Warning: Creating default object from empty value in /homepages/11/d132647312/htdocs/Amfone/mkportal/include/SMF/smf_out.php on line 47
Looking for someone very knowledgeable on the Henry 2KD Classic




 
The AM Forum
December 10, 2018, 08:15:45 PM *
Welcome, Guest. Please login or register.

Login with username, password and session length
 
   Home   Help Calendar Links Staff List Gallery Login Register  
Pages: [1]   Go Down
  Print  
Author Topic: Looking for someone very knowledgeable on the Henry 2KD Classic  (Read 920 times)
0 Members and 1 Guest are viewing this topic.
KU8L
Member

Offline Offline

Posts: 53


« on: September 17, 2018, 12:58:23 PM »

I have a 2KD Classic here for service.  Someone has been in it before me and there is a mod and some bad wiring.  Powers up but when received complaint was grid current ok and gts Ip but zero RF out.  Went thru all the output stuff--using a VNA.  Brand new 3-500s from RF Parts.  I found the main bias diode open.  Ordered an new one from Henry ($80.00 !!).  Put it in and it failed faster than I could see anything glitch.  Open.  It is a stack of silicon diodes in an epoxy rail.   THe fuse that is in series with it did not fail.

I'm wondering if there is a possible error in polarity of the other two diodes referencing B- to ground and causing a problem.  I see no evidence of grounds in the filament bypass caps or shorts in the transformers, etc.

I have a handful of the 50W zeners to replace the stacked original (13.00 each) but wondering if anyone has seen this before.  BTW, with the biase diode failed open, I got the expected full Ip current at idle.

The schematics are some of the worst I have seen in 55+ years of service work.

THanks for looking.  Off list is fine.

Curt
KU8L@flash.net
Logged
KF7WWW
Member

Offline Offline

Posts: 64


« Reply #1 on: September 17, 2018, 02:58:59 PM »

"BTW, with the biase diode failed open, I got the expected full Ip current at idle."

Sounds like grid to filament short somewhere to me.. All depends on how bad its been monkeyed with.. Have you checked the bypass caps? Visual inspection is not a real check.  ITs uncommon but a short or near short there will cause problems. 
I would also lower the fuse value for further testing..



" I'm wondering if there is a possible error in polarity of the other two diodes referencing B- to ground and causing a problem. "
Any raise in voltage from reference will cause problems ( that is more then the expected for metering )

Then again, Im sure you know this if the unit was brought to you for service. If all else checks ok. Try another set of tubes, just to be sure.
Logged
WBear2GCR
Member

Offline Offline

Posts: 3584


Brrrr- it's cold in the shack! Fire up the BIG RIG


WWW
« Reply #2 on: September 17, 2018, 03:20:40 PM »


It's difficult to see why the bias "diode" stack or zener should be $80... nothing magic there.
Was it RF bypassed? Needs to be, afaik.

Failed instantly?
Hmmm... iirc, it's in the cathode??

Could be a parasitic, possibly.

The bypass caps on the socket, and if it still uses resistors on the socket, they should be
checked too...

Most of the Henry amps have the B+ iron and the filament windings on the same core... makes it difficult to fire it up under lower B+.
But perhaps there is a way to fire it up with lower B+...?
There's something on the W8JI pages about a "glitch resistor" - might be worth looking into. Even if it is a temporary
installation...
Logged

_-_- bear WB2GCR                   http://www.bearlabs.com
KD6VXI
Contributing
Member
*
Offline Offline

Posts: 1890


Making AM GREAT Again!


« Reply #3 on: September 17, 2018, 09:01:25 PM »

Any amp I get here for repair gets a resistor in the b+.  If it's legal limit sized, an 8 ohm 10 watt.  Tubes with handles, or huge C in power supplies will get a 100 watt.  Why 8 ohms?  Got a deal.  If the tube shorts, etc. I have a two cent resistor go, not a higher priced part.

Pull the tubes.  Henry does the ass backwards design of running their filaments in series.  Insulate the hv connectors and turn the amp on. No problems?  Test the tubes with an ohm meter, filament pins to ground. If one shows a short, problem found.

And ditch the 80 dollar :zener:  A string of 6A10 or 10A10 diodes will do just as good.  For dynamic regulation stuff a few hundred mf cap across the cathode line to ground.

A 1.5 amp quick blow fuse in the cathode lead will be cheap insurance, too.  I out a cathode resistor in my amps now as well.  Overdrive the amp, replace the fuse.  Have a glitch?  The cathode fuse in concert with the glitch resistor and fuse will hopefully save transformers and zener.


--Shane
KD6VXI
Logged
DMOD
AC0OB - A Place where Thermionic Emitters Rule!
Contributing
Member
*
Offline Offline

Posts: 1216


« Reply #4 on: September 18, 2018, 02:34:32 AM »

1. Hopefully you have a HV probe such as 10kV probe to plug into your DMM. Without any RF drive, what is the B+ at the bottom end of the RF choke L1 when Keyed?

2. What is the bias voltage when keyed? A 10 or 50W 10-15V zener will work if the stud is grounded, such as http://www.nteinc.com/specs/5200to5299/pdf/nte5240a.pdf see for example NTE5254A or NTE5257A. Eimac actually specifies a 15V zener for over 3kV V plate.

3. When Keyed, does the relay function (pull-in)?

4. With no RF drive, what IP current are you seeing when keyed?
Logged

"What kind of Koolaid do they make you drink in the Physics Department?" Charlie Epps to Dr. Larry Fleinhardt, NUMB3RS   Smiley
KU8L
Member

Offline Offline

Posts: 53


« Reply #5 on: September 19, 2018, 10:17:05 AM »

Thanks Gentlemen:

I wasn't ignoring you, just really busy here.  I'll be checking all of the suggested points.  I even reached out to Henry to ask about sudden death issues with their diode stacks--no response. 

I have checked the B- rail clamping diode and found it good.  I really see no other mechanism that would cause enough current to open up the bias diode other than a grid/filament short or a ground fault in the filament circuits..none of which I have found. 

I have the tubes out now and they test OK but I may try another pair if I don't find something else.  THe sockets, bypass caps, an the transformer all seem OK but I did not hi-pot the transformer.

I am going to replace the main 3A 100PIV B- clamping diode just for safety--I wonder why there is a second diode in parallel to this one on the metering section--same wiring but much lighter rating.

Yes there were the proper bypass caps on the bias diode when replaced.

I plan to put in one of the 10 or 12V 50W zeners for the bias.  These are real zeners and will be installed reverse pol.  Henry docs are very confusing because the call the bias diode a zener in some places but it is really a silicon rectifier stack--so installed fwd direction. 

At that point, I'll be able to record more data on the various dynamic conditions with power on.

More to follow.

Curt
Logged
DMOD
AC0OB - A Place where Thermionic Emitters Rule!
Contributing
Member
*
Offline Offline

Posts: 1216


« Reply #6 on: September 20, 2018, 07:57:06 PM »

Thanks Gentlemen:

...I am going to replace the main 3A 100PIV B- clamping diode just for safety--I wonder why there is a second diode in parallel to this one on the metering section--same wiring but much lighter rating...


More to follow.

Curt

D105 is a 100V, 5W Zener that supplies the ALC circuit.

Safety diode D106 is a 100V 3A type or a 1N4720.

D107 is a type 1N4004 diode and is in series with the Ip meter and in series with a fuse and is shunted by a 150 ohm 2W resistor. There are no diodes in parallel with D107 or shouldn't be. The meter is in series with the bias circuit to measure plate current.

See the attached PDF file:

Any time I see a diode string used as bias it gets replaced by a zener for the bias  needed.

Phil - AC0OB

* Henry 2K Classic Biasing.pdf (51.73 KB - downloaded 31 times.)
Logged

"What kind of Koolaid do they make you drink in the Physics Department?" Charlie Epps to Dr. Larry Fleinhardt, NUMB3RS   Smiley
KU8L
Member

Offline Offline

Posts: 53


« Reply #7 on: September 20, 2018, 09:34:52 PM »

Like I mentioned, these are the worst schematics I have seen in a long time.

The Henry schematic I have dated 11-16-88  pvp  Shows D107 inseries with the Ip meter and R129 and the anode is shown tied directly to Ground  The cathode end is tied to the lower end of the .1ohm resistors AND the B- rail. (shown as Pin 2 of TB101 but the note says there is no TB101 in the KD version and wired direct)

Someone has clearly been inside this one and it appears some wiring was removed and resoldered.  in the area of D107.  I will have a look at it to see if they may have put it back to match this schematic which may be in error.  I'll post the PDF of this schematic in the morning so you can see it.

I do have a differnt schematic from a different version of the manual that shows the 2KD Classic PS and metering on the same page.  It is layed out like you diagram.    The one I referred to above has three pages--one for RF deck, one for the PS, and one for the metering.

Thanks

The serial number of this amp is:  54-427.   Sure would have been nice to have a indication on the manuals of range of serial numbers if they have different manuals.

Curt
Logged
DMOD
AC0OB - A Place where Thermionic Emitters Rule!
Contributing
Member
*
Offline Offline

Posts: 1216


« Reply #8 on: September 20, 2018, 11:06:05 PM »

I think the schematics are straight forward.

You have to determine what unit you have.

The 2K-Classic power supply has a C filtered power supply with a string of equalizing resistors across each Cap.

The 2K-ClassicX has a resonant choke power supply with a single HV capacitor.

The 2K-Classic has R119 across Diode D107.

The 2K-ClassicX has R115 across Diode D107.

Find out what unit you have and follow the specific power supply schematic.

In either case, the meter steering diode D107 goes to the B- rail.


Phil - AC0OB

Logged

"What kind of Koolaid do they make you drink in the Physics Department?" Charlie Epps to Dr. Larry Fleinhardt, NUMB3RS   Smiley
KU8L
Member

Offline Offline

Posts: 53


« Reply #9 on: September 21, 2018, 09:30:50 AM »

Hi Phil:  SOME of the schematics are fine.  Others not so much.  Diodes shown backwards, call outs for Zeners that aren't zeners, Zeners that are shown as diodes, etc. 

THe unit says 2KD-Classic on the label.   I don't know what year it is but ser no is 54-427.  Here is the front and meter schematic I was given with the unit.  I note the ser number on the front in handwriting is (maybe) much earlier--and the ID on the download was 1988manual-B.  Note the ground added to the end of D107.  This schematic looks like a 8 year old made it.

SO I am going to try to tell if the schematic you have referred to is (likely) the more correct one. 

I appreciate your patience and your help on this.  I'm doing this as favor to a friend but it had been in someone elses repair hands prior and not working--they just gave up.

* Henry-2K-Classic-1988-Manual-b_cover.pdf (675.03 KB - downloaded 30 times.)
* Henry-2K-Classic-1988-Manual-b.pdf (129.09 KB - downloaded 24 times.)
* Henry Radio--2KD-Classic--service,user--ID6988.pdf (99.5 KB - downloaded 34 times.)
Logged
DMOD
AC0OB - A Place where Thermionic Emitters Rule!
Contributing
Member
*
Offline Offline

Posts: 1216


« Reply #10 on: September 21, 2018, 06:46:52 PM »

The 2K-Classic was a free-standing Pedestal unit.

The 2KD-Classic was a Desktop unit that had a different metering setup.

On the 2KD-Classic because there was no need for wiring to enter from the bottom part of a pedestal, since everything was contained in the same level of the KD desktop, similar to an Ameritron AL-82.

As the metering schematic states, there is no TB101 on the 2KD-Classic because all wiring runs are on the same level from the metering to the PS. In addition, protection diodes are across the IP and Ig/Vs meters.

For the KD version, the B- rail still connects to the cathode of D107.

I think what happened was the guy drawing the KD metering circuit had not consulted the other power supply schematics because R121, for example, is a 20k 100W bleeder resistor and I don't see that it would make sense here. Other resistor values aren't recorded or listed.

I wish I had captured/drawn the KD Metering circuit the last time I had one in for upgrades, but the first schematic is what I think they meant, and the second schematic is what I think it "should be, " with the caveat the Ip meters had the same meter specs.

I would urge you to draw the metering circuit and record component values and post them here for future reference.


Phil - AC0OB





* Henry 2KD Ip Metering.pdf (75.14 KB - downloaded 26 times.)
Logged

"What kind of Koolaid do they make you drink in the Physics Department?" Charlie Epps to Dr. Larry Fleinhardt, NUMB3RS   Smiley
Pages: [1]   Go Up
  Print  
 
Jump to:  

AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
 AMfone 2001-2015
Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Page created in 0.055 seconds with 18 queries.