| Author |
Message |
    
Pinger
| | Posted on Tuesday, January 28, 2003 - 5:27 pm: | 
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I just put new transistors in this amp (sd1446). It originally had mrf455s. The amp seems to work, but it heats up relatively quickly. It draws about 20 amps at deadkey on all power levels.
Any ideas what could cause this? |
Bigbob
| | Posted on Tuesday, January 28, 2003 - 10:44 pm: |
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Improper biasing I suppose,different manufacturers.You just can't take 2 pills of any make and expect them to work without tuning,take it to a competent tech and he should be able to repair it,I'm assuming those are a matched pair,if not get 2 that are,that in and of itself can cause your problem.Bigbob |
Znut
| | Posted on Tuesday, January 28, 2003 - 10:24 pm: |
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Needs to be matched?
Couldn't find 455's? |
Pinger
| | Posted on Wednesday, January 29, 2003 - 10:41 am: |
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Well, 1446s are what i had. They have the same lot number, but as far as i know, they're not matched. |
Pinger
| | Posted on Tuesday, February 11, 2003 - 1:11 am: |
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If anyone has any ideas about it, please drop me an email. |
2600
| | Posted on Wednesday, February 12, 2003 - 1:24 am: |
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Sounds like a pretty simple pair of choices,
1) Redesign the amplifier to match the new transistors.
2) Put MRF455 parts back in that will match the design of the amp.
Bear in mind that the SD1446 is NOT designed for linear SSB operation. The MRF455 IS.
73 |
Pinger
| | Posted on Friday, February 21, 2003 - 1:19 am: |
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Well..the amp was given to me for "parts" and the guy said that it was trashed. I installed those new 1446's in place of the MRF455s, which were bad. After messing with the amp for a little while, I started paying more attention to the bias. The diode that runs in series with the large power resistor was in backwards. I assume that he tried replacing it and put it in backwards.
If anyone has a schematic for this amp, please drop me an email. |
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