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PeeCeeBee V4H GB

Yes, I think so. I am no expert but from what I have read, as long as the coat isn’t too thick, so as to introduce an insulating layer, the flat black color will increase emissivity substantially— vs. bare aluminum.

On Rod Elloitt’s site he has a list of surface finish versus emissivity for heatsinks. Polished Aluminum has an emissivity rating of 0.05, whereas black enamel painted Aluminum has an emissivity rating of 0.85 - 0.91.

Essentially, I sprayed just enough to make them look black, and then stopped.
 
After taking a bit of diversion into DHT amps and preamps (quite a bit of fun, and quite educational) I managed to hook up my PeeCeeBees last night for the first time in more than a year.

Though, I did enjoy my original PeeCeeBe build, I did not have big enough of heatsinks for the the voltage I was running. Even set to a low idle current, I couldn't run the amps more than 40 minutes before they were hot enough to cook an egg. So the amps were set aside.

A few weeks ago I was at one of my local Metal suppliers who had a bin of Aluminum plate remnants on super-sale. I picked up two hefty chunks 430 X 200 X 16 mm. $20 for both pieces. I cut some channels in the plates with my table saw to increase the surface area, and gave them a very thin but even coat of flat black spray paint to increase emissivity.

Even at 300ma bias on the MosFets, and few hours of near concert level listening, the heatsinks never got more than pleasantly warm--about like that of a nice heating pad for your sore back.

These are only Rev 1 units, but these are very fine sounding amps!!
I am very glad to get acquainted with them again.

So, thanks once more to shaan for a fine design, and a fine set of PCBs!
And cresnet, too! For I am using his SMPSs!

Best regards,
John

Hi John.

Very happy to know that you found the peeceebee to be up to your taste. In these strange times your post did put a smile on my face. :)

Thank you and happy listening.

:cheers:
 
After taking a bit of diversion into DHT amps and preamps (quite a bit of fun, and quite educational) I managed to hook up my PeeCeeBees last night for the first time in more than a year.

Though, I did enjoy my original PeeCeeBe build, I did not have big enough of heatsinks for the the voltage I was running. Even set to a low idle current, I couldn't run the amps more than 40 minutes before they were hot enough to cook an egg. So the amps were set aside.

A few weeks ago I was at one of my local Metal suppliers who had a bin of Aluminum plate remnants on super-sale. I picked up two hefty chunks 430 X 200 X 16 mm. $20 for both pieces. I cut some channels in the plates with my table saw to increase the surface area, and gave them a very thin but even coat of flat black spray paint to increase emissivity.

Even at 300ma bias on the MosFets, and few hours of near concert level listening, the heatsinks never got more than pleasantly warm--about like that of a nice heating pad for your sore back.

These are only Rev 1 units, but these are very fine sounding amps!!
I am very glad to get acquainted with them again.

So, thanks once more to shaan for a fine design, and a fine set of PCBs!
And cresnet, too! For I am using his SMPSs!

Best regards,
John

Thanks John, Are you enjoying the sound by now?
 
Oh rats!
I just toasted my left channel!

Out of curiosity to hear an all transistor set-up, I pulled out an older preamp that I always liked —based on Jensen 990 op-amps.
I turned on the power amp and a brief hum was followed by a puff of smoke, and then the amp shut down.

Do you think I might be able to get away with just replacing the power Mosfets on the PeeCeeBee?

Any advice where to start??


I think the left channel on the preamp must be oscillating, perhaps a problem with the DC servo. When I checked the DC offset, I got reading swinging from a few millivolts up to 1.2 volts DC and back agsin. Strange. Never gave me any trouble before, and the right channel is fine.

Too bad my curiosity got the best of me. It was sounding really good with the DHT preamp.
 
Hi John.

Sorry to hear that. This sometimes happens with the earlier revisions of the amp.


Check R25/R26, if they are burned replace the resistors.

Replace Q3/Q4 and Q9/Q10.

Check the MOSFETs for drain to source and source to drain continuity and notice the value shown in the meter, if it shows a short for either pair of the mosfets then make a cut in the source pin under the board for one of the MOSFETs on the shorted side (keep the cut away from the plastic body), make sure the source pin is disconnected from the solder joint and then repeat the drain-source and source-drain continuity test for that mosfet pair. This will isolate the dead mosfet(s). If the meter shows some value but not a dead short then the mosfets are fine.

I will suggest you also update the boards to Rev2. Check the schematic in the first post for R39/R40 and the gate-source diodes on the mosfets.

Make a cut in the long ground traces under the board just by R25 and R26, and scratch two points in the separated traces, then install one 4K7 resistor (R39/R40 in the schematic) between the scratched points for each cut. Get eight 1N4148 and eight 10V zener diodes (for both channels), install them across the MOSFET gate and source pins (pin 1 and 2) as shown in the schematic. With this mod installed the amp will not die in case of momentary overloads.

Afterwards turn VR1/VR2 to max resistance and VR3 to min resistance, remove the two jumpers and re-setup the channels. If you have any questions about anything feel free to post here.
 
Hi shaan,

Thanks so much for the detailed trouble shooting instructions! Very helpful and very generous of you.

R25 is indeed dead. That must have been the puff of smoke I saw.

The mosfets give random-ish value readings D-S and S-D, so maybe they survived. Hard to get, so that’s good.

I have BC556/546 and some 47R, but will need to order the kse340/350 (plus the resistors/diodes to update to rev2) and will report back.

I also need to dig into that preamp and see what is going on. After this experience, I may just bypass the DC servo circuit and install a good old trusty coupling cap.

Best regards,
John
 
Hi shaan,

Is it at all possible that just only R25 was fried?
I used a rather small resistor in that position. It may be 1/8 watt.
Is there an easy way with a DMM to test Q3/4 and Q9/10?

I ask only because with the thick PCB, it may be best to try and replace as few components as possible.

Best regards,
John
 
Hi shaan,

Is it at all possible that just only R25 was fried?
I used a rather small resistor in that position. It may be 1/8 watt.
Is there an easy way with a DMM to test Q3/4 and Q9/10?

I ask only because with the thick PCB, it may be best to try and replace as few components as possible.

Best regards,
John

It could be that only the resistor died. But in my experiments during rev2 development with manually inducing hard overloads I noticed that whenever either of these resistors dies it takes Q3/Q4 with it, but rarely Q9/Q10. Interestingly, both Q3 and Q4 would pass the base-emitter and base-collector diode test, but as soon as I power it up after replacing only the resistor, it would get burned again, but not after replacing Q3/Q4. So I would suggest that if you replace this resistor then also replace Q3/Q4.

Edit: do not run them at least until installing the rev2 mod as well.
 
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Hi shaan,

I replaced R25, Q3, Q4, and as long as I had the board out, I went ahead and replaced Q9, Q10. Everything powered up nicely. I did’t have touch the VAS bias, and only need a slight tweek on the DC offset to adjust from 13mV to bring it below 2mV.

Amp works and sounds great again!

Parts are coming for Rev2 fix.

Thanks so much for the guidance!!

Best regards,
John
 
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Update:

Fresh batch of V4H boards are home.

Kindly note that shipping to many countries from India is closed due to the current covid situation, and to the ones that are open delivery is taking a long time. Hopefully things will improve in the coming weeks.

Bests and stay safe everyone.
 

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Hi Pistollero.

Those resistors can be paralleled, four on each side. I'd recommend four of the 1.8ohm per rail.
Ok i will do that.
Regarding power supply, i need some advice also. I have a 2x40vac trafo + 2 bridges(nelson pass style) + 2x22000uf.
This is mono for each rail.
Do you recomend use bleed resistors after the 2x22000uf filter caps? If so could it be 2k2 2watt resistors?
Also on some schematics they use cl-60 thermistor in series with one side of the primary trafo.
Here is 220v line. Is ok to use or for 2x22000uf does not need?
What do you think?