As always an interesting video Stuart. The odd heater wire arrangement might have been something to do with lowering the current through the PCB tracks. Great fix that's bound to please your customer.
Stuart, Another interesting dive into an amp with issues. It seems to me that some manufacturers want to find ways to complicate things. This heater supply could have been done much easier. What do i know! Seemed like an easy fix.
There are 2 connectors to halve the current going through the connectors. I've had problems with heater connectors on PCB's before. If the connection is not perfect they heat up and can damage the PCB or the connector itself. It looked like the cables on the faulty connector were showing heat damage implying a bad connection.
This. The wires on the faulty side were very dark where they met the connector. It sure looked like heat damage. Halving the current is a good idea. Not routing heaters on the PCB is a better one.
@Splattle101 On the amplifier I worked on, I moved the heater wires from the PCB to small terminal blocks that were rated for the heater current, which is usually relatively high.
@@stuartukguitarampguy5830 I think this connection is underestimated by the design engineers. I took the heater cables off board and fed them through small high quality 10A spring terminal connectors. Our advantage is that the material cost for us to provide a slightly overrated but 100% reliable solution is not as relevant as the design engineers who have to try and supply a cost effective solution. Have a great weekend Stuart
Hello Stuart. What a bazaar way to wire the heaters. What were they thinking when the designed that one. . That's an impressive stash of control knobs. Take care Sturat.
great vid, did you ensure that the two heater branch's have the same end of the winding to pin 9 of the ECC valves, this can add hum if they are out of 0hase with each other. grwat vid.
STUART UK, How can you measure the tubes Transconductance in-circuit? The transconductance is the tubes GAIN at a certain Bias voltage. Do the transconductance formula would be Plate Current / divided by the Grids Bias Voltage = Transconducance?
I'm not sure why you'd ever want to do this? If you mean how to measure the gain of a stage, then I'd just use a scope on the inout and the output and calculate it.
@@stuartukguitarampguy5830 Some tube testers will have a transconductance test but its in siemen units, not in dB gain. I'm not sure why its in siemen units?
@@waynegram8907 Hi Wayne. TYhis is all a bit esoteric and not useful for practical amplifier repairs. I don;t even own a tube tester! I'm wondering why you are asking.
@@stuartukguitarampguy5830 Just asking if the transconductance is "factored into" the biasing of the output tubes? because I'm not sure why some tube testers measure the transconductance it must be for reasons which I'm not sure what they are.
@@waynegram8907 Transconductance is the gain of the tube. E.g. x100 or whatever. The bias is just the steady state DC bias required to get the valve to 'tickover'.
That's an interesting failure. I suspect they may have done the parallel tube heater wiring to reduce hum or something along those lines. Question is how/why did that fail?
@@stuartukguitarampguy5830 Seems to be some kind of unusual connector that is soldered directly to the PCB in lieu of just soldering wires directly to the board. Probably the contact to the wire inside failed... came loose or maybe the contact got oxidized. Don't know why they designed it that way... not very bulletproof in the long term.
I'm sure loads of people would provide the answer but I'll be the first. The heater supply is a.c. so it isn't critical which way round it's connected. The only issue is, there may be a slight him if the phase is incorrect.
I have known heater pcb tracks to fail. They are not up to the current carrying capacity over a long period of time or they blow if a heater fails. Never had this issue with the old point to point wiring.
Yes that makes sense but these heaters were carried by those thin yellow wires. I guess it could have been the short length of track. Not sure without taking the board out.
One of my always look for new uploads
Thanks James
Nicely spotted and good fix..cheers
Hi Richard Yes I got lucky spotting that early on.
Stuart does it again..Great job and great video as always.😊
Cheers Darrel.
Hi Stuart.. Excellent catch and repair..😊 Ed..UK..😊
Cheers Edward
As always an interesting video Stuart. The odd heater wire arrangement might have been something to do with lowering the current through the PCB tracks. Great fix that's bound to please your customer.
Yes defintely an odd one. Someone else has mentioned that maybe the two heater circuits are out of phase to reduce hum or something? Not really sure.
Stuart,
Another interesting dive into an amp with issues. It seems to me that some manufacturers want to find ways to complicate things. This heater supply could have been done much easier. What do i know!
Seemed like an easy fix.
Hi Michael. Yes it seemed overly complicated to split the heaters into two lots like that.
Thanks! Great work, Sir.
Thanks Tommy
There are 2 connectors to halve the current going through the connectors. I've had problems with heater connectors on PCB's before. If the connection is not perfect they heat up and can damage the PCB or the connector itself. It looked like the cables on the faulty connector were showing heat damage implying a bad connection.
This. The wires on the faulty side were very dark where they met the connector. It sure looked like heat damage. Halving the current is a good idea. Not routing heaters on the PCB is a better one.
@Splattle101 On the amplifier I worked on, I moved the heater wires from the PCB to small terminal blocks that were rated for the heater current, which is usually relatively high.
Ah ok. What a rubbish design though!
@@stuartukguitarampguy5830 I think this connection is underestimated by the design engineers. I took the heater cables off board and fed them through small high quality 10A spring terminal connectors. Our advantage is that the material cost for us to provide a slightly overrated but 100% reliable solution is not as relevant as the design engineers who have to try and supply a cost effective solution. Have a great weekend Stuart
Hello Stuart. What a bazaar way to wire the heaters. What were they thinking when the designed that one. . That's an impressive stash of control knobs. Take care Sturat.
Yes very odd! Thanks for watching.
great vid, did you ensure that the two heater branch's have the same end of the winding to pin 9 of the ECC valves, this can add hum if they are out of 0hase with each other. grwat vid.
Oooo, I didn't tbh. Seemed ok though.
STUART UK, How can you measure the tubes Transconductance in-circuit? The transconductance is the tubes GAIN at a certain Bias voltage. Do the transconductance formula would be Plate Current / divided by the Grids Bias Voltage = Transconducance?
I'm not sure why you'd ever want to do this? If you mean how to measure the gain of a stage, then I'd just use a scope on the inout and the output and calculate it.
@@stuartukguitarampguy5830 Some tube testers will have a transconductance test but its in siemen units, not in dB gain. I'm not sure why its in siemen units?
@@waynegram8907 Hi Wayne. TYhis is all a bit esoteric and not useful for practical amplifier repairs. I don;t even own a tube tester!
I'm wondering why you are asking.
@@stuartukguitarampguy5830 Just asking if the transconductance is "factored into" the biasing of the output tubes? because I'm not sure why some tube testers measure the transconductance it must be for reasons which I'm not sure what they are.
@@waynegram8907 Transconductance is the gain of the tube. E.g. x100 or whatever. The bias is just the steady state DC bias required to get the valve to 'tickover'.
That's an interesting failure. I suspect they may have done the parallel tube heater wiring to reduce hum or something along those lines. Question is how/why did that fail?
Yes I was unvlear what that black plastic thung was. It didn;t seem to be a connector you could unplug.
@@stuartukguitarampguy5830 Seems to be some kind of unusual connector that is soldered directly to the PCB in lieu of just soldering wires directly to the board. Probably the contact to the wire inside failed... came loose or maybe the contact got oxidized. Don't know why they designed it that way... not very bulletproof in the long term.
@@VegasCyclingFreak Yes that's almost certainly what happened. Nice one Orange!
How did you know you had the right polarity in the heaters?
I'm sure loads of people would provide the answer but I'll be the first. The heater supply is a.c. so it isn't critical which way round it's connected. The only issue is, there may be a slight him if the phase is incorrect.
I have known heater pcb tracks to fail. They are not up to the current carrying capacity over a long period of time or they blow if a heater fails. Never had this issue with the old point to point wiring.
Yes that makes sense but these heaters were carried by those thin yellow wires. I guess it could have been the short length of track. Not sure without taking the board out.