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 Post subject: 1960's Stereo Amplifier Kit - STE Model 621
PostPosted: Nov Sun 17, 2019 12:07 am 
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Joined: Feb Thu 02, 2012 2:19 am
Posts: 20
Location: Orange County, California 90720
In the early 1960's, there were a number of manufacturers offering stereo kits for sale. I have this solid state STE Stereo amplifier kit. The architecture involved 2 monoblock amplifiers and a power supply. This was a low cost entry into the audio market. There was a ad in the Radio-Electronics magazine with a price of $44.45. The circuit design had no transformers, 2 power transistors, and 5 ordinary transistors per amplifier. I did a total recap and got it working, but the volume will not decrease to zero. I have no schematic and am asking if anyone is familiar with this kit ? Any help would be greatly appreciated.
Thank you.
--Dennis


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 Post subject: Re: 1960's Stereo Amplifier Kit - STE Model 621
PostPosted: Nov Sun 17, 2019 1:54 pm 
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Joined: Nov Wed 30, 2016 7:35 pm
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Location: Sunbury, Ohio 43074
Might have to bite the bullet and draw out your own schematic on this one .....

Try cleaning the volume control pot... it may not be going all the way to zero.

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 Post subject: Re: 1960's Stereo Amplifier Kit - STE Model 621
PostPosted: Nov Mon 18, 2019 8:29 pm 
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Joined: Feb Thu 02, 2012 2:19 am
Posts: 20
Location: Orange County, California 90720
I received a great suggestion from a FaceBook group member. Early transistor amplifier designs were published in monthly periodicals like Popular Electronics and Radio Electronics. I will be perusing through the years 1961 thru 1963 to find a similar design. The transistor types are 2N301 power transistors and 2N1265/5 germanium types. The website for Popular Electronics is https://www.americanradiohistory.com/Po ... Pk1ttTX99o

I don't know of any site that has Radio Electronics issues. Any help here would be appreciated !

--Dennis

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 Post subject: Re: 1960's Stereo Amplifier Kit - STE Model 621
PostPosted: Nov Tue 19, 2019 4:36 pm 
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Joined: Aug Wed 24, 2011 4:35 am
Posts: 4594
Location: Sunnyvale CA
classicelectronics wrote:
I did a total recap and got it working, but the volume will not decrease to zero. I have no schematic and am asking if anyone is familiar with this kit ? Any help would be greatly appreciated.
Thank you.
--Dennis


Chasing through old electronics magazine is a good idea, I am sure something similar has been published. However, I can almost guarantee that the volume control is part of a voltage divider with, probably, a dual-gang 50K audio taper pot. This pot is no longer shorting the center tap to ground when turned all the way down, either because the ground is weak, or the pot has some defect or conductive debris near the low end of travel. Test that the low end of the pot is actually connected to the common return. It probably is a low-resistance but not zero, since I imagine you would have mentioned it if only one channel was like this. The chance of both pots in the dial gang pot being failed in a similar way are not zero, but the low sides are undoubtedly tied together and then supposed to be connected to the common return. So it is far more likely to have one problem affecting each channel in a common spot. Or, possibly, there is some debris or other obstruction of the pot not allowing the common shaft to rotate all the way to the end of travel.

Brett


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 Post subject: Re: 1960's Stereo Amplifier Kit - STE Model 621
PostPosted: Nov Wed 20, 2019 7:16 pm 
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classicelectronics wrote:
I don't know of any site that has Radio Electronics issues. Any help here would be appreciated ! --Dennis


Chop off the url to browse the entire list of publications at American Radio History: https://www.americanradiohistory.com

Here's the R-E page: https://www.americanradiohistory.com/Ra ... r_Page.htm

Southeast Technical I hadn't heard of. I was more familiar with SouthWest Technical Products Corp. (SWTPC). They sold many kits that were originally featured in Popular Electronics and Radio Electronics. I built a pair of their Universal Tiger monoblock power amps and the matching pre-amp. SWTPC produced lots of audio gear, then in the mid-70's they got heavily involved in computer kits that were very popular but pretty much broke them in the end when ready-to-run systems took over the home-computer/hobbyist market.

-Ed

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