Pioneer sa-7500 score and now Questions

J

jbpollock

Well-Known Member
I got a Pioneer SA-7500 at the junk store down the street for 5 dollars on account of a "short" that ended up just needing some deoxit to fix. I have put it in my bedroom system to replace a Realistic SA-1001. The only problem I now have with this amp is that when I use the tape monitor switch you have to jiggle it a bit to get the left channel to come back in. Does this sound like this switch needs a more liberal coat of deoxit, or is there an adjustment procedure that I need to try? The other question may be basic, but what are the "turn over" settings for on the bass and treble adjustments? I have no service manual and therefor no way to look it up.

Thanks!
 
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My guess is that the switch needs more cleaning and deoxit.
The turnover controls the frequency range the bass and treble knobs apply to.
For example, when the bass turnover is 100Hz, all frequencies below 100hz will be influenced by the bass control. When set to 50Hz, all frequencies below 50hz (which are only the _very_ low tones) will be influenced.
I don't know for sure if this is correct, so could someone correct me if I'm wrong?
Also, your amp might have other turnover frequencies but the idea remains the same off course.
 
Thanks for the info. So, If you use the turnover setting to set one range, does it "remember" that setting when you adjust the other range? Does this even make sense?

I guess I will try more deoxit. I was just hesitant to buy another can ($15 at radio shack for the smallest little can) if it wouldn't solve the problem.
 
Maybe you could await EchoWars or another specialist's answer to be sure if it's really the switch that is causing the problem.
Your question about the "memory" of the tone/turnover controls makes sense, but I'm afraid the answer is "no" :) (not completely sure about this, but I can't imagine that '70s amps have memory chips :) )
I'm lucky to have a SX-939 receiver which has two bass and two frequency controls, one for each turnover point.
 
Hi Bamboe..Thanks again for the replies. I drowned (almost) the tape monitor and loundness switches in deoxit and it solved the problem. There is no longer any static when switching sources and the speakers don't cut out at all. I am king of hooked on the sound already and I really like the look of the silver face with the wood cabinet surrounding it. Guess I will have to keep my eyes open for matching components.
 
I also just caught a SA-7500 on ebay for around $30. It shall have a defect channel. Let´s wait how it shows up...
 
Now I have it on the table: Cosmetically it's not so pretty, needs some cleaning, the bottom cover is missing. To the electronics: The right chanel is dead, both power transistors + the drivers are short, 3 resistors blown. The left chanel is running, but I'm wondering about the quiecent current. It is very unsymetricaly. I measure across one resistor 8mV and on the other 350mV. That makes me worried a bit. Offset voltage is OK. Any Ideas?

In addition the speaker relay is not switching, may be because of the dead chanel (I disconnected all bad transistors already).

Does anybody have a good chrossreference list from the 2SA..SD types to the european types? Here it´s hard to find the 2SB527, 2SD357, 2SB618A, 2SD588A, and one 2SA726 for my SX737. :scratch2:
 
In Europe, there should be lots of sources for Japanese transistors...much more than in the US. If the unit were here, I'd likely replace all the outputs with On-Semi MJ21193's and MJ21194's, and the drivers (if they are TO-220 style) with 2SC3944A's and 2SA1535A's, all of which are available from Digikey, who sells in Deutschland.
 
I´ve looked for the MJ's, but they don't match, it TO-3. What I need ar types in a butterfly housing with 2 coolings on the left and right. The Drivers may be OK. Do you have any Idea for the 2SA726, its a 120V low noise type with beta 350...650. I didn't find a repacement.
 
Echowars and Agger exhanging ideas is sort of reminiscent of when the supercomputers Colossus and Guardian started communicating in 'Colossus - The Forbin Project' Even though bystanders can't fully understand it, it's still an awesome thing to behold. :)
 
I just got an SA 7500 from a friend for free, but the 125V 4A fuse blows as soon as it's powered...Any ideas? its not plugged into anything right now (except the wall) and it is a bit dusty, but its in great shape other the dust...(at least as far as I can tell without hearing the thing...)
 
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