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SOHA II Builders Thread - Page 9

post #121 of 1676
Quote:
Originally Posted by wiatrob View Post
Full size templates are a great help, printed out to the right size and mounted on thin (file folder) card stock. Then a punch with a steady hand to mark the hole and guide your step bit (you do have a step bit don't you? )

I have been able to do quite nice work by hand this way.
No, that's something else I need to acquire

BTW You see them (step bits) being offered in sets of 3 with the 1st bit going 4,6,8,10,12 - the 2nd bit offering the same sizes as the 1st plus a few more, then a 3rd bit with a few more step sizes tagged on!, what the hell do you need the 1st two bits for then!, and why don't they make one of the set do 'odd' sizes i.e 5,7,9,11,13, etc - eh?
post #122 of 1676
Does anyone know of a good (cheap) source for the larger transformer, 15-0-15 1.5A needed to run tubes with 300ma heaters? I can find a Hammond at close to $60, Avel has it on their web page, but a search of the web comes up empty.
I am aware of AnTek, but their voltage is rated at no load, not full load.
I tried some GE 12BH7A's and like them better than the Sylvania 5963's I have been running. I am going to mount the regulator for heaters off board.
Has anyone measured current draw? I wonder how far over the ratings I am with the higher current tubes?
post #123 of 1676
Quote:
Originally Posted by Uncle Bob View Post
No, that's something else I need to acquire

BTW You see them (step bits) being offered in sets of 3 with the 1st bit going 4,6,8,10,12 - the 2nd bit offering the same sizes as the 1st plus a few more, then a 3rd bit with a few more step sizes tagged on!, what the hell do you need the 1st two bits for then!, and why don't they make one of the set do 'odd' sizes i.e 5,7,9,11,13, etc - eh?
Cheaper than a drill press I just got the one bit set - does most all I need it to...
post #124 of 1676
Thread Starter 
Quote:
Originally Posted by grendel23 View Post
Does anyone know of a good (cheap) source for the larger transformer, 15-0-15 1.5A needed to run tubes with 300ma heaters? I can find a Hammond at close to $60, Avel has it on their web page, but a search of the web comes up empty.
I am aware of AnTek, but their voltage is rated at no load, not full load.
I tried some GE 12BH7A's and like them better than the Sylvania 5963's I have been running. I am going to mount the regulator for heaters off board.
Has anyone measured current draw? I wonder how far over the ratings I am with the higher current tubes?
Have you removed R3P? If not, what's happening is that the voltage before the Heater regulator is probably pulling down close to the regulated voltage causing the regulator to drop out and produce a bad waveform at its output.

If you remove R3P (as per the website) you will cook the Heater regulator from the power dissipation with the small heatsink. But, if you use an offboard heatink you might be able to skim by with the 1A transformer. Might. You'll have to try it and measure the voltages both before and after the heater regulator to see if you'll be successful.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #125 of 1676
Quote:
Originally Posted by runeight View Post
If you remove R3P (as per the website) you will cook the Heater regulator from the power dissipation with the small heatsink. But, if you use an offboard heatink you might be able to skim by with the 1A transformer. Might. You'll have to try it and measure the voltages both before and after the heater regulator to see if you'll be successful.
I have not removed R3P. I only tried it for a few minutes to see how these tubes sound and see if it I want to run them bad enough to upgrade. They sound very good as the amp is now. I will probably buy a larger transformer, I just want to find a better price than I have found so far.
post #126 of 1676
Quote:
Originally Posted by grendel23 View Post
Does anyone know of a good (cheap) source for the larger transformer, 15-0-15 1.5A needed to run tubes with 300ma heaters?
How about Amveco TE62083, e.g. from Digi-Key?
post #127 of 1676
I'm new here and I want to say hello from Poland!
I want to buil SOHA II but I have some troubles with completing components to it. And the first question - can I use caps in PS with different capacitance then it is in the design? I mean C3P and C4P - I have 3300uF/50V? And second question - resistors. I have almost all Dale but some of them have slightly diferent value (not above 1% - e.g. 33kohm - I have 33,2kohm).
post #128 of 1676
Thread Starter 
Hi czegevara. Yes, you can use 3300u for C3 and C4 at 50V.

And you can probably use the Vishay resistors everywhere where their value is close, such as 33.2k, 1.82k, etc. Within 1% is no problem.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #129 of 1676
Thanks runeight. I thought so but I wont to make sure
post #130 of 1676
And one more question...
Im not familiar with tubes so can you explain in few words how a higher voltage powering tubes affect their working? How it affect sound quality? Always higher voltage = better sound? And can I adjust HV (55-100V) without any other changes in circuit??
And thanks for your patience for newbies
post #131 of 1676
Quote:
Originally Posted by Arkku View Post
How about Amveco TE62083, e.g. from Digi-Key?
Digi-Key is the one major vender I did not check. Thanks for the heads up.
post #132 of 1676
Thread Starter 
Quote:
Originally Posted by czegevara View Post
And one more question...
Im not familiar with tubes so can you explain in few words how a higher voltage powering tubes affect their working? How it affect sound quality? Always higher voltage = better sound? And can I adjust HV (55-100V) without any other changes in circuit??
And thanks for your patience for newbies
This is actually a hard question to answer.

Most tubes are designed to run at voltage higher than the SOHA II uses. When they run at higher voltages they are more linear and create less distortion. There are exceptions. The 6922 can run very happily at 100V.

So, theoretically, tubes should sound better at higher voltages. But, my experiences are that some tubes do very well at lower voltages. For example, in the SOHA II the 5963 sounds very good running at 60V even though it really should be running at 150V.

I know that this is not a great answer, but so much of audio is subjective and everyone's ears are different.

You can adjust the voltage from 55-100V while the amp is running as long as you do it slowly. If you change the voltage too fast, the e12 will trip, but if you change it slowly the e12 will not be tripped.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #133 of 1676
Hello again,

I've now finally had more time to work on my amp, and it's ready for initial tests. I adjusted P2L/P2R as per instructions on the website and got 220mV across R10L and R10R, but the relay on e12 won't trigger. When I measure the voltage across the coil on the relay, I can see it changing from zero to about 12V a few seconds after being powered on, but the relay stays silent and the connections won't change. I'm using the Omron relay in the official BoM.

Any ideas what might be wrong?
post #134 of 1676
In response to my own post; the polarity of the relay was reversed. I didn't even know that some relays require a certain polarity to trigger, and the greatest thing about this particular one is that the picture showing the + and the − on the top of the relay is reversed. It does say “bottom view”, and apparently it means that the picture is inverted, not that it depicts what's actually on the bottom of the relay right under the illustration. Gah.

Now it clicks.
post #135 of 1676
Thread Starter 
Arkku, I'm not sure what you did to fix the problem. Did you alter the traces on the board? I'm using the BoM relay and it worked without problems when installed according to the board's pad locations.

So, I'm trying to figure out if there is a problem that needs to be addressed.

Thanks for the help.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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