Hi all!
First, thanks for all the great information available on this site. I'm a complete novice to this vintage amp malarkey and so I've scoured it to find an answer to my woes - but to no avail.
I suppose first a little history. I picked this amp up and it sounded great! After about three months though, it would make a popping sound through the speakers and then play a lot quieter. (There is another post that sounded similar to this issue but nothing there I tried worked).
1. So, recommendation 1 always appears to be clean all the pots, so I did that. In fact I also did it when I first got the unit. That had no effect.
2: A fairly complete recap. There are a couple of bipolar caps that I haven't change yet. This was the start of my current woes. Initially, I just changed the large filter caps and switched it on. The relay at this point started to click intermittently - i.e. every few times I turned it on. I bit the bullet and recapped pretty much everything else on the main board and tone control board. This also didn't help - in fact the relay stopped clicking completely.
3. I turned my attention to the relay circuit protection. I have replaced TR601 to TR606 with those suggested by Avionic here:
TR601 2SC1918
---2SC1918----sub KSC1815
http://www.mouser.com/ProductDetail...=sGAEpiMZZMshyDBzk1/Wi8oN7VHZ91Ok9NiSl87vuMg=
TR602 2SA844----sub KSA1015
http://www.mouser.com/ProductDetail...=sGAEpiMZZMshyDBzk1/Wi8oN7VHZ91OkEdHsVWhAnIo=
TR604 and TR601 are not differential pairs like 6 & 5 and 3 & 2, so I changed TR 604 for a KSC1815 the same as TR601 is.
It was at this point I screwed something up and TR606 shorted - the relay started clicking again every time I switched on the amp - but without a few seconds wait and with suitably large pop to the speakers (DC I assume). I swapped out TR606 for a replacement and the relay no longer clicks.
4. I swapped out TR806 and TR805 with replacement transistors.
Some Measurements:
TR01
E: 14.4 mv
C:1.17 vdc - which I suspect is cause of the problem. (or a symptom at least!)
B: 0 mv
TR02
E: 14.4 mv
C:25.2 vdc
B: 0 mv
TR06:
E: 35.8 vdc
C: 12.4 mv
B: 40.6 vdc
D01: is only 60 mv not 24 volts as I read somewhere it should be. I checked the diode and it is operational.
TR425 48.9 vdc
TR426 48.9 vdc
TR427 -48.9 vdc
TR428 -48.9 vdc
TR806 and TR805 are not giving off a stable 36 and -36 vdc.
806 (I think)
E:-39
C:-25 and
B:-40
805
E: 25
C: 39
B: 25
Bias is at 19mv for each channel.
Mid point is 0.00 for L & E and R & E.
A small victory: I managed to 'patch' the lamps and get them working again. I'm not sure if the board the lamps are on being cracked is adding to the problems stated here. There is a resister there that gets very hot indeed.
I admit my own poor soldering may well be the cause, although I've gone over it and re-soldered where I've thought there may be a cold solder. Also forgive me if I've missed off a negative from the above measurements.
Any help much appreciated!
(As an aside, I did get an Akai 2600 up and running with info from this site, so my recapping skills can't be too bad!)
Stuart
First, thanks for all the great information available on this site. I'm a complete novice to this vintage amp malarkey and so I've scoured it to find an answer to my woes - but to no avail.
I suppose first a little history. I picked this amp up and it sounded great! After about three months though, it would make a popping sound through the speakers and then play a lot quieter. (There is another post that sounded similar to this issue but nothing there I tried worked).
1. So, recommendation 1 always appears to be clean all the pots, so I did that. In fact I also did it when I first got the unit. That had no effect.
2: A fairly complete recap. There are a couple of bipolar caps that I haven't change yet. This was the start of my current woes. Initially, I just changed the large filter caps and switched it on. The relay at this point started to click intermittently - i.e. every few times I turned it on. I bit the bullet and recapped pretty much everything else on the main board and tone control board. This also didn't help - in fact the relay stopped clicking completely.
3. I turned my attention to the relay circuit protection. I have replaced TR601 to TR606 with those suggested by Avionic here:
TR601 2SC1918
---2SC1918----sub KSC1815
http://www.mouser.com/ProductDetail...=sGAEpiMZZMshyDBzk1/Wi8oN7VHZ91Ok9NiSl87vuMg=
TR602 2SA844----sub KSA1015
http://www.mouser.com/ProductDetail...=sGAEpiMZZMshyDBzk1/Wi8oN7VHZ91OkEdHsVWhAnIo=
TR604 and TR601 are not differential pairs like 6 & 5 and 3 & 2, so I changed TR 604 for a KSC1815 the same as TR601 is.
It was at this point I screwed something up and TR606 shorted - the relay started clicking again every time I switched on the amp - but without a few seconds wait and with suitably large pop to the speakers (DC I assume). I swapped out TR606 for a replacement and the relay no longer clicks.
4. I swapped out TR806 and TR805 with replacement transistors.
Some Measurements:
TR01
E: 14.4 mv
C:1.17 vdc - which I suspect is cause of the problem. (or a symptom at least!)
B: 0 mv
TR02
E: 14.4 mv
C:25.2 vdc
B: 0 mv
TR06:
E: 35.8 vdc
C: 12.4 mv
B: 40.6 vdc
D01: is only 60 mv not 24 volts as I read somewhere it should be. I checked the diode and it is operational.
TR425 48.9 vdc
TR426 48.9 vdc
TR427 -48.9 vdc
TR428 -48.9 vdc
TR806 and TR805 are not giving off a stable 36 and -36 vdc.
806 (I think)
E:-39
C:-25 and
B:-40
805
E: 25
C: 39
B: 25
Bias is at 19mv for each channel.
Mid point is 0.00 for L & E and R & E.
A small victory: I managed to 'patch' the lamps and get them working again. I'm not sure if the board the lamps are on being cracked is adding to the problems stated here. There is a resister there that gets very hot indeed.
I admit my own poor soldering may well be the cause, although I've gone over it and re-soldered where I've thought there may be a cold solder. Also forgive me if I've missed off a negative from the above measurements.
Any help much appreciated!
(As an aside, I did get an Akai 2600 up and running with info from this site, so my recapping skills can't be too bad!)
Stuart