blowing rectifier valves - UK Vintage Radio Repair and Restoration Discussion Forum

newtube · 13th May 2009, 10:38 pm

Hello fella's,

I have just finished building a single end valve amp and encountered a problem

When i power the amp up all is fine for about 7 seconds and then the rectifier valve crackles and sparks, thus blowing the fuse i put in the iec socket.

All looks ok in the circuit and it seems to be wired correctly, what would cause this to happen gents?

Its fine with the rec valve removed, and i tried a different rec valve and the same happened.

Thanks,
Darran.

Steve_P · 13th May 2009, 10:43 pm

What valve is it?
Have you wired it right.
Are the smoothing caps in and are they OK?
Are the output valves (and others) OK and wired right.
Is the Mains Transformer OK and wired right.

Is it a kit or your own design?

Cheers,

Steve P.

Phil G4SPZ · 13th May 2009, 10:56 pm

It certainly sounds as though you may have a short-circuit across the rectifier valve output - 7 seconds is about the time it takes for the valve's heater to warm up and start passing current. Do as Steve P says and check the wiring very carefully.

newtube · 13th May 2009, 10:56 pm

Quote:

Originally Posted by Steve_P

What valve is it? JJ GZ34
Have you wired it right. Printed circuit board so ok there
Are the smoothing caps in and are they OK? all new and fitted well with correct polarity
Are the output valves (and others) OK and wired right. again, all new, 6l6gc.
Is the Mains Transformer OK and wired right. new hammond 373bx and seems wired corrctly

Is it a kit or your own design?

Based on a tubelab simple se board.

Thanks fella.

Cheers,

Steve_P · 13th May 2009, 11:01 pm

Take the other valves out and see if it does it. If it does then check for solder bridges, output transformer, coil in between smoothing caps, etc.

Then put the valves in (Output valve last) and see which stage (or stages) are causing this.

Cheers,

Steve P.

paulsherwin · 14th May 2009, 12:40 am

You almost certainly have a short circuit across the HT line. Valve rectifiers behave like this when subjected to serious overcurrent. Use a test meter to check the resistance - it should be very high.

Paul

Tim · 14th May 2009, 1:47 am

A 60 watt lightbulb in SERIES with the mains might limit the current enough for you to find the fault. If it glows brightly you have a problem.

Whaam68 · 14th May 2009, 7:06 am

Have you tried a different valve? I had something similar with a Russian valve that was duff.

HG MICKE · 14th May 2009, 8:03 am

Check the valve spec sheet,all valve rectifiers have a minimum anode limiter resistance.
This is measured from the anode to the centre tap of the transformer,add a fixed resistor in series with the anodes to bring the value up to the minimum qoted in the spec sheet.Also do not exceed the maximum reservoir capacitor value.

Colin

Heatercathodeshort · 14th May 2009, 8:43 am

We have all made mistakes when repairing or building electronic circuits. I would guess that this is a man made fault. First suspect is incorrect wiring to the main smoothing capacitor. If this is a printed circuit design, have you fitted it onto the board correctly?
Check the tag connections and make sure the negative tag goes to chassis and not the rectifier. What valves are used? I presume a valve rectifier such as the EZ81? Modern components often look similar. Daft I know but have you fitted a resistor into the position where a capacitor should be? I have been fooled by this in the past, even a diode?
You will need a very simple meter to trace this fault set on the standard ohms range. You will have to disconnect the supply from the rectifier cathode and check resistance to earth working through the choke/resistor smoothing arrangements and then on the the output stage. Possibly an incorrect connection on the output transformer? It appears to be a dead short so should be an easy one to trace. You will have to do it 'cold' to save whats left of the rectifier. Great suggestions from guys above. The use of a 60 watt bulb is a good investment. Hope you get it sorted. John.

newtube · 14th May 2009, 2:50 pm

Ok fella's, i have my meter working but i'm not sure where and what i should be looking for, or in fact how to use the meter properly

Can you give me some pointers in what to check and how. . . like you would for a five year old!

Thanks again,
Darran.

Station X · 14th May 2009, 2:58 pm

Set your meter to ohms and measure across the smoothing capacitors. The reading should be low initially as the capacitors charge and then rise to near infinity.

In your case you should find a low resistance and you'll then have to start disconnecting components to find where the problem is.

Posting a copy of the circuit would help.

Steve_P · 14th May 2009, 3:06 pm

Circuit and also both sides of the PCB. Then we can link the two.

Cheers,

Steve P.

Boom · 14th May 2009, 3:07 pm

Does the valve actually light up before the fireworks start? If not you might have the base wired incorrectly.

Steve_P · 14th May 2009, 3:16 pm

I wonder if he knows the difference between Directly and Indirectly heated cathodes? Looking back at the thread, he is using a GZ34 rectifier.

Data sheet for GZ34 here:

http://www.hifitubes.nl/weblog/wp-co...ilips-gz34.pdf

Cheers,

Steve P.

newtube · 14th May 2009, 3:27 pm

Quote:

Originally Posted by Steve_P

I wonder if he knows the difference between Directly and Indirectly heated cathodes? Looking back at the thread, he is using a GZ34 rectifier.

Data sheet for GZ34 here:

http://www.hifitubes.nl/weblog/wp-co...ilips-gz34.pdf

Cheers,

Steve P.

To answer that. . . . . . no mate.
I think i'm in above my head

newtube · 14th May 2009, 3:30 pm

Does this help guys?

http://www.tubelab.com/SimpleSE_schematic.htm
http://www.tubelab.com/SimpleSE_wiring.htm

Tim · 14th May 2009, 3:46 pm

Check you have both D1 and 2 round the correct way. Cathodes(the end with the bar) should be connected together.

Check wiring round rectifier valve(pinout etc. below) and for solder splats, bridges between tracks etc.I 'spose you have the valveholder soldered in the correct way round? Pin 8 should go to R2/C1/SW1

What happens if you use the semiconductor diode switch, (sw1)with the rectifier valve out and a lightbulb in series with the mains?

Valve pinout etc. here

http://www.r-type.org/exhib/aaa0997.htm

Good luck!

Steve_P · 14th May 2009, 3:50 pm

Pics of what you have made would come in handy too. Is that a home made PCB or one you bought?

Cheers,

Steve P.

Boom · 14th May 2009, 4:12 pm

What is the purpose of the weird arrangement with the diodes in parallel with the GZ34? This is the first time I have seen such a circuit and it's not something I would have thought suitable to chuck at a beginner.

13th May 2009, 10:38 pm	#1
newtube Triode Join Date: Mar 2009 Location: SHEFFIELD Posts: 38	blowing rectifier valves Hello fella's, I have just finished building a single end valve amp and encountered a problem When i power the amp up all is fine for about 7 seconds and then the rectifier valve crackles and sparks, thus blowing the fuse i put in the iec socket. All looks ok in the circuit and it seems to be wired correctly, what would cause this to happen gents? Its fine with the rec valve removed, and i tried a different rec valve and the same happened. Thanks, Darran.

13th May 2009, 10:43 pm	#2
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: blowing rectifier valves What valve is it? Have you wired it right. Are the smoothing caps in and are they OK? Are the output valves (and others) OK and wired right. Is the Mains Transformer OK and wired right. Is it a kit or your own design? Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

13th May 2009, 10:56 pm	#3
Phil G4SPZ Dekatron Join Date: Apr 2005 Location: Bewdley, Worcestershire, UK. Posts: 4,748	Re: blowing rectifier valves It certainly sounds as though you may have a short-circuit across the rectifier valve output - 7 seconds is about the time it takes for the valve's heater to warm up and start passing current. Do as Steve P says and check the wiring very carefully. __________________ Phil Optimist [n]: One who is not in possession of the full facts

13th May 2009, 11:01 pm	#5
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: blowing rectifier valves Take the other valves out and see if it does it. If it does then check for solder bridges, output transformer, coil in between smoothing caps, etc. Then put the valves in (Output valve last) and see which stage (or stages) are causing this. Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

14th May 2009, 12:40 am	#6
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,947	Re: blowing rectifier valves You almost certainly have a short circuit across the HT line. Valve rectifiers behave like this when subjected to serious overcurrent. Use a test meter to check the resistance - it should be very high. Paul

14th May 2009, 1:47 am	#7
Tim Dekatron Join Date: Jan 2003 Location: Bradford on Avon, Wiltshire, UK. Posts: 3,310	Re: blowing rectifier valves A 60 watt lightbulb in SERIES with the mains might limit the current enough for you to find the fault. If it glows brightly you have a problem. __________________ "Nothing is as dangerous as being too modern;one is apt to grow old fashioned quite suddenly."

14th May 2009, 7:06 am	#8
Whaam68 Hexode Join Date: Feb 2007 Location: Luton, Bedfordshire, UK. Posts: 456	Re: blowing rectifier valves Have you tried a different valve? I had something similar with a Russian valve that was duff.

14th May 2009, 8:03 am	#9
HG MICKE Pentode Join Date: Jul 2007 Location: London, UK. Posts: 165	Re: blowing rectifier valves Check the valve spec sheet,all valve rectifiers have a minimum anode limiter resistance. This is measured from the anode to the centre tap of the transformer,add a fixed resistor in series with the anodes to bring the value up to the minimum qoted in the spec sheet.Also do not exceed the maximum reservoir capacitor value. Colin

14th May 2009, 8:43 am	#10
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: blowing rectifier valves We have all made mistakes when repairing or building electronic circuits. I would guess that this is a man made fault. First suspect is incorrect wiring to the main smoothing capacitor. If this is a printed circuit design, have you fitted it onto the board correctly? Check the tag connections and make sure the negative tag goes to chassis and not the rectifier. What valves are used? I presume a valve rectifier such as the EZ81? Modern components often look similar. Daft I know but have you fitted a resistor into the position where a capacitor should be? I have been fooled by this in the past, even a diode? You will need a very simple meter to trace this fault set on the standard ohms range. You will have to disconnect the supply from the rectifier cathode and check resistance to earth working through the choke/resistor smoothing arrangements and then on the the output stage. Possibly an incorrect connection on the output transformer? It appears to be a dead short so should be an easy one to trace. You will have to do it 'cold' to save whats left of the rectifier. Great suggestions from guys above. The use of a 60 watt bulb is a good investment. Hope you get it sorted. John.

14th May 2009, 2:50 pm	#11
newtube Triode Join Date: Mar 2009 Location: SHEFFIELD Posts: 38	Re: blowing rectifier valves Ok fella's, i have my meter working but i'm not sure where and what i should be looking for, or in fact how to use the meter properly Can you give me some pointers in what to check and how. . . like you would for a five year old! Thanks again, Darran.

14th May 2009, 2:58 pm	#12
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: blowing rectifier valves Set your meter to ohms and measure across the smoothing capacitors. The reading should be low initially as the capacitors charge and then rise to near infinity. In your case you should find a low resistance and you'll then have to start disconnecting components to find where the problem is. Posting a copy of the circuit would help. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron. Last edited by Station X; 14th May 2009 at 5:07 pm. Reason: Self censorship.

14th May 2009, 3:06 pm	#13
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: blowing rectifier valves Circuit and also both sides of the PCB. Then we can link the two. Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

14th May 2009, 3:07 pm	#14
Boom Retired Dormant Member Join Date: Jan 2007 Location: Westbury, Wiltshire, UK. Posts: 2,451	Re: blowing rectifier valves Does the valve actually light up before the fireworks start? If not you might have the base wired incorrectly.

14th May 2009, 3:16 pm	#15
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: blowing rectifier valves I wonder if he knows the difference between Directly and Indirectly heated cathodes? Looking back at the thread, he is using a GZ34 rectifier. Data sheet for GZ34 here: http://www.hifitubes.nl/weblog/wp-co...ilips-gz34.pdf Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

14th May 2009, 3:30 pm	#17
newtube Triode Join Date: Mar 2009 Location: SHEFFIELD Posts: 38	Re: blowing rectifier valves Does this help guys? http://www.tubelab.com/SimpleSE_schematic.htm http://www.tubelab.com/SimpleSE_wiring.htm Last edited by Paul Stenning; 14th May 2009 at 6:59 pm. Reason: Link to files at original location to avoid copyright violation

14th May 2009, 3:46 pm	#18
Tim Dekatron Join Date: Jan 2003 Location: Bradford on Avon, Wiltshire, UK. Posts: 3,310	Re: blowing rectifier valves Check you have both D1 and 2 round the correct way. Cathodes(the end with the bar) should be connected together. Check wiring round rectifier valve(pinout etc. below) and for solder splats, bridges between tracks etc.I 'spose you have the valveholder soldered in the correct way round? Pin 8 should go to R2/C1/SW1 What happens if you use the semiconductor diode switch, (sw1)with the rectifier valve out and a lightbulb in series with the mains? Valve pinout etc. here http://www.r-type.org/exhib/aaa0997.htm Good luck! __________________ "Nothing is as dangerous as being too modern;one is apt to grow old fashioned quite suddenly." Last edited by Tim; 14th May 2009 at 3:54 pm.

14th May 2009, 3:50 pm	#19
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: blowing rectifier valves Pics of what you have made would come in handy too. Is that a home made PCB or one you bought? Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

14th May 2009, 4:12 pm	#20
Boom Retired Dormant Member Join Date: Jan 2007 Location: Westbury, Wiltshire, UK. Posts: 2,451	Re: blowing rectifier valves What is the purpose of the weird arrangement with the diodes in parallel with the GZ34? This is the first time I have seen such a circuit and it's not something I would have thought suitable to chuck at a beginner.