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Old 5th January 2009, 10:37 AM   #1031
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Unhappy Still no response from you

Hi Tad, as we were discussing in private emails, I still have not received my 4 PCB's for this GB. We discussed splitting the loss which both of us seemed to think was fair at the time.
Since then I have not received any more communications from you. Have you been getting my emails ? A simple response would be appreciated even if you did change your mind.

Thanks,
Marc.
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Old 5th January 2009, 01:47 PM   #1032
clm811 is offline clm811  United States
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Quote:
I found a nice enclosed ice cube type relay on ebay with a built in variable timer for about 5 bucks
I searched ebay, to no avail.
Can you give a model number, or more specific description?
TIA
-Chas
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Old 6th January 2009, 10:41 AM   #1033
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Chas,
This is the exact relay,http://cgi.ebay.com/TYCO-ELECTRONICS...3A0%7C293%3A1, But the price was only 5.00 dollars when I bought them. If you keep looking you might find some cheaper or this seller might take a whole lot less.
Tad
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Old 6th January 2009, 10:57 AM   #1034
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Chas, Here is another one much cheaper,http://www.electronicsurplus.com/com...1016-7234.htm, Just keep looking.
Tad
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Old 7th January 2009, 02:31 AM   #1035
clm811 is offline clm811  United States
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Quote:
Here is another one much cheaper,http://www.electronicsurplus.com/co...71016-7234.htm
Tad- It looks like a broken link.

Is there a similar relay listed here(?):
http://www.surplussales.com/Relays/RETimeD-2.html

TIA

-Chas
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Old 7th January 2009, 10:48 AM   #1036
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Chas,
The Surplus Sales site has quite a few good choices, but I do no know what price range you are willing to accept. First we need to know what voltages you have available to operate the relay. Then you can choose any of the relays with that coil rating and go from there. I liked the external resistor method of changing the time delay because it was simple and easy to incorporate into the chassis. Installing a simple pot works also and is more versatile. Be sure to choose the delay on/delay off which fits the application, they come in both forms.

Any setup you use to switch the mains power or DC off the thermistors after a predetermined time should work here.

Another option I like, proposed by Bob, is to build a complete separate power distribution unit with inrush surge protection and delay for all of the items in your arsenal. It could be something quite robust and have a mains power spike protector, like for computers and such, mounted in it. This also lets you turn everything on with one small low voltage switch. You can add earth ground hum isolators in there also. Real nice idea. This keeps you from going through this scenario on each build. Tad
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Old 7th January 2009, 08:23 PM   #1037
clm811 is offline clm811  United States
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Smile Thanks

Thanks all for taking the time to help with the multitude of questions.

There isn't another current thread specific to assembling an amp from Jens' boards, and there are several of us (newbies) who need additional information to complete our amp projects.

-Chas
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Old 8th January 2009, 10:47 PM   #1038
rob3262 is offline rob3262  United States
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Default small signal transistor matching

I need six matched sets of 4, 24 in all. Out of a pool of 50ea of onsemi MPSA42's and 92's, I had nothing. Not even close to matched gain.

Bought an additional 100ea Fairchilds, hoping to get some different gains. Which I did. But out of a pool of three hundred transistors I have two matching sets, 8 transistors total.

Is it common to have so few matches???
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Old 9th January 2009, 08:03 AM   #1039
clm811 is offline clm811  United States
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Quote:
Out of a pool of 50ea of onsemi MPSA42's and 92's, I had nothing... even close to matched gain.
Rob,

We (myself, along with Brutepuppy and WJH) found almost the same thing. The PNP's measured range was quite different from the NPN's in our similarly sized pool of devices, and we settled upon matched pairs of PNP's used together with matched pairs of NPN's("choice#3").

Please note, however, that in his construction notes Dr. Leach indicates DC offset may still not be a problem:


"Ideally, all four transistors should be matched. If this cannot be achieved, the second choice is for Q1 and Q3 to be matched and Q2 and Q4 to to be matched. The third choice is for Q1 and Q2 to be matched and Q3 and Q4 to be matched. The typical dc offset at the amplifier output is less than 50 mV. If you are concerned about how well the transistors are matched, I have seen amplifiers built without matching the input transistors, and they had no dc offset problems. "

Opinions?

-Chas
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Old 9th January 2009, 10:15 AM   #1040
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For what it is worth I did not match anything on my Leach and the total offset is less than 20mv. Matching is of course the best way to go, however sometimes you just want that thing to work.
Tad
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