Oh wow, those little diodes are getting way too hot. Does the bottom side of the board still look serviceable? Those are 31V zener diodes, I would replace each one with two zener diodes in series at half the voltage or three in series at 1/3 the voltage. You can twist the leads together and make a little arch of zener diodes. More zener body will drive the heat down.
On those 2W resistors that are getting too hot, use Vishay PR-03 and space them off the board a little more.
I do not recommend "audiophile" power supply caps because they have no specifications. Use a good quality name brand cap from a reputable vendor that will fit properly.
On those 2W resistors that are getting too hot, use Vishay PR-03 and space them off the board a little more.
I do not recommend "audiophile" power supply caps because they have no specifications. Use a good quality name brand cap from a reputable vendor that will fit properly.
having a 4 times higher current rated diode for a high frequency one will make the voltage drop a bit lower, sometimes equal with a 1x current low freq diode, depending on diode's type.Then the heat dissipation is done by its exposed surface to air, or ventilation. It needs to be a big diode and actually the only diodes that will not overheat will be the 8 amps minimum current ones as they have metal fins so the pcb will stay cool.
4 times higher current in a high speed switching diode than the current needed for a low frequency diode.
My CL-34 PSU PCB is in reasonable nick, though all the power caps (160 V + varieties) need to be replaced. If anyone needs a photograph of the track side let me know, I can move the cables out of the way and take a picture. I will probably remove the PCB totally (not this year though,) scan it and have a new one made, with a 2.4 mm FR4 and 2 oz. tracks. I will definitely see if I can replace existing zeners with 2 off higher wattage, half the rated voltage ones in series. I will in any case replace all the 1N4007s.
Kevin
Kevin
Film & foil are used in high current applications, such as a speaker crossover. Preamps are small signal devices, and except for audiophile appeal, metallized film like the Sprague 715P series, work just fine, since signal currents are so tiny. F & F certainly won't hurt in a preamp, but it's overkill, IMHO. You don't need a crane to lift a bag of groceries.
So if you have a 1N4007 running close at its 1A max. average current rating, you can't replace it by a UF4007 (also rated 1A max. average current)? You could only replace it by a fast switching diode that is rated for 4A max. average current?
Where does all this extra current goes to (if the power transformer can delive a 4 x higher current)? And how come the equipment draws 4 x more current, at the same voltage?
I still don't understand what you mean.
That's (again) not an answer to my questions. Where does your "4 times higher current" comes from and goes to? What does a doubling of the voltage drop over a diode has to do with the current quadrupling?
Hi,
None of the Zeners were defective, so I left the original diodes in even if they turn HOT in use.
I had to replace burned resistors but no diodes.
Well. if one looks at the trafo specs, the diodes are well within spec:
158 V @ 10 mA (1N4007)
340 V @ 38 mA (1N4007)
16.5 V @ 700 mA (S3V20 similar to 1N5402 - 200 V @ 3 A)
Possibly age is the problem so I will just put in new ones when I get to it and stand them off of the PCB.
The top surface of the PCB in mine is also black (sooty) so probably due to the zeners getting too hot from being used for many hundreds of hours by the previous owner. I'll put in 2 newer higher amperage rated ones per previous zeners (half the voltage rating of course per new zener.) Not terribly expensive.
The big power caps are another story. Will have to source these from Europe, UK or USA. Next year though.
158 V @ 10 mA (1N4007)
340 V @ 38 mA (1N4007)
16.5 V @ 700 mA (S3V20 similar to 1N5402 - 200 V @ 3 A)
Possibly age is the problem so I will just put in new ones when I get to it and stand them off of the PCB.
The top surface of the PCB in mine is also black (sooty) so probably due to the zeners getting too hot from being used for many hundreds of hours by the previous owner. I'll put in 2 newer higher amperage rated ones per previous zeners (half the voltage rating of course per new zener.) Not terribly expensive.
The big power caps are another story. Will have to source these from Europe, UK or USA. Next year though.
Last edited:
The photos in post #4 show a lot of scorching of the circuit board, but maybe the photos make it look worse than it is in reality.
If it is scorched bad though, than there is the chance of currents flowing through the carbon that formed on the surface of the circuit board. Did you try to get some of the scorched surface off?
If it is scorched bad though, than there is the chance of currents flowing through the carbon that formed on the surface of the circuit board. Did you try to get some of the scorched surface off?
Hi,
Yes it looks worse with the camera flash. I am currently restoring the area near the 1uf/0.47uf caps. I swapped the caps, upgraded the resistor to a 3W and made as much space as possible between the parts. Finally i added a small undervolted fan in front each channel.
Next step is gonna be the PS, i'm still waiting for the parts to arrive. I will upgrade the 2w to a 5w resistor, change the WZ310 to new 2x15v zener in serie and take em 10mm away from the pcb. Finally i will upgrade the caps to Panasonic 105° and mundorf 50uf+50uf 500v caps.
I will try to sand a little bit the burned pcb with very fine sand grits and then add a small sheet of dielectric thermal insulating foil on this area (it's part of my job so i have the correct materials for the task)
If it's still too hot near the zener after that i will add a small fan too
I think all this will do the job 😀
Yes it looks worse with the camera flash. I am currently restoring the area near the 1uf/0.47uf caps. I swapped the caps, upgraded the resistor to a 3W and made as much space as possible between the parts. Finally i added a small undervolted fan in front each channel.
Next step is gonna be the PS, i'm still waiting for the parts to arrive. I will upgrade the 2w to a 5w resistor, change the WZ310 to new 2x15v zener in serie and take em 10mm away from the pcb. Finally i will upgrade the caps to Panasonic 105° and mundorf 50uf+50uf 500v caps.
I will try to sand a little bit the burned pcb with very fine sand grits and then add a small sheet of dielectric thermal insulating foil on this area (it's part of my job so i have the correct materials for the task)
If it's still too hot near the zener after that i will add a small fan too
I think all this will do the job 😀
Last edited:
Did you finish the restoration?
I have a CL34 also and I'm planning to do about the same as you, so I'd like to know more about how things have progressed.
I have a CL34 also and I'm planning to do about the same as you, so I'd like to know more about how things have progressed.
I started a while ago to build a hybrid between a cl 34 clone and a morgan jones headphones amp and i wanted to ask something i don't really get from the schematic which shows just one channel and the few photo i gen find with the real thing :
there's a 56 kohm 1w resistor supplying v1 from v2 supply .Is that resistor unique to both channels or each channel have its own 56 kohm resistor.I think that question applies to all supply divider resistors...i ask that because using only one resistor to both channels is affecting v3 split point voltage a great deal making the lower valve of the WCF dissipating a lot more heat than the upper one .
Dear CL34 owner, as you all know the power board of our CL34 always burn, it's just a matter of time... To solve this problem i made a new complete board with double place for the 47+47uf in order to use regular 47uf x2 instead. The board seems to be identical for all region of the world, you have to check. Someone already asked me for one so i have one left i can send to a member of this forum for a fair price, i don't care to make profit. Send me a private message with a picture of your CL34 amp and my nickname on it (to be sure it's gonna really be usefull to you) and i'll get in touch with you
Have a nice day
Have a nice day