Recently bought these two units in the attempt to start aCC station. When i power up, the 6B gets about 25 plate current, ma - but the meter on the T8 still shows nothing. No readings on any setting.
Anyone have any experience with these two?
thank you - yes the T8 is supposed to couple it to the AC line.
The T-8 was a coupler that started getting bundled with some LPB transmitters.
The 6A transmitter in this scenario is one I do not know about, but I gather that it operates with tubes.
MICRO 1700 has the correct idea by testing it into a dummy load, which is a 50-ohm non-inductive load able to handle the Wattage.
it has 3 tubes that are new... it powers up and plate voltage slowly starts to rise to about 25... the T8 gets no reading on the meter at all
I have been told to recap? Any advice there?
also, is it possible to use a three prong plug to connect the t8 to the power line. at an outlet instead of the box?
Told to recap what?
The transmitter, or the coupler?
I would start with the transmitter.
yes- I am sorry... the transmitter. I looked at it and am not sure I could do that. any ideas?
i once fed a TH thru the T* and got no meters then either
Is there hum on the carrier?
Have you put audio into the
transmitter, and - if so - how does
the audio sound on a radio?
Is the transmit crystal firmly seated
in the socket - or - maybe the crystal
has a problem.
I guess what I'm really asking is - how
does the signal sound on a radio - but
if you have already checked that - -
then the problem is a mystery for the
time being.
Bruce, The DOGRADIO Group
as of yet, I have not been able to locate a carrier. I thought it was funny not to hear anything but thought it may be getting absorbed in the T8's dummy load.... it does have plate voltage though and I have heard audio I was feeding in inside the cabinet as well. just no on air signal nearby and no meters on the T8
This may not be helpful since I am not familiar with this particular equipment but tube transmitters need to be carefully tuned. The usual procedure is to apply just enough drive to the final tube to get a plate current and then tune the tank for a dip in the plate current. The drive is then increased and the tank is again tuned for the dip and then the drive is set to get the specified plate current. The dip depth and sharpness will vary with the load.
Again, I don't know this particular system but I hope this makes some sense and will help. This is how I used to tune the CC transmitters when on campus and is how I tune my low band tube rig now.
Neil
I found the application sheets for the 6A and 6B transmitters, which are the sales sheets originally sent out by LPB.
6A is a 4-Watt tube transmitter, and 6B is a 5-Watter.
The meter on the transmitter shows plate current, which was mentioned in the opening post.
As Neil said, the plate current should be tuned for a dip, not a peak.
In a paragraph titled "Quality Features of the 6B" it says, "The RF output will survive indefinite mismatch of any nature, something very difficult to achieve in many tube and most solid-state power amplifier circuits."
This sheet is dated 2/73 and the coupling unit mentioned on the back is T2, but I think the T8 was an improved coupler that soon became available.
The meter or its circuit components on the T8 might be faulty, so check each part in the path.
Have you taken voltage readings in the transmitter with a volt meter?
Like Bruce said, it would be a good idea to replace capacitors, as those do tend to become weathered after a long time.
MORE INFORMATION
I knew I'd seen papers on the T8 somewhere, and here it is, the last few pages of my manual for the LPB TX2-20 transmitter...
This is a set of operating instructions for the T8. Do you have that information? If not, I will type it into this thread for you.
Be sure to check the 3x 3Amp fuses.
NO. Using a 3-prong 119V AC connection will only put your coupling into HALF of your AC power system. But a 3-prong 220VAC plug will attach you to the full AC system, but the proper way of connecting is to have an electrician connect your coupler straight into the electric panel box... do not attempt this yourself unless your will is made out and funeral plans have been made.
A safer way to "do it yourself" is to use the "neutral injection method" of connecting to the power, but get your equipment checked out before advancing to that stage.
If your 6B is like my 6A, you should be
able to open it up easily and look at
the inside. {I kept the top off so I could
look at the glowing tubes.) There are
latches on the sides of the transmitter -
at least mine has latches - I hope
yours does. There should be a crystal
in there. Again - if your transmitter is
llike mine - this will be a large fundamental
crystal cut for a frequency in the
AM broadcast band. My 6A would
only transmit on one frequency. I
had a lot of trouble finding a good
channel in the AM BCB to trnsmit on.
Then, I finally found a crystal for
1020 kHz, which is empty here during
the day. That worked.
Do you want to check for a transmit
crystal first? Take your time. Have
the transwmitter off and unplugged.
Best wishes,
Bruce, The DOGRADIO Group