dallas rangemaster, biasing oc44

Started by treblebooster, December 27, 2016, 10:37:19 AM

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treblebooster

Dear friends,
first of all, happy holiday season!

I wrote a pm to RG but I think that some others could have such a trouble with a germanium transistor, so I post it here too in order to discuss it all together (RG could reply here instead of my pm).

I recently I had the occasion to get a nos oc44.
Following RG guide here http://www.geofex.com/article_folders/rangemaster/atboost.pdf

I'm able to obtain the right bias (around 7v) in these two ways:
1) pot (or fixed resistor) 10k, Rb1 82k, Re 2k7 (reaching resistors' limits that he suggested, I get 7.05 v)
2) pot (or fixed resistor) near 13k, Rb1 68k, Re 3k9 (keeping original resistors' values and just increasing a little the collector resistor I get 7.00 v)

My question is: which is the more preferable (or theoretically more correct) way of building it? And also: does the choice affect the sound or it doesn't matter at all, since both ways deliver 7v to the collector?

Thanks guys!  ;)

treblebooster

Sorry guys, the first post gave me a server error, I had to finish a work and I reposted it (I didn't know that the first message was posted). I kindly ask the admin to delete one of the two. My apologizes!

PRR

Welcome.

They are equivalent for all practical purposes.

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treblebooster

#3
Hi and thank you for your reply! I have an update: I did a little mistake...   :icon_redface:

In fact, the 470k was straight connected to the collector, after the 10k from the battery. Mistake due to many resistors in series in order to get the correct value (and the last one was connected in the wrong place, to the collector instead of the DC source).

anyway... I put this resistor in the right place and now I have 7,03 v (very correct value following RG article) keeping everything like original (10k collector, 68k from base to ground) except for the Re (emitter to ground), which now is set to 3k. RG's suggested limit is 2k7, so I assume that the transistor is fine and usable, would you agree? And also, would you suggest a different biasing such as trying to get a mid-way between Rb1 and Re (as imaginative example: 75k + 3k3) in order to give a minimum variation to both resistors, or do you think that 68k + 3k is acceptable?

At the moment, collector is 7,03 v and emitter is 0,71 v.

Cheers guys!  :) :)


PRR

> the transistor is fine and usable, would you agree?

I don't see a problem.

This isn't precision science. If it sounds good, use it. If it sounds bad, check voltages, and get more-like some known-good voltages. Tenth-Volt differences are unlikely to make any difference.
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