♫♪ My little cheap Circlophone© ♫♪

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#2,081
Mr, wg_ski,

Yes you are correct. Arctic Silver 5 is conductive paste as it contains silver metal particles in colloidal form. This is the most effective Thermal Paste currently available in the market. This is suitable for devices having isolated heat pads not suitable for TO3 devices.
 
#2,084
Low-end silpad is 0.5-2 W/m.K, thickness ~0.25mm

Keratherm red 6.5 W/m.K, thickness ~0.25mm, so about 0.1°C/W for TO3P

Gelid GP-EXTREME (the thermal pad for the discriminating overclocker) is 12W/m.K and 0.5mm thick, so it's the same Rth as Keratherm, but it is not reusable, it's quite squishy and tends to ooze from behind the transistor.

Thermal pastes for CPUs : 2-7 W/m.K

Wakefield 120 0.7 W/m.K

The transistors in the pic on the previous page have decent Rth from junction to case (about 2-3 °C/W) but the case is tiny so heat transfer to the heat sink is really bad. Even if the copper slug is stamped and not really flat, it more than makes up for it with surface area. Dissipated power is pretty low, 10W tops, so it works nicely. Next time I'll use a larger one to make it easier to mount.
 
#2,085
Mr Elvee, I have a querry.

I have come across NCC Series Amplifier circuit diagram on DIY forum which gave me a sense through the note that the Input transistor should have more Hfe than its counter part Feedback Transistor of the input pair to ensure correct offset. If this theory is correct than how to correctly find out Hfe value of both transistors.

I have assembled two prototype BJT and MOSFET and a Stereo MOSFET version of Circlophone at 35-0-35 V DC where I got a max of -6.5 mV DC as offset with matched input pair. Circuit diagram attached.
 

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#2,086
This Hfe requirement (relatively bizarre) stems from the unbalanced currents in the pair.
When the currents are balanced, as in the C and many other amplifiers, the Hfe's need to be matched.
Imbalance in a diff pair is generally carefully avoided, since it quickly increases the THD because the compensation mechanisms do not work any more.
 
#2,089
Hi Guys

I m complete Noob for discrete and I want to build this amp so asking for help

can we use KSC2690A for replacement of 2N3019 or 2N3501.
Also as this part is easily available on mouser ( economically )

Will be building it using TIP3055 ( BD140 as driver )

Is there any preference between TO-247 vs TO-3 package

Would transformer current rating for 18 0 18 @ 5Amps is sufficient for both 4 and 8 ohms ? In stereo

Thanks in advance
 
#2,090
>can we use KSC2690A for replacement of 2N3019 or 2N3501.
>Also as this part is easily available on mouser ( economically )

It looks like KSC2690 should work, It's Cob is slightly higher than perfect (19 vs 10), but it's in line with TTC004B that I used without any problems.

TTC004B also should be in stock.

Another option: use
KSC3505 or KSC3503 and simply add 4.7pF C-B capacitors.
 
#2,091
minek123 said:
>can we use KSC2690A for replacement of 2N3019 or 2N3501.
>Also as this part is easily available on mouser ( economically )

It looks like KSC2690 should work, It's Cob is slightly higher than perfect (19 vs 10), but it's in line with TTC004B that I used without any problems.

TTC004B also should be in stock.

Another option: use
KSC3505 or KSC3503 and simply add 4.7pF C-B capacitors.
Click to expand...

Thank you Minek

I see that the new transistor is available on element 14 - very economically for my side of the country.
 
#2,092
TTC004B and KSC3503 are better options for BJT C. I have tested KSC3503 in BJT prototype with excellent response. In MOSFET version I have used its counter part KSA1381. This stereo setup is continuously powered on for more than a month connected to my PC.
 
#2,093
Hi Katiyar,

I will go with KSC3503 (VAS) and TIP3055 with BD140 as driver , and BC546C for the other transistors or should I use KSC1845 for Q12 & Q13.

My two way bookshelf speakers are 8 ohms 6”.

So what would be a perfect combo of parts such that I could use it with TIP3055 @ 25 Vdc and later change over to MJL21194 for 50watts.

Without a lot of change of parts in the active components.

Thank you in advance.
 
#2,094
Mr Aditya. As you are from India I will advise you not to buy crap Chinese BD140 available very easily in the Indian market. You should instead purchase CDIL make BC546, BC556 and BD140. These transistors are genuine and performance is excellent. They will sustain the rated voltage. KSC3503 is an excellent choice for VAS. These are video transistors with 150Mhz BW.

As advised by Mr Minek 4.7pf capacitor is to be added between BC of KSC3503.

Good Luck
 
#2,096
The board I m interested in are by Prasi but he hasn’t replied back. The board you have shared here are lovely with support for both TO-247 and TO-3 package.

Currently I going to order the board from DAC.

My original plan was to buy all the parts from Element 14 and take the OnSemi TIP3055

CDIL 140 are out of stock with DAC as well as they do not stock BC546 from CDIL.
Also I am a little hesitant to venture to Lamington road.

Therefore since I have access to GST number it would be easy to pickup parts from element14.
 
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