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5R4GY solid state replacements...




 
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KK4YY
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« Reply #25 on: June 15, 2019, 03:27:18 PM »

Perry,

Last time I checked, the stock DX-100 modulator screen voltage came from the center-tap of the HV bleeder resistor. That puts about 375 volts on those screens no matter what your LV supply is.  If you want to take screen voltage from the LV supply, you'll need to switch it with a relay or something. Was that part of the mods you made?


Don


P.S. Nice video. That's the best I've ever heard George. Grin
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« Reply #26 on: June 16, 2019, 08:13:16 AM »

That's the best I've ever heard George. Grin

    Haha, he snuck in there! Don't get me started on George. Angry Angry Ive probably told him 6 times in that last couple months to LEAVE IT ALONE AND DON'T TOUCH IT, after helping him to get it to sound decent. And he'll come on the next day sounding like butt, folding his carrier back, so on and so forth. But, i know im not the first to fall into his trap! Still love the guy though. I think its great that he's running an Isotron and hits me at 20 over at times.

    Anyway, back to the topic at hand. If you read his "DX-100 Mods" page, theres many parts in there where he jumps around and things get confusing. Before the text I had quoted, he says this:
 
"RF Final Screen Supply

The screen voltage is derived from a divider in high voltage power supply. This is a poor method. Under normal operating conditions, screen current will cause that screen voltage to sag. In the original circuit, there is a large, 30KW, center tapped resistor, which establishes a half voltage point for the two electrolytics in the power supply, but under normal operation there is an imbalance of voltage, and the electrolytic from the top end of the hi-voltage supply to the center tapped resistor will wind up with over 450 volts across it, boom! - the electrolytic will break down! The screen voltage actually needs to be lowered. The screen voltage should be taken directly from the low voltage supply, through a relay. This is done when the PTT circuit is added. For example, a 4-pole relay is used to key up plate voltage, exciter B+, and modulator screens, as well as audio driver B+."

    The way he puts it, he makes it sound like hes talking about the screen voltage for the 6146's, to my novice behind anyway. I guess because its labled "RF Final Screen Supply" The way he put things in his post really confuses me. And took a long time to weed through. So ive gone with other folks' interpretation of the mods.

    Moving on. Looking through my notes, I have 349vdc on the center tap of the 30k bleeder resistor. What i did was add another 30k of resistance and it brought the screen voltage down to 278vdc according to my notes. The final grid bias I settled at is -32vdc to get the mod transformer idling around 70mA as Tim recommends. Now, I know that adding resistance isn't the correct way to lower the screen voltage. I had tried adding a relay and picking off the LV supply at one time, after switching to choke inpoot. My results weren't good. I dunno if the relay was not stout enough, but the audio was breaking up and very distorted when I tested it, so I added resistance instead by using the bleeder resistor off of my parts rig. I havent noticed any ill effects on anything from doing it that way, but maybe you'll have some insight on that. One thing I havent done is add negative feedback. I wonder how much of an improvement adding a negative feedback loop around both the 12AX7 and 12BY7 would be as far as reducing distortion. Ive read where guys have done this and it didnt really make any difference, so they took it out.

Thanks Don, and Happy Fathers Day.
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« Reply #27 on: June 16, 2019, 11:30:05 AM »

Perry,

Interesting. The common wisdom is to use a regulated voltage on the modulator screens for the best results. A series dropping resistor would give rather poor regulation. But if it works for you, then it works.

In stock form, the mod screens have a .1uf bypass cap hung on them. Did you add any more C there to try and hold the voltage up? Maybe a few hundred uF? That might be something to try.

I went through those kind of mods some months ago and ended up replacing the 1625's with 6DQ5's and driving audio to the screens from an external amp. No screen supply needed, just a zener for bias. I'm working on building an internal audio driver but that's moving slowly.

I haven't played with NFB so I can't comment on that.

For me, it's the process that's fun. Trying things, learning things, and making the Heathkit DX-100 into My DX-100. You can do the Timtron mods, put all the screws back in the cabinet, throw your soldering iron away, and be done - you'll have a very nice rig that way. But, if you sharpen your machete, you can try to cut a new path through the jungle and call it your own. Admittedly, many have done just that. There's hardly a tree left to fell in the DX-100 jungle. The journey is the best part. You've joined a long tradition of hams modifying their AM transmitters. I hope that you enjoy it as much as I have.


Don
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« Reply #28 on: June 16, 2019, 02:08:18 PM »

Perry,

It is likely that George goes on SSB and cranks the audio, uses the processor.
Then forgets where he had it set for AM...
I think it is that simple...
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« Reply #29 on: June 16, 2019, 02:27:11 PM »

Bear,
I didnt think about that. Good point. He's been getting a lot of compliments lately and guys saying its the best theyve ever heard him. He was up on 40m the other day sounding great. Happy fathers day to you as well bud.


Perry
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« Reply #30 on: June 16, 2019, 08:01:10 PM »

I homebrew my own SS replacements:


Phil - AC0OB

I have 5R4 tube bases and SS diodes, and could put together a couple 5R4 replacements. I understand how to connect the SS diodes to the tube pins, but do you use shrink tubing, any kind of enclosure? Any photos?

Brad
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« Reply #31 on: June 16, 2019, 08:40:12 PM »





I just daisy chained the diodes on an octal base and covered the devise with a pill bottle. Fits better than OJ's glove.

klc
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« Reply #32 on: June 16, 2019, 10:29:59 PM »

Perry,

It is likely that George goes on SSB and cranks the audio, uses the processor.
Then forgets where he had it set for AM...
I think it is that simple...


This is why I use pc based outboard processing.

With a mouse click, I have ssb wide, ssb for DX and am settings.

Makes life simple, although getting the rf out of the virtual air chain wasn't - - Shane
KD6VXI
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W3MMR
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« Reply #33 on: June 17, 2019, 07:59:26 AM »

I homebrew my own SS replacements:


Phil - AC0OB

I have 5R4 tube bases and SS diodes, and could put together a couple 5R4 replacements. I understand how to connect the SS diodes to the tube pins, but do you use shrink tubing, any kind of enclosure? Any photos?

Brad

Brad,
What diodes do you plan on using? These are the ones I was looking at. https://www.mouser.com/ProductDetail/Rectron/HVM12?qs=sGAEpiMZZMtbRapU8LlZD0IZEQvpG%2F8RJnSZSuW1xB0%3D

Perry,

It is likely that George goes on SSB and cranks the audio, uses the processor.
Then forgets where he had it set for AM...
I think it is that simple...


This is why I use pc based outboard processing.

With a mouse click, I have ssb wide, ssb for DX and am settings.

Makes life simple, although getting the rf out of the virtual air chain wasn't - - Shane
KD6VXI

Thats exactly why I DONT use my external rack with my Anan anymore. It automatically switches transmit profiles when I change modes, bands, whatever I have it set to do.

Perry,

Interesting. The common wisdom is to use a regulated voltage on the modulator screens for the best results. A series dropping resistor would give rather poor regulation. But if it works for you, then it works.

In stock form, the mod screens have a .1uf bypass cap hung on them. Did you add any more C there to try and hold the voltage up? Maybe a few hundred uF? That might be something to try.

I went through those kind of mods some months ago and ended up replacing the 1625's with 6DQ5's and driving audio to the screens from an external amp. No screen supply needed, just a zener for bias. I'm working on building an internal audio driver but that's moving slowly.

I haven't played with NFB so I can't comment on that.

For me, it's the process that's fun. Trying things, learning things, and making the Heathkit DX-100 into My DX-100. You can do the Timtron mods, put all the screws back in the cabinet, throw your soldering iron away, and be done - you'll have a very nice rig that way. But, if you sharpen your machete, you can try to cut a new path through the jungle and call it your own. Admittedly, many have done just that. There's hardly a tree left to fell in the DX-100 jungle. The journey is the best part. You've joined a long tradition of hams modifying their AM transmitters. I hope that you enjoy it as much as I have.


Don


Sounded good down this way last night Don. Wish it wasnt as crowded so we could have had a QSO, but hey, thats the AM window @ night in the Northeast.


Perry

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« Reply #34 on: June 17, 2019, 09:41:04 AM »


Sounded good down this way last night Don. Wish it wasnt as crowded so we could have had a QSO, but hey, thats the AM window @ night in the Northeast.


Yes, it is. And I wouldn't change it for the world.  Smiley
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« Reply #35 on: June 20, 2019, 11:37:38 PM »


Brad,
What diodes do you plan on using? These are the ones I was looking at. https://www.mouser.com/ProductDetail/Rectron/HVM12?qs=sGAEpiMZZMtbRapU8LlZD0IZEQvpG%2F8RJnSZSuW1xB0%3D


Perry,

I don't know why the diode you linked to wouldn't work. I forget what the current flow is at the HV rectifiers in the DX-100 PS so make sure the diodes you buy are appropriately rated.  I'm thinking I will use 1N5408 as I have them on hand.  I think they are 1KV jobs rated for at least two amps but I will have to check that.

I'm interested in SS rectifiers more as a trouble-shooting tool.  When I was working on my DX-100B, SS rectifiers in the HV supply would have allowed me to find a couple of problems more quickly at a much lower voltage and probably without the smoke.  Smiley

Brad
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« Reply #36 on: June 21, 2019, 05:51:54 PM »


I have 5R4 tube bases and SS diodes, and could put together a couple 5R4 replacements. I understand how to connect the SS diodes to the tube pins, but do you use shrink tubing, any kind of enclosure? Any photos?

Brad

Sorry, no pictures but I did use plenty of shrink tubing to and from the "tube saver" octal base. Since I had a cabinet surrounding the unit, I did not enclose the "tube saver" octal base.

I essentially did what WIG did and simply connected the 4, 1N5408s at the base and then to the resistor and then ran that to the input of the choke.

R* may have to be adjusted for your specific transformer voltage and how much HV B+ you want to allow.


Phil - AC0OB
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« Reply #37 on: June 22, 2019, 09:15:58 AM »


Brad,
What diodes do you plan on using? These are the ones I was looking at. https://www.mouser.com/ProductDetail/Rectron/HVM12?qs=sGAEpiMZZMtbRapU8LlZD0IZEQvpG%2F8RJnSZSuW1xB0%3D


Perry,

I don't know why the diode you linked to wouldn't work. I forget what the current flow is at the HV rectifiers in the DX-100 PS so make sure the diodes you buy are appropriately rated.  I'm thinking I will use 1N5408 as I have them on hand.  I think they are 1KV jobs rated for at least two amps but I will have to check that.

I'm interested in SS rectifiers more as a trouble-shooting tool.  When I was working on my DX-100B, SS rectifiers in the HV supply would have allowed me to find a couple of problems more quickly at a much lower voltage and probably without the smoke.  Smiley

Brad

hmm weird. Anyway, well Brad, the 1N5408's are whats in the SS rectifiers i already have, that are wreeking havoc when I put them into the HV supply. As soon as I key the radio, it blows the inline fuse I installed. I use a 6a fuse in normal operation, so i tried a 10a, still blew, so I knew something was up. At one point, it even welded my PTT relay together in the TX position. So just a heads up. On the other hand, if they end up working for you, then I know I have something else going on. I also tried just one of the rectifiers at a time, as opposed to 2, in both sockets to see if that would work and I still got the same result. So be careful, and let know how how ya make out! I'm very very curious to see.


Perry
W3MMR
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« Reply #38 on: June 22, 2019, 09:18:32 AM »


I have 5R4 tube bases and SS diodes, and could put together a couple 5R4 replacements. I understand how to connect the SS diodes to the tube pins, but do you use shrink tubing, any kind of enclosure? Any photos?

Brad

Sorry, no pictures but I did use plenty of shrink tubing to and from the "tube saver" octal base. Sine I had a cabinet surrounding the unit, I did not enclose the "tube saver" octal base.

I essentially did what WIG did and simply connected the 4, 1N5408s at the base and then to the resistor and then ran that to the input of the choke.

R* may have to be adjusted for your specific transformer voltage and how much HV B+ you want to allow.


Phil - AC0OB

Phil,
 The SS jobs i have, have 2- 1n5408G diodes inside connected as so: anode of 1 diode goes to pin 4, that diodes cathode is soldered to the other diodes cathode, which is connected to pin 8, and that diodes anode goes to pin 6. You said you used 4 diodes in each and it works fine? Are you using both sockets or just one? Thanks!!!


Perry
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« Reply #39 on: June 22, 2019, 10:29:35 AM »

Phil,
 The SS jobs i have, have 2- 1n5408G diodes inside connected as so: anode of 1 diode goes to pin 4, that diodes cathode is soldered to the other diodes cathode, which is connected to pin 8, and that diodes anode goes to pin 6. You said you used 4 diodes in each and it works fine? Are you using both sockets or just one? Thanks!!!


Perry
W3MMR


Perry, I used 4 diodes total (as per the schematic, Sheet 1) for a bit of extra reverse voltage headroom.

It is only necessary to use one socket as the HV supply current is around 350 mA.

Use at least #16 stranded, insulated, and shrink tubing cover for the wiring to and from the socket and resistor.  

Phil - AC0OB

* 5R4 SS Power Supply and Screen Regulator.pdf (88.1 KB - downloaded 30 times.)
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