Transistor replacement on GX-625
- Thread starter vfr800fiman
- Start date
All 12 are on the preamp board. There are 3 on each channel (LR) on both the mic and PB head inputs. They are the first 3 transistors on all 4 inputs, replace them all.
I bought mine from EBay, I think it was a bag of 100.
Good luck.
Make sure you get replacement transistors with a similar gain. The original 2SC458LG transistors have a notation of "D", which is an Hfe of 250-500. The replacement 2240's should have a similar gain rating.
I think the 2240's come in a "GR" and "BL" rating, which is 200-400 and 350-700 Hfe rating respectively. I think I went with the "GR" rating.
It would be a good idea to match them if you can, I didn't do this for mine and I can't really hear any difference. Of course mine had a channel that was distorted so anything was better
Glenn
I think the 2240's come in a "GR" and "BL" rating, which is 200-400 and 350-700 Hfe rating respectively. I think I went with the "GR" rating.
It would be a good idea to match them if you can, I didn't do this for mine and I can't really hear any difference. Of course mine had a channel that was distorted so anything was better
Glenn
My 2240 transistors came in but I'm a little confused about how to install them. The 2240 is ECB but read that the early 458s were BCE and the later ECB.
When looking at the writing on the transistor, the right leg of the transistor is soldered through a solid square printed on the PCB. Is this a symbol for the Base leg? Iron's hot so would appreciate some help. Thanks.
When looking at the writing on the transistor, the right leg of the transistor is soldered through a solid square printed on the PCB. Is this a symbol for the Base leg? Iron's hot so would appreciate some help. Thanks.
KentTeffeteller
Gimpus Stereophilus!
ReVox decks have excellent transistors as a rule and did not push them at their limits. Their main weaknesses in electronics are those Frako (technicians call them Flakos) electrolytics and the Wima caps. Replace those for better reliability and sonics. They're ticking time bombs. Akai machines had transistors which back then were pushed to the limits. Back when the machines were new, Akai used matched transistors. Due to the transistors being lesser quality then. New ones are 99% of the time in the high end of the Hfe range from good makers. And short of a device failure due to some anomaly, should never need replacements in the next 30 years.
Gee, looks like mine 
I was going to tell you that the service manual has a picture of the PC board showing the actual transistor symbol on the traces so you know how to install any transistor, just pay attention to the pinout of your particular device.
I actually have a bunch of capacitors to replace all those so called "Flaky" ones in this deck. I just haven't gotten around to doing it yet. If I remember right, they are the 10uF & 47uF electrolytic caps around those same transistors we are discussing.
Glad everything works now.
Glenn
I was going to tell you that the service manual has a picture of the PC board showing the actual transistor symbol on the traces so you know how to install any transistor, just pay attention to the pinout of your particular device.
I actually have a bunch of capacitors to replace all those so called "Flaky" ones in this deck. I just haven't gotten around to doing it yet. If I remember right, they are the 10uF & 47uF electrolytic caps around those same transistors we are discussing.
Glad everything works now.
Glenn
fc911c
New Member
Gee, looks like mine
I was going to tell you that the service manual has a picture of the PC board showing the actual transistor symbol on the traces so you know how to install any transistor, just pay attention to the pinout of your particular device.
I actually have a bunch of capacitors to replace all those so called "Flaky" ones in this deck. I just haven't gotten around to doing it yet. If I remember right, they are the 10uF & 47uF electrolytic caps around those same transistors we are discussing.
Glad everything works now.
Glenn
Are those bad caps only in the 625? How about the GX 636 646 or 747.
Thanks
Maybe Jan could chime in here, as I'm not sure of which models are affected. I'm pretty sure I read this somewhere on this forum, time for a search.
I'll look around and post the info here if I find it.
Glenn
I'll look around and post the info here if I find it.
Glenn
Here it is, post #6 from Jan:
http://www.audiokarma.org/forums/showthread.php?t=261455
http://www.audiokarma.org/forums/showthread.php?t=261455
fc911c
New Member
Thanks for taking the time to look. I have posted another question " intermitten recording problem" would you have any ideas about that?
Thanks
Frank
I don't own one so I can't comment.
You didn't match!
Well "a sweet playing and sounding deck" might be good enough for you - but having performed record/playback distortion tests (using an HP-339A) on various Akai decks that weren't quite hissy (yet)... It seems that when the transistors start failing, they first lose gain (beta) at which point there is only a mismatch and already - the distortion skyrockets. And that becomes part of the recording, not so much a failure, but you can't get rid of it, once its there, it's there forever. So matching pairs is the only way to get the distortion down to the original factory specs or even better.
-Steven L. Bender
Well "a sweet playing and sounding deck" might be good enough for you - but having performed record/playback distortion tests (using an HP-339A) on various Akai decks that weren't quite hissy (yet)... It seems that when the transistors start failing, they first lose gain (beta) at which point there is only a mismatch and already - the distortion skyrockets. And that becomes part of the recording, not so much a failure, but you can't get rid of it, once its there, it's there forever. So matching pairs is the only way to get the distortion down to the original factory specs or even better.
-Steven L. Bender
DougMac
Super Member
No, I didn't match
I read different opinions regarding the necessity of matching. Even in this thread there is some question of its necessity. It boiled down to a couple of factors. Since the deck was a pig in a poke which I obtained for free, I didn't want to go through the extra expense (which in the scheme of things isn't that much) and the extra time. Anyway, i planned it to be my back up machine to my Teac X-1000R. I don't do any recording, I'm just using them to digitize my old tape collection. The old tapes were recorded either on a V-M or a Viking 87 Pro.
I've been using the Akai for several months now and it still plays well, better than I was expecting. On both machines I hear a level of detail I don't remember hearing before. I guess the Viking could lay it down, but couldn't get it back.
Thanks for your concern, Steven. I also didn't recap the deck. Next go around I'll do both.
I read different opinions regarding the necessity of matching. Even in this thread there is some question of its necessity. It boiled down to a couple of factors. Since the deck was a pig in a poke which I obtained for free, I didn't want to go through the extra expense (which in the scheme of things isn't that much) and the extra time. Anyway, i planned it to be my back up machine to my Teac X-1000R. I don't do any recording, I'm just using them to digitize my old tape collection. The old tapes were recorded either on a V-M or a Viking 87 Pro.
I've been using the Akai for several months now and it still plays well, better than I was expecting. On both machines I hear a level of detail I don't remember hearing before. I guess the Viking could lay it down, but couldn't get it back.