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Author Topic: Drake T4X modification mods.  (Read 4602 times)
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WD8BIL
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« on: January 03, 2017, 09:29:03 AM »

6 years back I did the T4X mods posted on the AM Window. They are extremely easy and quite effective in producing a very good AM signal. I've been far more than satisfied with the results.

However, after 6 years of beating the crap outta the rig on AM some weak spots in the original Drake final setup have reared their ugly head and I thought it might be gentlemanly to pass on my remedies.

The weakest spot, and that which actually failed, is R36, a 3.3ohm 1/2 watt resistor shunting the plate current meter in the cathode line. It is located on the small vertical PC board underneath the chassis just outside the final tube socket shielded area. This resistor totally fried. Replace it with a 1 watt or greater. I used a 3.3ohm 3 watter I had in the junk box.

Doing a visual I noticed one of the 15ohm 1W cathode resistors at the final tube sockets was a bit brownish. Sure enuf when measured it was closer to 30ohms. I replaced both with 15ohm 3 watters.

Staying on the same assumptions I replaced the 68ohm 1/2W screen resistors with 1 watters.

Since this rig was primarily designed with SSB in mind, I figure the duty cycle AM puts on these parts is probably the reason they failed.

Here's the link to the T4X mods as posted and below I've attached a quickly doctored schematic of the changes.

http://www.amwindow.org/tech/htm/t4.htm


* T4X resistor scroating.png (114.1 KB, 1111x746 - viewed 551 times.)
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Todd, KA1KAQ
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« Reply #1 on: January 03, 2017, 01:11:28 PM »

The best sounding Drake I've worked or ever heard, Bud!
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known as The Voice of Vermont in a previous life
KE5YTV
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« Reply #2 on: January 03, 2017, 01:13:12 PM »

Thanks for the update. I've been eyeing these mods for my "B" line.
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Mike
KE5YTV  Dallas, TX
"The longest trip begins with a stop at the ATM."
WD8BIL
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« Reply #3 on: January 03, 2017, 01:13:34 PM »

Thanks Todd........ with these improvements it should be around for quite a while!

How's my SP-110?
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KB2WIG
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« Reply #4 on: January 03, 2017, 01:40:54 PM »


B,

 Did you really, really have to do the rebuild in the garage ? ? ?

KLC
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WD8BIL
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« Reply #5 on: January 03, 2017, 02:10:28 PM »

Quote
Did you really, really have to do the rebuild in the garage ? ? ?

No Wigger........ but that's where my parts store is right now!! Smiley

But with some of the other boatanchors that might not be a bad idea. I have a 1100 lb hoist mounted above the workbench out there!!
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WD8BIL
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« Reply #6 on: January 03, 2017, 02:52:30 PM »

Mike...... in step 5 of the instructions it tells ya to lift the cathode of the 6AU6 from ground and insert a 330 ohm decoupled with a 30uf cap.

In the T4XB the 6AU6 cathode grounding runs thru SW2. This shuts down the 6AU6 in the spot mode. I don't see any reason why you couldn't just remove this wire and directly ground the resistor and cap right at the 6AU6. It gives you the advantage of the modulator being on in spot mode. I use it to listen to myself in the receiver and adjust audio quality before getting on the air.

Also Mike, in the T4XB R36 is listed as 2.7 ohms.

Try the mod. You'll like it. Good AMing!

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Todd, KA1KAQ
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« Reply #7 on: January 05, 2017, 01:42:51 PM »


How's my SP-110?


The Bud Pro-110 is enjoying a rest since 2014 when it was retired from bedside receiver service. It has an intermittent that needs to be tracked down, but with an impending move at the time I didn't see an opportunity to get to it for a while.

For the time being, I think it's having a family reunion with its siblings under the basement stairs where it's cool and dry. I say 'think' because there are still 8-10 rigs bagged and stored in the garage. Hopefully this weekend they'll be moved in as well. Slowly catching up. Might even get a wire up again someday.

The matching Jensen is still wearing your packing job. You can see it on the lower right shelf next to the TR-6. I used the -110 to drive a big EV coaxial floor speaker from the 50s.


* Basement2.JPG (308.27 KB, 931x1400 - viewed 323 times.)

* Basement5.JPG (449.18 KB, 931x1400 - viewed 314 times.)
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KD6VXI
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Making AM GREAT Again!


« Reply #8 on: January 05, 2017, 07:22:29 PM »

What are the blue faceplate rigs?   Cool looking.

--Shane
KD6VXI
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