If C1 was tuning at only 10% mesh, the tank coil was probably set correctly. I would reverse the "squeezing" and put it right back where it was. Unfortunately it seems like something else may have gone wrong with the bias too. The tank circuit adjustments should have had no effect on idling current. If it remains high, check the bias diode string on the new board for shorted diodes.
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- Thread starter BJ radionut
- Start date
I concur with Shockwave. I could see no reason whatsoever why the plate idling current should change with a change in tank coil value. My thoughts were aimed at the bias circuit as well.
very very nice not sure if i missed it, what are you using as a t/r relay? need ideas for my larcan 6m 1kw amp. thanks.
This is the relay Warren and I have chosen for the Larcan amps. I like these because you do not have to wire in a coax jumper for the bypass line.The power rating is average power and will take more pep of course. Warren bought a box of them for his project as well as having a few on hand for customers I believe. Not sure if he has any left.
http://www.ebay.ca/itm/DOWKEY-COAXI...049?pt=LH_DefaultDomain_0&hash=item2c83ef5c49
UPDATE: Well it seems I may have found some issues.
#1: I made the mistake of reusing the original 3PDT relay supplied in the SB-221 kit. I am not sure now it was even functioning properly at all.
While looking at the contacts,(even though I had clean it before install) Most of the "plating" was gone from use. I also know now the coil was "weak", due to fact while checking the Bias path through the relay the coil opened during testing.(ceased to function!)
#2: Replaced old relay with NOS Potter-Brumfield 120v / 3PDT...Gold Contacts with larger(wider) throws and bigger "pads".
In retrospect, I should have used Vacuum Relays!!!
This is a mod that will happen if I can find some "reasonable" priced sets at Hamfests (DAYTON) over the next couple months.
#3: I had mentioned changes in resent posts of Idle current changes: I may have found this issue, the B- connection on the Plate meter was loose.
The meter connections were made using (2) Brass(double nut) set-ups. I had neglected to "polish" the brass and torque the (2) nuts properly.( just scared to damage the meter posts)
I added a star washer, then cleaned and carefully torqued the nuts together.
Idle Current on High Tap now rests at about 160 mA, which is a little higher than I wanted.
This however would still be in "acceptable" range for operation.
I measured the Bias voltage and found it to be slightly lower then anticipated. (5.9v vs. 6.5v ) I am not sure if I can add a Zener at the relay and "pull" this a little higher or not(?).
The diode stringer on the Harbach board would be almost impossible to change, due to it's size and placement. I am thinking maybe 7-9 volts would produce the desired 100-120 mA's that I expected to see.
The change of the relay, with the connection issues have "settled" the Tubes down. I am seeing more reasonable Plate current #'s than before.
Key down with 60 watts drive about 700 mA =1200w / with about 2700vdc (under load) plate voltage.
This still is higher than I would like; however PEP voice peaks are showing 800-1100 watts at 4-500 mA (if I can believe the meter!)
The tubes are running cool however and now don't look like "Red Delicious" apples on SSB into dummy load!!
PLUS it appears listening in another xcvr the Audio Distortion is gone! (I HOPE)
I'll try to work a little "scatter" this morning around Sunrise and see if I can get some reports.
4: I adjusted the Tank Coil back to it's original size and the C1 cap is meshed around 15% at peak.
I know now this 8-64 pf is to large. I need about half of this the be able to get a nice sharp "Dip" in the Plate current that I am use to seeing with my L4B on HF.
Well that's the news from the "Battle Front".
W9FNB reporting
All the Best
Gary
#1: I made the mistake of reusing the original 3PDT relay supplied in the SB-221 kit. I am not sure now it was even functioning properly at all.
While looking at the contacts,(even though I had clean it before install) Most of the "plating" was gone from use. I also know now the coil was "weak", due to fact while checking the Bias path through the relay the coil opened during testing.(ceased to function!)
#2: Replaced old relay with NOS Potter-Brumfield 120v / 3PDT...Gold Contacts with larger(wider) throws and bigger "pads".
In retrospect, I should have used Vacuum Relays!!!
This is a mod that will happen if I can find some "reasonable" priced sets at Hamfests (DAYTON) over the next couple months.
#3: I had mentioned changes in resent posts of Idle current changes: I may have found this issue, the B- connection on the Plate meter was loose.
The meter connections were made using (2) Brass(double nut) set-ups. I had neglected to "polish" the brass and torque the (2) nuts properly.( just scared to damage the meter posts)
I added a star washer, then cleaned and carefully torqued the nuts together.
Idle Current on High Tap now rests at about 160 mA, which is a little higher than I wanted.
This however would still be in "acceptable" range for operation.
I measured the Bias voltage and found it to be slightly lower then anticipated. (5.9v vs. 6.5v ) I am not sure if I can add a Zener at the relay and "pull" this a little higher or not(?).
The diode stringer on the Harbach board would be almost impossible to change, due to it's size and placement. I am thinking maybe 7-9 volts would produce the desired 100-120 mA's that I expected to see.
The change of the relay, with the connection issues have "settled" the Tubes down. I am seeing more reasonable Plate current #'s than before.
Key down with 60 watts drive about 700 mA =1200w / with about 2700vdc (under load) plate voltage.
This still is higher than I would like; however PEP voice peaks are showing 800-1100 watts at 4-500 mA (if I can believe the meter!)
The tubes are running cool however and now don't look like "Red Delicious" apples on SSB into dummy load!!
PLUS it appears listening in another xcvr the Audio Distortion is gone! (I HOPE)I'll try to work a little "scatter" this morning around Sunrise and see if I can get some reports.
4: I adjusted the Tank Coil back to it's original size and the C1 cap is meshed around 15% at peak.
I know now this 8-64 pf is to large. I need about half of this the be able to get a nice sharp "Dip" in the Plate current that I am use to seeing with my L4B on HF.
Well that's the news from the "Battle Front".
W9FNB reporting
All the Best
Gary
Sounds like you have it about all figured out. For the bias, I think like shockwave recommended 12v would serve you better. On some of the chicken band amps with 3400-4000vdc on the plate I have put 14 up to even 18v of bias on. I'm not sure on the 221 chassis, but I know like on the L4B the middle set of terminals on relay is for bias. If yours is set up the same. Then you can make your own string or large zener for bias. I install a 50k in series with bias diode string and just use the relay to bypass the cut off resistor when amp is keyed. Something to think about.
Since the tune cap is probably double of what you need. You may be able to install a reduction drive to tune cap so it is easier to fine tune. I'm sure with this amp on 6 meters. You only need 5-20pf max.
Mine set-up the same Crusher, stock set-up on the existing L4B.
I will go with the big Zener and Glitch resister/fuse set-up on the second one.
I'll be building up a slightly bigger power supply for #2 (around 3100vdc)
Nothing great but the xformer will have more current ability than stock from Drake.
This new xformer came out of and old 3-1000 amp...So anyway that's the scope.
Reports on the amp this morning were GOOD...Clean!....With most voice peaks at KW+ range and Plate current 3-500 mA's....
However I think CK was right again!....I think one of those old Doorknob caps is not liking 6m...I get a wisp of something getting warm on those long transmissions
...and it's coming from the top of the deck...either the one for coupling on the input, or maybe the blocking cap at the Tank Circuit....Looks like I need to check what would be a good sub for all of them at 6m freq's...they were all old/used ones from the parts bin...All checked good but....
So yes things are moving forward...
Work in Progress
Always nice to have Op's here to help an old yet young Jedi builder!!!!
73
All the Best
Gary
Could be blocking cap. Could be a cap used for padding. I also see a bypass cap for HV. Just a small tiny ceramic. That could be it as well. It was never intended for 6m. It will be located near HV board if I remember pic right. Near where you have feedthru for HV before plate choke.
TNX Waverider! Did find that the other day, but it's a little vague in spots.
I made it to FLA on "scatter" last two mornings. Reports were good working Locals about 100m away later yesterday morning also. So she is working
Not bad for living in a Coffee Cup at 750 ft. ASL with average terrain at 1000 ft at about 2m radius around me plus the 5ele only at 45 ft.
Crusher/Shockwave/CK ?.... diffidently got something "heating" on TX.
What should I be looking for to change the doorknob caps?
Coupling Cap on input and Plate blocking cap are both 1000 pf at 6KV...
Buffer Cap between B+ and Plate Choke 500 pf at 12KV....
Should my By-Pass caps be changed to another style?...Mylar/Mica? Voltage ratings?
Differently looking for recommendations...I Think I am getting closer...
THANKS to everyone's help!
Vacuum Relays are also on my list, a little frustrating but diffidently having fun with this project.
I am also considering moving the Tuned input circuit below chassis, this would shorten the coax connections by quite a few inches ??? Any thoughts on this?
It would be tough, underside is not very deep and if I change to Vacuum Relays this would make it even more cramped, as I would need a small 12vdc supply to run the relays...
All the Best
Gary
I made it to FLA on "scatter" last two mornings. Reports were good working Locals about 100m away later yesterday morning also. So she is working
Not bad for living in a Coffee Cup at 750 ft. ASL with average terrain at 1000 ft at about 2m radius around me plus the 5ele only at 45 ft.
Crusher/Shockwave/CK ?.... diffidently got something "heating" on TX.
What should I be looking for to change the doorknob caps?
Coupling Cap on input and Plate blocking cap are both 1000 pf at 6KV...
Buffer Cap between B+ and Plate Choke 500 pf at 12KV....
Should my By-Pass caps be changed to another style?...Mylar/Mica? Voltage ratings?
Differently looking for recommendations...I Think I am getting closer...
THANKS to everyone's help!
Vacuum Relays are also on my list, a little frustrating but diffidently having fun with this project.
I am also considering moving the Tuned input circuit below chassis, this would shorten the coax connections by quite a few inches ??? Any thoughts on this?
It would be tough, underside is not very deep and if I change to Vacuum Relays this would make it even more cramped, as I would need a small 12vdc supply to run the relays...
All the Best
Gary
The plate blocking cap, you said was 1000pf at 6kv. That's kinda borderline for a blocking cap if your at about 2800vdc on plate. At that high of a frequency, you could use 500pf at 15kv or 2x 200pf in parallel. On some of the doorknobs you have to do your homework as Shockwave pointed out about at 50mhz. Without having it in front of me, it's only guessing. The reason I say this, some of the higher value doorknobs while they may look good are very poorly rated for current. An example for say 10/11meters. A HEC 57 doorknob @ 1000pf @15kv is only rated for 2a. Bump that up to 50mhz and 1A might be max or less. That's why some guys will use 200pf and parallel 3-4. At 30mhz. They will handle 9a each versus a the 1000pf at 2a. You have to know what the components are rated for. Your older 6kv might only be rated at .5a at 50mhz.
Also, the bypass capacitor in picture 1. It is connected to HV feedthru as it enters deck. If plate choke has enough inductance. It shouldn't be a problem. But not the first time I have seen these go bad. It's also possible the plate choke is heating up. Either parasitic or not enough inductance. Didn't really pay much attention to underside. But could be a ceramic disc bypass cap heating up. I have seen those go poof before as well. Have to look at everything. Not just a few items.
Agreed. i tried to post from work earlier today but things were screwy and it just kept dropping connection.
I agree with the capacitor. I thought 1000pF was quite high. Sometimes higher value and the lower Xc associated with it is not better. Most capacitors have a lower current rating the higher you go. I have seen ceramic mica types rated for 20 amps at 1 MHz but only 1 amp in the HF range. Doorknob types are pretty much the same. Often you will see several in parallel in order to handle the current.
Vacuum relays have the same rating/ issue. I have seen 150A vacuum relays that by the time you used them for 10meters were only rated for about 13-15A.
