Calling all transistor savvy people!!

[Govmnt_Lacky]

I came across a batch of OLD transistors from Texas Instruments however, I cannot find any information about them online or anywhere! I am hoping someone out there can provide some info. They are TO-5 cased trannys and have the following numbers:

RT-146
RT162
RT145

I have many more that start with RT but these are just the ones on my desk right now. The 146 and 162 have obvious TI stamps on them (the state outline of Texas w/ T & I in the outline). The other does not have a marking like that.

Any Ideas 

[R.G.]

Test them.

Measure a silicon diode and a germanium diode with your DMM on the diode range so you can tell a silicon from a germanium with your meter. Then see if they're silicon or germanium by reading the junction voltages with your meter.

If you look for the junctions, this also tells you base, emitter and collector, although all TO5s have the collector connected to the case and the emitter closest to the index tab.

Then put them into the Geofex germanium tester and test leakage and gain. It works for silicon too, although leakage is going to be unmeasurable and gain will be a little low.

[jrod]

I have some TI transistors with RT #'s as well at home. The store I bought them from told me they were house numbered 2N404's. I can't remember the the #, but will check after work and let you know. Maybe they are the same as yours.

[Govmnt_Lacky]

Measure a silicon diode and a germanium diode with your DMM on the diode range so you can tell a silicon from a germanium with your meter. Then see if they're silicon or germanium by reading the junction voltages with your meter.

I am not really savvy on what you are saying here RG... could you elaborate?

If you look for the junctions, this also tells you base, emitter and collector, although all TO5s have the collector connected to the case and the emitter closest to the index tab.

I am with you here... 

Then put them into the Geofex germanium tester and test leakage and gain. It works for silicon too, although leakage is going to be unmeasurable and gain will be a little low.

What do you mean when you say "the gain will be a little low?" Doesn't that depend on the hFE range of that particular transistor?

I have some TI transistors with RT #'s as well at home. The store I bought them from told me they were house numbered 2N404's. I can't remember the the #, but will check after work and let you know. Maybe they are the same as yours.

I will look forward to your findings. Thanks for checking it out. 

[R.G.]

Measure a silicon diode and a germanium diode with your DMM on the diode range so you can tell a silicon from a germanium with your meter. Then see if they're silicon or germanium by reading the junction voltages with your meter.

I am not really savvy on what you are saying here RG... could you elaborate?

Almost all DMMs measure resistance by putting a constant current out the probes and then internally measuring the voltage which this creates through the resistance. If you put a diode on the probes, same thing happens, current goes through the diode (or not, if you have it backwards) and the meter reads the voltage internally. Silicon and germanium diodes have different forward voltages, so once you know what YOUR meter reads for a silicon versus germanium, you can easily tell them apart.

Then put them into the Geofex germanium tester and test leakage and gain. It works for silicon too, although leakage is going to be unmeasurable and gain will be a little low.

What do you mean when you say "the gain will be a little low?" Doesn't that depend on the hFE range of that particular transistor?

It does depend on the hfe of that particular transistor. However, the gain/leakage tester on my site is specialized for germanium, and is a quick and dirty circuit which is not independent of the transistor base-emitter voltage. The Vbe is lower for germanium parts than for silicon, so a silicon part gets a bit less base current than a germanium would. That means the collector current you measure is lower, and it makes the calculated gain for a silicon in that particular circuit a bit lower than it really is. The real transistor gain has a say in this, too, but all the calculations come out a bit low for silicon than if the circuit had been designed to be more accurate over varied transistors. It's a shortcoming of such a simple tester circuit, and I wanted you to be aware of it.

I have some TI transistors with RT #'s as well at home. The store I bought them from told me they were house numbered 2N404's. I can't remember the the #, but will check after work and let you know. Maybe they are the same as yours.

2N404 is a nice, if on average low hfe germanium. Used more for switching circuits than audio, but usable in the FF.

[jrod]

Ok, I checked those transistors I have and they are RT-146 by Texas Instruments.

The owner of the store I got them at told me he curve traced them and the specs were closest to 2N404, so he assumed that's what they are, but with house numbers. Like you, I've searched for info on them and found nothing. So, I have just always assumed they guy that sold them to me was right. He is very knowledgeable about transistors.

I have tried them in two circuits. They sound GREAT in a Fuzz Face, but not so good in a Tone Bender MKII, compared to OC75's which I am a big fan and prefer in an MKII.

It's been a while since I measured them. But, I remember they are very consistent with low leakage (well within R.G.'s suggest Fuzz Face range) and the gains are 110-150 range.

That is about all the info I have on the RT-146. I hope this helps.

I have some TI transistors with RT #'s as well at home. The store I bought them from told me they were house numbered 2N404's. I can't remember the the #, but will check after work and let you know. Maybe they are the same as yours.

2N404 is a nice, if on average low hfe germanium. Used more for switching circuits than audio, but usable in the FF.

Thanks for the info, R.G.! I always appreciate your input and knowledge! You are right, all the "real" 2N404's I have are fairly low gain, but these are consistently higher, so they may actually be something totally different.

Is there a simple way to explain the difference between a germanium transistor that is intended for switching circuits and one intended for audio purposes and why a switching works in an audio circuit like the Fuzz Face? Specifically considering the Fuzz Face, almost all germanium transistors I have tried sound good as long as they are low leakage and the "right" gain range. I've always wondered why a switching transistor, like the 2N404, would sound so good and even work.

[edvard]

2N404's were used in the Harmonic Percolator as well.
According to the Transistor Museum, the 2N404 was used extensively as a switching transistor in computer circuit boards because they were among the most consistent and robust transistors available at the time.
IIRC, "switching" transistors have to be able to operate at certain speeds and current levels, but beyond that, a transistor is a transistor; flavor accordingly.

[PRR]

> wondered why a switching transistor, like the 2N404, would sound so good and even work.

There's no key difference between a "switching" transistor and an "amplifier" transistor.

If a part has high gain, low leakage, and low noise, it would be a shame to use it to switch a lamp or relay. You sell it as an "Amplifier". Especially if that high gain falls-off at moderate current.

If you have parts that have moderate gain at high current, switch-users will buy them even if the noise is sky-high and (for lamp/relay use) if the part is a little slow or it leaks a little.

Many-many audio amplifiers are built with parts originally designated as "switches". IMHO, the maker's idea of "amplifier" is quite limited. We often turn to "switch" listings for high-current amplifiers. Especially now when low-noise and low-leakage is commonplace.

2N404 was VERY common in early audio.

2N404 hFE is not specified. It cost nearly $3 in days when $3 was big money (several packs of Camels) so you did not select. Circuits had to be designed to work with any reasonable hFE.

A private-number 2N404 could be a full-spec '404, a better-spec '404, or a reject '404. 2N404 is rated to block 24Vcer.... if you had to block 35V you could order 2N404A, and for a price TI would test parts and find you some 40V ones. Or if you only had 9V on tap, but were cheap, TI might sort through their '404 rejects and sell you the ones that broke-down between 10V and 23V, but under another type-number so they did not fall into 20V systems.

As long as you know you don't know what they are (the original contract is surely long-lost and forgotten), you can work with them. As Eddy says: Transistor is transistor.

[jrod]

Thanks, Edvard & PPR!

I appreciate the information. I have always wondered why a transistor would be marketed for a certain purpose. Now the switch vs amplifier makes perfect sense.

Like I said, the RT-146's sound very good in a Fuzz Face circuit. I will be curious to see how Govmnt Lacky's RT-145/162's work out.