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 Post subject: Re: New Drake 4B project
PostPosted: Nov Tue 24, 2020 6:15 pm 
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Joined: Oct Sun 11, 2020 7:40 pm
Posts: 64
Location: Guthrie, OK USA
rsingl wrote:
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


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 Post subject: Re: New Drake 4B project
PostPosted: Nov Wed 25, 2020 7:08 pm 
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Joined: Oct Sun 11, 2020 7:40 pm
Posts: 64
Location: Guthrie, OK USA
JohnnyColeman wrote:
rsingl wrote:
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


I checked the tubes in my T4XB and found the numbers different on my finals. How much different is OK?

Johnny


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 Post subject: Re: New Drake 4B project
PostPosted: Nov Wed 25, 2020 7:39 pm 
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Posts: 7694
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


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 Post subject: Re: New Drake 4B project
PostPosted: Nov Wed 25, 2020 7:47 pm 
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Joined: Oct Sun 11, 2020 7:40 pm
Posts: 64
Location: Guthrie, OK USA
rsingl wrote:
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


Thanks again Roger.

I just found some NOS 6GJ5 https://tubeworldexpress.com/products/6 ... -6gj5a-nos
I think I will snap up a couple pair for future use.

Thanks for the detailed pointers. I'm sure I can't afford your consultation fees.

I'll just say thanks frequently.

Johnny


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 Post subject: Re: New Drake 4B project
PostPosted: Nov Wed 25, 2020 10:42 pm 
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Location: Liberty, Missouri
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.

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 Post subject: Re: New Drake 4B project
PostPosted: Nov Wed 25, 2020 11:56 pm 
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Joined: Oct Sun 11, 2020 7:40 pm
Posts: 64
Location: Guthrie, OK USA
Mikeinkcmo wrote:
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.


Thanks again Mike. I may get through this project after all.

I will bite the bullet and buy a used D 104 soon.

Johnny


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 Post subject: Re: New Drake 4B project
PostPosted: Nov Thu 26, 2020 2:18 am 
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Mike,

I have bought a bunch of D-104 mics over the years and I have never had one with a dead element. But so many people report problems that I am cautious about advice to other hams. I suspect, like silver mica "disease" and the problem with 6146B tubes, it is in large part internet lore.

Rodger WQ9E


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 Post subject: Re: New Drake 4B project
PostPosted: Nov Thu 26, 2020 2:46 am 
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Rodger said;
Quote:
.... I suspect, like silver mica "disease" and the problem with 6146B tubes, it is in large part internet lore...
I agree.

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 Post subject: Re: New Drake 4B project
PostPosted: Nov Fri 27, 2020 5:03 pm 
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Joined: Oct Sun 11, 2020 7:40 pm
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Location: Guthrie, OK USA
The preselected on my T-4XB is very hard to turn. Ideas?

The slugs seem to be binding. Oil?


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 Post subject: Re: New Drake 4B project
PostPosted: Nov Fri 27, 2020 5:16 pm 
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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


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 Post subject: Re: New Drake 4B project
PostPosted: Nov Fri 27, 2020 6:46 pm 
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Joined: Oct Sun 11, 2020 7:40 pm
Posts: 64
Location: Guthrie, OK USA
rsingl wrote:
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


That worked. Thanks again Roger.

Johnny


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 Post subject: Re: New Drake 4B project
PostPosted: Dec Tue 08, 2020 7:28 pm 
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Posts: 64
Location: Guthrie, OK USA
I am unable to tune my T-4XB the normal way but I can tune and transmit CW if I tune it in x Lower and x CW. Does this point me to the Upper SSB filter as the problem?

Thanks,

Johnny


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 Post subject: Re: New Drake 4B project
PostPosted: Dec Tue 08, 2020 8:16 pm 
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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


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 Post subject: Re: New Drake 4B project
PostPosted: Dec Tue 08, 2020 8:43 pm 
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Joined: Oct Sun 11, 2020 7:40 pm
Posts: 64
Location: Guthrie, OK USA
rsingl wrote:
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


Roger,

The Lower (LSB) switch position sounds good and drives the radio to 30 watts at 28.4mHz. (Dummy Load)

The Upper (USB) switch position sounds very garbled and will not drive the radio to even ONE watt out. (Dummy Load)

Never boring around here!

Johnny


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 Post subject: Re: New Drake 4B project
PostPosted: Dec Tue 08, 2020 9:49 pm 
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Posts: 689
Location: Walker, MI
If your still looking for cables, a set of originals are here

http://nationwide-radio--amp-amp-amp--eq-sales-llc.mybigcommerce.com/rl-drake-original-b-line-4-piece-cable-set-with-label-kit-in-excellent-condition/

I am not associated with Nationwide radio sales other than a happy past customer.


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 Post subject: Re: New Drake 4B project
PostPosted: Dec Tue 08, 2020 10:09 pm 
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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


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 Post subject: Re: New Drake 4B project
PostPosted: Dec Tue 08, 2020 10:22 pm 
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Joined: Oct Sun 11, 2020 7:40 pm
Posts: 64
Location: Guthrie, OK USA
rsingl wrote:
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


Roger,

The carrier is dead on. I have checked that a couple of times.

Can you suggest a specific test for the USB filter? I probably have the necessary equipment.

Thanks,

Johnny


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 Post subject: Re: New Drake 4B project
PostPosted: Dec Tue 08, 2020 10:42 pm 
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Johnny,

I don't have the specs for those filters but the bandwidth (-6db point) is probably about 2.4 Khz. and the carrier should be down the curve so expect one filter to have one 6db point shifted around 400 hz above the 5.645 carrier frequency and the other below it. So each filter should have about the same response profile except one will have the profile above the carrier frequency and the other below it.

You can use a sweep generator and scope to profile the filters or you can graph a few points with a standard signal generator measuring the output with either a RF voltmeter or scope. Because you know one filter seems to be operating normally, you have a good reference.

When checking the filters, remember with the conversion scheme in the T-4X that sidebands are inverted in the 6AU6 mixer stage. So what is generated as a LSB signal coming out of the filter select section will be transmitted as a USB signal.

Rodger WQ9E


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 Post subject: Re: New Drake 4B project
PostPosted: Dec Fri 11, 2020 5:36 am 
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Joined: Oct Sun 11, 2020 7:40 pm
Posts: 64
Location: Guthrie, OK USA
rsingl wrote:
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


I have read a lot about Drake mods. VOX does not appeal to me. I wonder if I could trip that relay without a 6EV7.

Johnny


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 Post subject: Re: New Drake 4B project
PostPosted: Dec Wed 16, 2020 4:52 am 
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Joined: Oct Sun 11, 2020 7:40 pm
Posts: 64
Location: Guthrie, OK USA
I read an article recently that mentioned a more detailed or extensive alignment procedure than I have in the basic manual. I have a hunch I will need it. My R4XA and my T4XB both need to be gone completely through as soon as i fix all of the obvious problems. Anyone ever seen a copy of the detailed alignment?

Thanks,

Johnny


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