1 trimmer until the level at test pad 6 is about 10% higher than at test pad 5."

10% isn't much... unnoticeable i guess.

I also recall that on my build, there was a really narrow sweetspot on Bias1. It was quite important to get it right for a cleaner modulation.

Pad 2 with Filter Matrix selected 493KHz was 513KHz
Pad 2 with Slap Back selected 125,3KHz was 124KHz

Maybe it was the few KHz difference maybe the gain2 trim pot...

I don't think it's important at all to get the exact number. You have a good approximation and it should be perfectly ok.
Building your own stompbox / Re: Old telephone ringer stompbox
« Last post by GibsonGM on Yesterday at 09:26:42 AM »
Yes, per the article I linked above. I'm really just curious if it can be hacked to make something useable at manageable voltages that one can easily provide within a pedal context  :) 
Building your own stompbox / Re: Old telephone ringer stompbox
« Last post by MikeA on Yesterday at 09:13:01 AM »
Ringers are tightly tuned to a specific AC frequency, evolving from party lines where there were multiple instruments on one wire pair.  Different frequencies rang different houses.  I don't know the frequency scheme in EU, you should be able to Google it, but something like 20, 30, 40, 50 or 60 Hz.  Another scheme was 22, 33, 44, 55 or 66 Hz. Somewhere between 48 and 110 volts AC should do it.  After party lines went away, most phones were fixed in the 20-30 Hz range so I'd start there.
Building your own stompbox / Re: Old telephone ringer stompbox
« Last post by SeneX225 on Yesterday at 09:06:59 AM »
(I don't know why this self-quotation happened.)
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