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Old 19th January 2010, 06:25 PM   #31
sonidos is offline sonidos  United States
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Default C1 and C3

Ivey,

If you're watching this thread, what types of film caps have you tried for C1 and C3? I'll try polypropylene first....they are not that much $$$.
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Old 19th January 2010, 07:05 PM   #32
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Guys, you need a resistor between C2 and the base of Q2 on preamp circuit, not the SHORT.
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Old 19th January 2010, 11:06 PM   #33
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Default Capacitors

When we first built the unit we used Sprague's Black Diamonds. That was 1959-60. They were really not that good, if you were to compare them today, with the capacitors from China or Taiwan. They were the new plastic type at 10%. If it was not for their size, we would have used oiled filled capacitors.

The new metal film capacitors today (across the board) are of good qualitly. Regardless as to who makes them.

But if you desire the use of MKP capacitors. Please use them and let me know what your results are.

Take Care

Ivey

Last edited by Ivey; 19th January 2010 at 11:08 PM. Reason: grammar
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Old 19th January 2010, 11:37 PM   #34
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Default Steven:

Truly, there is no resistor on the base of Q2.

The 82k feedback resistor R6 and C4. provides base bias for Q2.

Putting a resistor on Q2's base may cause it to become unstable.

But go ahead, do some R & D, and let me know. Maybe with the more modern parts and materials. It may improve our old circuit.

Take Care

Ivey
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Old 21st January 2010, 06:58 PM   #35
sonidos is offline sonidos  United States
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Ivey,


Yes, and I am putting a list together of metal film resistors. Is it safe to say that you used carbon comp resistors in the original?

Many thanks for sharing your knowledge.
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Old 21st January 2010, 11:12 PM   #36
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Default Resistors:

Yes, we used the best carbon resistors available at the time. Dale, 5%.

There are people today who still enjoy the sound of carbon comp. resistors.

After years of study, about resistors. I still seek out carbon comp. resistors for three purposes. To use them in radio, power supplies and regulators. They are great in those roles. Because they do not add inductance or change the impedance of those circuits greatly. Some of my old friends, would not even give you one of their carbon comp. resistors. They have the old types, when making a good carbon comp. was an art form.

Some of the best carbon comp. resistors was used by Zenith and Muntz TV.

So if you get your hands on some of the old console TV's, you will have some good carbons. For they are far superior to what you can obtain today.

Take Care

Ivey
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Old 21st January 2010, 11:44 PM   #37
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This puts me in mind a little bit of the Dynaco PAT4 for some reason, probably because it used only 4 transistors a channel - 2 for line amp and 2 for phono preamp. It was something called a BC109 - I don't know how that would stack up to a 2n2222 sonically. I had one of those for a few years.

I once built a compact transistor phono preamp using MPSA18's selected for hfe's up around 1000. Initially I used only one transistor per channel and it sounded better than I expected, but a little low on gain, so I added a second gain stage using the same type transistor, and that's when the solid state grain really started to become noticeable to me.
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Old 22nd January 2010, 12:21 AM   #38
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Default Thoriated:

What is "Fly over Country"?

Yes the BC-109, is an outstanding transistor in its own right. But I feel that the BC-107, is more useful.

One have to understand the history of transistor finance, in order to get an operational picture of transistor use and development.

It was cost that made designers, design as they did in those days. Transistors were new and expensive, compared to Tubes. A new 12AX7 would cost you 93 cent. You got two tubes in one. One 2N2222A, military grade, would cost $15.00 dollars.

When Motorola, discovered how to grow crystals cheaply, the prices dropped to a low of $4.00 dollars. But still, compared to tubes. It was expensive.

The db gain is all important in phono amps and in the use of transistors. A two transistor set up could give you as much as 35-40 db gain, depending on the transistor used. Looking at transistors with a hfe of 100-300 @
5v/2ma. You have a large range to chose from. And adding an emitter follower, enhances the current gain, that your will obtain and the lower impedance needed to drive capacitive loads and load matching.

With transistors costing 3-5 cents by the hundreds, It is only good practice to use general purpose transistors in your designs, when designing phono amps today.

The title "general purpose" is not what people think it is. An example of a general purpose transistor is the 2N3904. Some of its hfe gain spec's are off the chart at low amp transmission levels. Its power output is good over a given range, its noise level is a mere total 5 db. Plus it has good freq response and switching response.

When you use very high gain transistors. Your designing problems are increased, because you must design out all the unwanted noise, freq pick up, and a host of other ills that come with that type of transistor. And shielding. You may need to incorporate shielding.

The Pat-4 is a good preamp. I have the design of it. It was a good unit. And still is today.

Take Care

Ivey.
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Old 22nd January 2010, 12:49 AM   #39
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Hi, Ivey -

'Flyover Country' is the part of the US that elite jet setters fly over when they travel between the east and west coasts

With the one stage phono preamp I made, the RIAA characteristic was obtained through feedback, so probably not the best equalization topology possible from a sound quality perspective. But I built it when I was still pretty young.

I didn't know that good small signal transistors were still that expensive in the mid sixties. Were germanium transistors as hard to design with for reliability as I have read?

Last edited by thoriated; 22nd January 2010 at 12:58 AM.
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Old 22nd January 2010, 01:02 AM   #40
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Default Thoriated:

No, Ge were easy, just like silicon. But they were heat sensitive. And they never made good power Ge. transistors, because of the heat issue.

To be honest about, Ge transistors have better tonal quality than most silicon units They are still being made, for use in guitar effects equipment. I built all of my grandsons guitar effect equipment. Now his friends are hounding at me.
No chance. Family yes, others no. I am retired, I just did not want my wife and daughter ganging up on me.

The 1960 saw the price of transistors fall. By the end of the 1960's transistor prices were down to about $1.00. But the of IC's was through the roof.


Take Care


Ivey
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