KRIS 600 SSB-New Project

[Dmans]

Kris 600 SSB Update

Today was a productive day.

Medium Voltage power supply was rebuilt.
From this:

To this:

The High Voltage supply was finished. Filter capacitors and bleeder resistors replaced.
From this:

To this:

The replacement keying circuit was finished.
From this:

To this:

The keying circuit was built using the schematic of the Kris Big Boomer. It is very sensitive and will key with a little less than 1 watt. It did handle a 20 watt input just fine. The electrolytic "sticking out like a sore thumb" is the drop out Cap for the relay. It was left that way so that the owner could change it relatively easily if he desires for SSB. (This unit does not have an AM/SSB switch.)

A new fan was installed today as well. The original fan rattled and started very slowly. After running a couple minutes it finally got to full speed. When at full speed it was a vibrating mess! Not worth the effort to try to repair it when this replacement was $6.00 new!

The amp works showing about 125 watts output with 2 watts in on AM and roughly 250 watts modulated but the input match is not great. It shows about 2.5-3.0:1 when keyed. Not great is an understatement-it is terrible!
The Driver air variable is not meshed at all for full output and there is no trimmer for input matching/tuning on the driver tube. The Tune and Load air variables are about 1/2 to 2/3 meshed for full output. (Bad driver tube???)

Still left to do-
Solve the poor input tuning SWR (I'm open for suggestions here!)
Install a resettable circuit breaker on the rear panel (owners request)
Install the MOV's on the AC line cord
Install a Fast Blow fuse on the transformer high voltage winding output to the bridge rectifier

73's
David

 

[loosecannon]

Dmans,

here is a link to the thread where i restored/rebuilt a kris power pump:

https://www.worldwidedx.com/threads/kris-power-pump-upgrade-restoration.183792/

all of the kris amps are very similar. I had a lot of help from Nomad on this, and would not have been able to redesign this amp without it.

check out the schematic i drew up for it and you will see what i did for the input tuning.

i did not like the idea that the 'drive' trimmer was under the chassis and meant to be a 'set it and forget it' type of thing.

mine was converted to be a straight three tube amp instead of one driving two, which eliminated the drive control. if you choose to keep yours as it is, you might consider a way to access that drive control from outside the radio.

good luck with the build! i will be following along.
LC

 

[Dmans]

loosecannon,
I will re-read the link to your Power Pump rebuild.

This is not my amp but the owner asked me if I could convert it to a straight 4 (it is currently 1-6JG6A driving 3-6LQ6's).
Since your Power Pump was a 1 driving 2, how closely do you think your schematic will line up to this model?
I'm not sure I have the equipment to do that but it would be best for his needs as he wants to drive it with an Anytone AT6666. I'm not sure the Anytone would put out what little this amp was originally intended to have as drive. The owner does only use it on SSB as well. The owner believes it should put out about 450 watts-I don't think it will be that high but maybe 300 watts without much issue.

Questions:
Can the 6JG6A be swapped for a 6LQ6? (I know the tube socket is the same but it would require some changes to the wiring) I'm pretty sure the 6JG6A cannot be used in a straight 4 configuration with 3 6LQ6's.
Would the tank coil have to be changed? If so, how can I determine what the new tank coils should be? Trial and error?
If the 6JG6A were swapped for a 6LQ6, what would become of the front panel "Drive" air variable?

There is a trimmer cap (463) on each of the cathodes of the 6LQ6's now, adding one to the "driver tube" socket would not be an issue if changed to a straight 4 configuration. At this point, maintaining a 1 driving 3 configuration, I am considering adding a trimmer to the cathode of the driver to see if the input match can be brought to an acceptable level. Other thoughts are adding a parallel capacitor to the "Driver Tune" air variable to see what becomes of the input match.

In the end, the best option for the intended use of this amp is the straight 4 configuration, I'm just not sure how to make that happen.

73's
David

 

[Hurricane145]

The old tube amps like that were mostly bought in a time when CB base radios were tube rigs. The tube rigs were not as fussy about the input SWR and most tube rigs had a plate and load adjustment in the rear of the rig to maximize the output and adjust for some mismatch.

You might want to look into a tuned input circuit for it if the input SWR is a problem. That might not be too difficult since it will be a single band amplifier, no band switching to worry about.

 

[Dmans]

Update to the Kris 600SSB project

It is operational but still has a high input SWR. (Approximately 2.0:1)

loosecannon,
Your Power Pump rebuild/restore schematic has a 2 uh coil and a 463 trimmer added for input tune. Since you converted it to a straight 3, I'm curious how close this arrangement will line up to the 6JG6A driver section of this amp. I added a very similar arrangement to my Hygain 482 but I did add control grid bias to the amp (adding to the mismatch on the input side) and it has 2 6KM6 tubes in it.
So what would be a good starting point for an input coil to "dial in" the input SWR? (As in, wire gage, number of turns, coil diameter etc.)

Performance wise, the amp is drawing 3.5 amps of line current (120vac) and 0.8 amps on one of the high voltage windings of the transformer.(Sidenote: The amp was built with a 10a line fuse!) These were measured while transmitting in order to size the circuit breaker (owners request) and the "Fast Blow" fuse for the high voltage winding. When I get the input SWR dialed in, I will re-measure the current draw and size the breaker and Fast Blow fuse accordingly.

Currently the amp output measures 200 watts with 3 watts in on AM and about 275-300 watts output on SSB with 10 watts in. I suspect a soft tube somewhere in this unit but don't have a substitute (or 4!) to find it.

Any and all ideas on dialing in the input SWR appreciated.

73's
David

 

[Shadetree Mechanic]

Update to the Kris 600SSB project

It is operational but still has a high input SWR. (Approximately 2.0:1)

loosecannon,
Your Power Pump rebuild/restore schematic has a 2 uh coil and a 463 trimmer added for input tune. Since you converted it to a straight 3, I'm curious how close this arrangement will line up to the 6JG6A driver section of this amp. I added a very similar arrangement to my Hygain 482 but I did add control grid bias to the amp (adding to the mismatch on the input side) and it has 2 6KM6 tubes in it.
So what would be a good starting point for an input coil to "dial in" the input SWR? (As in, wire gage, number of turns, coil diameter etc.)

Performance wise, the amp is drawing 3.5 amps of line current (120vac) and 0.8 amps on one of the high voltage windings of the transformer.(Sidenote: The amp was built with a 10a line fuse!) These were measured while transmitting in order to size the circuit breaker (owners request) and the "Fast Blow" fuse for the high voltage winding. When I get the input SWR dialed in, I will re-measure the current draw and size the breaker and Fast Blow fuse accordingly.

Currently the amp output measures 200 watts with 3 watts in on AM and about 275-300 watts output on SSB with 10 watts in. I suspect a soft tube somewhere in this unit but don't have a substitute (or 4!) to find it.

Any and all ideas on dialing in the input SWR appreciated.

73's
David

Nice build and great work you are doing here. I too am interested in how to figure out what is needed for input tuning. I think I read somewhere about using the MFJ antennalizer to measure amplifier inputs. It seems that if the current C and L of the input were known, the compesating values could be calculated. I will be following along just trying to learn.
Chris

 

[Dmans]

STM,
I'm trying to learn all the time. Might be a case of teaching an old dog.....................

I certainly don't have the equipment I would like to have to properly repair this unit. All the information I can find seems to require more money in test equipment than I have in my house to properly measure tubes, load capacitance, plate resistance, etc.

This unit does however belong to a good friend of mine that cannot (i.e. Physically unable) repair it himself. Seeing as it sat in a Truck Stop CB shop for 6 months and he asked me (more than once), I told him I would give it a shot for whatever the parts cost to make it safe and operate correctly or as close to original as possible.

I'm ready to have it finished. It's been here a month already and my own little projects are backing up. I did take a couple hours today to get back on the 148GTL (AKA "The Turd") and almost forgot where I left off. Finally whipped the non adjusting final bias issue. (Somebody swapped in some parts to make it swing? or key more? or make it key less or to make it cause final transistors to disappear magically???)
At least I repaired something today!

73's
David

 

[kopcicle]

I did take a couple hours today to get back on the 148GTL (AKA "The Turd")

Tied the clarifier over to TX but not happy with the total slide. It has more slide on the positive direction than the negative direction. Trying to get that evened out to no more than 1 channel in both directions (as time allows).

or something like that

With the as installed OEM varactor getting 20KHz linear is "if wishes were fishes..."
It is common to see all the capacitance piled up on one end.

Then you have to deal with the series capacitance of the crystal , along with stray capacitance, and a hand full of small value inductors, only then can you deal with the resistance bridge. Now I'm senile or lazy but I remember something about standard or reverse audio taper potentiometers , can't remember which counteracts the non linear characteristic of the varactor . So you have some work to do

http://www.farnell.com/datasheets/60830.pdf

 

[Handy Andy]

Logarithmic "Audio Taper"
Linear "Linear taper"

Good to see someone remembers - there are several threads that could use this input...

 

[kopcicle]

Andy,
I just don't remember if we used forward or reverse taper

 

[Handy Andy]

It is in how you approach the Varactor...

In your source voltage to operate the Varactor, you need the log taper portion of the pot's resistance higher than otherwise you'd need to offset the ground reference to center slot to obtain the most non-linear response - read Expotentiates - then your "taper" faces (your log-response) to that side to provide slide (Range of rotation that has maximum change of resistitance) for maximum effect of offset against that non-linear range of operation the varactor has- an EQ issue.

Take a look at SVC251 Varactor...

​

...the graphs' biggest slide is between 0.5VDC to about 1.7VDC open load - subjected to interpretation (high impedance non-loading idealized)

But you need to work against a non-linear "hump" from 0.2V to about 0.5VDC - that is where you can apply your maximum slide taper resistance against the hump and the center slot and the rest of the taper - which provides less resistive change over the longer range of rotation - faces towards the higher voltage...

So in setting "balance" - set your voltage divider to weigh heavily on the ground side for that Logarithmic taper of the pot - as you approach center slot - the resistance becomes more linear and therefore the voltage source of this circuit can be adjusted to apply the proper voltage which would be about 0.5 to 0.7 VDC (For Center Slot) - so that part of the log taper needs less resistive element and action against the divider.

Is that what you needed to know?

 

[Dmans]

I put the final touches on the Kris last week and it is back at home with it's rightful owner.
After some trial and error, I was able to get the input tamed down with a coil of 12ga wire, 1/2" diameter, 6 turns and approximately 1" long. An Arco 463 trimmer at the feedpoint of the coil allowed me to tune the input SWR to 1.5:1.
See the pic below. Tuning coil and capacitor at the bottom of the picture towards the front of the chassis. I added metal oxide varistors across the 120vac input line. The red caps at the upper right in the picture below.

Input current draw was measured and a 7 amp circuit breaker added (Owners request) in place of the original fuse holder. A ground lug was added to the chassis using an existing hole and slightly enlarging it for a larger screw and wing nut.
See below.

The high voltage current was measured on one leg of the feed to the bridge rectifier and a 1 amp fast blow fuse was installed. The rectifier diodes were also replaced with 1N5408 diodes.

Other modifications/changes made (but no pictures) were tying together both poles of the power switch and replacing all of the 3Kv ceramic capacitors with 4Kv ceramic capacitors. I did try a 12v zener diode on the 12 volt circuit to regulate the voltage (the original problem was the keying transistor fried and a poor attempt to repair it) but the keying circuit would not operate. The 12v leg has about 19vdc unkeyed and 14.7vdc when keyed. I thought keeping it at 12v would extend the life of the transistors used in the keying circuit?? I guess time will tell how long it holds up.

The final performance of this little gem is 325-350watts in SSB mode when driven with 8 watts from my 139XLR. Performance on AM was about 275 peak output watts when driven with 8 peak watts.

I do believe the driver tube is weak. It began to get the "Red Glow of Death" when testing. It was a dull red but will not get any better. Without another 6JG6A to test in its place, it went home to its owner.

Update to the update.
The owner of this amp, a good friend of mine, brought me another project that I will begin on after Christmas. Our deal with these amps is that he pays for the parts only. I am only doing these repairs to learn for myself and to stay busy in all of my off time!
Incidentally he did give me a working amplifier that has a 6KV6A driver that I offered to him for the Kris. Giving me the amplifier is a breach of our deal! But it is a bit scary inside and the first thing I did to it was unsolder the power cord! Another project for another day. Once the 6KV6A gets delivered and installed, I will update the health of this unit.

73's
David

 

[nomadradio]

You really ought to consider adding some fixed negative grid bias to these tubes, at least to the driver.

The overheating you observed will occur when the radio's carrier level is too low.

Just one problem. Turn the radio's carrier up enough to control the driver tube's heating and you will overdrive the final tubes. Or at least push the carrier high enough to reduce your audio level. Sounds backwards but if you key this amplifier with no drive at all, the tubes draw more current than they do with a carrier driving them.

Makes this one a bad idea for sideband with the factory setup. The AM drive carrier gets partly rectified by the tubes' grids, and the negative voltage this generates inside the tube controls the plate current. With no carrier, the plate current is uncontrolled, and high enough to overheat the anode.

I need to come up with a "generic" description of how to add fixed grid bias to these tubes. Takes two 1N5408 rectifiers, two .01uf disc caps, a 1000uf 25-Volt filter cap and a 1k 5W resistor.

But it's late and I'll just wimp out of a full description for now.

The parts to accomplish this were left out of the original design to reduce parts cost and assembly labor both, IMHO.

I'll see if I can dig up a procedure that I've already posted for this.

73

 

[Dmans]

Nomad,
Since the driver in this Kris is a 6JG6, would the negative grid bias be wired to pins 1 & 7, the G2 connections?
In my Hygain (6KM6 tubes)the negative grid bias was wired to pins 2 & 6, the G1 connections?

73's
David

 

[nomadradio]

G1 connections get the negative bias. Leave the G2 pins grounded.

73