Hi troystg - I went and checked the photo's of the boards that I sent to Carlos and they were cut exactly the same way. Then I went and looked at the photo of the monoblock amp and that board looks as if it were cut the same too - but the leads from the power xsistors were soldered in place without being "bent" - so I'm thinking that Steve intended this for easier soldering of the xsistors to the board. But this is speculation on my part - Steve is the guy to answer this question. Don't know if this helps much or not. 😕
quote:
Originally posted by Steve Dunlap
The rest of the TO220 devices will dissipate about 0.35W each and should not need heat sinking. I run them warm on purpose.
Which purpose?
I have been waiting for someone to ask that question. At 10mA of current the transistors run at an elevated temperature for two reasons. One reason is the increased gain and linearity. The other is that this pretty much swamps any change in die temperature caused by changing output current in these devices.
Originally posted by Steve Dunlap
The rest of the TO220 devices will dissipate about 0.35W each and should not need heat sinking. I run them warm on purpose.
Which purpose?
I have been waiting for someone to ask that question. At 10mA of current the transistors run at an elevated temperature for two reasons. One reason is the increased gain and linearity. The other is that this pretty much swamps any change in die temperature caused by changing output current in these devices.
troystg said:
http://www.diyaudio.com/forums/showthread.php?postid=1685969#post1685969
I rx'ed PCB's today.
Is there a reason the PCB is cut at the output transistor holes? 😕
I have been waiting for this question also. This was to make the initial assembly easier (as Tom correctly noted) and to make repairs easier when needed. With this arrangement the power transistors could be pre mounted to the heat sink and properly torqued down. The heat sink was then installed through the back of the chassis, screwed in place and the transistors soldered through a covered slot in the bottom. It made sense at the time. I no longer do this as the amp has proven to be very reliable. Not one failure (except blown fuses) in over 10 years.
Steve Dunlap said:
Thank you Steve. I actually simulated the circuit but I have used 2SB649/2SD669 because I assumed them sufficient for that position, and current in my SIM is around 16,5mA which gives 550mW of dissipation – a bit too much for TO126 case without any heatsink. Now I noticed that you used TO220 case units and if in real circuit current is really 10mA, it might be OK if you say so.
boraomega said:
The current is set at 10mA with the values shown in the schematic. If you have16.5mA, then something is different in your sim. The current is set by the resistor values and will not change much at all with changes in transistors. TO220 transistors are rated for 2W dissipation (at 25C ambient) and even though the inside of the amp is usually warmer than that, I feel that .35W is acceptable. Years of use without failures also indicate that this is a safe level.
I received my boards, also. Thanks Steve - very well made boards
A couple of questions/observations:
- There is a small misprint on the silk-screen & stuffing guide - D7,8,9,10 are named Q7,8,9,10. It's obvious that these are diodes on the board as they only have two pins and the cathode mark, so a minor mistake, really.
- I'm interested in only using the board as output for a Tube front end so I just want to confirm that I should not stuff D11 & D12 (or all the input parts).
- This tube preamp will be output through a trafo - what bias voltage do I need to apply to the base of Q7,Q10?
- Finally, I was hoping to use MJE15030/1 as the bias transistors Q7,8,9 & Q 10,11,12. I don't believe these need to be matched - is this correct?
A couple of questions/observations:
- There is a small misprint on the silk-screen & stuffing guide - D7,8,9,10 are named Q7,8,9,10. It's obvious that these are diodes on the board as they only have two pins and the cathode mark, so a minor mistake, really.
- I'm interested in only using the board as output for a Tube front end so I just want to confirm that I should not stuff D11 & D12 (or all the input parts).
- This tube preamp will be output through a trafo - what bias voltage do I need to apply to the base of Q7,Q10?
- Finally, I was hoping to use MJE15030/1 as the bias transistors Q7,8,9 & Q 10,11,12. I don't believe these need to be matched - is this correct?
A couple of questions/observations:
- There is a small misprint on the silk-screen & stuffing guide - D7,8,9,10 are named Q7,8,9,10. It's obvious that these are diodes on the board as they only have two pins and the cathode mark, so a minor mistake, really.
Yes, those are diodes. They are 1N4148.
- I'm interested in only using the board as output for a Tube front end so I just want to confirm that I should not stuff D11 & D12 (or all the input parts).
That is correct.
-This tube preamp will be output through a trafo - what bias voltage do I need to apply to the base of Q7,Q10?
I assume that one side (leg) of the transformer secondary will be the hot and the other will be ground. If this is the case then no other bias is needed. If the input is capacitor coupled then you should add the one Meg trim pots shown in a previous post. With the very low DC path of the transformer secondary there should be very little offset.
- Finally, I was hoping to use MJE15030/1 as the bias transistors Q7,8,9 & Q 10,11,12. I don't believe these need to be matched - is this correct?
Matching is always a good thing. It is not necessary for proper operation and probably could not be achieved with those transistors without a fairly large number to choose from. If you do decide to match then only the NPN/PNP pair at each location need to be matched. So Q7 and Q10, Q8 and Q11, and Q9 and Q12 would be matched.
- There is a small misprint on the silk-screen & stuffing guide - D7,8,9,10 are named Q7,8,9,10. It's obvious that these are diodes on the board as they only have two pins and the cathode mark, so a minor mistake, really.
Yes, those are diodes. They are 1N4148.
- I'm interested in only using the board as output for a Tube front end so I just want to confirm that I should not stuff D11 & D12 (or all the input parts).
That is correct.
-This tube preamp will be output through a trafo - what bias voltage do I need to apply to the base of Q7,Q10?
I assume that one side (leg) of the transformer secondary will be the hot and the other will be ground. If this is the case then no other bias is needed. If the input is capacitor coupled then you should add the one Meg trim pots shown in a previous post. With the very low DC path of the transformer secondary there should be very little offset.
- Finally, I was hoping to use MJE15030/1 as the bias transistors Q7,8,9 & Q 10,11,12. I don't believe these need to be matched - is this correct?
Matching is always a good thing. It is not necessary for proper operation and probably could not be achieved with those transistors without a fairly large number to choose from. If you do decide to match then only the NPN/PNP pair at each location need to be matched. So Q7 and Q10, Q8 and Q11, and Q9 and Q12 would be matched.
OK everybody, as far as the matching of bias transistors is concerned - what is the best T220 device for this function and would likely give the best yield in complimentary pairs? i.e I don't want to have to buy a shed load to get the 6 matched pairs needed for two monoblock amps and they need to be widely available.
I know the MJE15030/1 are notoriously difficult to match ( I already have some of these but unmatched), so what about the original devices 2SA1306B/2SC3298B? Would 20 of each give the 6 matched pairs?
I'm surmising that a device spec similar to the originals is what is needed: VCeo ~160, IC ~1.5A. But maybe Steve can advise here?
I can get 2SA968/2SC2338 locally in RS for €1.50 - €1.70 each so 20 of each would cost me €64 - more than I wanted to spend for 6 matched pairs & I don't need the other 14 of each device.
So, anybody interested in putting together a small group buy for suitable matched devices? I would do it but local prices are exorbitant in this neck of the woods.
I know the MJE15030/1 are notoriously difficult to match ( I already have some of these but unmatched), so what about the original devices 2SA1306B/2SC3298B? Would 20 of each give the 6 matched pairs?
I'm surmising that a device spec similar to the originals is what is needed: VCeo ~160, IC ~1.5A. But maybe Steve can advise here?
I can get 2SA968/2SC2338 locally in RS for €1.50 - €1.70 each so 20 of each would cost me €64 - more than I wanted to spend for 6 matched pairs & I don't need the other 14 of each device.
So, anybody interested in putting together a small group buy for suitable matched devices? I would do it but local prices are exorbitant in this neck of the woods.
Here's my list of likely devices:
2SA968/2SC2338
2SA1930/2SC5171
2SA1837/2SC4793
2SA1006/2SC3336
2SA1507/2SC3902
2SB631/2SD600
2SB649/2SD669
2SA1220A/2SC2690A
2SA968/2SC2338
2SA1930/2SC5171
2SA1837/2SC4793
2SA1006/2SC3336
2SA1507/2SC3902
2SB631/2SD600
2SB649/2SD669
2SA1220A/2SC2690A
Hi John
Perhaps Steve Dunlap could do this 🙂
Steve, would you be able to put together a Group Buy of matched pairs for these 3 pairs of transistors?
🙂
Perhaps Steve Dunlap could do this 🙂
Steve, would you be able to put together a Group Buy of matched pairs for these 3 pairs of transistors?
🙂
Hi KL,
Did you get your boards yet?
I already emailed Steve about this as I thought he might still have some parts that would suit. I wasn't sure if he had the time or energy to do this for so little reward - group buys are such a pin, I believe!
If he's not able to do this perhaps he could give us the important specs for these transistors & we can source something suitable ourselves or guide us from his experience in the expected matched pair yield we might get from 20 of each 2SA1306B/2SC3298B?
Did you get your boards yet?
I already emailed Steve about this as I thought he might still have some parts that would suit. I wasn't sure if he had the time or energy to do this for so little reward - group buys are such a pin, I believe!
If he's not able to do this perhaps he could give us the important specs for these transistors & we can source something suitable ourselves or guide us from his experience in the expected matched pair yield we might get from 20 of each 2SA1306B/2SC3298B?
I have no prevision when my boards will arrive.
The one will carry them is busy with some deadlines...he cannot travell to brazil before January, 15.
And this do not means he will come january, 16..... this means he can come february, or latter.
I am sorry Steve and forum folks...but i have to wait.... and without complain, as i am lucky to have a friend alike Duda, the one is always ready to help and to bring precious electronics to me.
So...it is all rigth...but i will have to wait.
regards,
Carlos
The one will carry them is busy with some deadlines...he cannot travell to brazil before January, 15.
And this do not means he will come january, 16..... this means he can come february, or latter.
I am sorry Steve and forum folks...but i have to wait.... and without complain, as i am lucky to have a friend alike Duda, the one is always ready to help and to bring precious electronics to me.
So...it is all rigth...but i will have to wait.
regards,
Carlos
KL,
What we are asking Steve is offering a part kit which he said in the other thread that he was not able to do without the help of Tom. Hopefully all is well with Tom & his Wife, Susan (and the dog) and maybe he can get involved?
What we are asking Steve is offering a part kit which he said in the other thread that he was not able to do without the help of Tom. Hopefully all is well with Tom & his Wife, Susan (and the dog) and maybe he can get involved?
Is there anyone else interested in these matched transistors for the bias section of the amp - register your interest here so we could possibly get a group buy started.
I have found a source for 2SA1837/2SC4793 (Steve validates these good to use) for €0.50 + shipping. I'm told that we can get 6 matched complimentary pairs out of 20 + 20. If there are more interested in these we could get 12 matches out of 30 +30 or 18 matches out of 40 + 40.
Let me know here what interest there is in this & I'll look into a group buy!
I have found a source for 2SA1837/2SC4793 (Steve validates these good to use) for €0.50 + shipping. I'm told that we can get 6 matched complimentary pairs out of 20 + 20. If there are more interested in these we could get 12 matches out of 30 +30 or 18 matches out of 40 + 40.
Let me know here what interest there is in this & I'll look into a group buy!
I can also get 2SC5200/2SA1943 for €2 + shipping so if there is interest in matched pairs of these let me know also!
It appears the 2SA1306B/2SC3298B transistors have been discontinued. The important specs in a replacement are the voltage and current. A 150V or greater device is recommended and easy to find. The current should be 1A. Most TO220 transistors will have this minimum current capability. I like to use a low current device as they have better bandwidth.
I still have a large stock of 2AS1837/2SC4793 transistors that I can sell for $3 a pair. Shipping will be the same for a set of 6 pair as for the boards. I will match them also for this price. I do not know what these sell for in the various locations I have shipped boards to, so this may not be a fair price where you are located. If you are interested, E-mail me directly.
I also have all the other parts except cases, but I will need help putting together a part kit. I don't know what you would want to be included so I have no idea what the price would be. What would you like to see in a parts kit?
I still have A LOT of parts that I am no longer able to use. If you are looking for something, E-mail me and ask. I don't plan to put together a list but I have a good idea what I have in stock. I hope I am not violating any forum rules by making this offer.
I still have a large stock of 2AS1837/2SC4793 transistors that I can sell for $3 a pair. Shipping will be the same for a set of 6 pair as for the boards. I will match them also for this price. I do not know what these sell for in the various locations I have shipped boards to, so this may not be a fair price where you are located. If you are interested, E-mail me directly.
I also have all the other parts except cases, but I will need help putting together a part kit. I don't know what you would want to be included so I have no idea what the price would be. What would you like to see in a parts kit?
I still have A LOT of parts that I am no longer able to use. If you are looking for something, E-mail me and ask. I don't plan to put together a list but I have a good idea what I have in stock. I hope I am not violating any forum rules by making this offer.
Hey Steve,
That sounds like a winner!
I guess matched output trannies would also be of interest to those building these amps. Maybe you could give a price on matched pairs of these if you have any suitable in stock?
3 matched pairs are needed, I believe, including the drivers. Could these be included along with the 6 bias pairs for the same shipping charge? - it would make it more attractive to outlying regions!
That sounds like a winner!
I guess matched output trannies would also be of interest to those building these amps. Maybe you could give a price on matched pairs of these if you have any suitable in stock?
3 matched pairs are needed, I believe, including the drivers. Could these be included along with the 6 bias pairs for the same shipping charge? - it would make it more attractive to outlying regions!
jkeny said:
I do have suitable output transistors. I will need to check prices. The shipping should be the same.
Is there interest in a parts kit? So far only two people have expressed any interest.
Even though I stated that I did not have cases for these amps several people have ask about them anyway. Do you think there would be interest in a thread on building your one cases? I am talking about good looking cases that you would be proud to show off and yet still affordable. If this thread were started, where should I place it?
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