Johnny,

I believe all of the original D-104 elements are either ceramic or crystal and they are designed to work into a high impedance.

HOWEVER-a lot of the original elements died so when buying from Ebay you may get one with a dead original element or one where the element died and was replaced with something else so it is a bit of a gamble. In my experience, original ceramic elements held up well but the crystal elements are often dead or severely degraded.

It is possible to retrofit a condenser or dynamic element to the D-104, in the past kits were available from various sellers to do so but I don't know if that is still the case. A lot of later D-104 microphones have a preamp built into the base because that is what the large CB market wanted. In many cases, the ceramic element is still fine and it is the preamp that has died and you can just bypass it. You don't need the preamp for your T-4XB anyway so if the D-104 you get has one I would bypass it to avoid future issues.

The Drake T-4 series presents a very high microphone input impedance and a wide variety of microphones will work well and easily with it. In general, even a microphone designed for lower impedance will work into a high impedance input but with a different audio response; the reverse isn't true and a high impedance microphone generally won't provide sufficient output when looking into a very low impedance load. A few rigs (some Icom sets come to mind) used a condenser microphone that requires voltage from the rig to operate and this type won't work with your T-4XB.

Rodger WQ9E

Thanks again Roger,

I'll keep looking. Maybe I can find a kit for a D 104.

Johnny

Rather than use a tube checker, put the finals in one at a time using the same socket for each test.

To conduct this test:
1. Disconnect the AC-4 from the T-4XB every time before going into the final cage to protect yourself from HV.
2. Place one final tube into the T-4XB and with the bias set to maximum (which results in minimum plate current), key the microphone in SSB mode with the drive at zero and slowly decrease the bias until this tube indicates half of the normal idling current for the T-4XB. Carefully note that position on the meter.
3. Disconnect the AC-4, remove the final tube (it will be somewhat hot), and insert the other final tube in its place.
4. Reconnect the power supply and without touching the bias control, again key the rig in SSB mode and note the idling current.
5. A reasonably well matched set of tubes will have very similar idling current.

NEVER try to run the test with both tubes at once with just the plate of one disconnected or you may destroy the screen grid of the disconnected tube.

Rodger WQ9E

It has been my experience that finding a bad D-104 ELEMENT is probably pretty rare. I've bought 25 or more of these mics over the years and only had one with a problem, and that was a mechanical problem due to someone crushing the diaphragm, and I was actually able to repair it.

.... I suspect, like silver mica "disease" and the problem with 6146B tubes, it is in large part internet lore...

The slug rack could be the reason but usually it is the little reduction drive that is the reason for stiff motion. A few drops of synthetic oil will probably restore its motion. You can also put a drop on each end of the slug rack at the contact points but I suspect the reduction drive is the reason.

If you haven't already run across these, read through VE3EFJ's excellent "Drake Notes" document: http://www.zerobeat.net/drakelist/drake ... odtoc.html

and the PTO in these sets will need lubrication. VE3EFG covers it in his Drake Notes and you will also find info here: http://www.wb4hfn.com/DRAKE/DrakeArticl ... ke_PTO.htm

PTO lubrication is very simple and it avoids potentially expensive damage from wear. I do it for every vintage Drake that crosses my bench. If the slug mechanism drive is sticky/stiff, then you can be sure that the PTO is also in need of attention.

Rodger WQ9E

Johnny,



I don't have time to pull my schematic now but going from recall, in Tune the filters are bypassed so you are likely looking at a dirty switch contact. Set to X-Cw or X-AM the carrier oscillator is shifted to put the signal into the LSB filter passband but that doesn't happen for tune mode.

If the carrier oscillator is set up correctly AND you have proper sounding audio on both LSB and USB then both filters are OK.

Rodger WQ9E

Johnny,

Just to clarify:

You are tuning up using CW and then with the same audio gain setting the output is low with USB?

If so then the USB filter may be defective. First double check to make certain that the carrier oscillator is dead on 5.645 Mhz. If so then either there is a defective/dirty switch contact in the sideband filter selection section or your USB filter has died. It does happen but it isn't common with the T-4 series filters like it is with the early TR-3 filters.

Rodger WQ9E

Johnny,

I believe all of the original D-104 elements are either ceramic or crystal and they are designed to work into a high impedance.

HOWEVER-a lot of the original elements died so when buying from Ebay you may get one with a dead original element or one where the element died and was replaced with something else so it is a bit of a gamble. In my experience, original ceramic elements held up well but the crystal elements are often dead or severely degraded.

It is possible to retrofit a condenser or dynamic element to the D-104, in the past kits were available from various sellers to do so but I don't know if that is still the case. A lot of later D-104 microphones have a preamp built into the base because that is what the large CB market wanted. In many cases, the ceramic element is still fine and it is the preamp that has died and you can just bypass it. You don't need the preamp for your T-4XB anyway so if the D-104 you get has one I would bypass it to avoid future issues.

The Drake T-4 series presents a very high microphone input impedance and a wide variety of microphones will work well and easily with it. In general, even a microphone designed for lower impedance will work into a high impedance input but with a different audio response; the reverse isn't true and a high impedance microphone generally won't provide sufficient output when looking into a very low impedance load. A few rigs (some Icom sets come to mind) used a condenser microphone that requires voltage from the rig to operate and this type won't work with your T-4XB.

Rodger WQ9E