Discussion in 'Amplitude Modulation' started by KA4KOE, Sep 12, 2019.
Thinking about another big box. Any thoughts on T-3's? I do know they are not common.
YES THEY ARE NOT VERY COMMON.
I THINK THE ONLY PLACE YOU WILL FIND ONE IS HERE
HAVE FUN IN YOUR SEARCH
73 - K1LKP
They're around... see 1-2 for sale every year or so (that's with casual looking, not a full-on hunt for one). They definitely tend to be quirky: full of relays and interlocks and connectors, that tend to have reliability issues. But when they run well, they're impressive.
I've been chasing a hum issue in the speech amp of my F model for quite some time now. With the cramped chassis and interlocks, even basic measurement-taking can be rather time-consuming.
WA1HLR and some others have published now tried & true mods to improve the audio quality if you're looking for that sort of thing, but using a good mic on the 600 ohm input they put out pretty good audio in stock form.
The T-368 PTOs seem to be a lot more available than the actual units. Obviously, there were a significant number of spare parts made for these transmitters.
Using one of the PTOs as the basis for construction of a home-brew transmitter is something to be considered.
Speaking of PTOs, I have a concern with the PTO in one of my 75A-4s, but the ones in the 75A-2, -3, late 51J series receivers and most likely the T-368 transmitter, are similarly constructed.
The ball bearing on the main tuning shaft appears shot (the smaller ball bearing on the main tuning shaft, not the larger one on the passband tuning pulley attached to the front of the PTO). The tuning shaft binds in spots; the feel is typical of a bad ball bearing. A drop of oil helped slightly but did not resolve the problem.
A good replacement bearing was salvaged from a junked PTO found in my parts collection. After disassembling the junker I understand how the PTO is put together: a small e-ring, which rides in a groove in the tuning shaft, holds the bearing in place, and snugs up against the ball bearing to prevent any forward-to-backward slop in the shaft and tuning slug.
The problem is reassembly: re-engaging the e-ring into that groove in the shaft where it fits over the bearing. The e-ring was easily removed, using a couple of small screwdrivers (I probably need a proper e-ring tool to get it back in place). When the e-ring is removed, a cup-shaped washer inside the sealed unit acts like a spring and pulls the tuning shaft back slightly, just far enough to move the groove partially inside the bushing on the bearing. The purpose of this springy washer is to maintain tension between the ring and the bearing, to prevent front-to-back motion. Once removed, the e-ring won't go back into the groove because it is too thick to fit into the remaining gap. I'm afraid to try to brute-force the ring into the groove out of fear of damaging the shaft or the bearing.
I'd be interested in hearing from anyone who has serviced one of these PTOs, and how you re-engaged the e-ring.
I use a T-368 PTO master oscillator/multiplier unit as a VFO for all my transmitters. It is now so highly modified that it would be very difficult to ever be made to work in a T-368 again. I found it to have a slight drift when turned off during receive and back on when transmitting. The drift was enough to be a problem on 40m CW when the other operator was using a highly selective CW filter. My solution was to let the oscillator tube run all the time, shielding the unit and filtering all external leads well enough to make it inaudible in the receiver.
I've never owned a T368. Personal feelings here: I don't care for rigs that hide away the tubes so you can't see them. The T3 in some ways has great construction but one or two others have alluded to the problems that all the chassis connects pose. I've known of enough T3s out there that give their owners grief that I've never pursued one, however you'd think that the connectors being a mechanical problem, would be fairly easy to deal with. I believe this is the arrangement whereby you slide a chassis in and it seats with a bunch of plugs or jacks in the back of the cabinet. In any event, you have a 500 watt rig, and if I wanted a mil. surplus 500 watt rig, I think I'd prefer a BC-610I. However the 610 has its problems and limitations also.
I have another option I am pursuing.
I hear a number of them on the air, they sound good and seem to keep working.
Its a big heavy general coverage transmitter full of quality parts.
These days, you should be able to pick up a T368 or bc610 without much trouble.
Actually moving it might be anther thing...the K7DYY rig might be easier!
That is a good assessment.
I think I have an alternate solution. Yes, the DYY is reliable AND boring.