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Texas Star 1200 DX Hotplate

turbo chicken

New Member
Sep 9, 2013
5
0
1
37
I have a Texas Star 1200 I'm looking for a good tech to upgrade this amplifier. I wanna keep the ab1 biasing but just Beef up the components and possibly add some more filtering. I wanna a clean amplifier i can be long winded on. Any suggestions for a good tech? I was told about Crusher in Ky but haven't found a contact yet.
 

RadioGuy772

Active Member
Dec 30, 2013
106
45
28
Unless you have a tech with a scope, power supplies to power it, and a spectrum analyzer, and KNOWS HOW TO USE IT, then leave it alone. Guys changing all the fixed capacitors to trimmers in attempt to get more power out of it will ruin the amplifier. Not a lot of amp builders understand the texas star designs anyways, because of the way they route the B+ to the bias supply along the same route the RF takes, and other little interesting differences between the design and typical CB amplifiers.

Can I ask...what are you trying to do? Just drive it with 70 or so watts PEAK, and give it a good voltage / current source, maybe order a fan kit for it if it doesn't have one, and leave it alone.

If you really want to, the bias circuit can be re-worked, as of right now, it is a voltage divider design, and depending on drive, and voltage source, it can, just like a lot of CB amplifiers actually change class of operation during use. (AB, B, C)
 

Crusher

Well-Known Member
May 12, 2007
838
370
73
Really the only upgrade I would suggest is to regulate the bias on each 2 pill / transistor section. Doesn't matter how clean the amp can be, if you use a junk radio or a class C modulator to drive it. Then your right back at square 1.
 

Crusher

Well-Known Member
May 12, 2007
838
370
73
These amps are not made to be driven hard. I would use no more than a single 2290 to drive this with. And that should be biased AB. Fan kit is a must.
 
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Shockwave

Sr. Member
Sep 19, 2009
3,780
3,280
273
This amp is not so bad in it's stock configuration. It does not suffer from RF getting into the bias supply like the smaller ones because it has a dedicated contact on another relay to switch the bias. It just has medium sized power transistors. Many used the SRF-2072.

"Beefing up" and "clean" are two different things which often oppose each other. The cost of beefing it up simply is not worth the results. If you took the time to replace all the finals with 2SC2879's you still need to rematch the input and output impedances to the new lower level in order to see the power gain.

It could easily cost $500 to do this job right and you'll gain a whopping 1/2 S-unit. That's why I say skip that goal and move onto running clean with a good duty cycle that will allow you to be long winded. This usually means reducing power below maximum ratings and adding some filtering.

Rather than running the 1200 PEP, give up a 1/2 S-unit and run the amp at 600 watts PEP. That will make a dramatic improvement with Inter Modulation Distortion. Adding external low pass filters on both the input and output of this amp will snuff out all the objectionable harmonics rather well assuming it's being used in the upper HF bands.

The last thing to address would be some fans to get rid of heat during those long transmissions.
 
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