Quad 33/405 Issues - UK Vintage Radio Repair and Restoration Discussion Forum

Bookman · 6th Mar 2018, 2:42 pm

I chanced upon a 405 plus 2 x 33PAs plus an FM3 and was advised that there was a hum associated with them. Just connecting a pair of speakers and a reduced Voltage to the 405 resulted immediately in a loud hum to both speakers.
Changing C5 & C10 on both channels cured this immediately. I then tried one of the 33s with a CD input and after needing to spray the pots I thought what a nice sound. The second 33 is however a problem in that there is a loud hum when this is connected.
Without any checking and without any diagrams I noticed that the brown square component with textured leads connected across the on/off switch is quite visibly cracked. I presume this is a surge arrestor of some description but I am loathed to unsolder it and see if the problem remains.
Does anyone have any comments?

The FM3 works fine but I lost my patience trying to remove one of the indication bulbs. It seems the holders are difficult to get so my question is has anyone pursued an LED mod?

nutteronthebus · 6th Mar 2018, 4:38 pm

Hi DADA have all the diagrams you need plus they do an upgrade kit for the 33 pre amp. I have changed the lamps on the FM3 ( the one for the dial illumination for a LED ) the other ones I got the lamps from Maplin

but they have now gone bust. The RIFA cap across the mains switch needs to be replaced (search RIFA X2 ) http://www.dadaelectronics.eu/Home.htm

Dave

nutteronthebus · 6th Mar 2018, 4:44 pm

Also there are two resistors on the 405 board that feed the input op-amp (R7, R8 3.3k). They are underrated (0.45W into 0.25W resistor). When they burn out (not if), it takes out the output and driver transistors. Replace them and space them off the board.
(ii) the ROE electrolytic caps on the 405 board should be replaced. One sits above a very hot resistor, and will be cooked, probably with a cracked and browned case. Fit the replacement on the other side of the board to keep it out the way of the resistor.

teetoon · 6th Mar 2018, 5:11 pm

The 33 hum won't be caused by the mains filter cap.
The brown ones don't usually give a problem, but then again they are quite old now, it's the Rifa caps that are soldered directly on the back of the switch that usually split or go pop and make a nasty mess and smell.
I removed the cap in mine when it showed signs of splitting and never bothered to replace it.

The hum is more than likely failed smoothing caps in the power supply. They will be quite old by now and Quad were reknowned for their low spec components

David..

Bookman · 6th Mar 2018, 7:45 pm

Many thanks to all of the feedback. I noticed how some of the soldering especially around the resistors alluded to had in fact been warm at some time and had given the appearance of a dry joint.
One thing that alarmed me the most; if not eerily was how silent the system was with the 405 and 33 both energised and the CD powered up. I inserted the cd and within seconds the music started. Never before have I come across such a hifi set up.
Regards
Joe

Ted Kendall · 6th Mar 2018, 9:15 pm

Quote:

Originally Posted by teetoon

The hum is more than likely failed smoothing caps in the power supply. They will be quite old by now and Quad were reknowned for their low spec components

Whoever set this hare running needs a dose of common sense. Granted, the odd resistor was under-rated and some electrolytics fail after twice the design life of the unit. The fact that there are a few stock faults is testament to their general reliability - and most of the competition isn't still around to be afflicted by these maladies. The component quality was well up to contemporary standards, and it's only the longevity and utility of these products which has made it any sort of issue, But then success always attracts knockers...

teetoon · 6th Mar 2018, 9:27 pm

Well I wasn't knocking Quad at all as someone who owns 2x 33's 3x FM3's 2x 303's and a 405, I love em.
But there seem to be a lot of problems with caps, and those resistors you mention were definitely down to penny pinching.

No offence meant anyway

David.

Ted Kendall · 6th Mar 2018, 10:44 pm

None taken. and nothing personal - it's just that this refrain is so common and for the most part so ill-founded. Given that Peter Walker himself reckoned that ten years was a fair life for a Quad product, it is pretty remarkable that many a fifty (or more) year old veteran can be brought back to spec with relative ease. OK, it is a pain that the 303 only works as intended with 3055s so slow as to be unobtainable, but this was a very elegant design in its day - fifty years ago this year! - and the first transistor amplifier to show a clean pair of heels to valve types in all respects. To castigate Walker for not driving his crystal ball with due care and attention borders on the daft.

I remember when the mains tranny went on my FM4 - I wound up the lady on the Quad end of the 'phone with "well this is dreadful - the thing's only been running twelve years!" She either thought it a great joke or had the grace to laugh anyway...

My tally is 2x33, 303, FM3, 405/2, 44, 2x34, FM4...so perhaps I am already daft!

6th Mar 2018, 2:42 pm	#1
Bookman Hexode Join Date: Aug 2017 Location: Taunton, Somerset, UK. Posts: 318	Quad 33/405 Issues I chanced upon a 405 plus 2 x 33PAs plus an FM3 and was advised that there was a hum associated with them. Just connecting a pair of speakers and a reduced Voltage to the 405 resulted immediately in a loud hum to both speakers. Changing C5 & C10 on both channels cured this immediately. I then tried one of the 33s with a CD input and after needing to spray the pots I thought what a nice sound. The second 33 is however a problem in that there is a loud hum when this is connected. Without any checking and without any diagrams I noticed that the brown square component with textured leads connected across the on/off switch is quite visibly cracked. I presume this is a surge arrestor of some description but I am loathed to unsolder it and see if the problem remains. Does anyone have any comments? The FM3 works fine but I lost my patience trying to remove one of the indication bulbs. It seems the holders are difficult to get so my question is has anyone pursued an LED mod?

6th Mar 2018, 4:38 pm	#2
nutteronthebus Hexode Join Date: Jun 2011 Location: Glossop, Derbyshire, UK. Posts: 487	Re: Quad 33/405 Issues Hi DADA have all the diagrams you need plus they do an upgrade kit for the 33 pre amp. I have changed the lamps on the FM3 ( the one for the dial illumination for a LED ) the other ones I got the lamps from Maplin but they have now gone bust. The RIFA cap across the mains switch needs to be replaced (search RIFA X2 ) http://www.dadaelectronics.eu/Home.htm Dave __________________ Any tool can be used as a hammer but a screwdriver makes the best chisel

6th Mar 2018, 4:44 pm	#3
nutteronthebus Hexode Join Date: Jun 2011 Location: Glossop, Derbyshire, UK. Posts: 487	Re: Quad 33/405 Issues Also there are two resistors on the 405 board that feed the input op-amp (R7, R8 3.3k). They are underrated (0.45W into 0.25W resistor). When they burn out (not if), it takes out the output and driver transistors. Replace them and space them off the board. (ii) the ROE electrolytic caps on the 405 board should be replaced. One sits above a very hot resistor, and will be cooked, probably with a cracked and browned case. Fit the replacement on the other side of the board to keep it out the way of the resistor. __________________ Any tool can be used as a hammer but a screwdriver makes the best chisel

6th Mar 2018, 5:11 pm	#4
teetoon Heptode Join Date: Dec 2010 Location: Barnstaple, N.Devon, UK. Posts: 557	Re: Quad 33/405 Issues The 33 hum won't be caused by the mains filter cap. The brown ones don't usually give a problem, but then again they are quite old now, it's the Rifa caps that are soldered directly on the back of the switch that usually split or go pop and make a nasty mess and smell. I removed the cap in mine when it showed signs of splitting and never bothered to replace it. The hum is more than likely failed smoothing caps in the power supply. They will be quite old by now and Quad were reknowned for their low spec components David..

6th Mar 2018, 7:45 pm	#5
Bookman Hexode Join Date: Aug 2017 Location: Taunton, Somerset, UK. Posts: 318	Re: Quad 33/405 Issues Many thanks to all of the feedback. I noticed how some of the soldering especially around the resistors alluded to had in fact been warm at some time and had given the appearance of a dry joint. One thing that alarmed me the most; if not eerily was how silent the system was with the 405 and 33 both energised and the CD powered up. I inserted the cd and within seconds the music started. Never before have I come across such a hifi set up. Regards Joe

6th Mar 2018, 9:27 pm	#7
teetoon Heptode Join Date: Dec 2010 Location: Barnstaple, N.Devon, UK. Posts: 557	Re: Quad 33/405 Issues Well I wasn't knocking Quad at all as someone who owns 2x 33's 3x FM3's 2x 303's and a 405, I love em. But there seem to be a lot of problems with caps, and those resistors you mention were definitely down to penny pinching. No offence meant anyway David.

6th Mar 2018, 10:44 pm	#8
Ted Kendall Dekatron Join Date: Jul 2008 Location: Kington, Herefordshire, UK. Posts: 3,670	Re: Quad 33/405 Issues None taken. and nothing personal - it's just that this refrain is so common and for the most part so ill-founded. Given that Peter Walker himself reckoned that ten years was a fair life for a Quad product, it is pretty remarkable that many a fifty (or more) year old veteran can be brought back to spec with relative ease. OK, it is a pain that the 303 only works as intended with 3055s so slow as to be unobtainable, but this was a very elegant design in its day - fifty years ago this year! - and the first transistor amplifier to show a clean pair of heels to valve types in all respects. To castigate Walker for not driving his crystal ball with due care and attention borders on the daft. I remember when the mains tranny went on my FM4 - I wound up the lady on the Quad end of the 'phone with "well this is dreadful - the thing's only been running twelve years!" She either thought it a great joke or had the grace to laugh anyway... My tally is 2x33, 303, FM3, 405/2, 44, 2x34, FM4...so perhaps I am already daft! Last edited by Ted Kendall; 6th Mar 2018 at 10:51 pm.