Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: rzenc on July 20, 2011, 02:42:10 pm
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I installed the attached circuit on a new amp. First power on, no problems...LED's lited...than I realised I forgot to groundthe circuit...So I grounded it and voila..magic smoke coming out of it... I immediately disconnected the whole relay supply in order to search for damaged stuffs... Holy crap I must Batman! 3 UF4007's just cracked...reservoir cap (4700uF @ 25V) smoked too... and everything seemed to be working so fine....I checked P.T. and it's working alright without the relay circuit. The only things connected were heater wiring and relay circuit - Heaters kept working alright after this...
Help please!!!! can't seem to find what's going on... All help is greatly appreciated and all ideas are welcome!!!
Thanks in advance
Best Regards
Rzenc
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Does the filament winding have a center tap that's connected to ground? If so you can't connect the bridge to ground also. Just let your relay power supply float or use a separate transormer.
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Does the filament winding have a center tap that's connected to ground? If so you can't connect the bridge to ground also. Just let your relay power supply float or use a separate transormer.
Oh man... It does have a CT on heater winding, which is grounded...
I have used this plan with 100R's as an artificial CT and no smoke... I will try it again floating.
Many thanks for your help!!!!!!
I will report back.
Thanks again.
Best regards
Rzenc
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Just let your relay power supply float .
Finally had time to mess with it again.., so relay P.S. is floating. LED's turn on, however relays aren't ticking...
I checked voltages and here is what I got:
With both LED's off and no relay on the socket I measured 8.7VDC @ second e-cap (100uF);
Turned on first LED - which should turn on relay for O.D. circuit and measured on the same node 4.9VDC, which happens to be exactly what I measured when switching O.D. off and turning LO END on, 4.9VDC.
I switched both circuits on and got 4VDC @ the same node.
Then I installed relay's - OMRON 5VDC relay. I measured 2.7 ~2.8 VDC drop on relay coil. I know they aren't ticking since I measured continuity between poles and there was no change on status of relay pins.
Should I raise available DC voltage to coils? Either by means of another AC supply – install a small P.T. – or drop first R value from 180ohms to – say – 100ohms?
Should the coils see full 5VDC in order to get activated?
I also raised second e-cap from 100uF to 3300uF and no change on the scenario, except that LED’s were glowing brighter.
Thanks in advance!
Best Regards,
Rzenc
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Just put a shorting jumper across that first resistor and see if the relays will energize. Relay coils are more about current than a specific voltage. Measure the voltage across the coil when both relays are energized just for reference. It's OK if it's a little high or low.
Relays require more current (or voltage) to actually 'pull in' than required to stay pulled in. IOW, it may take 4 to 5 volts to energize a relay but once energized, it may only take 2 or 3 volts to stay energized.
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180 ohms seems a bit low, too, for the LED dropping resistor. I'd probably use at least a 470 to 1k ohm there.
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180 ohms seems a bit low, too, for the LED dropping resistor.
Good point.
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Just put a shorting jumper across that first resistor and see if the relays will energize. Relay coils are more about current than a specific voltage. Measure the voltage across the coil when both relays are energized just for reference. It's OK if it's a little high or low.
Relays require more current (or voltage) to actually 'pull in' than required to stay pulled in. IOW, it may take 4 to 5 volts to energize a relay but once energized, it may only take 2 or 3 volts to stay energized.
180 ohms seems a bit low, too, for the LED dropping resistor.
Good point.
Got home now... I will try it and report back.
Many thankz!!!!
Best Regards
Rzenc
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Ok, so I changed LED dropping resistor from 180R to 1K. Voltage available raised a bit. It’s @ 8.85VDC right @ relay socket. LED’s are not so bright as before. When O.D. relay is engaged, voltage drop across it’s coil measures 3.19VDC…Relay’s are not ticking yet….
Next, I installed a jumper to bypass 180R and when turning on circuit it shows a 7.31VDC drop across relay coil, but still no joy…
I measured continuity between relay pins so know if it was engaging or not…
Is there something else left to try?
I updated the schema in order to show how it's actually wired.
All help welcome!! :worthy1:
Thanks in advance,
Best Regards
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OMRON 5VDC relay
There are a bunch of different 5v relays. Which relay do you have? What physical size? Can you post a pic? Measure the actual coil resistance. How many ohms?
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Stamped Code on relay side: 11Z8YH
OMRON G5A-234P
RESISTIVE:
0.5A 60VAC; 0.5A 60VDC
5VDC
COIL RESISTANCE: 126.6 measured directly on relay pins
Many thanks for your help Steve!
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That relay only needs 40mA at 5v to operate. Are you sure its not energizing? You probably can't hear it click. Try this... Put the tip of a long skinny screwdriver on the relay and put the end of the handle in your ear. Operate the relay. Do you hear/feel it click?
Or, connect your ohm meter to pins 3 and 6 (common and normally open contacts). Should read open. Operate the relay. Should read zero.
If it still ain't working there's something simple that's wrong, ie, maybe diode is backward, or wiring error, or you mis-identified the pins. Verify it's wired IAW the attached pic...
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Are your jacks grounded? (They can't be.)
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Are your jacks grounded? (They can't be.)
Jack's are referenced to floating ground - it's neutrik plastic cliff type jacks.
Sluckey:
I have triple checked everything but will do once again as I arrive home, not in town today
Many thanks for the help guys!!!
Best regards
Rzenc
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Have you checked the orientation of your snubber diodes?
Jim
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Finally got time to try to solve this...
Have you checked the orientation of your snubber diodes?
Jim
Would it damage the relay if I take out the diode just to try to energize it and check if it's clicking?
TiA
Best Regards
Rzenc
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No, it shouldn't damage it at all to test.
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No, it shouldn't damage it at all to test.
Thanks jojokeo!
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If you have the diodes backwards, the relays will never engage - and might explain the strange voltage drops you are seeing.
Good luck!
Jim
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:think1:
I found 1 problem!!! I reversed supply wires to relays pins... after much observation, the drawing Steve posted came to my mind and I saw my mistake... :BangHead: I was returning the + side of the relay coil to ground... duhhh....
I'm still working and have something bizarre going on... keep ya posted!!
Many thanks for all the help provided by all of you!!!!!
Best Regards friends
Rzenc
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I was returning the + side of the relay coil to ground... duhhh....
That's not a problem. That relay coil doesn't care which direction current flows. The relay itself is not polarized. The polarity markings on that drawing are for convention only. But, that will kill the diodes, likely fail shorted.
HOWEVER, you must connect the cathode of the despiking diode to the same side of the coil that you connect the positive voltage. The diode is totally unnecessary to the relay operation. It's sole purpose is to kill the CEMF that is developed by the coil when current is switched off. That CEMF will likely cause a popping sound in your amp without the diode. In digital circuits, it can cause all kind of problems.
Did you ever try the ohm meter check? The relay circuit is really very simple. Just like a flashlight, turn the switch on lights up (energizes). Turn the switch off, it goes dark, (de-energizes).
Try this... Steal a fresh 9volt battery from a stompbox. Connect the battery, the relay coil, a switch, and a 80Ω resistor in series. Test by operating the switch. If you can't hear a click, use an ohm meter to check contact operation.
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I was returning the + side of the relay coil to ground... duhhh....
That's not a problem. That relay coil doesn't care which direction current flows. The relay itself is not polarized. The polarity markings on that drawing are for convention only. But, that will kill the diodes, likely fail shorted.
HOWEVER, you must connect the cathode of the despiking diode to the same side of the coil that you connect the positive voltage. The diode is totally unnecessary to the relay operation. It's sole purpose is to kill the CEMF that is developed by the coil when current is switched off. That CEMF will likely cause a popping sound in your amp without the diode. In digital circuits, it can cause all kind of problems.
Did you ever try the ohm meter check? The relay circuit is really very simple. Just like a flashlight, turn the switch on lights up (energizes). Turn the switch off, it goes dark, (de-energizes).
Try this... Steal a fresh 9volt battery from a stompbox. Connect the battery, the relay coil, a switch, and a 80Ω resistor in series. Test by operating the switch. If you can't hear a click, use an ohm meter to check contact operation.
Well, I tried reversing diodes but it did no good...I noted that cathode show point to the positive side of the coil...but it did not work - even with diodes pointing 'right and wrong' - but when I swithced the wires around (+ diode) it worked... :w2:
I decided to build a protoboard to solve it...now I can get both relays to work, but no simultanimously.. when I engage only 1 relay it works beautiful, but when I engage the other, the first relay open the contacts... no matter which way I engage them first... Do I need more voltage to operate them?
I will measure voltages around the circuit ASAP and post them... Hope to solve it soon... :cry:
I tried the 9V battery trick and it worked with 1 relay..then I assembled it on the power supply intended for it's operation and I'm getting the expected results, but the damn relay open it's contacts when the other is engaged...
Many thanks!!!
Best Regards
Rzenc
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After re-reading this entire topic, I changed the power supply node and voila...both relays working.. and they kept engaged when kicking the other relay into operation!!!!
I redraw the schem as it is now...it's still in the protoboard.. When I come back home I will proceed to the amp itself...
I would like to thank all for your kind attention and help!!!!!!!!!!!!!!!!!!!!!!!! :worthy1: :worthy1: :worthy1: :worthy1: :worthy1: :worthy1:
If we were close I would invite you all for beer!!! :occasion14: :d2: :thumbsup:
Just hope the amp cooperates now..
Many thanks guys!!!!
Best Regards
Rzenc
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rzence, could you add part numbers to your relay schem for the relays that you're using? I'd like to save it for future reference. Thx, J
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Here it is bro!
If you use this circuit, let me know how it turns out.
Best Regards
Rzenc
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Glad to hear you got it working rzenc. :icon_biggrin:
So you took out the 180 dropping R and 2'nd E. cap? The dropping R was dropping too much voltage to the relay?
What was the voltage at the 2'nd E. cap?
Thanks, Brad :think1:
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Thanks!!!