You have to be accurate and meticulous with this sort of thing.
If you get a short in the wrong place you can easily burn out the HT winding on the power transformer or damage the rec tube. You should check all connections twice before power up.
You have no discharge protection on this amp!
Put a 2 Watt 470K 500v from the 330uf positive to ground it will run warm but it gives a leakage after power off. Don't put it across the 47uF..
Make sure the EL34 bias voltage across the cathode resistors is correct..before you run it long term.
I guess the chassis is earthed<<just checking..
I'll step back now because I'm dominating the thread...have fun..
Regards
M. Gregg
If you get a short in the wrong place you can easily burn out the HT winding on the power transformer or damage the rec tube. You should check all connections twice before power up.
You have no discharge protection on this amp!
Put a 2 Watt 470K 500v from the 330uf positive to ground it will run warm but it gives a leakage after power off. Don't put it across the 47uF..
Make sure the EL34 bias voltage across the cathode resistors is correct..before you run it long term.
I guess the chassis is earthed<<just checking..
I'll step back now because I'm dominating the thread...have fun..
Regards
M. Gregg
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Brill all working and getting stereo. Running through a pair of very old Keith Monks Elfs is adequately loud and sounds not at all bad.
Thank you everyone especially M Gregg for teaching me how to debug a valve circuit. memo to self for next project use a parallel tag strip it makes circuit tracing easier, also build both sides absolutely symmetrical again this makes tracing and fault finding easier.
Now to start playing with this to see what changes different valves make and whether there are significant improvements to be made changing coupling capacitors! Any suggestions of what to try first most welcome.
Thanks again!
Avo 111
Thank you everyone especially M Gregg for teaching me how to debug a valve circuit. memo to self for next project use a parallel tag strip it makes circuit tracing easier, also build both sides absolutely symmetrical again this makes tracing and fault finding easier.
Now to start playing with this to see what changes different valves make and whether there are significant improvements to be made changing coupling capacitors! Any suggestions of what to try first most welcome.
Thanks again!
Avo 111
M.Gregg,
Thanks. As for discharge what I have been doing is using my meter to discharge watching the voltage drop off. The problem isn't the power supply caps, these seem to discharge pretty quickly. The coupling caps however seem to have voltages well over 110 V on power down!
Chassis is earthed and there was also a random green and yellow wire from the mains transformer so I bolted this to chassis ground. The signal ground is connected to chassis ground only at one point in the middle of the tag strip close to where the transformer grounds and output transformer grounds are connected.
AVO111
Thanks. As for discharge what I have been doing is using my meter to discharge watching the voltage drop off. The problem isn't the power supply caps, these seem to discharge pretty quickly. The coupling caps however seem to have voltages well over 110 V on power down!
Chassis is earthed and there was also a random green and yellow wire from the mains transformer so I bolted this to chassis ground. The signal ground is connected to chassis ground only at one point in the middle of the tag strip close to where the transformer grounds and output transformer grounds are connected.
AVO111
The PSU caps will discharge because the tubes are conducting, however if ever the tubes don't warm up and conduct for some reason or you ever power it up with the tubes removed the PSU caps will hold charge..the meter is OK but if you forget and most people do even to the next day and get a shock..the coupling caps my give you a tingle but the PSU caps can deliver current that can kill you.
The higher the capacitance in the PSU the more dangerous it is..high voltage is bad, high voltage with current is lethal.
NB you should always test with a meter before you touch anything as a matter of good practice. PSU caps in HV situations can also recharge after initial discharge even when the unit is off due to dielectric absorption the Bleed/discharge resistor prevents this..
Regards
M. Gregg
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Yes I totally agree! having spent many years around three phase temporary supplies the meter is always out before I touch ANYTHING electrical that has been is or could have been connected to anything! It is the things that seem innocuous that can surprise or even kill you. My closest to death experience involved a 110V DC shock to earth across my chest from a totally surprising switch that was very faulty! I still have the scar and a good story!
I will get around to putting a resistor across that cap need a visit to Maplins first!
The amp has a habit of dropping the right channel for no apparent reason once it has been running for a while . Switching off and on again clears it for a bit. Grrr! I didn't think this was a microsoft design
AVO 111
I will get around to putting a resistor across that cap need a visit to Maplins first!
The amp has a habit of dropping the right channel for no apparent reason once it has been running for a while . Switching off and on again clears it for a bit. Grrr! I didn't think this was a microsoft design
AVO 111
The amp has a habit of dropping the right channel for no apparent reason once it has been running for a while . Switching off and on again clears it for a bit. Grrr! I didn't think this was a microsoft design
Probably worth re-soldering the connections on that channel in case you have a dry joint. The other possibility is a short that is expanding with temperature.
The maplin 500v MF 470K will work fine..
http://www.maplin.co.uk/p/metal-film-2w-470k-ohm-resistor-d470k
The two worse shocks I have had are one off the anode cap of a B/W CRT <<good job it was Black and White..trying to look at the screen while adjusting in the back<<hadn't got a mirror on site at the time!
The other was two phases on 440V AC but not a across the chest..A set of slip rings hidden inside old rotating equipment from a different supply not the one with LOTO fitted. Dropped a spanner and reached into get it out! didn't even know they were there.. both threw me off the equipment and knocked me sick for about an hour..but you survive if you are lucky..It was many years ago...I find I'm very very cautious now..if it can happen it probably will happen!
Regards
M. Gregg
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It's amazing what shocks we survive
Regards
AVO111
Have fun..test before you touch.
Regards
M. Gregg
That was a nasty shock you received. Sometimes we tend to overlook and incident happened without knowing. We got to concentrate and check carefully.
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