I have a HK citation A preamp that is all orignal and it works. I am looking to recapp it . So in preperation I'm looking at the HK branded germanium transistors. Is there anyway to tell what type the transistor was used ? The only info I could find is the schematic ,which only has EBC voltages and either NPN or PNP . Any ideas or suggestions ?
Harman Kardon transistors
- Thread starter calman46
- Start date
The schematic says "Pre 1963" on it, so you have to assume that these are probably germanium, like you already do. The unit works, so aside from curiosity, why are you wanting to know the specific part numbers? It seems like it would be a real problem to find replacements since that technology has been overtaken by silicon, and only NOS parts would be available if you could find 'em. That's a big if!
They (germanium) are typically noisy and susceptible to temperature variation...but if they did fail you could do a thevinin analysis of the circuit, deduce the requirements, and specify your own replacement. You might have to modify the associated resistors value to make it right as well.
The only other thing might be to find a service manual or some more info from Harmon Kardon, but they've changed hands over the years and the documentation is going to be hard to find. I did a quick search and couldn't find anything. Harmon Kardon thoughtfully put their own part number on the schematic instead of the real transistor number.
Good luck!
They (germanium) are typically noisy and susceptible to temperature variation...but if they did fail you could do a thevinin analysis of the circuit, deduce the requirements, and specify your own replacement. You might have to modify the associated resistors value to make it right as well.
The only other thing might be to find a service manual or some more info from Harmon Kardon, but they've changed hands over the years and the documentation is going to be hard to find. I did a quick search and couldn't find anything. Harmon Kardon thoughtfully put their own part number on the schematic instead of the real transistor number.
Good luck!
From my searching around HK didn't do SM that early . I need to look inside of one of the SR models also as no SM there either but from the same time . I think earlest SM is the 230 which list the HK and equivalent replacement transistors , but the HK numbers are different . Just preparing for the worst 
,thanks
,thanks
I found this - it might have some clues but no specific information on the transistors that I saw. I read a thread on AK that had a touched on a cap replacement for this model preamp. At the end of the thread one of the posters mentioned that an article in a 1963 Journal of the Audio Engineering Society went into great depth about the design of the HK Citation A.
http://www.aes.org/journal/toc/
http://www.aes.org/journal/toc/
Voltage is just one several factors that you would need to address to select a suitable replacement.
I don't know if this guy is still in business but he is/was selling articles from the Audio Engineering magazine - he quotes $6 per article.
http://www.roger-russell.com/magrevaudio.htm#a1963
I don't know if this guy is still in business but he is/was selling articles from the Audio Engineering magazine - he quotes $6 per article.
http://www.roger-russell.com/magrevaudio.htm#a1963
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