Forums :: NEW! Web Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Oct Tue 19, 2021 4:20 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 24 posts ]  Go to page Previous  1, 2
Author Message
 Post subject: Re: Help rebiasing my bagpipes to Si!
PostPosted: Aug Mon 30, 2021 9:47 pm 
Member
User avatar

Joined: Apr Mon 20, 2020 3:45 pm
Posts: 48
Location: somewhere in the northeast US
Usually Lurking wrote:
Most common PNP silicon transistors will work in this circuit, with some changes to the base bias. 2N4403 or something. The output circuit may work as-is.

The PNP oscillator transistor can be biased with a single resistor from collector to base. Shoot for 4-5 V DC at the collector. Try 220k and adjust as required.

See if increasing R15 to 15k from 10k biases TR4 about right.

If you do not already have a stock of resistors, Jameco and Mouser sell kits of 1/4W resistors. You will probably need an assortment to get the chanter tuning right anyway.

The unijunction parts are silicon, but are not as common as they once were. It is possible to make substitutes for these using two resistors and either small SCRs, or a pair of transistors each.

Ted


Wow, thanks for all the data! I think I still have some old 2n4403s lying around from a project a few years ago. Might have to try with that. As for the UJTs, its a shame to see them become so rare, especially with all the creative circuits (such as this one) I have come across that implement them. Thank goodness for NTE though! :) What resistor values would you suggest for the
SCR replacement if I do end up needing to use it? (My knowledge on the math and...stuff when it comes to electronics isn't very good.) I have always thought that SCRs and UJTs behaved similarly, so its interesting to know that they can work in the same applications (with minor modifications)

_________________
In truth, happiness is a 10 pound bag of 7-segment LEDs. -Fran Blanche


Top
 Profile  
 
 Post subject: Re: Help rebiasing my bagpipes to Si!
PostPosted: Aug Mon 30, 2021 10:37 pm 
Member

Joined: Jan Thu 16, 2020 12:29 am
Posts: 1562
Timmy73 wrote:
As for the UJTs, its a shame to see them become so rare, especially with all the creative circuits (such as this one) I have come across that implement them. Thank goodness for NTE though! :) What resistor values would you suggest for the
SCR replacement if I do end up needing to use it? (My knowledge on the math and...stuff when it comes to electronics isn't very good.) I have always thought that SCRs and UJTs behaved similarly, so its interesting to know that they can work in the same applications (with minor modifications)



UJT's are not that rare, there are multiple types and easily available on ebay. You might have to persuade your Dad to let you use ebay.

An SCR behaves as a diode that is non conducting, if you trigger it on with a gate pulse, it then behaves as a normal diode, that is if there is anode to cathode current. As soon as that anode-cathode current falls to zero (or a very low value) the SCR latches off again. In some circuits to switch off the SCR, the anode and cathode are simply momentarily shorted out for this application. The the terminals on the SCR are the anode, cathode and gate. A Triac is like a bidirectional SCR. The SCR can make a relaxation oscillator, like a UJT.

The three terminals of the UJT are the Emitter, and the other two are labelled B2 and B1 (base 1 and Base 2). UJT's, were often used in gate triggering circuits for SCR's for AC power control. The UJT can be wired easily to produce narrow pulses and the arrangement, a relaxation oscillator, the UJT exhibits "negative resistance", meaning as its emitter current increases (typically over a range of about 2uA to 10mA) the E to B1 voltage drops.

If you are using UJT's. BJT's SCR's etc, it pays to read up on their operation. The little book I suggested is very helpful for the UJT.


Top
 Profile  
 
 Post subject: Re: Help rebiasing my bagpipes to Si!
PostPosted: Sep Wed 01, 2021 1:43 am 
Member
User avatar

Joined: Jun Sun 22, 2008 2:03 am
Posts: 1059
Location: Burke, VA 22015
It looks like the once popular 2N2646 UJT is still in production. I had some on order along with some 2N6027 PUTs from a large US distributor. The price came out to $1.50 a piece (shipping included), much cheaper than NTE. This should be compatible with the TIS43. I'm glad to send you some FOC for this project.

_________________
Binh


Top
 Profile  
 
 Post subject: Re: Help rebiasing my bagpipes to Si!
PostPosted: Sep Wed 01, 2021 7:59 am 
Member

Joined: Jan Thu 16, 2020 12:29 am
Posts: 1562
It is interesting where UJT's can turn up. Sometimes (rarely) they turn up as the vertical scan oscillator in a video monitor . I have attached a circuit of a video monitor that uses one. It has a common technique to speed up the discharge of the timing capacitor, to make a better sawtooth wave, by adding a BJT. UJT oscillators are extremely easy to synchronize to an external sync pulse, the one in this set syncs immediately to either 50 Hz or 60Hz vertical sync pulses.

I have one other video monitor, the type used in the IBM-5155 computer, that uses two transistors wired as a PUT for the vertical scan oscillator, also a little unusual.


Attachments:
ujt2.jpg
ujt2.jpg [ 530.83 KiB | Viewed 227 times ]
Top
 Profile  
 
Post New Topic Post Reply  [ 24 posts ]  Go to page Previous  1, 2

All times are UTC [ DST ]


Who is online

Users browsing this forum: Paul Dietenberger and 8 guests



Search for:
Jump to:  


































Privacy Policy :: Powered by phpBB