Quad 405 /AM8/16 - UK Vintage Radio Repair and Restoration Discussion Forum

reddish75 · 2nd Feb 2017, 6:54 pm

Hi,

One of my quad am8/16's has develop a buzz annoyingly I've tracked it down to the am8/16 card by pulling the power to it, no buzz through the 405 cards when I have done this, apply power back to the am8 board and buzz,.

So question is does anyone in the know have any subs for the transistors which are, bc414b and the 2n3702?

Thanks

Chris

mhennessy · 2nd Feb 2017, 7:27 pm

The transistor types aren't critical, so there are many possible substitutions. I forget what I used in the clones I built 15+ years ago, but possibilities include BC107 and BCY71, BC548 and BC558, BC337 and BC327.

However, I'd be amazed if they are at fault. I'd be suspecting capacitors first of all.

reddish75 · 2nd Feb 2017, 8:47 pm

Hi Mark

All electro and tant caps have been replaced I would reckon the rest reliable enough, back to the transistors, what about the bc550 or the 560?

nutteronthebus · 2nd Feb 2017, 9:17 pm

Hi Chris I can let you have a few spare BC550 for postage

Dave

mhennessy · 3rd Feb 2017, 12:55 am

Yes, BC550/560 are fine...

I've serviced many of these, and have only ever changed the 2 electrolytics on the crossover PCB - I've never had a tant fail. And TBH, I've only changed those caps because it made sense to do so while it was all apart - the hum has always come from the Quad 405 boards. Obviously, YMMV.

The regulator transistor (TR11) runs slightly warm, so it might be worth looking at that. Popping a 'scope across the 30V rail will show up any ripple. If needed, the BFX85 is available from Rapid Electronics, but again, it's not critical and there are many equivalents that would do the job. I always check the series resistor (R37), as that runs hot, but although normally a bit discoloured with age, it's always within spec. I replace it with a bigger one, spaced away from the board.

Good luck!

2nd Feb 2017, 6:54 pm	#1
reddish75 Hexode Join Date: Nov 2010 Location: Manchester, UK. Posts: 251	Quad 405 /AM8/16 Hi, One of my quad am8/16's has develop a buzz annoyingly I've tracked it down to the am8/16 card by pulling the power to it, no buzz through the 405 cards when I have done this, apply power back to the am8 board and buzz,. So question is does anyone in the know have any subs for the transistors which are, bc414b and the 2n3702? Thanks Chris

2nd Feb 2017, 7:27 pm	#2
mhennessy Dekatron Join Date: Jul 2007 Location: Evesham, Worcestershire, UK. Posts: 4,244	Re: Quad 405 /am8/16 The transistor types aren't critical, so there are many possible substitutions. I forget what I used in the clones I built 15+ years ago, but possibilities include BC107 and BCY71, BC548 and BC558, BC337 and BC327. However, I'd be amazed if they are at fault. I'd be suspecting capacitors first of all.

2nd Feb 2017, 8:47 pm	#3
reddish75 Hexode Join Date: Nov 2010 Location: Manchester, UK. Posts: 251	Re: Quad 405 /am8/16 Hi Mark All electro and tant caps have been replaced I would reckon the rest reliable enough, back to the transistors, what about the bc550 or the 560? Last edited by reddish75; 2nd Feb 2017 at 9:01 pm.

2nd Feb 2017, 9:17 pm	#4
nutteronthebus Hexode Join Date: Jun 2011 Location: Glossop, Derbyshire, UK. Posts: 487	Re: Quad 405 /am8/16 Hi Chris I can let you have a few spare BC550 for postage Dave __________________ Any tool can be used as a hammer but a screwdriver makes the best chisel

3rd Feb 2017, 12:55 am	#5
mhennessy Dekatron Join Date: Jul 2007 Location: Evesham, Worcestershire, UK. Posts: 4,244	Re: Quad 405 /AM8/16 Yes, BC550/560 are fine... I've serviced many of these, and have only ever changed the 2 electrolytics on the crossover PCB - I've never had a tant fail. And TBH, I've only changed those caps because it made sense to do so while it was all apart - the hum has always come from the Quad 405 boards. Obviously, YMMV. The regulator transistor (TR11) runs slightly warm, so it might be worth looking at that. Popping a 'scope across the 30V rail will show up any ripple. If needed, the BFX85 is available from Rapid Electronics, but again, it's not critical and there are many equivalents that would do the job. I always check the series resistor (R37), as that runs hot, but although normally a bit discoloured with age, it's always within spec. I replace it with a bigger one, spaced away from the board. Good luck!