Replacement output transistors for QL-600A

madders

Active Member
Hi,

Can anyone recommend which transistors to use to replace the 2sd234 output transitors on the power amp board in the QL-600a (AWH-005 - it's the same board in the SA-500a).

I already tried ksd526 but these don't sound good. It's very distorted unless I turn the idle current up to around 80mv, then the amp gets too hot.

I switched back the 2sd234s in one channel and idle drops to 20mv (without adjusting the trimpot) and it sounds good and runs cooler.

Thanks!
 
Thanks zebulon! I can give them a try but I don't have anything else to order so I have to pay £12 delivery. And I had to pay that when I ordered the ksd526s.
 
Nice little unit.
Interesting as to why? Toshiba 2SD234? ksd526 was a good choice. I do not know if TIP31A would be alright, even a MJE15032? I am not sure if I have even looked at a QL-600A, quad something, bootstrap Amp design. Yup a new one to me, AWH-005, now we are going back. Okay, single supply, ecap coupled to speaker.
Did you replace both o/p pair Q9,11(10,12) with the same part?
VR1,2 sets the center, symmetrical clipping on +/-
VR3,4 sets the bias as measured from TP1 to #6(TP2 to #7) 30mA * 0.5 = 15mV
 
Hi rcs

Nice little unit.
It's great. And it's not that little. It's only 10watts, but it's the same size as the SA-9100, they look great together. I love the VU meters.

Interesting as to why? Toshiba 2SD234? ksd526 was a good choice. I do not know if TIP31A would be alright, even a MJE15032?
I have no idea what's causing the problem. I could order both the TIP31A and MJE to try them both. What I noticed is that with the inputs from the tone amp board disconnected (or shorted to ground), the bias is significantly lower (from around 80mv down to 20mv). Also with the tone board connected, adjusting the treble all the way CCW or CW increases the idle to around 120mv (and the heatsink gets hot fast). When I retried with the original 2SD234s (you're right, they do say Tosihiba on them), connecting / disconnecting the inputs from the tone amp makes negligible difference (1-2mV) and same when adjusting the treble (seems to fluctuate a couple of mV then settle back at around 20mV). I don't kow if this makes sense, but it seems the KSD526 are much more sensitive to the small amount of current generated by the tone amp (but it's only a couple of transistors). This is with the volume all the way down, inputs and speakers disconnected.

Did you replace both o/p pair Q9,11(10,12) with the same part?
Yes. In fact I replaced all the BJTs on the board. I got the list from another thread on here somewhere:
Q1-4 KSC1845
Q5-6 KSC2383
Q7-8 KSA1013
Q9-12 KSD526

VR1,2 sets the center, symmetrical clipping on +/-
VR3,4 sets the bias as measured from TP1 to #6(TP2 to #7) 30mA * 0.5 = 15mV
Thanks! I got the procedure from zebulon about 12 months ago. The schematic I have shows 85mA on pin 8 so I've been adjusting the idle to about 21mV.
http://audiokarma.org/forums/index.php?threads/ql600a-alignment.810003/
 
I do like the look too, I guess I should say the little bro to my QX-9900 :) 85mA bias!
What I noticed is that with the inputs from the tone amp board disconnected (or shorted to ground), the bias is significantly lower (from around 80mv down to 20mv).
Interesting, does not sound like it should do this. I am guessing that you have some leakage in these coupling caps. Have you changed any, limited history? Was thinking to change them both to film or UKL, start with C1,2 on AWH-005(PA), see what that does
then possibly C7,8 on AWG-009(control) Once you are in there again, does it make sense to recap all?
 
The QX-9900 looks really nice, but it's huge!

Have you changed any, limited history? Was thinking to change them both to film or UKL, start with C1,2 on AWH-005(PA), see what that does
then possibly C7,8 on AWG-009(control) Once you are in there again, does it make sense to recap all?
Yes I already recapped the whole amp. I used WIMA MKS2 for C1 and C2 on AWH-005 and UPW for the rest of that board (I could change to UKL though if it will make a difference). On AWG-009 I used WIMA MKS2 for C7, C8 and C1, C2 and the rest UPW.

For the whole amp, I replaced the blue sanyo CSSA with either MKS2 or UKL, and the grey CEAs with UPWs.
 
Hi,

Can anyone recommend which transistors to use to replace the 2sd234 output transitors on the power amp board in the QL-600a (AWH-005 - it's the same board in the SA-500a).

I already tried ksd526 but these don't sound good. It's very distorted unless I turn the idle current up to around 80mv, then the amp gets too hot.

I switched back the 2sd234s in one channel and idle drops to 20mv (without adjusting the trimpot) and it sounds good and runs cooler.

Thanks!

Any of these TO-220 audio frequency amplifiers should work as they have Vcbo, Vceo, Pd, and Ic all meet or exceed that of the 2SD234:
  • MJE15034
  • MJE15032
  • MJE15030
  • MJE15028
  • BD809
  • TIP41C
  • TIP41BG
  • TIP31CG
  • TIP31BG
  • KSD526
  • KSD1408
The MJE150xx ones are probably the ones most-often-used for low power output transistors.

You may want to check the hfe gain code of the your 2SD234 devices and choose one of the above replacements and a gain code that meet or exceed that of the original device.

The fT is also a factor, but less so than the above parameters. If you get more than one potential match from above that have a matching or exceeding hfe, then you may want to choose the replacements that have a fT meeting or exceeding the 2SD234's 3 MHz fT.

Added note: you also want to find a replacement with a matching pinout, especially on devices that are attached to a heatsink. Those are often hard to twist the legs to fit the right PCB pinout.
 
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Thanks dlucy! I've taken a picture of the orignal 2sd234s:

20190202_161825.jpg

I think the O is the gain code (70-140). The KSD526s I ordered were Y (120-240). I didn't realise when I ordered them, but I see these are the only ones Mouser stock anyway. The Y have a higher hfe, so they should be okay? It's not easy to compare because it's a range, so does the replacement need to cover both the minimum and maximum values?

Does anyone know what other symbol means on the bottom right? The other two transistors are in the amp, but they have the same symbols (each slightly different). So 2 with one symbol (Q9/10?), and 2 with the other (Q11/12?). I didn't notice they were different when I took them out, so not sure which is which.
 
I think the O is the gain code (70-140). The KSD526s I ordered were Y (120-240). I didn't realise when I ordered them, but I see these are the only ones Mouser stock anyway. The Y have a higher hfe, so they should be okay? It's not easy to compare because it's a range, so does the replacement need to cover both the minimum and maximum values?

Yes, that trailing letter is often the gain code. I don't know if it is always the gain code, but in my experience it is most times the gain code.

Yes, a slightly higher gain code should be fine. In my amateur experience.
 
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