Preamp before Texas Star dx250

[81bronco]

Good Afternoon!

PLEASE dont flame me too hard if this has been asked a million times but i honestly searched and didnt find anything.

Does anybody know how to build a 15-20 watt amp? The reason i ask is my Uniden was peaked and tuned and puts out exactly 4 watts. I would like to drive my Texas Star DX250 with close to 20 watts input which TS says is OK. This will result in peak output from the 250.

I was also looking at the KL35. Would this do the same thing, or am i just asking for trouble?

Thanks!

 

[fodendaf]

If TS says so then it's fine. Though you would have better audio from the kl40 as it has a ssb switch so its probably ab biased. Far cheaper to buy an amp rather than build one. I suppose you could do with a variable power knob on the amp also but I don't see one on any of the low powered models.

 

[81bronco]

If TS says so then it's fine. Though you would have better audio from the kl40 as it has a ssb switch so its probably ab biased. Far cheaper to buy an amp rather than build one. I suppose you could do with a variable power knob on the amp also but I don't see one on any of the low powered models.

Will the KL40 overdrive my TS? It says 20 watts max into the TS. I have a HP202 meter to watch my average power output to make sure i am not overdriving the TS, still want to make sure the TS is safe!

Also my Uniden does not have a SSB switch, so does my preamp need it?

Thanks for the help!

 

[Robb]

Your stock 4w radio will have a PEP ('peak envelope power') wattage rating of 12-16w - already. No preamp is necessary for the TS-250 at all. In fact, it is usually suggested by TS to turn the AM carrier down from 4w to 1.5 watts dead key (dead key=mic gain set @ 0) for a cleaner, cooler operation.

 

[fodendaf]

It's not a preamp, it's a driver amplifier. It won't overdrive the TS if you keep the input drive from the uniden down. If you can't do that yourself or get an amp with a variable power on it you'll have to hire a tech to match the radio power to the amp daisy chain. You don't need the ssb switch but you will get more compliments on your audio if you do use that amplifier over the other.
The easiest way to find out is there too much output from the driver is to hook it up and quickly get a power reading from it.

 

[81bronco]

It's not a preamp, it's a driver amplifier. It won't overdrive the TS if you keep the input drive from the uniden down. If you can't do that yourself or get an amp with a variable power on it you'll have to hire a tech to match the radio power to the amp daisy chain. You don't need the ssb switch but you will get more compliments on your audio if you do use that amplifier over the other.
The easiest way to find out is there too much output from the driver is to hook it up and quickly get a power reading from it.

Thanks! So lets say i have the CB>KL40>DX250>HP202>antenna. Would I watch the HP202 to get the average output of 250 or would that cause my PEP to be way to high coming out of the TS? I know the HP202 doesnt show peak, only average and i have read that its not even that good at doing that on the 100 and 1K scales?

Thanks again guys. Just dont like that smell of buring electronics!
Phil

 

[81bronco]

Your stock 4w radio will have a PEP ('peak envelope power') wattage rating of 12-16w - already. No preamp is necessary for the TS-250 at all. In fact, it is usually suggested by TS to turn the AM carrier down from 4w to 1.5 watts dead key (dead key=mic gain set @ 0) for a cleaner, cooler operation.

Robb, My 202 does show 4 watts on the HP202 meter. I also have 1.5W DK. MY 202 shows a peak of about 130 watts. So your saying if i ran the KL35 i would smoke the TS? I wish i knew a way to measure PEP! I also forgot to say the CB is the old school Uniden PC78XL with the early finals, made in the Phillipines.
Thanks again guys.

 

[fodendaf]

Rather than risk the TS I would hook it up like so CB>KL40>HP202>antenna then see that it's under 20watts(PEP). Then if all is well hook it up like you say. I never had a meter that read PEP. I used just get a deadkey reading that said 4 watts and then whistle to get a PEP reading. Some will laugh at that but that's what most people do.
Incidentally the ts250 uses 2 2sc2290's that each are rated for 80watts PEP but i suppose Texas star has a good idea of what an amp will take at its limits.

 

[81bronco]

Rather than risk the TS I would hook it up like so CB>KL40>HP202>antenna then see that it's under 20watts(PEP). Then if all is well hook it up like you say. I never had a meter that read PEP. I used just get a deadkey reading that said 4 watts and then whistle to get a PEP reading. Some will laugh at that but that's what most people do.
Incidentally the ts250 uses 2 2sc2290's that each are rated for 80watts PEP but i suppose Texas star has a good idea of what an amp will take at its limits.

So while I whistle as long as my average reading is under 20 watts I am good? Also in a former life I was an avionics tech on the C-17 and I was looking at the wiring diagram of the DX250 and seeing that it’s exactly the same as DX350 except for the power transistors and the number of turns on T1. I am thinking that if I have my 20 watts while I whistle; I will than verify the 250 and possibly swap transistors in the TS to bring it up to 350 specs.

This all started with a simple CB purchase and now is starting to become an obsession!

 

[Robb]

Texas Star Export Feature Chart

 

[fodendaf]

Yea should be. But bear in mind that the pep input you read probably related to max ssb input which could be twice the am pep input. It's all very confusing and I wish I understood it myself. Robb is giving you good advice to not overdrive your TS. They are a nice amp and rather than modifying it you could swap it with someone for a 1x4 davemade or fatboy.

 

[81bronco]

Yea should be. But bear in mind that the pep input you read probably related to max ssb input which could be twice the am pep input. It's all very confusing and I wish I understood it myself. Robb is giving you good advice to not overdrive your TS. They are a nice amp and rather than modifying it you could swap it with someone for a 1x4 davemade or fatboy.

I found a place here in portland that will measure my PEP for free. Downside is i need to take it all out of my bronco . I think that will be the safest route to make sure eveyrthing is on the up and up, and if i decide to swap to the 2SC2879 I will do that at a later time. I really dont want to swap to a Davesamde or anything else because i had a custom box made for the TS and the HP202.

Also Rob you are saying DO NOT run the KL40 becuase i am only measuring average power not PEP with my HP202 meter. If i run the KL40 and set up readings on the 202 to 250watts i will smoke the amp?

Thanks again guys!