I'm working on a pair of PT300's for a friend. These were bought >10 years ago for $5/pair, and occupied a place of reverence on a shelf till last week. Now he wants them fixed. I've fixed almost everything, but the RF output on one of them is very low, perhaps 10mW. The other is doing 7.5 watts which is acceptable. I am looking for the manual or even just a schematic so It will be easier to work on the transmitter portion. These are on 43.120, and will later have to be moved to the 6M band. From reading other posts, that should not be too hard to do with the documentation (assuming I can find it. Motorola does not have it any more).
Anyway I wanted to share pictures of them:
http://www.bunkerofdoom.com/PT300/index.html
BR
Patrick
PT300 VHF Low band repair and 6M conversion
Moderator: Queue Moderator
Re: PT300 VHF Low band repair and 6M conversion
7 Watts is too much for a PT300, reduce the level to about 5W.
Other than an alignment issue or a bad trimmer, the other one probably has a blown PA transistor. Germanium transistors are where the moniker "Three Legged Fuse" comes from.
The manuals are available on eBay all the time. A 42-50 MHz model will do 6 meters without any conversion, just re-align it. The boards are the same as an HT-200, except for the PA deck, so an HT-200 manual will also work for most of the radio.
Many PT-200/300's these days are in blown-up condition because someone tried to power them up from a bench supply with reversed polarity. The radios use PNP transistors and the battery wire color code polarity is the opposite of what you would think. The usual symptoms are blown audio output transistors and a blown PA transistor.
Some of these radios won't meet sensitivity specs these days due to a defective Permakay filter. Yes, I know someone is going to say that Permakays carried a lifetime warranty, but good luck making a claim on it...
Other than an alignment issue or a bad trimmer, the other one probably has a blown PA transistor. Germanium transistors are where the moniker "Three Legged Fuse" comes from.
The manuals are available on eBay all the time. A 42-50 MHz model will do 6 meters without any conversion, just re-align it. The boards are the same as an HT-200, except for the PA deck, so an HT-200 manual will also work for most of the radio.
Many PT-200/300's these days are in blown-up condition because someone tried to power them up from a bench supply with reversed polarity. The radios use PNP transistors and the battery wire color code polarity is the opposite of what you would think. The usual symptoms are blown audio output transistors and a blown PA transistor.
Some of these radios won't meet sensitivity specs these days due to a defective Permakay filter. Yes, I know someone is going to say that Permakays carried a lifetime warranty, but good luck making a claim on it...
Re: PT300 VHF Low band repair and 6M conversion
I have just finished scanning a PT300 Low-Band manual into PDF, so it should be available on the Repeater-Builder site shortly. I intend to follow up with a couple of high-band manuals shortly.